CHAPTER 2 DIODE APPLICATIONS CHAPTER 2
DIODE APPLICATIONS
1. An open primary or secondary winding of a power supply transformer results in
0 V
2. The output frequency of a half-wave rectifier is _________to/of the input frequency
Equal
3. What is the average value of the half-wave rectified voltage given 25 V as its peak amplitude? 7.95 V
4. The PIV rating of the bridge diodes is __________to/than that required for the center-tapped configuration.
Less
5. Diode circuits used to clip off portions of signal voltages above or below certain levels,
Clippers
6. The output frequency of a full-wave rectifier is ________ the input frequency
Twice
7. A transformer is generally specified based on _____________rather than the turns ratio, Secondary voltage
8. The period of a full-wave rectified voltage is ____________ that of a half-wave rectified voltage Half
9. The indication of the effectiveness of the filter is called
Ripple factor
10. Eliminates the fluctuations in the rectified voltage and produces a relatively smooth dc voltage
Filter
11. Circuit that maintains a constant dc voltage for variations in the input line voltage or in the load Regulator
12. A type of full-wave rectifier that uses two diodes connected to the secondary of a center-tapped transformer
Center-tapped rectifier
13. Use clamping action to increase peak rectified voltages without the necessity of increasing the transformer’s voltage rating
Voltage multipliers
14. Maximum voltage appearing across the diode in reverse bias
PIV
15. Caused by the charging and discharging of the filter capacitor
Ripple voltage
16. A systematic process of isolating, identifying, and correcting a fault in a circuit or system
Troubleshooting
17. Allows unidirectional current through the load during the entire 360° of the input cycle
Full-wave rectifier
18. Allows current through the load only during one-half of the cycle.
Half-wave rectifier
19. Generally used because of the surge current that initially occur s when power is first turned on Slow-blow type fuse
20. A figure of merit used to specify the performance of a voltage regulator
regulation
CHAPTER 3 SPECIAL- PURPOSE DIODES CHAPTER 3
SPECIAL- PURPOSE DIODES
1. Diodes that were designed to operate in reverse breakdown
Zener diode
2. A device that operates in reverse bias photodiode
3. A zener diode operating in breakdown acts as a Voltage regulator
4. A positive temperature means that the zener voltage
Increases with an increase in temperature on decreases with decrease in temperature.
5. A diode that always operates in reverse-bias and is doped to maximize the inherent capacitance of the depletion region is
Laser
6. When the light-emitting diode (LED) is forward-biased, __________pass the pn junction and recombine with____________ in the _________material.
Electrons, holes, p-type
7. The first visible red LEDs were produced using GaAsp
8. The normalized output of the visible red, yellow, green and blue LED peaks at __________________ (nm) respectively.
660,590,540, and 460
9. Organic LEDs and LEDs produce light through the process of __________ and ___________
respectively.
Electrophophorescence and electroluminescence 10. An increase in the amount of light intensity produces an increase in
Reverse current
11. A diode that can be used as a variable-resistance device controlled by light intensity.
Photodiode
12. A diode that operates only with majority carriers Schottky diode
13. A diode that takes advantage of the variable forward resistance characteristic.
PIN diode
14. No reverse leakage current Schottky diode
15. Diode used in VHF and fast switching applications
Step- Recovery diode
16. When a PIN diode is forward-biased, it acts like a
Current-controlled variable resistance
17. If a tunnel diode is placed in series with the tank circuit and biased at the center of the negative-resistance portion of its characteristic curve, a _________ will result in the output.
