Q6. What is the relative length of the time constant for the diode-capacitor combination in a damper (long or short)?
Q7. What is the relative length of the discharge time constant with respect to the charge time constant of a damper (long or short)?
Q8. A positive damper clamps which extremity of the output signal to 0 volts?
Q9. To which polarity does a positive damper with positive bins clamp the most negative extremity of the output waveform (positive or negative)?
Q10. What type damper (with bias) clamps the most negative extremity of the output waveform to a negative potential?
Q11. A negative damper damps which extremity of the output waveshape to 0 volts?
Q12. A negative damper with negative bias clamps the most positive extremity of the output wave shape to what polarity (positive or negative)?
Q13. What type of bias (positive or negative) is added to a negative damper for the most positive extremity of the wave shape to be clamped above 0 volts?
Q14. What would be the output of a negative clamper with a bias potential of −5 volts and an input voltage swing from +50 to −50 volts?
The common-base transistor clamper is similar to the dual diode limiter in figure 4-15, except for the addition of a transistor. In the previous clampers, we have clamped the output signal to a reference. In the transistor common-base clamper, we want to clamp the amplitude of the input to no more than nor less than certain values in the output. Also, we do not want phase inversion in the output. View (A) of figure 4-24 shows such a circuit. The transistor does not amplify the input and the output is not inverted. However, the two diode circuits serve to clamp the output between −2 volts and −8 volts, no matter what the varying input positive and negative extremes.
4-30
Look at view (B) as we continue. The input signal is a square-wave pulse type signal that varies in amplitude. Without an input signal, Q1 conducts and provides current through R1. This develops the output (collector to ground) potential which is assumed to be approximately −5 volts (VCC − ER1) for this discussion.
From T0 to T1 the output follows the input because of the increasing emitter-base forward bias. However, at T1 the collector voltage reaches −2 volts and D2 is forward biased. D2 conducts and limits the output to −2 volts (the value of B3). D2 conducts until T2 when the input decreases below −2 volts. At this time, D2 cuts off and the output again follows the input because of the decreasing forward bias on Q1. At T3 the input reaches −8 volts and forward biases D1. D1 conducts and any further increase (beyond −8 volts) of the input has no effect on the output. When the input returns to a value more positive than −8 volts, D1 cuts off and the output again follows the input. This circuit action is the same for all inputs. The output remains the same as the input except that both positive and negative extremes are clamped at −2 and −8 volts, respectively.
Timing circuits and circuits which require a particular shape or "spike" of voltage, may use SHAPING circuits. Shaping circuits can be used to cause wave shapes, such as square waves, sawtooth waves, and trapezoidal waves, to change their shape. Shaping circuits may be either series RC or series RL circuits. The time constant is controlled in respect to the duration of the applied waveform. Notice that the wave shapes mentioned did not include the sine wave. These RC or RL shaping circuits do not change the shape of a pure sine wave.
The series RC and RL circuits electrically perform the mathematical operations of INTEGRATION and DIFFERENTIATION. Therefore, the circuits used to perform these operations are called INTEGRATORS and DIFFERENTIATORS. These names are applied to these circuits even though they do not always completely perform the operations of mathematical integration and differentiation.
4-31
Pure sine waves are basic wave shapes from which other wave shapes can be constructed. Any waveform that is not a pure sine wave consists of two or more sine waves. Adding the correct frequencies at the proper phase and amplitude will form square waves, sawtooth waves, and other nonsinusoidal waveforms.
 You will see that a complex wave consists of a fundamental frequency plus one or more HARMONIC frequencies. The shape of a nonsinusoidal waveform is dependent upon the type of harmonics present as part of the waveform, their relative amplitudes, and their relative phase relationships. In general, the steeper the sides of a waveform, that is, the more rapid its rise and fall, the more harmonics it contains.
The sine wave which has the lowest frequency in the complex periodic wave is referred to as the FUNDAMENTAL FREQUENCY. The type and number of harmonics included in the waveform are dependent upon the shape of the waveform. Harmonics have two classifications — EVEN numbered and ODD numbered. Harmonics are always a whole number of times higher than the fundamental frequency and are designated by an integer (whole number). For example, the frequency twice as high as the fundamental frequency is the SECOND HARMONIC (or the first even harmonic).
View (A) of figure 4-25 compares a square wave with sine waves. Sine wave K is the same frequency as the square wave (its fundamental frequency). If another sine wave (L) of smaller amplitude but three times the frequency (referred to as the third harmonic) is added to sine wave K, curve M is produced. The addition of these two waveforms is accomplished by adding the instantaneous values of both sine waves algebraically. Curve M is called the resultant. Notice that curve M begins to assume the shape of a square wave. Curve M is shown again in view (B).
4-32
As shown in view (B), when the fifth harmonic (curve N with its decreased amplitude) is added, the sides of the new resultant (curve P) are steeper than before. In view (C), the addition of the seventh harmonic (curve Q), which is of even smaller amplitude, makes the sides of the composite waveform (R) still steeper. The addition of more odd harmonics will bring the composite waveform nearer the shape of the perfect square wave. A perfect square wave is, therefore, composed of an infinite number of odd harmonics. In the composition of square waves, all the odd harmonics cross the reference line in phase with the fundamental.
A sawtooth wave, shown in figure 4-26, is made up of both even and odd harmonics. Notice that each higher harmonic is added in phase as it crosses the 0 reference in view (A), view (B), view (C), and view (D). The resultant, shown in view (D), closely resembles a sawtooth waveform.
4-34
Figure 4-27 shows the composition of a peaked wave. Notice how the addition of each odd harmonic makes the peak of the resultant higher and the sides steeper. The phase relationship between the harmonics of the peaked wave is different from the phase relationship of the harmonics in the composition of the square wave. In the composition of the square wave, all the odd harmonics cross the
4-35
reference line in phase with the fundamental. In the peaked wave, harmonics such as the third, seventh, and so forth, cross the reference line 180 degrees out of phase with the fundamental; the fifth, ninth, and so forth, cross the reference line in phase with the fundamental.
Q15. What is the harmonic composition of a square wave?
Q16. What is the peaked wave composed of?
Q17. What is the fundamental difference between the phase relationship of the harmonics of the square wave as compared to the harmonics of a peaked wave?
The harmonic content of a square wave must be complete to produce a pure square wave. If the harmonics of the square wave are not of the proper phase and amplitude relationships, the square wave will not be pure. The term PURE, as applied to square waves, means that the waveform must be perfectly square.
Figure 4-28 shows a pure square wave that is applied to a series-resistive circuit. If the values of the two resistors are equal, the voltage developed across each resistor will be equal; that is, from one pure square-wave input, two pure square waves of a lower amplitude will be produced. The value of the resistors does not affect the phase or amplitude relationships of the harmonics contained within the square waves. This is true because the same opposition is offered by the resistors to all the harmonics presented. However, if the same square wave is applied to a series RC circuit, as shown in figure 4-29, the circuit action is not the same.
4-36
The RC INTEGRATOR is used as a waveshaping network in communications, radar, and computers. The harmonic content of the square wave is made up of odd multiples of the fundamental frequency. Therefore SIGNIFICANT HARMONICS (those that have an effect on the circuit) as high as 50 or 60 times the fundamental frequency will be present in the wave. The capacitor will offer a reactance (XC) of a different magnitude to each of the harmonics
This means that the voltage drop across the capacitor for each harmonic frequency present will not be the same. To low frequencies, the capacitor will offer a large opposition, providing a large voltage drop across the capacitor. To high frequencies, the reactance of the capacitor will be extremely small, causing a small voltage drop across the capacitor. This is no different than was the case for low- and high- pass filters (discriminators) presented in chapter 1. If the voltage component of the harmonic is not developed across the reactance of the capacitor, it will be developed across the resistor, if we observe Kirchhoff's voltage law. The harmonic amplitude and phase relationship across the capacitor is not the same as that of the original frequency input; therefore, a perfect square wave will not be produced across the capacitor. You should remember that the reactance offered to each harmonic frequency will cause a change in both the amplitude and phase of each of the individual harmonic frequencies with respect to the current reference. The amount of phase and amplitude change taking place across the capacitor depends on the XC of the capacitor. The value of the resistance offered by the resistor must also be considered here; it is part of the ratio of the voltage development across the network.
The circuit in figure 4-30 will help show the relationships of R and XC more clearly. The square wave applied to the circuit is 100 volts peak at a frequency of 1 kilohertz. The odd harmonics will be 3 kilohertz, 5 kilohertz, 7 kilohertz, etc. Table 4-1 shows the values of XC and R offered to several
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harmonics and indicates the approximate value of the cutoff frequency (XC = R). The table clearly shows that the cutoff frequency lies between the fifth and seventh harmonics. Between these two values, the capacitive reactance will equal the resistance. Therefore, for all harmonic frequencies above the fifth, the majority of the output voltage will not be developed across the output capacitor. Rather, most of the output will be developed across R. The absence of the higher order harmonics will cause the leading edge of the waveform developed across the capacitor to be rounded. An example of this effect is shown in figure 4-31. If the value of the capacitance is increased, the reactances to each harmonic frequency will be further decreased. This means that even fewer harmonics will be developed across the capacitor.
4-38
Table 4-1.—Resistive and reactive values
5th 31.8 K Ω 25 K Ω
7th 22.7 K Ω 25 K Ω
9th 17.7 K Ω 25 K Ω
11th 14.5KΩ 25 KΩ
The harmonics not effectively developed across the capacitor must be developed across the resistor to satisfy Kirchhoff's voltage law. Note the pattern of the voltage waveforms across the resistor and capacitor. If the waveforms across both the resistor and the capacitor were added graphically, the resultant would be an exact duplication of the input square wave.
When the capacitance is increased sufficiently, full integration of the input signal takes place in the output across the capacitor. An example of complete integration is shown in figure 4-32 (waveform eC). This effect can be caused by significantly decreasing the value of capacitive reactance. The same effect would take place by increasing the value of the resistance. Integration takes place in an RC circuit when the output is taken across the capacitor.
4-39
The amount of integration is dependent upon the values of R and C. The amount of integration may also be dependent upon the time constant of the circuit. The time constant of the circuit should be at least 10 TIMES GREATER than the time duration of the input pulse for integration to occur. The value of 10 is only an approximation. When the time constant of the circuit is 10 or more times the value of the duration of the input pulse, the circuit is said to possess a long time constant. When the time constant is long, the capacitor does not have the ability to charge instantly to the value of the applied voltage. Therefore, the result is the long, sloping, integrated waveform.
Q18. What are the requirements for an integration circuit?
Q19. Can a pure sine wave be integrated? Why?
The RL circuit may also be used as an integrating circuit. An integrated waveform may be obtained from the series RL circuit by taking the output across the resistor. The characteristics of the inductor are such that at the first instant of time in which voltage is applied, current flow through the inductor is minimum and the voltage developed across it is maximum. Therefore, the value of the voltage drop across the series resistor at that first instant must be 0 volts because there is no current flow through it. As time passes, current begins to flow through the circuit and voltage develops across the resistor. Since the circuit has a long time constant, the voltage across the resistor does NOT respond to the rapid changes in voltage of the input square wave. Therefore, the conditions for integration in an RL circuit are a long time constant with the output taken across the resistor. These conditions are shown in figure 4-33.
Q20. What characteristic of an RL circuit allows it to act as an integrator?
If either an RC or RL circuit has a time constant 10 times greater than the duration of the input pulse, the circuits are capable of integration. Let's compute and graph the actual waveform that would result
4-40
from a long time constant (10 times the pulse duration), a short time constant (1/10 of the pulse duration), and a medium time constant (that time constant between the long and the short). To accurately plot values for the capacitor output voltage, we will use the Universal Time Constant Chart shown in figure 4-34.
You already know that capacitor charge follows the shape of the curve shown in figure 4-34. This curve may be used to determine the amount of voltage across either component in the series RC circuit. As long as the time constant or a fractional part of the time constant is known, the voltage across either component may be determined.
In figure 4-35, a 100-microsecond pulse at an amplitude of 100 volts is applied to the circuit. The circuit is composed of the, 0.01µF capacitor and the variable resistor, R. The square wave applied is a pure square wave. The resistance of the variable resistor is set at a value of 1,000 ohms. The time constant of the circuit is given by the equation:
Substituting values:
T = 1,000 · 0.01µF
4-41
Since the time constant of the circuit is 10 microseconds and the pulse duration is 100 microseconds, the time constant is short (1/10 of the pulse duration). The capacitor is charged exponentially through the resistor. In 5 time constants, the capacitor will be, for all practical purposes, completely charged. At the first time constant, the capacitor is charged to 63.2 volts, at the second 86.5 volts, at the third 95 volts, at the fourth 98 volts, and finally at the end of the fifth time constant (50 microseconds), the capacitor is fully charged. This is shown in figure 4-36.
