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Unit 5 - Practice Quiz

ECE182 50 Questions
0 Correct 0 Wrong 50 Left
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1 According to the Barkhausen criterion, what is the required condition for the magnitude of the loop gain () to achieve sustained oscillations?

A.
B.
C.
D.

2 Which of the following represents the Barkhausen criterion for the total phase shift around the feedback loop?

A.
B.
C.
D.

3 Oscillators generate continuous waveforms by fundamentally employing which type of feedback?

A. Negative feedback
B. Positive feedback
C. No feedback
D. Both positive and negative feedback equally

4 If the loop gain magnitude of an oscillator circuit falls below 1, what happens to the oscillations?

A. They grow exponentially
B. They are sustained at a constant amplitude
C. They progressively decay and die out
D. They become purely sinusoidal

5 To reliably initiate oscillations from noise when power is first applied, practical oscillators are designed such that the initial loop gain magnitude is:

A. Slightly less than 1
B. Exactly 1
C. Slightly greater than 1
D. Zero

6 In an RC phase shift oscillator utilizing an inverting amplifier, what is the total phase shift that must be provided by the RC feedback network?

A.
B.
C.
D.

7 How many identical RC stages are minimally required in the feedback network of a standard RC phase shift oscillator?

A. 1
B. 2
C. 3
D. 4

8 What is the frequency of oscillation () for a 3-stage RC phase shift oscillator constructed with identical resistors () and capacitors ()?

A.
B.
C.
D.

9 What is the minimum required magnitude of voltage gain () for the amplifier in a standard 3-stage RC phase shift oscillator to sustain oscillations?

A. 1
B. 3
C. 29
D. 1/29

10 RC phase shift oscillators are most commonly preferred for applications in which frequency range?

A. Audio frequencies (AF)
B. Radio frequencies (RF)
C. Microwave frequencies
D. Optical frequencies

11 If the value of every capacitor in an RC phase shift oscillator is doubled, how does the new frequency of oscillation relate to the original frequency ()?

A.
B.
C.
D.

12 What is the formula for the frequency of oscillation () of a Wien-bridge oscillator having equal and components in its series and parallel feedback branches?

A.
B.
C.
D.

13 What phase shift is introduced by the lead-lag RC feedback network of a Wien-bridge oscillator exactly at its resonant frequency?

A.
B.
C.
D.

14 Because the Wien-bridge feedback network provides phase shift at resonance, which type of amplifier must be utilized to satisfy the Barkhausen criterion?

A. Inverting amplifier
B. Non-inverting amplifier
C. Differential amplifier
D. Summing amplifier

15 What is the attenuation factor () of the feedback network in a standard Wien-bridge oscillator at the resonant frequency?

A. 1
B. 1/3
C. 1/29
D. 3

16 Based on the standard attenuation factor, what is the minimum required voltage gain of the amplifier in a Wien-bridge oscillator?

A. 1
B. 3
C. 29
D. 1/3

17 Which component is historically employed in the feedback loop of a Wien-bridge oscillator to provide automatic amplitude stabilization?

A. A thermistor or an incandescent lamp
B. A large inductor
C. A Zener diode in reverse breakdown
D. A high-power BJT

18 The resonant feedback circuit (tank circuit) of a Hartley oscillator is characterized by having:

A. Two capacitors and one inductor
B. Two inductors and one capacitor
C. Three capacitors
D. Three inductors

19 Assuming no mutual inductance, what is the equivalent inductance () of the tank circuit in a Hartley oscillator?

A.
B.
C.
D.

20 What is the general expression for the frequency of oscillation of a Hartley oscillator (neglecting mutual inductance)?

A.
B.
C.
D.

21 If mutual inductance () exists between the two coil sections in a Hartley oscillator, the equivalent inductance () becomes:

A.
B.
C.
D.

22 Hartley and Colpitts oscillators are most suitable for generating signals in which frequency range?

A. Generating 50 Hz AC mains signals
B. Generating extremely low frequency (ELF) signals
C. Generating high frequency (RF) signals
D. DC voltage generation

23 The resonant feedback circuit (tank circuit) of a Colpitts oscillator is composed of:

A. Two inductors and one capacitor
B. Two capacitors and one inductor
C. One resistor and two capacitors
D. Three inductors

24 What is the equivalent capacitance () of the tank circuit in a Colpitts oscillator?

A.
B.
C.
D.

25 What is the primary advantage of a Colpitts oscillator over a Hartley oscillator?

A. It is easier to tune using a single variable component
B. It provides better frequency stability at high frequencies
C. It requires no capacitors
D. It operates at lower frequencies

26 In a common-emitter Colpitts oscillator, what is the phase shift provided by the LC tank circuit?

A.
B.
C.
D.

27 Which modification to the Colpitts oscillator improves its frequency stability by adding a third capacitor in series with the inductor?

