18)
Refer to the figure above. To reduce the duty cycle to less than 50%, which of the following circuit
changes would be necessary?
18)
A)
Increase the size of R1.
B)
Connect a diode in parallel with R2.
C)
Reduce the size of R1.
D)
Reduce the size of R2.
Answer:
B
A)
B)
C)
D)
19)
The higher resonant frequencies of a crystal are called
19)
A)
decades.
B)
octaves.
C)
undertones.
D)
overtones.
Answer:
D
A)
B)
C)
D)
20)
Which of the following cannot be used as the amplifier element within an oscillator?
20)
A)
Thermistor
B)
BJT
C)
FET
D)
Op–amp
Answer:
A
A)
B)
C)
D)
21)
Which of the following oscillator types does not use any inductors?
21)
A)
Hartley oscillator
B)
Wien–bridge
C)
Colpitts oscillator
D)
Clapp oscillator
Answer:
B
A)
B)
C)
D)
7
22)
In order to sustain oscillations in a feedback oscillator, the gain should be ________ so the product
of AV× B equals ________.
22)
A)
reduced, less than one
B)
reduced, one
C)
increased, more than one
D)
increased, much greater than one
Answer:
B
A)
B)
C)
D)
23)
The 555 timer contains
23)
A)
5 comparators.
B)
2 comparators.
C)
3 comparators.
D)
4 comparators.
Answer:
B
A)
B)
C)
D)
24)
The closed–loop voltage gain, ACL, for a Wien–bridge oscillator is
24)
A)
slightly greater than 1.
B)
less than 1.
C)
exactly 1.
D)
3, after the oscillations have built up.
Answer:
D
A)
B)
C)
D)
25)
The Hartley oscillator uses
25)
A)
a tickler coil.
B)
only resistors and capacitors.
C)
a tungsten lamp.
D)
two inductors.
Answer:
D
A)
B)
C)
D)
8
26)
Refer to the figure above. If the value of VCC = 5 V, the output voltage would be
26)
A)
a square wave that varies between 0 V and 5 V.
B)
5 V dc.
C)
a square wave of 10 Vp–p.
D)
a sine wave.
Answer:
D
A)
B)
C)
D)
9
27)
Refer to the figure above. Which of these circuits is known as a Colpitts oscillator?
27)
A)
(a)
B)
(b)
C)
(c)
D)
None of the above.
Answer:
A
A)
B)
C)
D)
10
28)
One way to recognize a Hartley oscillator is by the
28)
A)
tapped capacitors in the tank circuit.
B)
transformer used for feedback.
C)
three lead networks in the feedback path.
D)
tapped inductors in the tank circuit.
Answer:
D
A)
B)
C)
D)
29)
Of the following oscillator circuit components, the one that exhibits the piezoelectric effect is the
29)
A)
inductor.
B)
capacitor.
C)
resistor.
D)
crystal.
Answer:
D
A)
B)
C)
D)
30)
A very stable oscillator is needed to operate on a single frequency. A good choice might be a
30)
A)
VCO.
B)
Clapp.
C)
crystal.
D)
Hartley.
Answer:
C
A)
B)
C)
D)
31)
The RC feedback network used in the Wien–bridge oscillator has a maximum output voltage when
31)
A)
XL= R.
B)
R = 0 .
C)
XC = XL.
D)
R1 = R2 and XC1 = XC2.
Answer:
D
A)
B)
C)
D)
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
32)
The Twin–T Oscillator is a popular choice because it works well over a wide range of frequencies.
32)
Answer:
True
False
33)
Positive feedback is required for an oscillator to operate properly.
33)
Answer:
True
False
34)
An RC phase–shift oscillator uses feedback from a tank circuit.
34)
Answer:
True
False
11
35)
To operate properly, an oscillator requires an external ac input signal.
35)
Answer:
True
False
36)
Crystal oscillators are very stable.
36)
Answer:
True
False
37)
An oscillator can produce many types of outputs such as sine, triangle, or square waves.
37)
Answer:
True
False
12