Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
Current–series feedback ________ the output impedance of an op–amp.
1)
A)
increases
B)
has no effect on
C)
reduces by half
D)
decreases
Answer:
A
A)
B)
C)
D)
2)
The feedback circuit connection shown here is ________.
2)
A)
voltage series feedback
B)
current series feedback
C)
current shunt feedback
D)
voltage shunt feedback
Answer:
D
A)
B)
C)
D)
3)
Current–series feedback ________ the bandwidth of an op–amp.
3)
A)
decreases
B)
increases
C)
reduces by half
D)
has no effect on
Answer:
B
A)
B)
C)
D)
4)
In a practical phase–shift oscillator, each RC circuit section produces a ________.
4)
A)
60° phase shift
B)
90° phase shift
C)
180° phase shift
D)
30° phase shift
Answer:
A
A)
B)
C)
D)
1
5)
Voltage–series feedback ________ the bandwidth of an op–amp.
5)
A)
decreases
B)
has no effect on
C)
reduces by half
D)
increases
Answer:
D
A)
B)
C)
D)
6)
Which of the following is not a requirement for oscillator operation?
6)
A)
The circuit must fulfill the Barkhausen criterion.
B)
The feedback network must contain an RC circuit.
C)
The circuit must provide positive feedback.
D)
The circuit must initially be triggered into operation.
Answer:
B
A)
B)
C)
D)
7)
The ________ margin is defined as the angle of 180° minus the magnitude of the angle at which the
value |A| is unity (0 dB).
7)
A)
feedback
B)
error
C)
gain
D)
phase
Answer:
D
A)
B)
C)
D)
8)
The total phase shift around a negative feedback loop of a common–emitter circuit is ________.
8)
A)
90°
B)
45°
C)
180°
D)
360° or 0°
Answer:
D
A)
B)
C)
D)
9)
The positive feedback circuit in a Wien–bridge oscillator is used to ________.
9)
A)
control the gain of the circuit
B)
determine the frequency of operation
C)
bias the negative feedback network
D)
prevent unwanted oscillations
Answer:
B
A)
B)
C)
D)
2
10)
The circuit recognition feature of the Hartley oscillator is a ________.
10)
A)
pair of tapped inductors in parallel with a capacitor
B)
feedback transformer with a capacitor in parallel with its primary winding
C)
pair of tapped capacitors in parallel with an inductor and a third small–value capacitor
D)
pair of tapped capacitors in parallel with an inductor
Answer:
A
A)
B)
C)
D)
11)
Positive feedback is used to produce a special type of circuit called a(n) ________.
11)
A)
feedback regulator
B)
noninverting amplifier
C)
oscillator
D)
inverting amplifier
Answer:
C
A)
B)
C)
D)
12)
Crystal–controlled oscillators have ________.
12)
A)
very stable output frequencies
B)
extremely simple biasing circuits
C)
very low operating frequencies
D)
All of the above
Answer:
A
A)
B)
C)
D)
13)
The biggest advantage that LC oscillators have over RC oscillators is the fact that LC oscillators
generally ________.
13)
A)
require less physical space
B)
can be operated at a much higher frequency
C)
can be constructed more economically
D)
None of the above
Answer:
B
A)
B)
C)
D)
3
14)
The tank circuit shown here is for a ________ oscillator.
14)
A)
crystal
B)
Colpitts
C)
phase shift
D)
Hartley
Answer:
B
A)
B)
C)
D)
15)
The advantage of negative feedback is ________.
15)
A)
lower output impedance
B)
voltage gain that is more stable
C)
higher input impedance
D)
All of the above
Answer:
D
A)
B)
C)
D)
16)
Negative current feedback ________.
16)
A)
decreases Ai
B)
decreases bandwidth
C)
increases Ai
D)
increases Av
Answer:
A
A)
B)
C)
D)
17)
Positive feedback is also called ________.
17)
A)
regressive feedback
B)
Barkhausen oscillation
C)
additive feedback
D)
degenerative feedback
Answer:
B
A)
B)
C)
D)
4
18)
The circuit recognition feature of the Colpitts oscillator is ________.