Notice that the leading edge of the square wave taken across the capacitor is rounded. If the time constant were made extremely short, the rounded edge would become square.
The time constant, in figure 4-36 can be changed by increasing the value of the variable resistor (figure 4-35) to 10,000 ohms. The time constant will then be equal to 100 microseconds.
This time constant is known as a medium time constant. Its value lies between the extreme ranges of the short and long time constants. In this case, its value happens to be exactly equal to the duration of the input pulse, 100 microseconds. The output waveform, after several time constants, is shown in figure
4-42
4-37. The long, sloping rise and fall of voltage is caused by the inability of the capacitor to charge and discharge rapidly through the 10,000-ohm series resistance.
At the first instant of time, 100 volts is applied to the medium time-constant circuit. In this circuit, 1TC is exactly equal to the duration of the input pulse. After 1TC the capacitor has charged to 63.2 percent of the input voltage (100 volts). Therefore, at the end of 1TC (100 microseconds), the voltage across the capacitor is equal to 63.2 volts. However, as soon as 100 microseconds has elapsed, and the initial charge on the capacitor has risen to 63.2 volts, the input voltage suddenly drops to 0. It remains there for 100 microseconds. The capacitor will now discharge for 100 microseconds. Since the discharge time is 100 microseconds (1TC), the capacitor will discharge 63.2 percent of its total 63.2-volt charge, a value of 23.3 volts. During the next 100 microseconds, the input voltage will increase from 0 to 100 volts instantaneously. The capacitor will again charge for 100 microseconds (1TC). The voltage available for this charge is the difference between the voltage applied and the charge on the capacitor (100 - 23.3 volts), or 76.7 volts. Since the capacitor will only be able to charge for 1TC, it will charge to 63.2 percent of the 76.7 volts, or 48.4 volts. The total charge on the capacitor at the end of 300 microseconds will be 23.3 + 48.4 volts, or 71.7 volts.
Notice that the capacitor voltage at the end of 300 microseconds is greater than the capacitor voltage at the end of 100 microseconds. The voltage at the end of 100 microseconds is 63.2 volts, and the capacitor voltage at the end of 300 microseconds is 71.7 volts, an increase of 8.5 volts.
The output waveform in this graph (eC) is the waveform that will be produced after many cycles of input signal to the integrator. The capacitor will charge and discharge in a step-by-step manner until it finally charges and discharges above and below a 50-volt level. The 50-volt level is controlled by the maximum amplitude of the symmetrical input pulse, the average value of which is 50 volts.
If the resistance in the circuit of figure 4-35 is increased to 100,000 ohms, the time constant of the circuit will be 1,000 microseconds. This time constant is 10 times the pulse duration of the input pulse. It is, therefore, a long time-constant circuit.
The shape of the output waveform across the capacitor is shown in figure 4-38. The shape of the output waveform is characterized by a long, sloping rise and fall of capacitor voltage.
4-43
At the first instant of time, 100 volts is applied to the long time-constant circuit. The value of charge on the capacitor at the end of the first 100 microseconds of the input signal can be found by using the Universal Time Constant Chart (figure 4-34). Assume that a line is projected up from the point on the base line corresponding to 0.1TC. The line will intersect the curve at a point that is the percentage of voltage across the capacitor at the end of the first 100 microseconds. Since the applied voltage is 100 volts, the charge on the capacitor at the end of the first 100 microseconds will be approximately 9.5 volts. At the end of the first 100 microseconds, the input signal will fall suddenly to 0 and the capacitor will begin to discharge. It will be able to discharge for 100 microseconds. Therefore, the capacitor will discharge 9.5 percent of its accumulated 9.5 volts (.095 × 9.5 = 0.90 volt). The discharge of the 0.90 volt will result in a remaining charge on the capacitor of 8.6 volts. At the end of 200 microseconds, the input signal will again suddenly rise to a value of 100 volts. The capacitor will be able to charge to 9.5 percent of the difference (100 − 8.6 = 91.4 volts). This may also be figured as a value of 8.7 volts plus the initial 8.6 volts. This results in a total charge on the capacitor (at the end of the first 300 microseconds) of 8.7 + 8.6 = 17.3 volts.
Notice that the capacitor voltage at the end of the first 300 microseconds is greater than the capacitor voltage at the end of the first 100 microseconds. The voltage at the end of the first 100 microseconds is 9.5 volts; the capacitor voltage at the end of the first 300 microseconds is 17.3 volts, an increase of 7.8 volts.
The capacitor charges and discharges in this step-by-step manner until, finally, the capacitor charges and discharges above and below a 50-volt level. The 50-volt level is controlled by the maximum amplitude of the square-wave input pulse, the average value of which is 50 volts.
Q21. What is the numerical difference (in terms of the time constant) between a long and a short time- constant circuit?
Q22. What would happen to the integrator output if the capacitor were made extremely large (all other factors remaining the same)?
DIFFERENTIATION is the direct opposite of integration. In the RC integrator, the output is taken from the capacitor. In the differentiator, the output is taken across the resistor. Likewise, this means that when the RL circuit is used as a differentiator, the differentiated output is taken across the inductor.
4-44
An application of Kirchhoff's law shows the relationship between the waveforms across the resistor and capacitor in a series network. Since the sum of the voltage drops in a closed loop must equal the total applied voltage, the graphical sum of the voltage waveforms in a closed loop must equal the applied waveform. Figure 4-39 shows a differentiator circuit with the output taken across a variable resistor.
With the variable resistor set at 1,000 ohms and the capacitor value of 0.01 microfarad, the time constant of the circuit is 10 microseconds. Since the input waveform has a duration of 100 microseconds, the circuit is a short time-constant circuit.
At the first instant of time in the short time-constant circuit, the voltage across the capacitor is 0. Current flows through the resistor and causes a maximum voltage to be developed across it. This is shown at the first instant of time in the graph of figure 4-40.
As the capacitor begins accumulating a charge, the voltage developed across the resistor will begin to decrease. At the end of the first time constant, the voltage developed across the resistor will have decreased by a value equal to 63.2 percent of the applied voltage. Since 100 volts is applied, the voltage across the resistor after 1TC will be equal to 36.8 volts. After the second time constant, the voltage across the resistor will be down to 13.5 volts. At the end of the third time constant, eR will be 5 volts and at the
4-45
end of the fourth time constant, 2 volts. At the end of the fifth time constant, the voltage across the resistor will be very close to 0 volts. Since the time constant is equal to 10 microseconds, it will take a total of 50 microseconds to completely charge the capacitor and stop current flow in the circuit.
As shown in figure 4-40 the slope of the charge curve will be very sharp. The voltage across the resistor will remain at 0 volts until the end of 100 microseconds. At that time, the applied voltage suddenly drops to 0, and the capacitor will now discharge through the resistor. At this time, the discharge current will be maximum causing a large discharge voltage to develop across the resistor. This is shown as the negative spike in figure 4-40. Since the current flow from the capacitor, which now acts like a source, is decreasing exponentially, the voltage across the resistor will also decrease. The resistor voltage will decrease exponentially to 0 volts in 5 time constants. All of this discharge action will take a total of 50 microseconds. The discharge curve is also shown in figure 4-40. At the end of 200 microseconds, the action begins again. The output waveform taken across the resistor in this short time-constant circuit is an example of differentiation. With the square wave applied, positive and negative spikes are produced in the output. These spikes approximate the rate of change of the input square wave.
The output across the resistor in an RC circuit of a medium time constant is shown in figure 4-41. The value of the variable resistor has been increased to a value of 10,000 ohms. This means that the time constant of the circuit is equal to the duration of the input pulse or 100 microseconds. For clarity, the voltage waveforms developed across both the resistor and the capacitor are shown. As before, the sum of the voltages across the resistor and capacitor must be equal to the applied voltage of 100 volts.
At the first instant of time, a pulse of 100 volts in amplitude with a duration of 100 microseconds is applied. Since the capacitor cannot respond quickly to the change in voltage, all of the applied voltage is felt across the resistor. Figure 4-41 shows the voltage across the resistor (eR) to be 100 volts and the voltage across the capacitor (eC) to be 0 volts. As time progresses, the capacitor charges. As the capacitor voltage increases, the resistor voltage decreases. Since the time that the capacitor is permitted to charge is 100 microseconds (equal to 1TC in this circuit), the capacitor will charge to 63.2 percent of the applied
4-46
voltage at the end of 1TC, or 63.2 volts. Because Kirchhoff's law must be followed at all times, the voltage across the resistor must be equal to the difference between the applied voltage and the charge on the capacitor (100 − 63.2 volts), or 36.8 volts.
At the end of the first 100 microseconds, the input voltage suddenly drops to 0 volts. The charge on the capacitor (−63.2 volts) becomes the source and the entire voltage is developed across the resistor for the first instant.
The capacitor discharges during the next 100 microseconds. The voltage across the resistor decreases at the same rate as the capacitor voltage and total voltage is maintained at 0. This exponential decrease in resistor voltage is shown during the second 100 microseconds in figure 4-41. The capacitor will discharge 63.2 percent of its charge to a value of 23.3 volts at the end of the second 100 microseconds. The resistor voltage will rise in the positive direction to a value of −23.3 volts to maintain the total voltage at 0 volts.
At the end of 200 microseconds, the input voltage again rises suddenly to 100 volts. Since the capacitor cannot respond to the 100-volt increase instantaneously, the 100-volt change takes place across the resistor. The voltage across the resistor suddenly rises from −23.3 volts to +76.7 volts. The capacitor will now begin to charge for 100 microseconds. The voltage will decrease across the resistor. This charge and discharge action will continue for many cycles. Finally, the voltage across the capacitor will rise and fall by equal amounts both above and below about a 50-volt level. The resistor voltage will also rise and fall by equal amounts to about a 0-volt level.
If the time constant for the circuit in figure 4-39 is increased to make it a long time-constant circuit, the differentiator output will appear more like the input. The time constant for the circuit can be changed by either increasing the value of capacitance or resistance. In this circuit, the time constant will be increased by increasing the value of resistance from 10,000 ohms to 100,000 ohms. Increasing the value of resistance will result in a time constant of 1,000 microseconds. The time constant is 10 times the duration of the input pulse. The output of this long time-constant circuit is shown in figure 4-42.
4-47
At the first instant of time, a pulse of 100-volts amplitude with a duration of 100 microseconds is applied. Since the capacitor cannot respond instantaneously to a change in voltage, all of the applied voltage is felt across the resistor. As time progresses, the capacitor will charge and the voltage across the resistor will be reduced. Since the time that the capacitor is permitted to charge is 100 microseconds, the capacitor will charge for only 1/10 of 1TC or to 9.5 percent of the applied voltage. The voltage across the resistor must be equal to the difference between the applied voltage and the charge on the capacitor (100 − 9.5 volts), or 90.5 volts.
At the end of the first 100 microseconds of input, the applied voltage suddenly drops to 0 volts, a change of 100 volts. Since the capacitor is not able to respond to so rapid a voltage change, it becomes the source of 9.5 volts. This causes a −9.5 voltage to be felt across the resistor in the first instant of time. The sum of the voltage across the two components is now 0 volts.
During the next 100 microseconds, the capacitor discharges. The total circuit voltage is maintained at 0 by the voltage across the resistor decreasing at exactly the same rate as the capacitor discharge. This exponential decrease in resistor voltage is shown during the second 100 microseconds of operation. The capacitor will now discharge 9.5 percent of its charge to a value of 8.6 volts. At the end of the second 100 microseconds, the resistor voltage will rise in a positive direction to a value of −8.6 volts to maintain the total circuit voltage at 0 volts.
At the end of 200 microseconds, the input voltage again suddenly rises to 100 volts. Since the capacitor cannot respond to the 100-volt change instantaneously, the 100-volt change takes place across the resistor. This step-by-step action will continue until the circuit stabilizes. After many cycles have passed, the capacitor voltage varies by equal amounts above and below the 50-volt level. The resistor voltage varies by equal amounts both above and below a 0-volt level.
The RC networks which have been discussed in this chapter may also be used as coupling networks. When an RC circuit is used as a coupling circuit, the output is taken from across the resistor. Normally, a long time-constant circuit is used. This, of course, will cause an integrated wave shape across the capacitor if the applied signal is nonsinusoidal. However, in a coupling circuit, the signal across the resistor should closely resemble the input signal and will if the time constant is sufficiently long. By referring to the diagram in figure 4-42, you can see that the voltage across the resistor closely resembles the input signal. Consider what would happen if a pure sine wave were applied to a long time-constant RC circuit (R is much greater than XC). A large percentage of the applied voltage would be developed across the resistor and only a small amount across the capacitor.