Constant sinusoidal voltage 18. The tunnel diode is only used at VHF
19. In a varactor diode, what happens to the capacitance if the reverse-bias voltage decreases a. Increases
20. The varactor capacitance ratio is also known as a. Tuning ratio
CHAPTER 4 BIPOLAR JUNCTION TRANSISTORS
CHAPTER 4
BIPOLAR JUNCTION TRANSISTORS
1. Which is the least of the three transistor currents? Base
2. The ratio of the dc collector current to the dc base current of the transistor is,
dc beta/dc current gain
3. the ratio of the dc collector current to the dc emitter current
dc alpha
4. Determine the base current given dc beta=100 , dc alpha=0.85, and IC= 3.70mA
0.037mA
5. Nonconducting state of a transistor Cutoff
6. State of a BJT in which the collector current has reached maximum and is dependent of the base current Saturation
7. Neither the base-emitter nor the base-collector junctions are forward-biased
cutoff
8. dc beta varies with
collector current and temperature
9. hFE varies with which transistor current/s? Collector only
10. Converts light energy to electrical signal Phototransistor
11. Devices used to electrically isolate circuits Optocouplers
12. A key parameter in optocouplers is the CTR. CTR standsfor
Current transfer ratio
13. Indication of how efficiently a signal is coupled from input to output
CTR
14. RF transistors are designed to operate at EHF
15. What transistor category/ies uses plastic or metal packages?
General-purpose transistors
16. To operate as an amplifier, BE junction must be forward-biased and the BC junction must be reverse-biased. This is called
Forward-reverse bias
17. In a phototransistor, what transistor current/s is produced and controlled by light?
Base
18. Two basic package types Through-hole and surface mount
19. The process of increasing the power, voltage, or current by electronic means.
Amplification
CHAPTER 5
TRANSISTOR BIAS CIRCUITS
1. What biasing method is common in switching circuits?
Base bias
2. A Base bias in linear region shows that it is Directly dependent on dc beta
3. In an emitter-feedback bias, if the collector currentincreases, the emitter voltage Increases 4. What happens to the base voltage in no. 10? Increases
5. In an emitter-feedback, the increase in base voltage _________ the base current. Reduces
6. For collector-feedback bias, what provides the bias for the base-emitter junction? Collector voltage 7. As temperature goes up in a collector-feedback circuit, βDC and VBE goes _______ and
__________, respectively. Up and down
8. Collector-feedback bias provides good stability using negative feedback from
Collector to base
9. Innovations in technology would allow a doubling of the number of transistors in a given space every year and that the speed of those transistors would increase. This prediction is widely known as Moore’s law
10. If an amplifier is not biased with correct dc voltages on the input and output, it can go ___________ when an input signal is applied. Saturation or cutoff
11. Given a voltage-divider biased BJT, determine IC given VCC, R1, R2, RC, and RE which are 10V, 10kohms, 4.7kohms, 1kohm, and 470ohms respectively. Use βDC= 100.
5.31mA
12. What is the value of VCE in no.20? 2.19 V
13. If an emitter resistor is added to a base bias circuit, what is the value of the emitter current given VCC, RE, RC, and RB as 10V, 1kΩ, 470Ω, and 180kΩ, respectively. Use βDC=100.
3.32mA
14. Calculate for VCE in no. 22 5.12 V
15. If the dc beta in the preceding drops half of its originalvalue, find the percent change in IC. 39.16%
16. What is the percent change in VCE? 27.17%
17. The region along the load line including all points between saturation and cutoff
Linear region
18. A voltage divider for which loading effects can be neglected
Stiff voltage divider
19. The base bias circuit arrangement has poor stability because its Q-point varies widely with Dc beta
20. The purpose of biasing a circuit is to establish a proper stable ________.
Q-point
21. The process of returning a portion of a circuit’s output back to the input in such a way as to oppose or aid a change in the output
CHAPTER 6 BJT AMPLIFIERS CHAPTER 6
BJT AMPLIFIERS
1. Amplifiers designed to handle small __________ signals are referred to as small-signal amplifiers. ac only
2. Which of the r parameters is the most important? r’e
3. Determine the ac emitter resistance that is operating with a dc emitter current of 5mA. 5.0 Ω
4. If βac=hfe, αac=? hfb
5. Which of the three amplifier configurations exhibit high voltage gain and high current gain?
Common-emitter
6. An amplifier configuration which has a voltage gain of approximately 1, a high input resistance and current gain,
Common-collector
7. An amplifier configuration which provides high voltage gain with a maximum current gain of 1. Common-base
8. Which of the amplifier configurations is the most appropriate for certain applications where sources tend to have low-resistance outputs?
Common-base
9. In a common-emitter amplifier, any change in input signal voltage results in
Opposite change in collector signal voltage 10. The ac voltage gain is the ratio of
ac output voltage at the collector to ac input voltage at the base
11. the reduction in signal voltage as it passes through a circuit
attenuation
12. the overall voltage gain of the common-emitter amplifier is the product of the voltage gain from base to collector and
reciprocal of the attenuation
13. Without the bypass capacitor, the CE amplifier’s emitter is no longer at ac ground. How does this affect the amplifier?
