Deck 18: Oscillators

Question 1

Phase-shift oscillators are rarely used because

A) they are very difficult to produce.
B) their output amplitudes are very hard to regulate.
C) their output frequencies tend to be extremely unstable.
D) they require the use of an op-amp.

Answer 1

their output frequencies tend to be extremely unstable.

Question 2

A Clapp oscillator has in its feedback network.

A) a pair of tapped capacitors in parallel with an inductor
B) a pair of tapped inductors in parallel with a capacitor
C) a transformer with a capacitor in parallel with its primary winding
D) a pair of tapped capacitors in parallel with an inductor and a third small-value capacitor

Answer 2

a pair of tapped capacitors in parallel with an inductor and a third small-value capacitor

Question 3

The circuit in Figure has the following values: RFC = 100 μH, L = 10 μH, C1 = 1 μF, and C2 = 33 μF. What is the output frequency of the circuit?

A) 74.5 kHz
B) 25.6 kHz
C) 12.8 kHz
D) 51.1 kHz

Answer 3

51.1 kHz

Question 4

The Barkhausen criterion states that the product of voltage gain and current gain in an oscillator must equal one 1).

Question 5

Positive feedback is also called

A) degenerative feedback.
B) additive feedback.
C) regenerative feedback.
D) regressive feedback.

Question 6

The negative feedback circuit in a Wien-bridge oscillator is used to

A) determine the frequency of operation.
B) control the gain of the circuit.
C) bias the positive feedback network.
D) prevent unwanted oscillations.

Question 7

The circuit in Figure has the following values: RFC = 1 mH, L1 = 100 μH, L2 = 22 μH, and C1 = 0.001 μF. Assuming that the mutual inductance in the circuit is too low to be considered, what is the approximate output frequency of the oscillator?

A) 456 kHz
B) 152 kHz
C) 503 kHz
D) 2.2 MhZ

Question 8

The positive feedback circuit in a Wien-bridge oscillator is used to

A) determine the frequency of operation.
B) control the gain of the circuit.
C) bias the negative feedback network.
D) prevent unwanted oscillations.

Question 9

Which of the following is not a requirement for oscillator operation?

A) The circuit must fulfill the Barkhausen criterion.
B) The circuit must initially be triggered into operation.
C) The feedback network must contain an RC circuit.
D) The circuit must provide positive feedback.

Question 10

In a positive feedback system, the feedback signal and the amplifier input signal are

A) in phase.
B) 45° out of phase.
C) 90° out of phase.
D) 180° out of phase.

Question 11

A three-stage BJT amplifier is found to be producing unwanted oscillations. Which of the following will solve the problem?

A) Reducing the overall voltage gain of the amplifier
B) Using a regulated dc power supply
C) Increasing the supply voltage for the amplifier
D) Replacing the BJTs with JFETs

Question 12

The Wien-bridge oscillator is limited to output frequencies that are around 1 MHz or less.

Question 13

An oscillator is a circuit that

A) converts ac to dc.
B) converts dc to ac.
C) converts one ac frequency to another frequency.
D) performs all of the above conversions.

Question 14

The circuit in Figure has the following values: RFC = 100 μH, C1 = 1 μF, and C2 = 33 μF. What is the feedback factor αv) of the circuit?

A) 0.03
B) 33
C) 0.01
D) 100

Question 15

The circuit in Figure has the following values: RFC = 100 μH, C1 = 1 μF, and C2 = 33 μF. What is the value of Av for the circuit?

A) 0.03
B) 33
C) 0.01
D) 100

Question 16

The circuit in Figure has the following values: RFC = 1mH, L1 = 91 μH, L2 = 20 μH. What is the feedback factor?

A) 45.45
B) 4.55
C) 0.22
D) 111

Question 17

A Colpitts oscillator has in its feedback network.

A) a pair of tapped capacitors in parallel with an inductor
B) a pair of tapped inductors in parallel with a capacitor
C) a transformer with a capacitor in parallel with its primary winding
D) a pair of tapped capacitors in parallel with an inductor and a third small-value capacitor

Question 18

An oscillator has the following values: Av = 188 and α = 0.0048. Which of the following statements is true?

A) The circuit has a constant amplitude output.
B) The output from the circuit fades out after several cycles.
C) The output from the circuit clips after several cycles.
D) None of the above statements are true.

Question 19

A Hartley oscillator has in its feedback network.

A) a pair of tapped capacitors in parallel with an inductor
B) a pair of tapped inductors in parallel with a capacitor
C) a transformer with a capacitor in parallel with its primary winding
D) a pair of tapped capacitors in parallel with an inductor and a third small-value capacitor

Question 20

In a practical phase-shift oscillator, each RC circuit produces a 60° phase shift.

Question 21

A big advantage that LC oscillators have over RC oscillators is the fact that LC oscillators can generally be operated at much higher frequencies.

Question 22

Which of the following is considered the most durable when manufacturing CCOs?

A) Lead crystal
B) Rochell salt
C) Quartz
D) Tourmaline

Question 23

At fp, a crystal has impedance.

A) low
B) high

Question 24

Which of the following is considered the least expensive when manufacturing crystal oscillators?

A) Lead crystal
B) Rochell salt
C) Quartz
D) Tourmaline

Question 25

The inherent resonant frequency of a crystal is determined by .

A) the L and C values in the circuit
B) the ʺcut of the crystalʺ frequency
C) the physical dimensions of the crystal
D) All of the above.

Question 26

What type of crystal has the best frequency properties?

A) Lead crystal
B) Rochell salt
C) Quartz
D) Tourmaline

Question 27

A 20 MHz crystal is used to produce a 200 MHz oscillator output frequency. This is called operation.

A) resonant mode
B) overtone mode
C) harmonic mode
D) Pierce
Chapter 18 Oscillators Answer Key

Question 28

Which of the following is not used as crystals in oscillator circuits?

A) Lead crystal
B) Rochell salt
C) Quartz
D) Tourmaline

Question 29

When crystals are exposed to an electric field, they vibrate at a constant rate. This is called .

A) the over tone mode
B) the CCO effect
C) the piezoelectric effect
D) None of the above.

Question 30

At fs, a crystal has impedance.

A) high
B) low

Question 31

CCOs have

A) very low operating frequencies.
B) very stable output frequencies.
C) extremely simple biasing circuits.
D) All of the above.