Q23. What is the difference between an RC and an RL differentiator in terms of where the output is developed?
A counting circuit receives uniform pulses representing units to be counted. It provides a voltage that is proportional to the frequency of the units.
With slight modification, the counting circuit can be used with a blocking oscillator to produce trigger pulses which are a submultiple of the frequency of the pulses applied. In this case the circuit acts as a frequency divider.
The pulses applied to the counting circuit must be of the same time duration if accurate frequency division is to be made. Counting circuits are generally preceded by shaping circuits and limiting circuits (both discussed in this chapter) to ensure uniformity of amplitude and pulse width. Under those conditions, the pulse repetition frequency is the only variable and frequency variations may be measured.
4-48
Q24. Name a common application of counting circuits.
The POSITIVE-DIODE COUNTER circuit is used in timing or counting circuits in which the number of input pulses are represented by the output voltage. The output may indicate frequency, count the rpm of a shaft, or register a number of operations. The counter establishes a direct relationship between the input frequency and the average dc output voltage. As the input frequency increases, the output voltage also increases; conversely, as the input frequency decreases, the output voltage decreases. In effect, the positive counter counts the number of positive input pulses by producing an average dc output voltage proportional to the repetition frequency of the input signal. For accurate counting, the pulse repetition frequency must be the only variable parameter in the input signal. Therefore, careful shaping and limiting of the input signal is essential for you to ensure that the pulses are of uniform width and that the amplitude is constant. When properly filtered and smoothed, the dc output voltage of the counter may be used to operate a direct reading indicator.
Solid-state and electron-tube counters operate in manners similar to each other. The basic solid-state (diode) counter circuit is shown in view (A) of figure 4-43. Capacitor C1 is the input coupling capacitor. Resistor R1 is the load resistor across which the output voltage is developed. For the purpose of circuit discussion, assume that the input pulses (shown in view (B)) are of constant amplitude and time duration and that only the pulse repetition frequency changes. At time T0, the positive-going input pulse is applied to C1 and causes the anode of D2 to become positive. D2 conducts and current ic flows through R1 and D2 to charge C1. Current ic, develops an output voltage across R1, shown as eout.
4-49
The initial heavy flow of current produces a large voltage across R1 which tapers off exponentially as C1 charges. The charge on C1 is determined by the time constant of R1 and the conducting resistance of the diode times the capacitance of C1. For ease of explanation, assume that C1 is charged to the peak value before T1.
At T1 the input signal reverses polarity and becomes negative-going. Although the charge on capacitor C1 cannot change instantly, the applied negative voltage is equal to or greater than the charge on C1. This causes the anode of D2 to become negative and conduction ceases. When D2 stops conducting e out is at 0. C1 quickly discharges through D1 since its cathode is now negative with respect to ground. Between T1 and T2 the input pulse is again at the 0-volt level and D2 remains in a nonconducting state. Since the very short time constant provided by the conduction resistance of D1 and C1 is so much less than the long time constant offered by D2 and R1 during the conduction period, C1 is always completely discharged between pulses. Thus, for each input pulse, a precise level of charge is deposited on C1. For each charge of C1 an identical output pulse is produced by the flow of ic through R1. Since this current flow always occurs in the direction indicated by the solid arrow, the dc output voltage is positive.
At T2 the input signal again becomes positive and the cycle repeats. The time duration between pulses is the interval represented by the period between T1 and T2 or between T3 and T4. If the input- pulse frequency is reduced, these time periods become longer. On the other hand, if the frequency is increased, these time intervals become shorter. With shorter periods, more pulses occur in a given length of time and a higher average dc output voltage is produced; with longer periods, fewer pulses occur and a lower average dc output voltage is produced. Thus, the dc output is directly proportional to the repetition frequency of the input pulses. If the current and voltage are sufficiently large, a direct-reading meter can be used to indicate the count. If they are not large enough to actuate a meter directly, a dc amplifier may be added. In the latter case, a pi-type filter network is inserted at the output of R1 to absorb the instantaneous pulse variations and produce a smooth direct current for amplification.
From the preceding discussion, you should see that the voltage across the output varies in direct proportion to the input pulse repetition rate. Hence, if the repetition rate of the incoming pulses increases, the voltage across R1 also increases. For the circuit to function as a frequency counter, some method must
4-50
be employed to use this frequency-to-voltage relationship to operate an indicator. The block diagram in view (A) of figure 4-44 represents one simple circuit which may be used to perform this function. In this circuit, the basic counter is fed into a low-pass filter and an amplifier with a meter that is calibrated in units of frequency.
A typical schematic diagram is shown in view (B). The positive pulses from the counter are filtered by C2, R2, and C3. The positive dc voltage from the filter is applied to the input of amplifier A. This voltage increases with frequency; as a consequence, the current through the device increases. Since emitter or cathode current flows through M1, an increase in amplifier current causes an increase in meter deflection. The meter may be calibrated in units of time, frequency, revolutions per minute, or any function based upon the relationship of output voltage to input frequency.
Q25. What establishes the value of the current that flows in the output of figure 4-43?
Q26. What is the purpose of D1 in figure 4-43?
Reversing the connections of diodes D1 and D2 in the positive-counter circuit (view (A) of figure 4- 43) will cause the circuit to respond to negative pulses and become a negative-counter circuit. Diode D2 conducts during the time the negative pulse is applied and current flows in the opposite direction through R1, as was indicated by the arrow. At the end of the negative pulse, D1 conducts and discharges C1. The current through R1 increases with an increase in pulse frequency as before. However, if the voltage developed across R1 is applied to the same control circuit, as shown in view (A) of figure 4-44, the increase in current will be in a negative direction and the amplifier will conduct less. Thus, the effect is opposite to that of the positive counter.
The STEP-BY-STEP (STEP) COUNTER is used as a voltage multiplier when a stepped voltage must be provided to any device which requires such an input. The step counter provides an output which increases in one-step increments for each cycle of the input. At some predetermined level, the output voltage reaches a point which causes a circuit, such as a blocking oscillator, to be triggered.
4-51
A schematic diagram of a positive step counter is shown in view (A) of figure 4-45. For step counting, the load resistor of the positive-counting circuit is replaced by capacitor C2. This capacitor is relatively large in comparison to C1. Each time D2 conducts, the charge on C2 increases as shown in view (B). The steps are not the same height each time. They decrease exponentially with time as the voltage across C2 approaches the input voltage.
As long as C2 has no discharge path, the voltage across its terminals increases with each successive step until it is equal in amplitude to the applied pulse. The voltage across C2 could be applied to a blocking-oscillator circuit to cause the oscillator to pulse after a certain amount of voltage is applied to it.
The circuit in figure 4-46, (view A) and (view B), may be used as a frequency divider. When used in this manner, Q1 is used as a single-swing blocking oscillator that is triggered when the voltage across C2 becomes great enough to forward bias Q1. At other times, the transistor is cut off by the bias voltage developed in the section of R2 that is between the ground and the slide.
4-52
The action of the counter can best be understood by referring back to figure 4-45. Assume C2 is 10 times larger than C1 and the peak voltage is 10 volts. C1 will assume 9/10 of the positive input voltage at T0, while C2 will assume only 1/10, or 1 volt in this example. At T1 the input will drop in a negative direction and D2 will be cut off. The cathode of D1 will become more negative than its anode and conduct, discharging C1. The charge on C2 will remain at 1 volt because it has no discharge path. At T2 the second pulse will be applied. The 1-volt charge on C2 will oppose the 10 volts of the second pulse, and the applied voltage for the capacitors to charge will be 9 volts. C2 will again charge 10 percent, or 0.9 volt. This is in addition to the initial charge of volt. At the end of the second pulse, the voltage on C2 will be 1.9 volts. At T3 the third pulse will be 10 volts, but 1.9 volts will oppose it. Therefore, the applied
4-53
voltage will be 10 − 1.9 volts, or 8.1 volts. C2 will charge to 10 percent of 8.1 volts, or .81 volt. The voltage on C2 will become 1 + .9 + .81, or 2.71 volts. Successive input pulses will raise C2 by 10 percent of the remaining voltage toward 10 volts until the blocking oscillator works. If the oscillator bias is set so that Q1 begins conduction at 3.8 volts, this will continue until 3.8 volts is exceeded. Since the fourth step is 3.5 volts and the fifth is 4.1 volts, the 3.8-volt level is crossed at the fifth step. If the oscillator goes through 1 cycle of operation every fifth step and C2 is discharged at this point, this circuit would be a 5- to-1 divider.
The circuit can be made to divide by 3, 4, or some other value by setting the bias at a different level. For example, if the bias is set at 2.9 volts, conduction will occur at the fourth step, making it a 4-to-1 divider.
The counting stability of the step counter is dependent upon the exponential charging rate of capacitor C2. As C2 increases to higher steps, the voltage increments are less and less. If the ratio becomes too great, the higher steps become almost indiscernible. For this reason, accuracy decreases as the ratio increases. When you desire to count by a large number, 24 for example, a 6-to-1 counter and a 4- to-1 counter are connected in cascade (series). A more stable method of counting 24 would be to use a 2:1, 3:1, 4:1 counter connected in cascade. Most step counters operate on a ratio of 5 to 1 or less.
Q27. What is the difference between a positive counter and a step counter?
This chapter has presented information on wave shaping. The information that follows summarizes the important points of this chapter.
A LIMITER is a device which limits or prevents some part of a waveform from exceeding a specified value.
In a SERIES LIMITER, the diode is in series with the output. It can limit either the negative or positive alternation of the input signal.
In a SERIES-POSITIVE LIMITER, the diode is in series with the output which is taken across the resistor. It removes the positive alternation of the input signal.
In a SERIES-POSITIVE LIMITER WITH BIAS, the bias potential will either aid or oppose the flow of current. When aiding forward bias, only a portion of the positive input pulse is removed. When the bias aids the reverse bias, all of the positive and a portion of the negative pulse is removed.
4-54
The SERIES-NEGATIVE LIMITER limits the negative portion of the input pulse. The difference between a series-negative limiter and a series-positive limiter is that the diode is reversed in the negative limiter.
A SERIES-NEGATIVE LIMITER with bias is the same as the series-positive limiter with bias, but the outputs are opposite. When bias aids forward bias, only a portion of the negative input is removed. When bias aids reverse bias, all of the negative and a portion of the positive input is removed.
4-55
In a PARALLEL LIMITER, a resistor and diode are connected in series with the input signal. The output is taken across the diode.
In the PARALLEL-POSITIVE LIMITER, the positive portion of the input signal is limited when the diode conducts.
The PARALLEL-NEGATIVE LIMITER diode is reversed from that of the parallel positive limiter to limit only a portion of the negative input signal.
The DUAL-DIODE LIMITER combines the parallel negative limiter with negative bias (reverse bias) and the parallel positive limiter with positive bias (reverse bias). It will remove parts of the positive and negative input signal.
4-56
A CLAMPING CIRCUIT effectively clamps or ties down the upper or lower extremity of a waveform to a fixed dc potential. Clamping does not change the amplitude or shape of the input waveform.
A POSITIVE CLAMPER will clamp the lower extremity of the input waveform to a dc potential of 0 volts.
4-57
A NEGATIVE CLAMPER will clamp the upper extremity of the input waveform to a dc potential of 0 volts.
A COMMON-BASE TRANSISTOR CLAMPER clamps the collector voltage to a reference level.

If the odd harmonics of a sine wave are added algebraically, the result is a square wave. A PERFECT SQUARE WAVE is composed of an infinite number of odd harmonics in phase with the fundamental wave.
4-58
A SAWTOOTH WAVE is made up of different harmonics, both odd and even.
A PEAKED WAVE is made up of odd harmonics that are in phase and out of phase with the fundamental.
4-59
INTEGRATION takes place in an RC circuit with the output taken across the capacitor. The amount of integration is dependent upon the time constant of the circuit. Full integration takes place when the time constant of the RC circuit is at least 10 times greater than the duration of the input pulse. An RL circuit is also used as an integration circuit. The output is taken across the resistor and the time constant of the circuit is 10 times greater than the input pulse.
4-60
DIFFERENTIATION is the opposite of integration. In the differentiator, the output is taken across the resistor. Full differentiation takes place when the time constant of the circuit is 1/10 that of the input pulse.
A COUNTING CIRCUIT receives uniform pulses, representing units to be counted, and produces a voltage output proportional to its frequency.
ANSWERS TO QUESTION Q1. THROUGH Q27.
A1. Negative.
A2. Positive.
A3. Biasing.
A4. The diode.
A5. Conducting, cutoff.
A6. Short time constant.
A7. Long time constant.
A8. Most negative.
A9. Positive potential.
A10. Positive clamper with negative bias.
A11. Most positive.
A12. Negative potential.
A13. Positive bias.
A14. -5 volts.