It decreases the ac voltage gain
14. The measure of how well an amplifier maintains its design values over changes in temperature, Stability
15. Swamping is a method used to minimize the effect of the ____________without reducing the voltage gain to its minimum value.
ac emitter resistance
16. ___________ contains two transistors. The collectors of two transistors are connected and the emitter of the first drives the base of the second. Darlington pair
17. _____________ consists of two types of transistors, npn and a pnp.
Complementary Darlington
18. An amplifier configuration in which the input signal is capacitively coupled to the emitter and the output is capacitively coupled from the collector, Common-base
19. Which of the amplifier configurations is/are useful at high frequencies when impedance matching is required?
Common-base
20. The power gain of a common-base amplifier is approximately equal to
Voltage gain
21. BJT amplifier that produces output that are a function of the difference between two input voltages,
Differential amplifier
22. Ideally, a diff-amp provides a very high gain for single-ended or differential signals and
_____________ gain for common-mode signals. 0
23. Input signals are out of phase Differential amplifier
CHAPTER 7 POWER AMPLIFIERS CHAPTER 7
POWER AMPLIFIERS
1. It is the product of Q-point current and voltage of a transistor with no signal input
2. The ____________ of an amplifier is the ratio of the output signal power supplied to a load to the total power from the dc supply.
Efficiency
3. Which amplifier operates in the linear region for 180 deg. Of the input cycle when biased in cutoff and is in cutoff for 180 deg?
Class B
4. These amplifiers are biased to conduct for slightly more than 180 deg.
Class AB
5. An amplifier that is generally used in Radio Frequency applications Class C
6. Implemented with a laser diode Current mirror
7. An amplifier that is biased below cutoff and is normally operated with resonant circuit load Class C
8. The four classes of power amplifiers are classified based on the percentage of the ____________which the amplifier operates in its ________region Input cycle, linear
9. It is the ratio of the output power to the input power
Power gain
10. Product of the rms load current and the rms load voltage
Output power
11. A type of class B amplifier with two transistors in which one transistor conducts for one half-cycle and the other conducts for the other half-cycle
Push-pull
12. Amplifiers that are generally used in Radio Frequency Applications.
Class C amplifiers
13. Another term for complementary Darlington Sziklai pair
14. An advantage of push-pull class B and class AB amplifiers over class A
Efficiency
15. The Q-point is at _________ at class B operation
Cutoff
16. Operates in the linear region where the output signal is an amplified replica of the input signal Class A
17. Amplifiers that have the objective of delivering power to a load
Power amplifers
18. When the Q-point is at the center of the ac load line, a maximum class ________ signal can be obtained.
A
19. The maximum efficiency of capacitively coupled class A amplifier cannot be higher than
25%
20. The low efficiency of class A amplifiers limits their usefulness to small power applications that require usually less than ________.
1 W
CHAPTER 8 FIELD –EFFECT TRANSISTORS CHAPTER 8
FIELD –EFFECT TRANSISTORS 1. FETs are preferred device in low-voltage switchingapplications; while______ transistor is generally used in high-voltage switching applications.
IGBT
2. What type of JFET operates with a reverse-biased pn junction to control current in the channel? JFET
3. An n-channel universal transfer characteristic curve is also known as
Transconductance curve
4. The change in drain current for a given change in gate-to-source voltage with the drain-to-source voltage constant
Forward transconductance
5. What is the most common type of JFET bias? Self-bias
6. It is a method for increasing the Q-point stability of a self-biased JFET by making the drain current essentially independent of gate-to-source voltage Current-source bias
7. What JFET bias uses a BJT as a constant-current source?
Current-source bias
8. For increased Q-point stability, the value of RS in the self-bias circuit is increased and connected to a negative supply voltage. This sometimes called Dual-supply bias
9. VGS varies quite a bit for JFET self-bias and voltage-divider bias but ID is much more stable with Voltage-divider bias
10. ____________ is sometimes called depletion/enhancementMOSFET. D-MOSFET
11. LDMOSFET has a lateral channel structure and is a type of
Enhancement MOSFET
12. It is an example of the conventional E-MOSFET designed to achieve higher power capability
VMOSFET
13. Following are the three ways to bias a MOSFET except
Current-source bias
14. The insulated-gate bipolar transistor combines which two transistors that make it useful in high-voltage and high-current switching applications? BJT and MOSFET