A. Hartley Oscillator
B. Clapp Oscillator
C. Wien-bridge Oscillator
D. Phase Shift Oscillator

28 The internal voltage divider of a standard 555 timer IC consists of:

A. Three resistors
B. Three resistors
C. Two resistors
D. Four resistors

29 In a 555 timer, the threshold comparator triggers when the voltage at Pin 6 exceeds what internal reference voltage?

A.
B.
C.
D.

30 In a 555 timer, the trigger comparator sets the internal flip-flop when the voltage at Pin 2 drops below what reference level?

A.
B.
C.
D. Ground

31 Pin 7 of the 555 timer is known as the Discharge pin. It is internally connected to the collector of which type of transistor?

A. PNP BJT
B. N-channel MOSFET
C. NPN BJT
D. JFET

32 Which pin of the 555 timer can be used to alter the upper reference voltage, and is typically bypassed to ground with a capacitor to prevent noise?

A. Pin 2 (Trigger)
B. Pin 4 (Reset)
C. Pin 5 (Control Voltage)
D. Pin 8 ()

33 How many stable states does a monostable multivibrator possess?

A. Zero
B. One
C. Two
D. Three

34 An astable multivibrator is also commonly referred to as a:

A. One-shot multivibrator
B. Flip-flop
C. Free-running oscillator
D. Schmitt trigger

35 What is the approximate formula for the output pulse width () of a 555 timer configured as a monostable multivibrator, using resistor and capacitor ?

A.
B.
C.
D.

36 What is the approximate frequency of oscillation () for a 555 timer configured as a standard astable multivibrator with resistors , , and capacitor ?

A.
B.
C.
D.

37 In a standard 555 astable multivibrator configuration, the duty cycle of the output square wave is always:

A. Exactly 50%
B. Less than 50%
C. Greater than 50%
D. 100%

38 How can a standard 555 astable multivibrator be modified to achieve exactly a duty cycle?

A. By removing
B. By adding a diode in parallel with
C. By connecting Pin 5 to ground directly
D. By using a larger value for

39 What is the primary defining function of a Voltage-Controlled Oscillator (VCO)?

A. An oscillator that generates a constant frequency output
B. An oscillator whose output amplitude is controlled by an input voltage
C. An oscillator whose output frequency is determined by a DC control voltage
D. A voltage regulator that produces oscillations

40 Which of the following ICs is a widely used dedicated Voltage-Controlled Oscillator (VCO) capable of generating highly linear square and triangular waves?

A. IC 555
B. IC 741
C. IC 566
D. IC 3140

41 In an ideal Voltage-Controlled Oscillator, the relationship between the applied control voltage () and the output frequency () is designed to be:

A. Logarithmic
B. Linear
C. Exponential
D. Inversely proportional squared

42 The conversion gain or sensitivity () of a Voltage-Controlled Oscillator is typically measured in:

A. Volts per Hertz (V/Hz)
B. Hertz per Volt (Hz/V)
C. Radians per second
D. Degrees per Volt

43 When utilizing a 555 timer IC as a rudimentary VCO, the external modulating control voltage is applied to which pin?

A. Pin 2
B. Pin 4
C. Pin 5
D. Pin 7

44 What type of underlying oscillator topology does the IC 566 VCO use to generate its waveforms?

A. LC tank oscillator
B. Relaxation oscillator
C. Crystal oscillator
D. Phase shift oscillator

45 What are the three essential building blocks of a Phase-Locked Loop (PLL)?

A. Phase detector, low-pass filter, and VCO
B. Phase detector, high-pass filter, and VCO
C. Voltage comparator, integrator, and differentiator
D. Multiplier, envelope detector, and Schmitt trigger

46 In a Phase-Locked Loop (PLL), the phase detector compares the phase of the external input signal against the phase of the signal produced by the:

A. Low-pass filter
B. External reference clock
C. VCO
D. Error amplifier

47 What is the primary function of the low-pass filter within a Phase-Locked Loop (PLL)?

A. To amplify the input signal
B. To convert the input frequency to a DC voltage
C. To remove high-frequency noise from the phase detector output and determine loop dynamics
D. To shift the phase of the VCO output by

48 The range of frequencies over which a PLL can maintain synchronism (lock) with an input signal after it has been initially locked is called the:

A. Capture range
B. Lock range
C. Free-running range
D. Pull-in range

49 The range of input frequencies over which an unlocked PLL can successfully acquire lock with an incoming signal is known as the:

A. Capture range
B. Lock range
C. Holding range
D. Bandwidth

50 How does the Capture Range () of a Phase-Locked Loop generally compare to its Lock Range ()?

A.
B. always
C.
D. They are completely unrelated
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