4-61
A15. It is composed of an infinite number of odd harmonics in phase with the fundamental.
A16. It is composed of odd harmonics some of which are out phase with the fundamental.
A17. All the odd harmonics are in phase with the fundamental in the square wave. This is not true of the odd harmonics in the peaked wave.
A18. The time constant is long and the output is taken across the capacitor in an RC circuit.
A19. A pure sine wave cannot be integrated; it contains no harmonics.
A20. The ability of the inductor to oppose a change in current.
A21. The time-constant value of a long time constant-circuit is 10 times the value of the input pulse duration. The short time-constant circuit has a time constant of 1/10 of the pulse duration.
A22. A more complete integration of the waveform would result from the long time constant.
A23. In an RC circuit the output is taken across the resistor. In the RL circuit the output is taken across the inductor.
A24. Frequency counters or frequency dividers.
A25. The frequency of the voltage input.
A26. To provide a quick discharge path for C1.
A27. The load resistor in a positive counter is replaced by a capacitor in a step counter.
AI-1
AMPLITUDE STABILITY—Amplitude stability refers to the ability of the oscillator to maintain a constant amplitude in the output waveform.
ASTABLE MULTIVIBRATOR—A multivibrator which has no stable state. Also called free-running because it alternates between two different output voltage levels during the time it is on. The frequency is determined by the RC time constant of the coupling circuit.
ATTENUATION—The ability of a filter circuit to reduce the amplitude of unwanted frequencies to a level below that of the desired output frequency.
BANDPASS FILTER—A filter which allows a narrow band of frequencies to pass through the circuit. Rejects or attenuates frequencies which are either higher or lower than the desired band of frequencies.
BAND-REJECT FILTER—Rejects the passage of current for a small band of frequencies. Allows current to flow at frequencies either above or below this band.
BANDWIDTH—The range of frequencies included between upper and lower frequencies.
BISTABLE MULTIVIBRATOR—A multivibrator that has two stable states. It remains in one of the states until a trigger is applied. It then flips to the other stable state and remains there until another trigger is applied. Also referred to as a flip-flop.
BUFFER AMPLIFIER—An amplifier which isolates one circuit from another. It decreases the loading effect on an oscillator by reducing the interaction between the load and the oscillator.
CAPACITIVE REACTANCE—The opposition, expressed in ohms, offered to the flow of an alternating current by capacitance. The symbol for capacitive reactance is Xc.
CLAMPER—A circuit in which either the upper or lower extremity of a waveform is fixed at a desired value.
COMPLEX WAVE—A waveform other than a sine wave.
COUNTER—A circuit which counts input pulses.
CRYSTAL OVEN—Closed oven maintained at a constant temperature in which a crystal and its holder are enclosed to reduce frequency drift.
DAMPED WAVE—A sinusoidal wave in which the amplitude steadily decreases with time. Often associated with energy loss.
FILTER CIRCUIT—Network of resistors, inductors, and/or capacitors which offers opposition to certain frequencies.
FLYWHEEL EFFECT—The ability of a resonant circuit to operate continuously because of stored energy or energy pulses.
AI-2
FREQUENCY CUTOFF—The frequency at which the filter circuit changes from an action of rejecting the unwanted frequencies to an action of passing the desired frequencies. Conversely, the point at which the filter circuit changes from an action in which it passes the desired frequencies to an action in which it rejects the undesired frequencies.
FREQUENCY STABILITY—Refers to the ability of an oscillator to accurately maintain its operating frequency.
HALF-POWER POINT—Point on either side of resonance curve at which the power is approximately 70 percent of the maximum value.
HARMONIC—Integral multiples of a fundamental frequency. For example, the harmonics of 60 hertz are 120 hertz, 180 hertz, 240 hertz, and so forth.
HIGH-PASS FILTER—A filter that passes a majority of the high frequencies on to the next circuit and rejects, or attenuates, the lower frequencies. Also called a low-frequency discriminator.
INDUCTIVE REACTANCE—The opposition to the flow of an alternating current (expressed in ohms) caused by the inductance of a circuit. The symbol for inductive reactance is XL.
IMPEDANCE—Total opposition to alternating current flow. Impedance may consist of any combination of resistance, inductive reactance, and capacitive reactance. The symbol for impedance is Z.
LIMITER—A device which prevents (limits) a waveform from exceeding a specified value. LOWER-FREQUENCY CUTOFF—The lowest frequency a circuit will pass. LOW-PASS FILTER—A filter that passes a majority of the low frequencies on to the next circuit and
rejects, or attenuates, the higher frequencies. Also called a high-frequency discriminator. MULTIVIBRATOR—A form of relaxation oscillator which comprises two stages that are coupled so
that the input of one is derived from the output of the other.
MONOSTABLE MULTIVIBRATOR—A multivibrator which has one steady state. A signal (trigger) must be applied to cause change of states.
NATURAL FREQUENCY—See Resonance Frequency. NEGATIVE CLAMPER—The upper extremity of the output waveshape is clamped to a dc potential of
0 volts.
OSCILLATOR—An oscillator is a nonrotating device which produces alternating current. The frequency is determined by the characteristics of the device.
PARALLEL LIMITER—A resistor and diode connected in series with the input signal. The output is taken across the diode.
PARALLEL-NEGATIVE LIMITER—A resistor and diode connected in series with the input signal. The output is taken across the diode and the negative alternation is eliminated.
PARALLEL-POSITIVE LIMITER—A resistor and diode connected in series with the input signal. The output is taken across the diode and the positive alternation of the input signal is eliminated.
AI-3
PARALLEL-RESONANT CIRCUIT—A resonant circuit in which the source voltage is connected across a parallel circuit (formed by a capacitor and an inductor) to furnish a high impedance to the frequency at which the circuit is resonant. Often referred to as a tank circuit.
PERIODIC WAVE—A waveform that undergoes a pattern of changes, returns to its original pattern, and then repeats the same pattern of changes. Examples are square waves, rectangular waves, and sawtooth waves.
POSITIVE CLAMPER—The lower extremity of the output waveshape is clamped to a dc potential of 0 volts.
PULSE—Signal characterized by a rapid rise and decay from an initial level.
PULSE OSCILLATOR—A sine-wave oscillator that is turned on and off at specific times. Also known as a ringing oscillator.
PULSE-REPETITION FREQUENCY (PRF)—The number of times in 1 second that a waveform repeats itself.
PULSE-REPETITION RATE (PRR)—Same as Pulse-Repetition Frequency (prf). Q—Figure of merit (efficiency) of a circuit or coil. Ratio of inductive reactance to resistance. QUIESCENT STATE—Time during which a tube or transistor of an electrical circuit is not performing
its active function.
RC CONSTANT—Time constant of a resistor-capacitor circuit. Equal in seconds to the resistance value multiplied by capacitance value.
RC DIFFERENTIATOR—An RC circuit in which the output is taken from the resistor.
RC INTEGRATOR—An RC circuit in which the output is taken from the capacitor.
RC NETWORK—A circuit containing resistances and capacitances arranged in a particular manner to perform a specific function.
RC OSCILLATOR—An oscillator in which the frequency is determined by resistive and capacitive elements.
REGENERATIVE FEEDBACK—The process by which a portion of the output power of an amplifying device is fed back to reinforce the input.
RESONANCE—The condition in a circuit containing inductance and capacitance in which the inductive reactance is equal and opposite to the capacitive reactance. This condition occurs at only one frequency and the circuit in that condition is said to be in resonance. The resonant frequency can be changed by varying the values of either the capacitance or inductance.
RESONANT CIRCUIT—A circuit that contains both inductance and capacitance and is resonant at one frequency (XL = XC).
RESONANT FREQUENCY—That frequency in a given resonant circuit at which the inductive and capacitive values are equal and cancel each other.
RL DIFFERENTIATOR—An RL circuit in which the output is taken from the inductor.
AI-4
RL INTEGRATOR—An RL circuit in which the output is taken from the resistor.
SELECTIVITY—The ability of a circuit to discriminate between frequencies.
SERIES-FED OSCILLATOR—An oscillator in which dc power is supplied to the amplifier through the tank circuit or a portion of the tank circuit.
SERIES LIMITER—The diode is connected in series with the output and the output is taken across the resistor. Either the positive or negative alternation of the input wave is eliminated.
SERIES-NEGATIVE LIMITER—The diode is connected in series with the output and the output is taken across the resistor. Eliminates the negative alternation of the input wave.
SERIES-PARALLEL CIRCUIT—A circuit in which two or more parallel or series combinations are in series with each other.
SERIES-POSITIVE LIMITER—The diode is connected in series with the output and the output is taken across a resistor. Eliminates the positive alternation of the input wave.
SERIES-RESONANT CIRCUIT—A resonant circuit in which the source voltage is connected in series with a capacitor and an inductor (also in series) to furnish a low impedance at the frequency at which the circuit is resonant.
SHAPING CIRCUIT—A circuit which alters the shapes of input waveforms.
STEP-BY-STEP-COUNTER—A counter which provides an output for each cycle of the input in one- step increments.
SHUNT-FED OSCILLATOR—An oscillator which receives its dc power for the transistor or tube through a path both separate from and parallel to the tank circuit.
TANK CIRCUIT—A tuned circuit used to temporarily store energy. Also referred to as a parallel- resonant circuit.
TICKLER COIL—Small coil connected in series with the collector or plate circuit of a transistor or tube and inductively coupled to a base or grid-circuit coil to establish feedback or regeneration.
TIME CONSTANT—Time required for an exponential quantity to change by an amount equal to .632 times the total change that can occur.
TRIGGER—Short pulse, either positive or negative, which can be used to cause an electrical function to take place.
TUNED CIRCUIT—Circuit consisting of inductance and capacitance which can be adjusted for resonance at a desired frequency.
UPPER-FREQUENCY CUTOFF—The highest frequency a circuit can pass.
INDEX-1
INDEX-2
2-21 to 2-24 RL integrators, 4-38 RLC circuits, frequency effects on, 1-3 to 1-5 S Series limiters, 4-1 to 4-9 Series RC circuits, 4-18, 4-19 Series/parallel a.c. circuits, review of, 1-3 to
review of series/parallel a.c. circuits, 1-3 to 1-5
INDEX-3
Information: The text pages that you are to study are provided at the beginning of the assignment questions.
1
Textbook assignment: Chapter 1, “Tuned Circuits,” pages 1-1 through 1-52. _________________________________________________________________________________
1-1. An inductor presents which of the following types of electrical opposition to ac current flow?
1. Reactance 2. Resistance 3. Inductance 4. Capacitance
1-2. Which of the following electrical characteristics determines the magnitude of inductive reactance?
1. Resistance 2. Frequency only 3. Inductance only 4. Frequency and inductance
1-3. Which of the following values represents an inductive reactance?
1. XC = 2,220 ohms 2. XL = 220 ohms 3. L = 22 millihenries 4. C = 22 microfarads
1-4. What formula is used to calculate inductive reactance?
1.
3.
2.
4.
1-5. In an ac circuit, how does inductive
reactance respond to an increase in applied frequency?
1. Inductive reactance increases 2. Inductive reactance decreases 3. Inductive reactance remains the same
1-6. What term describes the opposition to ac
that causes current to lead voltage?
1. Resistance 2. Conductance 3. Inductive reactance 4. Capacitive reactance
1-7. In an ac circuit, how does capacitive
reactance respond to an increase in applied frequency?
1. Capacitive reactance increases 2. Capacitive reactance decreases 3. Capacitive reactance remains the
1-8. In an ac circuit, what is the term that describes the TOTAL opposition to current flow?
1. Impedance 2. Inductance 3. Resistance 4. Capacitance
1-9. In an ac circuit that contains an inductive reactance of 7,250 ohms and a capacitive reactance of 9,775 ohms, what is the resultant reactance?
1. - 2,525 ohms 2. -10,250 ohms 3. 2,525 ohms 4. 10,250 ohms
1-10. When an ac circuit is at resonance, what is the relationship between XL and XC
1. XL is equal to XC 2. XL is less than XC 3. XL is greater than XC
2
1-11. What formula is used to calculate resonant frequency?
1.
3.
2.
4.
1-12. In a tank circuit, how does the resonant
frequency of the circuit respond to an increase in (a) capacitance and (b) inductance?
1. (a) Increases (b) increases 2. (a) Increases (b) decreases 3. (a) Decreases (b) decreases 4. (a) Decreases (b) increases
1-13. In a resonant circuit, what is the phase angle between voltage and current?
1. 0 degrees 2. 90 degrees 3. 180 degrees 4. 270 degrees
1-14. In a resonant circuit, how does resistance change, if at all, in response to an increase in frequency?
1. Increases 2. Decreases 3. Remains the same
1-15. In a series-LC circuit, which of the following component characteristics describes circuit action (a) below the resonant frequency and (b) above the resonant frequency?