15. What are the three terminals of IGBT? Gate, collector, emitter
16. In terms of switching speed, __________ switch fastest and _____________ switch slowest.
MOSFETs, BJTs
17. In a MOSFET, the process of removing or depleting the channel of charge carriers and thus decreasing the channel conductivity
Depletion
18. The ratio of change in drain current to a change in gate-to source voltage in a FET
Transconductance
19. A FET is called a ______________ because of the relationship of the drain current to the square of a term containing gate-to-source voltage
Square-law device
20. Combines features from both the MOSFET and the BJT that make it useful in voltage and high-current switching applications.
IGBT
21. Has a lateral channel structure and is a type of enhancement MOSFET designed for power applications.
LDMOSFET
CHAPTER 9 FET AMPLIFIERS AND SWITCHING CIRCUITS
CHAPTER 9
FET AMPLIFIERS AND SWITCHING CIRCUITS
1. An amplifier that primarily uses only MOSFETs. Class D
2. A process in which an input signal is converted to a series of pulses with widths that varies
proportionally to the amplitude of the input signal. PWM
3. It removes the modulating frequency and harmonics and passes only the original signal to the output.
Low-Pass Filter
4. The voltage gain of a common-drain amplifier is always
Slightly less than 1
5. The load resistance connected to the drain of a common-source amplifier reduces ____________ Voltage gain
6. What is the relationship between the input resistance of a common-gate amplifier to its transconductance?
They are inversely proportional
7. The efficiency of a class D amplifier approaches 100%
8. The input signal is applied to the gate and the output is taken from source
Common-drain
9. A nonlinear amplifier in which the transistors are operated as switches
Class D
10. A device that switches an analog signal on and off
Analog switch
connect sample portions of their analog input signals to single output in a time sequence
Analog multiplexer
12. Used in low-power digital switching circuits CMOS
13. Amplifier commonly used as frequency multiplier
Class C
14. The least efficient amplifier Class A
15. An amplifier that is biased below cutoff Class c
16. A class of amplifier that operates in the linear region for only a small part of the input cycle Class C
17. In a class AB amplifier, if the VBE drops are not matched to the diode drops or if the diodes are not in thermal equilibrium with the transistors, this can result in
Thermal runaway
CHAPTER 10 AMPLIFIER FREQUENCY RESPONSE
CHAPTER 10
AMPLIFIER FREQUENCY RESPONSE
1. The frequency at which the output power drops to one-half of its midrange value
Corner frequency
2. At the critical frequencies the output voltage is 70.7% of its midrange value. What is the value of voltage gain in dB?
-3 dB
3. What is the other term for lower critical frequency?
All of the above
4. The condition where the gain is down 3 dB is logically called _________ of the amplifier response -3 dB point
5. The upper and lower dominant critical frequencies are sometimes called
Half-power frequencies
6. A characteristic of an amplifier in which the
product of the voltage gain and the bandwidth is always constant when the roll-off is -20 dB/ decade. Gain-bandwidth product
7. Critical frequencies are values of frequency at which the RCcircuits reduce the voltage gain to ____________ of its midrange value.
70.7%
8. An octave of frequency change is a ________ -times change
2
9. Which of the following has no effect on the low-frequency response?
Internal transistor capacitances
10. What is the gain that occurs for the range of frequencies between the lower and upper critical frequencies?
Midrange gain
11. Which of the following is not a method in frequency response measurement?
Roll-off measurement
12. If the voltage gain is less than one, what is the value of the dB gain?
Negative
13. A plot of dB voltage gain versus frequency on semilog graph paper
Bode plot
14. The critical frequency at which the curve “breaks” into a -20dB/decade drop
Lower break frequency
15. The change in gain or phase shift over a specified range of input signal frequencies
Frequency response
16. A unit of logarithmic gain measurement and is commonly used to express amplifier response Decibel
17. The lower and upper critical frequencies of an amplifier can be determined using the
_____________ method by applying a voltage step to the input of the amplifier and measuring the rise and fall times of the resulting output voltage
Step-response method
18. The coupling an bypass capacitors of an amplifier affect the _________ frequency response: high or low
19. The internal transistor capacitances affect the _________ frequency response: high or low High
20. Two frequency response measurement Frequency/amplitude and step
21. The Miller input and output capacitances for a BJT inverting amplifier depends on
Voltage gain
22. When dB is negative, it is usually called_______ Attenuation
CHAPTER 11 THYRISTORS CHAPTER 11
THYRISTORS
1. It is like the four-layer diode but with the added gate connection
SCR
2. This is the maximum continuous anode current that the device can withstand in the conduction state under specifies conditions.