18)
A)
a pair of tapped inductors in parallel with a capacitor
B)
a feedback transformer with a capacitor in parallel with its primary winding
C)
a pair of tapped capacitors in parallel with an inductor and a third small–value capacitor
D)
a pair of tapped capacitors in parallel with an inductor
Answer:
D
A)
B)
C)
D)
19)
The feedback amplifier is unstable if the Nyquist curve plotted ________ the (–1 + j0) point and it is
otherwise stable.
19)
A)
does not come close to
B)
encloses (encircles)
C)
passes to the left of
D)
passes right over
Answer:
B
A)
B)
C)
D)
20)
The Q of a crystal is typically ________.
20)
A)
5000
B)
1,000,000
C)
20,000
D)
500,000
Answer:
C
A)
B)
C)
D)
21)
An oscillator has the following values: Av = 188 and = 0.00488. Which of the following statements
is true?
21)
A)
The output from the circuit fades out after several cycles.
B)
The circuit has a constant amplitude output.
C)
The output from the circuit clips after several cycles.
D)
None of the above
Answer:
A
A)
B)
C)
D)
22)
A Colpitts oscillator has C1= 1 µF, C2= 33 µF and L = 4.7 mH. What is the approximate operating
frequency of the circuit?
22)
A)
12.8 kHz
B)
25.6 kHz
C)
2.356 kHz
D)
None of the above
Answer:
C
A)
B)
C)
D)
5
23)
In a positive feedback system, the feedback signal and the amplifier input signal are ________.
23)
A)
45° out of phase
B)
in phase
C)
90° out of phase
D)
180° out of phase
Answer:
B
A)
B)
C)
D)
24)
The total phase shift around a positive feedback loop for a common–emitter circuit is ________.
24)
A)
90°
B)
360° or 0°
C)
45°
D)
180°
Answer:
D
A)
B)
C)
D)
25)
The effect that is responsible for the resonant quality of a crystal is known as the ________ effect.
25)
A)
piezoelectric
B)
Miller
C)
Barkhausen
D)
hysteresis
Answer:
A
A)
B)
C)
D)
26)
The feedback circuit connection shown here is ________.
26)
A)
current shunt feedback
B)
voltage shunt feedback
C)
voltage series feedback
D)
current series feedback
Answer:
C
A)
B)
C)
D)
27)
The ________ margin is defined as the negative of the value of |A| decibels at the frequency at
which the phase angle is 180°.
27)
A)
feedback
B)
error
C)
gain
D)
phase
Answer:
C
A)
B)
C)
D)
6
28)
An amplifier has a gain–bandwidth product of 200 MHz. A feedback network is added that has a
feedback factor (1 +A) of 18.88. What is the gain–bandwidth product for the circuit with the
added feedback network?
28)
A)
18.88 MHz
B)
10.59 MHz
C)
200 MHz
D)
None of the above
Answer:
C
A)
B)
C)
D)
29)
Voltage–series feedback ________ the output impedance of an op–amp.
29)
A)
increases
B)
reduces by half
C)
decreases
D)
has no effect on
Answer:
C
A)
B)
C)
D)
30)
Adding a negative voltage–feedback network to an amplifier has no effect on the value of ________
for the circuit.
30)
A)
signal distortion
B)
input impedance
C)
frequency response
D)
None of the above
Answer:
D
A)
B)
C)
D)
31)
The output impedance of a voltage–shunt feedback amplifier ________ the output impedance of its
op–amp.
31)
A)
has no effect on
B)
is increased when compared to
C)
is decreased when compared to
D)
is reduced by half when compared to
Answer:
D
A)
B)
C)
D)
7
32)
The tank circuit shown here is for a ________ oscillator.
32)
A)
crystal
B)
Colpitts
C)
phase shift
D)
Hartley
Answer:
D
A)
B)
C)
D)
33)
The negative feedback circuit in an op–amp Wien–bridge oscillator is used to ________.
33)
A)
prevent unwanted oscillations
B)
bias the positive feedback network
C)
determine the frequency of operation
D)
control the gain of the circuit
Answer:
D
A)
B)
C)
D)
34)
Calculate the voltage gain for voltage series feedback when the amplifier gain is A = –2000 and =
–1/50.
34)
A)
–1/50
B)
–48.78
C)
–2000
D)
50
Answer:
B
A)
B)
C)
D)
35)
Current–series feedback ________ the input impedance of an op–amp.