1. (a) Inductive (b) Capacitive 2. (a) Inductive (b) Resistive 3. (a) Capacitive (b) Inductive 4. (a) Capacitive (b) Resistive
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3
Figure 1A.—Series-resonant circuit.
IN ANSWERING QUESTIONS 1-16 THROUGH 1-21, REFER TO FIGURE 1A. 1-16. What is the resonant frequency for the
circuit?
1. 1.592 MHz 2. 92 MHz 3. 159.2 MHz 4. 1,592 MHz
1-17. What is the value of inductive reactance?
1. 1.97 ohms 2. 97 ohms 3. 199.7 ohms 4. 1,997 ohms
1-18. If the resonant frequency is 7.96 MHz, what is the value of capacitive reactance?
1. 500 ohms 2. 1,000 ohms 3. 2,000 ohms 4. 4,000 ohms
IN ANSWERING QUESTIONS 1-19 THROUGH 1-21, ASSUME THE SOURCE FREQUENCY IN FIGURE 1A IS ABOVE THE RESONANT FREQUENCY. SELECT THE ANSWERS THAT DESCRIBE HOW AN ABOVE-RESONANCE FREQUENCY WILL CAUSE THE CIRCUIT CHARACTERISTICS IN THE QUESTIONS TO RESPOND WHEN COMPARED TO THEIR VALUES AT RESONANCE. 1-19. Impedance.
1. Increases 2. Decreases 3. Remains the same
1-20. Current.
1. Increases 2. Decreases 3. Remains the same
1-21. Voltage drops across the reactances.
1. Increases 2. Decreases 3. Remains the same
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4
Figure 1B.—Series-resonant circuit curves.
IN ANSWERING QUESTIONS 1-22 AND 1-23, REFER TO FIGURE 1B. 1-22. Response curve B for a series-resonant
circuit represents which of the following circuit characteristics?
1. Power 2. Voltage 3. Current 4. Impedance
1-23. At resonance, which of the following series-resonant circuit values is at a maximum value?
1. Circuit current 2. Voltage across L 3. Voltage across C 4. Circuit impedance
1-24. In a series-resonant circuit operating at fr, what term describes the impedance of the circuit?
1. Resistive 2. Inductive only 3. Capacitive only 4. Capacitive-inductive
Figure 1C.—Parallel-resonant circuit.
IN ANSWERING QUESTIONS 1-25 THROUGH 1-27, REFER TO FIGURE 1C. 1-25. In the parallel-resonant circuit, what is
the phase relationship between the current in the inductor and the current in the capacitor?
1. Inductor current is in phase with
capacitor current 2. Inductor current is 45 degrees out of
phase with capacitor current 3. Inductor current is 90 degrees out of
phase with capacitor current 4. Inductor current is 180 degrees out of
1-26. In the parallel-resonant circuit, what is the phase relationship between voltage in the inductor and the voltage in the capacitor.
1. Inductor voltage is in phase with
capacitor voltage 2. Inductor voltage is 45 degrees out of
phase with capacitor voltage 3. Inductor voltage is 90 degrees out of
phase with capacitor voltage 4. Inductor voltage is 180 degrees out of
5
1-27. In the parallel-resonant circuit, which of the following circuit conditions is NOT normal?
1. XC equals XL 2. IC equals IL 3. Iline is minimum 4. Iline is maximum
Figure 1D.—Parallel-resonant circuit curves.
IN ANSWERING QUESTIONS 1-28 AND 1-29, REFER TO FIGURE 1D. 1-28. In the figure, what does response curve A
represent?
1. Current 2. Impedance 3. Reactance 4. Resistance
1-29. What does response curve B represent?
1. Power 2. Impedance 3. Reactance 4. Resistance
1-30. As a parallel-resonant circuit approaches resonance, which of the following circuit actions takes place?
1. Impedance decreases 2. Oscillating current increases 3. Inductance increases 4. Capacitance decreases
1-31. When a parallel-resonant circuit operates BELOW resonance, which of the following component characteristics describes circuit action?
1. Inductive 2. Capacitive 3. Resistive
1-32. When a parallel-resonant circuit operates ABOVE resonance, which of the following component characteristics describes circuit actions?
1. Inductive 2. Capacitive 3. Resistive
1-33. In a parallel-resonant circuit, which of the following circuit conditions is observed?
1. Oscillating current is less than line
current 2. Oscillating current is greater than line
current 3. Line current is maximum 4. Impedance is minimum
1-34. What is the level of impedance offered at resonance in (a) a series-resonant circuit and (b) a parallel-resonant circuit?
1. (a) High (b) high 2. (a) High (b) low 3. (a) Low (b) low 4. (a) Low (b) high
1-35. The ability of a resonant circuit to separate currents of desired frequencies from those of undesired frequencies makes them useful in which of the following circuit applications?
1. Filters 2. Counters 3. Amplifiers 4. Voltage dividers
6
1-36. The Q of a circuit is a measure of circuit
1. quality 2. permeance 3. conductance 4. inductive reactance
1-37. Which of the following circuit values has the greatest effect on the figure of merit of the circuit?
1. Reactance 2. Inductance 3. Resistance 4. Capacitance
1-38. What formula is used to figure the Q of a coil?
1.
3.
2.
4.
1-39. On which of the following coil
characteristics is the Q of a coil dependent?
1. Size 2. Length 3. Material 4. All of the above
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1-40. A series-resonant circuit, which of the following conditions results in a voltage gain?
1.
2.
3. 4.
1-41. In a parallel-resonant circuit, Q is used to figure which of the following circuit values?
1. Voltage gain 2. Voltage loss 3. Circulating tank current 4. Circulating line current
1-42. To determine bandwidth, you would use which of the following mathematical expressions?
1.
3.
2.
4.
1-43. To calculate (figure) the half-power
points of a resonant circuit, which of the following mathematical expressions should you use?
1. .707 x Imin 2. .707 x Imax 3. .637 x Imin 4. .637 x Imax
7
Figure 1E.—Response curve.
IN ANSWERING QUESTIONS 1-44 THROUGH 1-46, REFER TO FIGURE 1E. 1-44. In the response curve, what is the
resonant frequency?
1. 50 kHz 2. 70 kHz 3. 100 kHz 4. 140 kHz
1-45. What is the bandwidth?
1. 10 kHz 2. 20 kHz 3. 30 kHz 4. 40 kHz
1-46. If the Q of the circuit represented by the response curve is 100, what is the bandwidth?
1. 1 kHz 2. 10 kHz 3. 20 kHz 4. 30 khz
Figure 1F.—Filter circuit.
IN ANSWERING QUESTION 1-47, REFER TO FIGURE 1F. 1-47. If the applied frequency to the circuit is
1. (a) XC increases (b) XL increases 2. (a) XC increases (b) XL decreases 3. (a) XC decreases (b) XL decreases 4. (a) XC decreases (b) XL increases
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8
_______________________________________ TO ANSWER QUESTIONS 1-48 THROUGH 1-50, SELECT FROM COLUMN B THE CIRCUIT WHICH DESCRIBES THE CIRCUIT OPERATION IN COLUMN A. CHOICES IN COLUMN B MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. A. CIRCUIT
B. CIRCUIT
1-48. Passes the majority of current below a specific frequency and opposes current above that frequency.
1. 2. 3. 4.
1-49. Passes the majority of current above a specific frequency and opposes current below that frequency.
1-50. Passes a narrow band of frequencies and opposes all others.
1-51. The action of a filter circuit that reduces the amplitude of unwanted frequencies below the amplitude of the desired frequency is known as
1. attenuation 2. amplification 3. discrimination 4. impedance matching
1-52. The frequency beyond which a filter circuit no longer passes current is referred to as the
1. filter frequency 2. cutoff frequency 3. resonant frequency 4. response frequency
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9
Figure 1G.—Filter circuits.
TO ANSWER QUESTIONS 1-53 AND 1-54, SELECT FROM FIGURE 1G THE CIRCUIT DIAGRAM WHICH MATCHES THE CIRCUIT NAME IN EACH QUESTION. CHOICES IN THE FIGURE MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. 1-53. Band-reject filter.
1. A 2. B 3. C 4. D
1-54. High-pass filter.
1. A 2. B 3. C 4. D
Figure 1H.—Filter circuit.
IN ANSWERING QUESTIONS 1-55 AND 1-56, REFER TO THE CIRCUIT IN FIGURE 1H. 1-55. L1 and C1 in the circuit offer what type
of opposition to (a) frequencies near resonance and (b) all other frequencies?
1. (a) Minimum (b) minimum 2. (a) Minimum (b) maximum 3. (a) Maximum (b) maximum 4. (a) Maximum (b) minimum
1-56. In the type of filter circuit in the figure, what is/are the "cutoff point(s)?"
1. Upper frequency limit only 2. Lower frequency limit only 3. Both upper and lower frequency
1-57. In a series-resonant circuit that is operating at resonance, what is the amplitude of the applied voltage compared to (a) inductor voltage and (b) capacitor voltage?
1. (a) Lower (b) lower 2. (a) Lower (b) higher 3. (a) Higher (b) higher 4. (a) Higher (b) lower
10
Figure 1I.—Series-RCL circuit at resonance.
IN ANSWERING QUESTIONS 1-58 THROUGH 1-60, REFER TO FIGURE 1I. 1-58. With the circuit in the figure at
resonance, what is the circuit current?
1. 1 ampere 2. 2 amperes 3. 3 amperes 4. 0.5 ampere
1-59. If Ea were increased to 60 volts at the resonant frequency, what would be the voltage drop across the capacitor?
1. 10 volts 2. 20 volts 3. 30 volts 4. 60 volts
1-60. If the circuit is at resonance, what is
circuit impedance?
1. 10 ohms 2. 20 ohms 3. 30 ohms 4. 40 ohms
11
Textbook assignment: Chapter 2, “Oscillators,” pages 2-1 through 2-38. ___________________________________________________________________________________
2-1. A sinusoidal oscillator can be regarded as
which of the following types of amplifiers?
1. One that produces a trapezoidal wave 2. One that produces a sine wave 3. One that produces a square wave 4. One that produces a sawtooth wave
2-2. Wave generators are classified according to the
1. input wave shape 2. output wave shape 3. current in the output 4. voltage in the output
2-3. An IDEAL sinusoidal oscillator would produce which of the following outputs?
1. A square wave of constant frequency
and amplitude 2. A square wave of varying frequency
and amplitude 3. A sine wave of constant frequency and
amplitude 4. A sine wave of varying frequency and
2-4. What three circuits are most commonly used as frequency determining devices?
1. Class C amplifier, class B amplifier,
and class A amplifier 2. Crystal-controlled oscillator, RC
oscillator, and LC oscillator 3. Common-emitter amplifier, common-
4. Transformer coupler, RC coupler, and direct coupler
2-5. Which of the following circuits is NOT a
relaxation oscillator?
1. A multivibrator 2. A sawtooth generator 3. A blocking oscillator 4. A sinusoidal oscillator
2-6. Which of the following definitions
describes the basic oscillator?
1. A nonrotating device producing alternating current
2. A rotating device producing alternating current
3. A nonrotating device producing direct current
4. A rotating device producing direct current
2-7. Amplitude stability in an oscillator is the
1. produce an increased amplitude in the output
2. produce a variable amplitude in the output
3. maintain a constant frequency in the output
4. maintain a constant amplitude in the output
2-8. Frequency stability in an oscillator refer to
1. maintain a constant operating frequency
2. maintain a variable operating amplitude
3. maintain a constant amplitude 4. vary operating frequency
12
2-9. What is the purpose of a buffer amplifier?
1. To provide a direct connection between the oscillator and the load
2. To amplify the output signal of the oscillator
3. To remove frequency distortion from the oscillator
4. To prevent load variations from affecting the oscillator
2-10. Why is class A bias used in oscillators?
1. To develop low power 2. To develop maximum power 3. To maintain low distortion 4. To maintain high efficiency
2-11. When a group of RC networks is used for regenerative feedback, which of the following waveform actions takes place in each successive stage?
1. Waveform is rectified 2. Amplitude is decreased 3. Amplitude is increased 4. Amplitude is held constant
2-12. When RC networks are connected in cascade (series), what amount of phase shift should you see?
1. The sum of the phase shifts of each RC
network 2. The difference between the phase shifts
of each RC network 3. The product of the phase shifts of each
RC network 4. The square of the phase shifts of each
2-13. Which of the following terms describes the gradual amplitude reduction in an oscillator?
1. Damping 2. Phase shift 3. Regeneration 4. Flywheel effect
2-14. Which of the following formulas can be used to figure frequency in an LC tank circuit?
1.
2.
3.
4.