Average forward current
3. What bilateral thyristor functions basically like two parallel SCRs turned in opposite directions with a common gate terminal?
Triac
4. ____________ does not belong to the thyristor family because it does not have a four-layer type of construction.
UJT
5. It can be used a trigger device for SCRs and triacs. UJT
6. It is a type of three-terminal thyristor that is triggered into conduction when the voltage at the anode exceeds the voltage at the gate.
PUT
7. A region of forward bias in which the device has a very high forward resistance and is in the off state Forward-blocking region
8. A method for turning-off the SCR that basically requires momentarily forcing current through the SCR in the direction opposite to the forward conduction
Forced commutation
9. The value of gate current necessary to switch the SCR from the forward-blocking region to the forward-conduction region under specified conditions.
Gate Trigger Current
10. A four-layer semiconductor device that operates essentially as does the conventional SCR except that it can also be light-triggered.
LASCR
11. Functions basically like two parallel 4- layer diodes turned in opposite directions.
Diac
12. A diac with gate terminal Triac
13. A four-terminal thyristor that has two gate terminals that are used t trigger the device on and off Silicon Controlled Device (SCS)
14. A type of three-terminal thyristor that is triggered into conduction when the voltage at the anode exceeds the voltage at the gate.
Programmable Unijunction Transistor (PUT) 15. The characteristic of a UJT that determines its turn-on point
Standoff-ratio
16. The four-layer diode is also called Shockley diode
17. The region that corresponds to the on condition of the SCR where there is forward current from anode to cathode through the very low resistance of the SCR Forward_ conduction region
18. The SCR can only be turned on using its _________ terminal
Gate
19. Acts as the trigger source in the LASCRs Light
20. A thyristor that conducts when the voltage across its terminals exceeds the breakover potential
4-layer diode
21. Basic methods of for turning off an SCR Anode current interruption and forced commutation
CHAPTER 12 THE OPERATIONAL AMPLIFIER
CHAPTER 12
THE OPERATIONAL AMPLIFIER
1. The measure of an amplifier’s ability to reject common-mode signals
CMRR
2. It is the typical value of input offset voltage in the ideal case.
0 V
3. It is the dc current required by the inputs of the amplifier to properly operate the first stage. Input bias current
4. It is the resistance viewed from the output terminal of the op-amp Output impedance
5. The total resistance between the inverting and noninverting inputs
Differential input impedance
6. Differential impedance is measured by determining the change in ___________ for a given change in differential input voltage.
Bias current
7. Common temperature coefficient for the offset current
0.5nA/°C
8. Functions of negative feedback in an op-amp Stabilize gain and increase frequency response 9. The voltage gain of an op-amp with external feedback
Closed-loop voltage gain
10. A special case of the noninverting amplifier where all of the output voltage is fed back to the inverting input by a straight connection
Voltage-follower configuration
11. The value of the frequency at which the gain steadily decreases to a point where it is equal to unity
Unity-gain frequency Or unity gain bandwidth 12. It is always equal to the frequency at which the op-amp’s open- loop gain is unity or 0 dB. Gain-bandwidth product
13. The relative angular displacement of a
time-varying function relative to a reference. Phase shift
14. The three terminals of the basic op-amp not including power and ground
Inverting input, noninverting input, and output 15. It has the highest input impedance and the lowest output impedance of the three amplifier
configurations Voltage-follower
16. The _________ of an op-amp equals the upper critical frequency.
Bandwidth
17. Two types of op-amp input operation. Differential mode and common-mode
18. A ____________ differentiator uses a capacitor in series with the inverting input.
Ideal
19. An ideal op-amp has ___________ value for voltage gain, bandwidth, and input impedance. Infinite
20. What should be the output voltage of an op-amp when the differential input is zero
Zero
21. The ideal op-amp has __________ output impedance
Zero
22. The three basic op-amp configurations Inverting, noninverting, and voltage follower 23. The closed-loop voltage gain is _________ than the open-loop voltage gain. (more or less)
Less
24. Does the gain of an op-amp decreases
or increases as frequency increases above the critical frequency
Decreases
25. Devices such as the diode and the transistor which are separate devices that
are individually packaged and interconnected in a circuit with other devices to form a complete, functional unit.