35)
A)
reduces by half
B)
has no effect on
C)
decreases
D)
increases
Answer:
D
A)
B)
C)
D)
36)
For oscillations to exist and the voltage to sustain the loop operations, the Barkhausen Criterion tells
us that the loop gain A must be exactly equal to ________.
36)
A)
equal to the reciprocal of
B)
unity (1)
C)
more than one
D)
minus one
Answer:
B
A)
B)
C)
D)
8
37)
The input impedance of a voltage–shunt feedback amplifier ________ the input impedance of its
op–amp.
37)
A)
is increased when compared to
B)
has no effect on
C)
is reduced by half when compared to
D)
is decreased when compared to
Answer:
D
A)
B)
C)
D)
38)
The electrical equivalent circuit for a crystal actually models ________ effects.
38)
A)
optoelectrical
B)
thermal
C)
electromechanical
D)
electrical noise
Answer:
C
A)
B)
C)
D)
39)
A Colpitts oscillator has values of Cl= 1 µF, C2= 33 µF, and L = 100 µH. What is the frequency of
oscillation?
39)
A)
100.5 kHz
B)
20.3 kHz
C)
16.155 kHz
D)
12.154 kHz
Answer:
C
A)
B)
C)
D)
40)
Voltage–series feedback ________ the input impedance of an op–amp.
40)
A)
has no effect on
B)
decreases
C)
increases
D)
reduces by half
Answer:
C
A)
B)
C)
D)
41)
At the ________ a crystal acts as a short circuit.
41)
A)
non–resonant frequency
B)
parallel–resonant frequency
C)
series–resonant frequency
D)
None of the above
Answer:
C
A)
B)
C)
D)
9
42)
Negative voltage feedback ________.
42)
A)
decreases bandwidth
B)
increases Ai
C)
decreases Av
D)
increases Av
Answer:
C
A)
B)
C)
D)
43)
At the ________ a crystal acts as an open circuit.
43)
A)
parallel–resonant frequency
B)
series–resonant frequency
C)
non–resonant frequency
D)
None of the above
Answer:
A
A)
B)
C)
D)
44)
Calculate the gain of a negative feedback amplifier having A = –2000 and = – 1/16.
44)
A)
–2000
B)
125
C)
–1/16
D)
–125
Answer:
B
A)
B)
C)
D)
45)
A Hartley oscillator has the following values: RFC = 1 mH, L1= 100 µH, L2= 22 µH, and C = 0.001
µF. Assuming that the mutual inductance in the circuit is too small to be considered, what is the
approximate output frequency of the oscillator?
45)
A)
503 kHz
B)
152 kHz
C)
456 kHz
D)
None of the above
Answer:
C
A)
B)
C)
D)
46)
Calculate the input impedace for voltage series feedback when the amplifier has Ri= 10 k,
amplifier gain is A = –2000, and = – 1
50.
46)
A)
input impedance with feedback 50
B)
input impedance with feedback 10 k
C)
input impedance with feedback 244
D)
input impedance with feedback 410 k
Answer:
D
A)
B)
C)
D)
10
47)
When the reactances in the RLC leg of a crystal are equal and opposite, the resulting condition is
know as ________.
47)
A)
parallel resonance
B)
Barkhausen criterion
C)
cutoff
D)
series resonance
Answer:
D
A)
B)
C)
D)
48)
The Barkhausen criterion states that ________ in an oscillator.
48)
A)
= 10
B)
Av= 1
C)
= –1
D)
None of the above
Answer:
B
A)
B)
C)
D)
11
Answer Key
Testname: C14
1)
A
2)
D
3)
B
4)
A
5)
D
6)
B
7)
D
8)
D
9)
B
10)
A
11)
C
12)
A
13)
B
14)
B
15)
D
16)
A
17)
B
18)
D
19)
B
20)
C
21)
A
22)
C
23)
B
24)
D
25)
A
26)
C
27)
C
28)
C
29)
C
30)
D
31)
D
32)
D
33)
D
34)
B
35)
D
36)
B
37)
D
38)
C
39)
C
40)
C
41)
C
42)
C
43)
A
44)
B
45)
C
46)
D
47)
D
48)
B