2-15. Which of the following actions best describes the piezoelectric effect?
1. Produces an dc output voltage for a
given ac input voltage 2. Produces an output voltage for a given
mechanical input 3. Produces a mechanical output for a
given input voltage 4. Both 2 and 3 above
2-16. The piezoelectric effect is the property of a crystal which produces which of the following electrical characteristics?
1. Resistance 2. Inductance 3. Capacitance 4. Each of the above
13
2-17. What is the schematic symbol for a crystal?
1.
2.
3.
4.
2-18. What electrical characteristic makes the frequency stability of a crystal better than that of an LC tank circuit?
1. Higher Q 2. Higher inductance 3. Higher resistance 4. Higher capacitance
2-19. How is feedback described?
1. Control of a circuit output signal by the input signal
2. Control of a circuit input signal by the output of the previous circuit
3. Transfer of a portion of the output circuit energy to control the input of the circuit
4. Transfer of a portion of the input circuit energy to control the output circuit
2-20. Which of the following terms describes the types of feedback?
1. Degenerative and regenerative 2. Negative and positive 3. Both 1 and 2 above 4. Bypassed and unbypassed
2-21. What type of feedback aids an input signal?
1. Positive 2. Negative 3. Bypassed 4. Degenerative
2-22. What type of feedback opposes an input signal?
1. Positive 2. Unbypassed 3. Degenerative 4. Regenerative
2-23. What type of feedback is used to sustain oscillations?
1. Bypassed 2. Negative 3. Degenerative 4. Regenerative
2-24. What oscillator uses a tickler coil for feedback?
1. Hartley 2. Colpitts 3. Armstrong 4. RC phase-shift
2-25. What oscillator uses a tapped coil for feedback?
1. Hartley 2. Colpitts 3. Armstrong 4. RC phase-shift
14
2-26. What oscillator uses split capacitors for feedback?
1. Hartley 2. Colpitts 3. Armstrong 4. RC phase-shift
_______________________________________ TO ANSWER QUESTIONS 2-27 THROUGH 2-29, SELECT THE CONFIGURATIONS IN COLUMN B THAT MATCH THE AMPLIFIER CHARACTERISTICS IN COLUMN A. CHOICES IN COLUMN B MAY BE USED ONCE, MORE THAN ONCE OR NOT AT ALL. A. CHARACTERISTICS 2-27. Voltage gain is
2-28. Low power gain
2-29. Feedback signal requires phase shift
B. CONFIGURATIONS 1. Common-base 2. Common-gate 3. Common-emitter 4. Common-collector
2-30. Which of the following statements best describes tank current in a series-fed oscillator?
1. The dc path is through the tank circuit 2. The dc path does not go through the
tank circuit 3. The ac path is through the tank circuit 4. The ac path does not go through the
2-31. In a shunt-fed, tuned-collector Armstrong oscillator, what blocks the dc component from the tank circuit?
1. A resistor 2. A capacitor 3. An inductor 4. A transistor
2-32. Which of the following circuit arrangements aid in the frequency stability of an oscillator?
1. A regulated power supply 2. A common bias source for the emitter
and collector 3. Both 1 and 2 above 4. Separate bias sources
Figure 2A.—Tuned-base Armstrong oscillator.
IN ANSWERING QUESTIONS 2-33 THROUGH 2-37, REFER TO FIGURE 2A. 2-33. The frequency of the output signal of the
oscillator is determined by what components?
1. R1 and L1 2. L2 and C1 3. L3 and C4 4. R3 and C3
2-34. Forward bias for the amplifier is developed by what component?
1. R1 2. R2 3. R3 4. L1
15
2-35. The resonant frequency is tuned to the desired value by what component?
1. C1 2. C2 3. L3 4. L1
2-36. What is the maximum degree of phase shift provided between the base and collector of Q1?
1. 0 degrees 2. 90 degrees 3. 120 degrees 4. 180 degrees
2-37. Temperature stability of the oscillator is
improved by what component?
1. R1 2. R2 3. R3 4. C4
2-38. What feature in a Hartley oscillator differs from an Armstrong oscillator?
1. Tickler coil 2. Split inductor 3. Split coupling 4. Split capacitance
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Figure 2B.—Series-fed, tuned-base Hartley oscillator.
IN ANSWERING QUESTIONS 2-39 THROUGH 2-42, REFER TO FIGURE 2B. 2-39. What components are part of the
frequency-determining device of this oscillator?
1. C1, L1, and L2 2. C2, L1, and L2 3. C3, L1, and L2 4. CE, RE, and RB
2-40. What circuit component prevents thermal runaway?
1. L1 2. CE 3. RB 4. RE
2-41. The low resistance of L2 could place a short across the emitter-to-base junction network of Q1 and RE. What component in the circuit prevents this from happening?
1. C1 2. C2 3. C3 4. CE
16
2-42. When a positive signal is coupled to the base of Q1, what happens to (a) collector current and (b) emitter current?
1. (a) Increases (b) increases 2. (a) Increases (b) decreases 3. (a) Decreases (b) decreases 4. (a) Decreases (b) increases
2-43. A tuned-base Hartley oscillator is described as "shunt fed" when
1. ac flows through the tank circuit 2. dc flows through the tank circuit 3. ac does not flow through the tank
circuit 4. dc does not flow through the tank
2-44. Which of the following advantages does the Colpitts oscillator have over the Armstrong and Hartley oscillators?
1. Easier to tune 2. Wider frequency range 3. Better frequency stability 4. All of the above
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Figure 2C.—Oscillator.
IN ANSWERING QUESTIONS 2-45 THROUGH 2-47, REFER TO FIGURE 2C. 2-45. What type of oscillator is shown in the
figure?
1. Common-base Hartley 2. Common-base Colpitts 3. Common-emitter Colpitts 4. Common-collector Hartley
2-46. What component is the collector load resistor?
1. R1 2. R2 3. R3 4. R4
2-47. What resistors provide the base bias?
1. R1, R2 2. R2, R3 3. R3, R4 4. R2, R4
17
2-48. What class of biasing does the RC oscillator use?
1. A 2. B 3. C 4. AB
2-49. In an RC network, (a) what type of
impedance is presented and (b) does the current lead or lag?
1. (a) Inductive (b) leads 2. (a) Inductive (b) lags 3. (a) Capacitive (b) lags 4. (a) Capacitive (b) leads
2-50. In the phase-shift oscillator, a phase shift of 180 degrees for regenerative feedback is provided by what minimum number of RC networks?
1. One 2. Two 3. Three 4. Four
2-51. What determines the phase angle of an RC network?
1. Input voltage 2. Output voltage 3. Values of resistance and inductance 4. Values of resistance and capacitance
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Figure 2D.—Phase-shift oscillator.
IN ANSWERING QUESTIONS 2-52 THROUGH 2-56, REFER TO FIGURE 2D. 2-52. What is the maximum amount of phase
shift provided by Q1 in the figure?
1. 0 degrees 2. 60 degrees 3. 90 degrees 4. 180 degrees
2-53. What type of feedback is provided through the RC networks to the base of Q1?
1. Neutral 2. Negative 3. Regenerative 4. Degenerative
2-54. At any other than the desired frequency, what type of feedback is provided by the circuit?
1. Neutral 2. Positive 3. Regenerative 4. Degenerative
2-55. What components make up the frequency- determining device?
1. C1, C2, CE, R1, R2, RB 2. C2, C3, CE, R2, RB, RE 3. C1, C2, C3, R1, R2, RB 4. Cout, C1, C2, R1, R2, RE
18
2-56. What is the maximum amount of phase
shift provided by the C3-RB network?
1. 90 degrees 2. 80 degrees 3. 70 degrees 4. 60 degrees
2-57. Which of the following is the correct formula for the resonant frequency of a phase-shift oscillator?
1.
3.
2.
4.
2-58. Which of the following oscillators is used
to provide a highly stable output at a very precise frequency?
1. Crystal 2. Hartley 3. Colpitts 4. Armstrong
2-59. The frequency of a crystal-controlled oscillator is determined by which of the following physical actions?
1. Type of cut 2. Accuracy of cut 3. Thickness of grinding 4. All of the above
2-60. Why is the crystal in a crystal-controlled oscillator often installed in a temperature- controlled oven?
1. To increase frequency without
changing the crystal 2. To decrease frequency without
changing the crystal 3. To provide better amplitude stability 4. To provide better frequency stability
Figure 2E.—Frequency response of a crystal.
IN ANSWERING QUESTIONS 2-61 THROUGH 2-64, REFER TO FIGURE 2E. THE LETTERS A, B, C, D, AND E ARE POINTS ON THE FREQUENCY-RESPONSE CURVE FROM WHICH YOU SHOULD SELECT ANSWERS TO THE QUESTIONS. 2-61. At what point on the curve does a crystal
act as a series-tuned circuit?
1. A 2. B 3. C 4. D
2-62. At what point does the crystal act inductively?
1. A 2. B 3. C 4. D
2-63. Below series resonance, a crystal acts capacitively at what point on the curve?
1. A 2. B 3. C 4. E
2-64. At what point does the crystal act purely as a parallel-resonant circuit?
1. B 2. C 3. D 4. E
19
2-65. How is the Q of a crystal determined? 1. Type of cut used 2. Type of holder used 3. Accuracy of the grinding 4. All of the above
2-66. An oscillator that is turned ON for a specific period of time, then is turned OFF and remains OFF until required at a later time, is which of following types?
1. LC 2. Pierce 3. Pulsed 4. Crystal
Figure 2F.—Oscillator circuit.
IN ANSWERING QUESTIONS 2-67 THROUGH 2-70, REFER TO FIGURE 2F. 2-67. What circuit is shown in the figure?
1. Pierce oscillator 2. Pulsed oscillator 3. Colpitts oscillator 4. Armstrong oscillator
2-68. Sine waves are generated in the emitter circuit of Q1 during which of the following time periods of the input gate?
1. T0 to T1 and T1 to T2 2. T0 to T1 and T2 to T3 3. T1 to T2 and T3 to T4 4. T1 to T3 and T0 to T4
2-69. The frequencies in the output are
determined by what two circuit parameters?
1. Input gate time and the time the circuit
is turned OFF 2. Output gate time and the time the
circuit is turned ON 3. Input gate time and the resonant
frequency of the tank circuit 4. Output gate time and the resonant
2-70. If the resonant frequency of the tank circuit were 5 megahertz and transistor Q1 were cut off for 500 microseconds, what maximum number of cycles of the tank frequency would be present in each pulse of the output?
1. 500 cycles 2. 1,500 cycles 3. 2,500 cycles 4. 3,500 cycles
2-71. What is the fourth harmonic of a 2-megahertz signal?
1. 6 megahertz 2. 2 megahertz 3. 8 megahertz 4. 4 megahertz
2-72. What is the highest multiplication factor normally used in frequency multipliers?
1. One 2. Two 3. Three 4. Four
20
2-73. As the multiplication factor in a frequency multiplier circuit is increased, what happens to the output signal (a) amplitude and (b) frequency?
1. (a) Increases (b) increases 2. (a) Increases (b) decreases 3. (a) Decreases (b) decreases 4. (a) Decreases (b) increases
2-74. In a buffer amplifier, what is the impedance in the (a) input and (b) output?
1. (a) Low (b) low 2. (a) Low (b) high 3. (a) High (b) high 4. (a) High (b) low
21
Textbook assignment: Chapter 3, “Waveforms and Wave Generators,” pages 3-1 through 3-56. _____________________________________________________________________________________
3-1. A waveform that repeats the same pattern
1. periodic wave 2. sporadic wave 3. aperiodic wave 4. transverse wave
3-2. Which of the following waveforms is sinusoidal?
1. Sine wave 2. Square wave 3. Sawtooth wave 4. Rectangular wave
3-3. The time required to complete one full cycle of a square wave is referred to as the
1. pulse-repetition rate 2. pulse-repetition time 3. pulse-repetition cycle 4. pulse-repetition frequency
3-4. What term(s) describes the number of
times in one second that a square wave repeats itself?
1. The pulse-repetition frequency (prf) 2. The pulse-repetition rate (prr) 3. Both 1 and 2 above 4. The pulse-repetition time (prt)
3-5. A square wave with a prf of 1,250 hertz has a prt of
1. 8 microseconds 2. 80 microseconds 3. 800 microseconds 4. 8,000 microseconds
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22
Figure 3A.—Square wave.
IN ANSWERING QUESTIONS 3-6 THROUGH 3-10, SELECT THE CORRESPONDING LETTER IN FIGURE 3A WHICH DESCRIBES THE PORTION OF THE WAVEFORM IN EACH OF THE FOLLOWING QUESTIONS.
3-6. The leading edge of the pulse.
1. C 2. D 3. E 4. F
3-7. The trailing edge of the pulse.