Discrete components
26. Most op-amps operate with how many dc supply voltage?
27. Datasheets often refer to the open-loop voltage gain as the ______________
Large-signal voltage gain
CHAPTER 13 BASIC OP-AMP CIRCUITS CHAPTER 13
BASIC OP-AMP CIRCUITS
1. A common interfacing process often used when a linearanalog system must provide inputs to a digital system.
A/D conversion
2. Method of A/D conversion that uses parallel comparators to compare the linear input signal with various reference voltages developed by a voltage divider
Flash
3. Produces an output that is proportional to the rate of change of the input voltage
Differentiator
4. The difference between the UTP and the LTP Hysteresis voltage
5. Used to generate pulse waveform from the sine wave output of the audio generator. Voltage comparator
6. When the output is at the maximum positive voltage and the input exceeds UTP, the output switches to the _________ negative voltage Maximum
7. Uses a capacitor in the feedback path which is open to dc. This implies that the gain at dc is the open-loop gain of the op-amp.
Practical integrator
8. Gives an op-amp noise immunity Hysteresis
9. Used to detect positive and negative voltages by connecting a fixed reference voltage source to the inverting input of a zero-level detector.
Nonzero-Level detection 10. A good example of hysteresis Thermostat
11. A comparator with three trigger points Schmitt Trigger
12. The output of Schmitt trigger is Pulse waveform
13. In a comparator with output bounding, what type of diode is used in the feedback loop?
Zener
14. Necessary components for the design of a bounded comparator
Rectifier and zener diodes
15. Type of circuit that uses comparators Nonzero-level detector
16. Variations of the basic summing amplifier Averaging and scaling amplifier
17. Differentiation of a ramp input produces a step output with an amplitude proportional to the _________
Slope
18. Another term for flash Simultaneous
19. Integration of a step input produces a ramp output with the slope proportional to the _________
Amplitude
CHAPTER 14 SPECIAL PURPOSE OP-AMP CIRCUITS
CHAPTER 14
SPECIAL PURPOSE OP-AMP CIRCUITS 1. Provides dc isolation between input and output Isolation amplifier
2. Ratio of the output current to the input voltage Transconductance
3. Transconductance is __________ of an OTA Gain
4. A comparator with hysteresis where the input voltage is large enough to drive the device into its saturated states
Schmitt trigger
5. The ______________ of a number is the power to which the base must be raised to get that number. Logarithm
6. An amplifier that produces an output that is proportional to the logarithm of the input.
Log amplifier
7. Used in applications where it is necessary to have an output current that is controlled by an input voltage.
Voltage-to-current converter
8. The circuit used to detect the peak of the input voltage and store that peak voltage on a capacitor. Peak detector
9. The exponent to which the base e must be raised in order to equal a given quantity.
Natural logarithm
10. In an OTA, transconductance varies with _________.
Bias current
11. Amplifiers that are often used in HF
communication systems, including fiber optics, for processing wide dynamic range signals.
Log and antilog amplifiers
12. The key characterisctic of an instrumentation amplifier
CMRR
13. The voltage gain of instrumentation amplifier is set by a
Resistor
14. The log amplifier may use the ___________ junction of a BJT in the feedback loop
Base-emitter
15. The main purpose of an instrumentation amplifier is to amplify _____ signals that are riding on _____ common-mode voltages.
small, large
16. The ___________ of an OTA is the input voltage times the transconductance
Output current
17. The operation of log and antilog amplifiers is based on the __________ characteristics of a pn junction
Nonlinear (logarithmic)
18. A log amplifier has a pn junction in the feedback loop, and an antilog amplifier has a pn junction in __________ with the input
Series
19. In a peak detector, an op-amp is used as a __________ to charge a capacitor through a diode to the peak value of the input voltage.
Comparator
20. A basic instrumentation amplifier is formed by three op-amps and ________ resistors, including the gain setting resistor.
Seven (7)
21. An oscillator that can be either amplitude or pulse modulated by the signal from the input amplifier High-frequency oscillator