Deck 16: Oscillators

Question 1

Figure 6
Refer to Figure 6. If a capacitor is place from CONT to ground it will

A)change the output frequency
B)change the output duty cycle
C)both A and B
D)none of the above

Answer 1

D

Question 2

Figure 1
Refer to Figure 1. Assume the frequency of Vout is 6.0 kHz and R1 = R2. The value of each of these resistors is

A)3.6 k▲
B)5.6 k▲
C)27 k▲
D)8.9 k▲

Answer 2

B

Question 3

Figure 6
Refer to Figure 6. The output is a

A)pulses with a duty cycle >50%
B)square wave (duty cycle = 50%)
C)pulses with a duty cycle <50%
D)tringle wave

Answer 3

A

Question 4

Figure 1
Refer to Figure 1. The JFET acts as a

A)signal reference
B)voltage- controlled current source
C)inverting amplifier
D)voltage- controlled resistor

Question 5

Figure 3 A simplified oscillator circuit.
Refer to Figure 3. The type of oscillator represented is a

A)Hartley
B)Armstrong
C)Clapp
D)Colpitts

Question 6

Figure 1
Refer to Figure 5. The output of this circuit is a

A)square wave
B)sine wave
C)sawtooth wave
D)triangle wave

Question 7

Figure 6
Refer to Figure 6. The capacitor voltage is between

A)1/3 VCC and 2/3 VCC
B)0 V and 2/3 VCC
C)1/3 V_CC and V_CC
D)0 V and V_CC

Question 8

Closed- loop gain for a feedback oscillator is expressed as

A)Av/B
B)AvB + 1
C)1/B
D)AvB

Question 9

At startup, a feedback oscillator requires a closed- loop gain of

A)exactly +1
B)exactly -1
C)0
D)none of the above

Question 10

Figure 3 A simplified oscillator circuit.
Refer to Figure 3. Assume the circuit is working normally; the output frequency is approximately

A)100 kHz
B)333 kHz
C)3.33 MHz
D)1.0 MHz

Question 11

Figure 2
Refer to Figure 2. The portion in the dashed box is

A)a phase shift network
B)a notch filter
C)a lead- lag network
D)none of the above

Question 12

Figure 2
Refer to Figure 2. Rf determines the

A)gain
B)output frequency
C)both A and B
D)none of the above

Question 13

The overall response of a twin- T feedback network is that of a

A)parallel resonant circuit
B)bandpass filter
C)lead- lag network
D)notch filter

Question 14

Figure 1
Refer to Figure 1. When adjusted properly the signal at the non- inverting input of the op- amp is

A)2/3 Vout
B)1/3 Vout
C)1/2 V_out
D)none of the above

Question 15

Figure 2
Refer to Figure 2. The circuit is

A)a Colpitts oscillator
B)a twin- T oscillator
C)a Wien bridge oscillator
D)none of the above

Question 16

Figure 6
Refer to Figure 6. The circuit can be configured as a VCO by applying

A)disconnecting the THRESH and applying a variable voltage to it
B)a variable voltage to the CONT pin
C)disconnecting the RESET and applying a variable voltage to it
D)none of the above

Question 17

Figure 1
Refer to Figure 1. The output of the circuit when adjusted properly is a

A)square wave
B)sinusoidal wave
C)swept frequency
D)triangle wave

Question 18

Figure 3 A simplified oscillator circuit.
Refer to Figure 5. This is an example of a

A)function generator
B)voltage- controlled oscillator
C)twin- T oscillator
D)relaxation oscillator

Question 19

Figure 3 A simplified oscillator circuit.
Refer to Figure 3. If the inductor is changed for one twice as large, the resonant frequency will be

A)doubled
B)unchanged
C)halved
D)none of the above

Question 20

Figure 3 A simplified oscillator circuit.
Refer to Figure 3. The fraction of the output that is fed back is

A)0.50
B)0.20
C)0.90
D)0.10

Question 21

Figure 4
Refer to Figure 4. The output frequency is determined by C1 and

A)R1 and R3
B)R1 and R2
C)R2 and R3
D)R1, R2, and R3

Question 22

The major advantage of crystal oscillators is its accuracy and stability.

Question 23

An Armstrong oscillator

A)is the most widely used of high- frequency oscillators
B)uses a "tickler coil" in the feedback loop
C)uses 3 capacitors in the feedback circuit
D)uses a tapped inductor to generate feedback

Question 24

Figure 2
Refer to Figure 2. The op- amp serves to

A)amplify the feedback signal
B)shift the phase of the feedback signal by 90°
C)both A and B
D)none of the above

Question 25

Feedback oscillators start because of thermally induced noise.

Question 26

The Hartley oscillator develops the feedback voltage across a capacitor.

Question 27

Assume a feedback oscillator uses an inverting amplifier and a sample of the output is fed back. The feedback network needs to shift the phase

A)270°
B)180°
C)0°
D)90°

Question 28

An internal capacitor in a 555 timer determines the free- running frequency.

Question 29

During steady state operation, the closed- loop gain for a Wien- bridge oscillator is 3.

Question 30

Figure 4
Refer to Figure 4. The two outputs are a

A)square wave and a triangle wave
B)square wave and a sine wave
C)sawtooth wave and a triangle wave
D)sawtooth wave and a sine wave

Question 31

A VCO uses a control voltage to set the output amplitude.

Question 32

All oscillators use positive feedback.

Question 33

The equivalent circuit for a quartz crystal is a series- parallel RLC circuit.