1. A 2. B 3. C 4. D
3-8. The positive alternation.
1. C 2. D 3. E 4. F
3-9. The amplitude of the pulse.
1. A 2. B 3. C 4. D
3-10. The pulse-repetition time of the pulse.
1. C 2. D 3. E 4. F
3-11. What type of waveform is used to furnish a linear rise in current for electromagnetic cathode ray tubes?
1. Square wave 2. Sawtooth wave 3. Trapezoidal wave 4. Rectangular wave
3-12. Which of the following multivibrators must have a signal applied (triggered) to change states?
1. Astable 2. Bistable 3. Monostable 4. Both 2 and 3 above
3-13. Which of the following multivibrators is also called a free running multivibrator?
1. Astable 2. Bistable 3. Monostable 4. Both 2 and 3 above
3-14. Which of the following waveforms could be the output of the astable multivibrator?
1. Sine wave 2. Sawtooth wave 3. Rectangular wave 4. Trapezoidal wave
23
IN ANSWERING QUESTIONS 3-15 AND 3-16, REFER TO FIGURE 3B. 3-15. The time necessary for Q2 in the circuit
to become saturated is controlled by what RC network?
1. R1, C1 2. R2, C1 3. R3, C2 4. R4, C2
3-16. Which of the following conditions exist in the outputs of the figure from T0 to T1?
1. Q1 saturated, Q2 saturated 2. Q1 saturated, Q2 cutoff 3. Q1 cutoff, Q2 cutoff 4. Q1 cutoff, Q2 saturated
3-17. What multivibrator is a square or rectangular-wave generator with only one stable condition?
1. Astable 2. Bistable 3. Monostable 4. Eccles-Jordan
3-18. What is the primary use for the monostable multivibrator circuit?
1. Filter 2. Amplifier 3. Oscillator 4. Pulse stretcher
Figure 3C.—Monostable multivibrator circuit.
IN ANSWERING QUESTIONS 3-19 AND 3-20, REFER TO FIGURE 3C. 3-19. In the stable state of the circuit, what will
be the condition of (a) Q1 and (b) Q2?
1. (a) Cutoff (b) cutoff 2. (a) Cutoff (b) saturated 3. (a) Saturated (b) saturated 4. (a) Saturated (b) cutoff
3-20. What is the discharge path for C1?
1. C1, Q2, ground, -VCC, Q1, and C1 2. C1, Q2, ground, +VBB, R5, Q1, and
C1 3. C1, Q2, R4, R2, +VBB, -VCC, R2, and
C1 4. C1, Q1, ground, -VCC, R2, and C1
24
3-21. In a bistable multivibrator, what minimum number of triggers is required to produce one gate?
1. One 2. Two 3. Three 4. Four
3-22. Which of the flip flops shown below is in
the SET state?
1.
2.
3.
4.
3-23. Which of the flip flops shown below is in the CLEAR state?
1.
2.
3.
4.
3-24. Which of the following pulses is used to change states in a flip flop? 1. A trigger pulse 2. A clipping pulse 3. A modulating pulse 4. An interference pulse
25
Figure 3D.—Flip-flop output 1 waveforms.
IN ANSWERING QUESTIONS 3-25 THROUGH 3-29, REFER TO FIGURE 3D. ASSUME THE FLIP-FLOP IS INITIALLY IN THE CLEAR STATE. SELECT THE WAVEFORM AT THE "1" OUTPUT IN THE FIGURE THAT WILL RESULT FROM THE INPUT PULSES SHOWN IN THE QUESTIONS. SOME CHOICES MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. 3-25.
1. A 2. B 3. C 4. D
3-26.
1. A 2. B 3. C 4. D
3-27.
1. A 2. B 3. D 4. E
3-28.
1. B 2. C 3. D 4. F
26
3-29.
1. A 2. B 3. E 4. F
3-30. The toggle input on a flip flop is used to cause which of the following circuit actions?
1. SET the flip flop 2. CLEAR the flip flop 3. Both 1 and 2 above 4. Sample the condition of the flip flop
3-31. The blocking oscillator is NOT suitable for which of the following circuit applications?
1. Counter circuit 2. Frequency divider 3. Switching circuit 4. Sine-wave generator
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27
Figure 3E.—Blocking oscillator.
IN ANSWERING QUESTIONS 3-32 THROUGH 3-37, REFER TO FIGURE 3E. 3-32. What is indicated by the dots at each end
of T1 in the figure?
1. 0-degree phase shift 2. 90-degree phase shift 3. 160-degree phase shift 4. 180-degree phase shift
3-33. Regenerative feedback to the base of Q1 is provided by what circuit component(s)?
1. L1 only 2. L2 only 3. L1 and L2 only 4. L1, L2, and C1
3-34. What circuit action is taking place from T0 to T1?
1. C1 is charging 2. C1 is discharging 3. L1 is discharging 4. IC is decreasing
3-35. THIS QUESTION HAS BEEN DELETED.
3-36. During what total time period is Q1
blocked?
1. T0 to T1 2. T1 to T2 3. T0 to T2 4. T2 to T3
3-37. In the blocking oscillator, which of the following circuit actions is the primary cause of parasitic oscillations?
1. Collapse of the magnetic field of L1 2. Expansion of the magnetic field of L1 3. Inductive coupling between L1 and
L2 4. C1 discharging through Q1
3-38. Which of the following circuit actions is a result of critical damping?
1. Rapid transient response without
overshoot 2. Rapid transient response with
overshoot 3. Slow transient response without
overshoot 4. Slow transient response with
3-39. What type of damping is caused by (a) high resistance and (b) low resistance?
1. (a) Overdamping
(b) Underdamping 2. (a) Underdamping
(b) Overdamping 3. (a) Critical damping
(b) Underdamping 4. (a) Overdamping
28
3-40. Applying synchronizing triggers with a frequency that is SLIGHTLY higher than the free-running frequency will cause a synchronized blocking oscillator to
1. divide in frequency 2. double in frequency 3. lock in at the higher frequency 4. stay locked at the free-running
Figure 3F.—Sawtooth waveform.
IN ANSWERING QUESTIONS 3-41 THROUGH 3-46, REFER TO FIGURE 3F AND MATCH THE WAVEFORM POINTS (OR TIME REFERENCES) TO THE TERMS IN THE QUESTIONS. SOME CHOICES MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. 3-41. Linear slope.
1. A to B 2. B to C 3. T0 to T2 4. T1 to T2
3-42. Physical length.
1. A to B 2. B to C 3. X 4. Y
3-43. Sweep time.
1. A to B 2. B to C 3. T0 to T1 4. T1 to T2
3-44. Fall time.
1. A to C 2. T0 to T1 3. T1 to T2 4. T0 to T2
3-45. Electrical length.
1. B to C 2. T0 to T1 3. T1 to T2 4. T0 to T2
3-46. Amplitude.
1. A to B 2. B to C 3. X 4. Y
3-47. The linearity of the rise voltage in a sawtooth wave is determined by which of the following circuit timing actions?
1. The time the capacitor is allowed to
charge 2. The time it takes the capacitor to fully
charge 3. The time the capacitor is allowed to
discharge 4. The time it takes the capacitor to fully
29
Figure 3G.—Transistor sawtooth generator.
IN ANSWERING QUESTIONS 3-48 THROUGH 3-53, REFER TO FIGURE 3G. 3-48. What component in the circuit develops
the output sawtooth waveform?
1. R1 2. R2 3. C1 4. C2
3-49. What is the purpose of Q1?
1. Acts as a switch 2. Allows C2 to charge 3. Inverts the negative gate 4. Serves as a common-collector
3-50. What is the maximum length of time C2 is allowed to charge?
1. 200 microseconds 2. 500 microseconds 3. 700 microseconds 4. 900 microseconds
3-51. If VCC were increased to 40 volts, which of the following parameters in the output sawtooth wave would increase?
1. Fall time 2. Amplitude 3. Sweep time 4. Linearity
3-52. What would be the effect on C2 if the negative gate length were increased?
1. Charge to VCC 2. Discharge to VCC 3. Charge to a larger percentage of VCC 4. Charge to a smaller percentage of VCC
3-53. What is the prf of the circuit?
1. 1,428 pulses per second 2. 1,450 pulses per second 3. 1,470 pulses per second 4. 1,482 pulses per second
3-54. In a sawtooth generator, a change in which of the following parameters will NOT affect the linearity of the output?
1. VCC 2. Resistance 3. Capacitance 4. Gate length
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30
Figure 3H.—Unijunction sawtooth generator.
IN ANSWERING QUESTIONS 3-55 THROUGH 3-59, REFER TO FIGURE 3H. 3-55. The output in the circuit is taken across
what component.
1. R1 2. B2 3. R1 4. C1
3-56. What is the discharge path for C1?
1. C1, R1, VCC, ground, and C1 2. C1, emitter B2, VCC, ground, and C1 3. C1, B1, emitter, and C1 4. C1, B1, B2, VCC, ground, and C1
3-57. What part of the waveform is sweep time?
1. A to D 2. B to C 3. C to D 4. C to E
3-58. What is the action of C1 when the emitter-to-B1 junction is (a) reverse biased and (b) forward biased?
1. (a) Charging (b) Discharging 2. (a) Discharging (b) Charging 3. (a) Charging (b) Charging 4. (a) Discharging (b) Discharging
3-59. To obtain a more stable output frequency, you could modify the circuit by applying (a) what type of triggers to (b) what circuit element.
1. (a) Positive (b) B1 2. (a) Positive (b) B2 3. (a) Negative (b) B2 4. (a) Negative (b) B1
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31
Figure 3I.—Transistor sawtooth generator.
IN ANSWERING QUESTIONS 3-60 THROUGH 3-64, REFER TO FIGURE 3I. 3-60. With no input voltage applied to the
circuit, what voltage should you read at the collector?
1. -20 volts 2. -17.5 volts 3. -2.5 volts 4. 0 volts
3-61. To what voltage is C1 allowed to charge?
1. 0 volts 2. -2.5 volts 3. -4.5 volts 4. -20 volts
3-62. To determine the percent of charge on C1, what formula is used?
1.
2.
3.
4.
3-63. Which of the following actions will improve the linearity of the sawtooth?
1. Increasing the value of C1 2. Increasing the value of R1 3. Increasing the gate length 4. Each of the above
3-64. What is the maximum amplitude of the output sawtooth signal?
1. 1.75 volts 2. 2.0 volts 3. 2.5 volts 4. 4.5 volts
3-65. If applied to a coil, what voltage waveform will cause a linear rise in current?
1. Square wave 2. Sawtooth wave 3. Rectangular wave 4. Trapezoidal wave
32
Figure 3J.—Trapezoidal waveform.
IN ANSWERING QUESTIONS 3-66 THROUGH 3-70, REFER TO FIGURE 3J AND MATCH THE WAVEFORM POINTS (OR TIME REFERENCES) TO THE TERMS IN THE QUESTIONS. SOME CHOICES MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. 3-66. Pulse-repetition time (prt).
1. T1 to T2 2. T0 to T3 3. A to B 4. B to C
3-67. Physical length.
1. T0 to T3 2. A to B 3. B to C 4. C to D
3-68. Electrical length.
1. T0 to T1 2. T1 to T2 3. T0 to T3 4. A to B
3-69. Jump voltage.
1. T0 to T1 2. T1 to T2 3. T0 to T3 4. A to B
3-70. Linear slope.
1. C to D 2. B to C 3. A to B 4. T0 to T3
THIS SPACE LEFT BLANK INTENTIONALLY.
33
Figure 3K.—Trapezoidal-wave generator with input
and output waveforms.
IN ANSWERING QUESTIONS 3-71 THROUGH 3-74, REFER TO FIGURE 3K. 3-71. The amplitude of the jump voltage is
1. (a) 0.5 volts (b) 5 volts 2. (a) 0.5 volts (b) 0.5 volts 3. (a) 5 volts (b) 0.5 volts 4. (a) 5 volts (b) 5 volts
3-72. Which of the following components and/or value(s) determines the amplitude of the jump voltage?
1. VCC only 2. R2 and VCC only 3. R3 and VCC only 4. R2, R3, and VCC
3-73. What is the minimum discharge time for C2?
1. 50 microseconds 2. 500 microseconds 3. 1,000 microseconds 4. 2,000 microseconds
3-74. Increasing which of the following values will NOT affect linearity of the circuit?
1. Resistance of R2 2. Capacitance of C2 3. Gate width 4. VCC
34
Textbook assignment: Chapter 4, “Wave Shaping,” pages 4-1 through 4-61. _____________________________________________________________________________________
4-1. A wave-shaping circuit which restricts
1. divider 2. clamper 3. limiter 4. oscillator
4-2. Limiting circuits are used in which of the following circuit applications?
1. Counting 2. Amplification 3. Wave generation 4. Circuit protection
4-3. In a series limiter, the diode is connected in
1. (a) Parallel (b) output 2. (a) Parallel (b) input 3. (a) Series (b) input 4. (a) Series (b) output
4-4. In a series limiter, a voltage is developed across the output resistor when
1. the anode of the diode is negative
with respect to the cathode 2. the anode of the diode is positive with
respect to the cathode 3. the cathode of the diode is positive
with respect to the anode 4. no current flows through the diode
4-5. The diode in a series-positive limiter is
(a) forward biased by what portion of the input signal and (b) reverse biased by what portion of the input signal?
1. (a) Positive (b) positive 2. (a) Positive (b) negative 3. (a) Negative (b) negative 4. (a) Negative (b) positive
4-6. How does the value of diode resistance compare to that of the resistor (a) during the limiting portion of the input and (b) during the nonlimiting portion?
1. (a) High (b) high 2. (a) High (b) low 3. (a) Low (b) low 4. (a) Low (b) high
4-7. Which of the following circuits is a series-positive limiter?
1.
3.
2.
4.
35
4-8. If a sine wave is applied to the input of a series-positive limiter, which of the following waveforms describes the output?
1.
3.
2.
4.
4-9. The amplitude of the output of a series-
diode limiter is figured using which of the following formulas?
1.
2.
3.
4.
 With forward bias, what is the output amplitude?
1. 28.95 volts 2. 29 volts 3. 29.85 volts 4. 29.95 volts
4-11. With reverse bias, what is the output amplitude?
1. .175 volt 2. 1.75 volts 3. 3.53 volts 4. 3.75 volts
4-12. In a series-positive limiter, where is the input signal applied?
1. Directly to the anode of the diode 2. Directly to the cathode of the diode 3. To the anode of the diode through a
series input resistor 4. To the cathode of the diode through
36
4-13. With a sine wave applied, which of the following circuits limits only a portion of the positive input signal?
1. Series-negative limiter with negative
bias 2. Series-negative limiter with positive
bias 3. Series-positive limiter with negative
bias 4. Series-positive limiter with positive
4-14. With a sine-wave input, which of the following types of series limiter allows only a portion of the negative input to be developed in the output?
1. Series-positive limiter without bias 2. Series-positive limiter with negative
bias 3. Series-positive limiter with positive
bias 4. Series-negative limiter without bias
4-15. In a series-negative limiter, how is the
diode biased (a) by the positive half of the input sine wave and (b) by the negative half?
1. (a) Reverse (b) forward 2. (a) Reverse (b) reverse 3. (a) Forward (b) reverse 4. (a) Forward (b) forward
THIS SPACE LEFT BLANK INTENTIONALLY.
Figure 4A.—Sine-wave input.
IN ANSWERING QUESTION 4-16, REFER TO FIGURE 4A. 4-16. If the input waveform shown in the
figure is applied to a series-negative limiter, which of the following waveforms will be the output?
1.
3.
2.
4.
4-17. In a series-negative limiter with positive bias, which of the following output circuit actions takes place?
1. Both positive half cycles are
eliminated 2. Both negative half cycles are
eliminated 3. All of the positive half cycles and a
4. All of the negative half cycles and a portion of the positive half cycles are eliminated
37
____________________________________ IN QUESTIONS 4-18 THROUGH 4-22, MATCH THE LIMITER CIRCUIT IN COLUMN A TO THE CIRCUIT DESCRIPTION IN COLUMN B. CHOICES MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL.
A. LIMITER CIRCUIT
4-18.
1. A 2. B 3. C 4. D
4-19.
1. A 2. B 3. E 4. F
B. CIRCUIT DESCRIPTION
A. Series-positive
B. Series-negative limiter with no bias
C. Series-positive limiter with negative bias
D. Series-positive limiter with positive bias
E. Series-negative limiter with negative bias
F. Series-negative limiter with positive bias
4-20.
1. C 2. D 3. E 4. F
4-21.
1. C 2. D 3. E 4. F
4-22.
1. C 2. D 3. E 4. F
_______________________________________ 4-23. In a parallel-diode limiter, (a) how is the
output taken and (b) under what diode condition is it developed?
1. (a) Across the resistor
(b) When the diode is cut off 2. (a) Across the resistor
(b) When the diode is conducting 3. (a) Across the diode
(b) When the diode is conducting 4. (a) Across the diode
4-24. In a parallel-positive limiter, where is the input sine wave applied?
1. At the anode of the diode 2. At the cathode of the diode 3. Through a series resistor to the anode
of the diode 4. Through a series resistor to the
38
4-25. Which of the following formulas is used to figure the output amplitude of a parallel-diode limiter?
1.
2.
3.
4.
4-26. THIS QUESTION HAS BEEN DELETED.
4-27. THIS QUESTION HAS BEEN
DELETED.
4-28. In a parallel-negative limiter, how is the diode biased (a) by the positive half of the input sine wave and (b) by the negative half? 1. (a) Forward (b) forward 2. (a) Forward (b) reverse 3. (a) Reverse (b) reverse 4. (a) Reverse (b) forward
4-29. If a sine wave is applied to a parallel- negative limiter with positive bias, what is the polarity of the output voltage? 1. Positive at all times 2. Negative at all times 3. Positive during the positive portion of
4. Negative during the positive portion of the input cycle and positive during the negative portion
Figure 4B.—Parallel-limiter input and output
waveforms. IN ANSWERING QUESTION 4-30, REFER TO FIGURE 4B. 4-30. If the diode in the parallel limiter were
reversed, what portions of the input waveform would be limited?
1. Positive peaks only 2. Negative peaks only 3. All hut the positive peaks would be
limited 4. All but the negative peaks would be
4-31. Which of the following circuits would be used to fix the upper or lower extremity of a waveform at a specific value?
1. Clamper 2. Limiter 3. Counter 4. Amplifier
39
Figure 4C.—Positive clamper.
IN ANSWERING QUESTIONS 4-32 AND 4-33, REFER TO FIGURE 4C. 4-32. When a negative input signal is present,
what components provide(s) the charge path for the capacitor?
1. Diode only 2. Resistor only 3. Both the resistor and diode
4-33. How does the length of time required for the capacitor to charge compare to the time for it to discharge?
1. Charge time is longer than discharge
time 2. Charge time is shorter than discharge
time 3. Charge and discharge times are the
4-34. In a positive clamper with positive bias, (a) what extremity of the waveform is clamped and (b) to what potential is it clamped?
1. (a) Upper (b) positive 2. (a) Upper (b) negative 3. (a) Lower (b) positive 4. (a) Lower (b) negative
4-35. In a positive clamper with negative bias,
(a) what extremity of the waveform is clamped and (b) to what potential is it clamped?
1. (a) Upper (b) positive 2. (a) Upper (b) negative 3. (a) Lower (b) negative 4. (a) Lower (b) positive
Figure 4D.—Clamper with bias.
IN ANSWERING QUESTIONS 4-36 AND 4-37, REFER TO FIGURE 4D. 4-36. With +10 volts of bias in the circuit,
what is the maximum negative output voltage?
1. -15 volts 2. -25 volts 3. -40 volts 4. -50 volts
4-37. With -15 volts of bias, to what voltage level is the output clamped?
1. +75 volts 2. +45 volts 3. -15 volts 4. -75 volts
40
Figure 4E.—Clamper circuits.
IN ANSWERING QUESTIONS 4-38 THROUGH 4-40, SELECT THE CIRCUIT IN FIGURE 4E THAT MATCHES THE CIRCUIT NAMED IN THE QUESTIONS. CHOICES MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. 4-38. Positive clamper with negative bias.
1. A 2. B 3. C 4. D
4-39. Negative clamper with negative bias. 1. A 2. B 3. C 4. D
4-40. Positive clamper with positive bias. 1. A 2. B 3. C 4. D
Figure 4F—Clamper circuit outputs.
IN ANSWERING QUESTIONS 4-41 THROUGH 4-43, SELECT THE OUTPUT IN FIGURE 4F WHICH IS PRODUCED BY THE CIRCUITS IN THE QUESTIONS. CHOICES MAY BE USED ONCE, MORE THAN ONCE, OR NOT AT ALL. 4-41. Positive clamper with positive bias.
1. A 2. B 3. C 4. D
4-42. Negative clamper with positive bias.
1. A 2. B 3. C 4. D
4-43. Negative clamper with negative bias.
1. A 2. B 3. C 4. D
41
4-44. Which of the following waves is NOT a complex wave?
1. Sine wave 2. Square wave 3. Rectangular wave 4. Trapezoidal wave
4-45. What is the harmonic content of a square
wave?
1. A combination of odd harmonics only 2. A combination of even harmonics
only 3. Both even and odd harmonic
4-46. What is the harmonic composition within a sawtooth wave?
1. Odd harmonics only 2. Even harmonics only 3. Both even and odd harmonics
4-47. With a square wave applied to a resistive
network, the circuit values of what components will NOT affect either the phases or amplitudes of the harmonics within the square wave?
1. Inductors 2. Resistors 3. Capacitors 4. Transformers
4-48. The time constant for full integration in an RC circuit should be what minimum number of times greater than the input- pulse duration?
1. 1 2. 5 3. 10 4. 20
4-49. Integration in a circuit takes place when the output is taken (a) across the capacitor in what type of circuit and (b) across the resistor in what type of circuit?
1. (a) Resistive only
(b) Resistive only 2. (a) Resistive only
(b) Resistive-inductive 3. (a) Resistive only
(b) Resistive-capacitive 4. (a) Resistive-capacitive
4-50. In an RC integrator, which of the following waveforms has the longest time constant?
1.
3.
2.
4.
42
4-51. In an RC differentiator, which of the following waveforms has the shortest time constant?
1.
2.
3.
4.
4-52. In a short time-constant integrator circuit, the maximum amplitude of the input pulse is 100 volts and the time constant of the circuit is 1/10 the duration of the input pulse. At the end of three time constants, what is the maximum voltage across the capacitor?
1. 36.8 volts 2. 63.2 volts 3. 86.5 volts 4. 95 volts
4-53. In a medium time-constant circuit, the maximum amplitude of the input pulse is 100 volts and the pulse length is one time constant. At the end of two time constants, what is the maximum voltage across the capacitor?
1. 23.3 volts 2. 48.4 volts 3. 71.7 volts 4. 100 volts
4-54. In a short time-constant differentiator
circuit, the maximum amplitude of the input pulse is 100 volts and the time constant of the circuit is 1/10 that of the input pulse. At the end of four time constants, what is the maximum voltage across the resistor? 1. 5 volts 2. 2 volts 3. 23.3 volts 4. 48.4 volts
4-55. In an RC differentiator circuit, the time
constant for the circuit and the input pulse are equal. At the end of one time constant, to what maximum percentage of the applied voltage is the capacitor charged?
1. 5 percent 2. 13.5 percent 3. 36.8 percent 4. 63.2 percent
4-56. In an RC network that is used as a
coupling circuit, (a) across what component is the output normally taken and (b) what is the relative length of the time constant?
1. (a) Capacitor (b) short 2. (a) Capacitor (b) long 3. (a) Resistor (b) long 4. (a) Resistor (b) short
43
4-57. In a positive-diode counter that provides accurate counting, what is the only variable allowed in the input signal? 1. Pulse width 2. Pulse duration 3. Pulse amplitude 4. Pulse-repetition frequency
Figure 4G.—Basic frequency counter.
IN ANSWERING QUESTIONS 4-58 THROUGH 4-60, REFER TO FIGURE 4G. 4-58. An input signal to the counter will cause
(a) what capacitor to charge through R1 and D2 and (b) what capacitor to discharge through D1?
1. (a) C1 (b) C1 2. (a) C1 (b) C2 3. (a) C2 (b) C1 4. (a) C2 (b) C2
4-59. What components produce the smooth dc output-voltage level?
1. C1, D1, and R1 2. C1, D2, and R1 3. C1, C2, and R1 4. C2, C3, and R2
4-60. When the input frequency is increased, what is the effect on (a) the input interval, (b) the number of pulses per given time and (c) the dc output voltage?
1. (a) Longer (b) less (c) higher 2. (a) Longer (b) more (c) lower 3. (a) Shorter (b) less (c) higher 4. (a) Shorter (b) more (c) higher
Figure 4H.—Step-counter frequency divider.
IN ANSWERING QUESTIONS 4-61 AND 4-62, REFER TO FIGURE 4H.
4-61. An output pulse will occur when the
charge on C2 1. builds a magnetic field in the base
winding 2. drops below the cutoff-bias level of
Q1 3. exceeds the bias level of Q1 4. reaches the source potential of the
4-62. What component develops the bias for Q1?
1. R1 2. R2 3. C2 4. T1