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WorksheetsElectronics #2: Operational Amplifier & Power Amplifier
Total questions: 53
Worksheet time: 19mins
Which of the following is (are) power amplifiers?
Class A
Class B or AB
Class C or D
All of the above
A differential amplifier....
is a part of an Op-amp
has one input and one output
has two outputs
answers (1) and (2)
By how much does the output signal vary for a class AB power amplifier?
360°
180°
Between 180° and 360°
Less than 180°
Which type of power amplifier is biased for operation at less than 180º of the cycle?
Class A
Class B or AB
Class C
Class D
When a differential amplifier is operated single-ended,..
the output is grounded
one input is grounded and signal is applied to the other
the output is not inverted
both inputs are connected together
In differential-mode, …………….
the gain is one
only one supply voltage is used
opposite polarity signals are applied to the inputs
the outputs are of different amplitudes
Which type of amplifier uses pulse (digital) signals in its operation?
Class A
Class B or AB
Class C
Class D
Which of the power amplifiers has the lowest overall efficiency?
Class A
Class B or AB
Class C
Class D
Which of the following describe(s) a power amplifier?
It can handle large power.
It can handle large current.
It does not provide much voltage gain.
All of the above
_______ amplifiers primarily provide sufficient power to an output load to drive a speaker from a few watts to tens of watts.
Small-signal
Power
Large-signal
None of the above
The main features of a large-signal amplifier is the circuit’s ________.
power efficiency
maximum power limitations
impedance matching to the output device
All of the above
Current cannot flow to ground through …….
a virtual ground
an ordinary ground
an a.c. ground
a mechanical ground
The common-mode voltage gain of a differential amplifier is equal to RC divided by ……..
2r’e
2RE
r’e
r’e/2
The input stage of an Op-amp is usually a ……….
differential amplifier
class B push-pull amplifier
CE amplifier
swamped amplifier
The input stage of an Op-amp is usually a ……….
differential amplifier
CE amplifier
class B push-pull amplifier
swamped amplifier
The common-mode voltage gain is ………
greater than differential voltage gain
equal to differential voltage gain
smaller than differential voltage gain
None of the above
In the common mode, ……………
both inputs are grounded
an identical signal appears on both the inputs
the outputs are connected together
the output signal are in-phase
The main features of a large-signal amplifier is the circuit’s ________.
power efficiency
maximum power limitations
impedance matching to the output device
All of the above
Class AB operation is ________ operation.
similar to class A
similar to class B
similar to class C
None of the above
Which operation class is generally used in radio or communications?
A
B
AB
C
Categorize the power efficiency of each class of amplifier, from worst to best.
A, B, AB, D
A, AB, D, B
A, AB, B, D
any of the above
What is the maximum efficiency of a class A circuit with a direct or series-fed load connection?
90%
78.5%
50%
25%
What is the ratio of the secondary voltage to the primary voltage with the turn ratio in the winding
N2/N1
(N1/N2)2
(N1/N2)1/3
N1 × N2
The common-mode gain is ………..
very high
very low
always unity
unpredictable
The differential gain is ………
very low
dependent on input voltage
very high
about 100
With zero volts on both inputs, an OP-amp ideally should have an output ………..
equal to the positive supply voltage
equal to the negative supply voltage
equal to CMRR
equal to zero
Of the values listed, the most realistic value for open-loop voltage gain of an OP-amp is
1
2000
100,000
80 dB
For an Op-amp with negative feedback, the output is ……
fed back to the inverting input
fed back to the noninverting input
increased
equal to the input
The use of negative feedback ………
reduces the voltage gain of an Op-amp
makes the Op-amp oscillate
makes linear operation possible
answers (1) and (2)
Negative feedback ………..
increases the input and output impedances
increases the input impedance and bandwidth
does not affect impedance or bandwidth
decreases the output impedance and bandwidth
A voltage follower ……….
has a voltage gain of 1
is noninverting
has no feedback resistor
has all of these
The maximum efficiency of a transformer-coupled class A amplifier is _______.
25%
50%
78.5%
63.6%
What is the maximum efficiency of a class B circuit?
90%
78.5%
50%
25%
How many transistors must be used in a class B power amplifier to obtain the output for the full cycle of the signal?
0
1
2
3
In class B operation, at what fraction of VCC should the level of VL(p) be to achieve the maximum power dissipated by the output transistor?
0.5
0.636
0.707
1
The Op-amp can amplify
a.c. signals only
d.c. signals only
both a.c. and d.c. signals
neither d.c. nor a.c. signals
The input offset current equals the ……….
difference between two base currents
collector current divided by current gain
average of two base currents
none of these
The tail current of a differential amplifier is …….
half of either collector current
two times either collector current
equal to either collector current
equal to the difference in base currents
The node voltage at the top of the til resistor is closes to ……….
collector supply voltage
zero
emitter supply voltage
tail current times base resistance
Class B operation is provided when the dc bias leaves the transistor biased just off, the transistor turning on when the ac signal is applied.
True
False
Which of the following is (are) the disadvantage(s) of a class B complementary-symmetry circuit?
It needs two separate voltage sources.
There is crossover distortion in the output signal.
It does not provide exact switching of one transistor off and the other on at the zero-voltage condition.
All of the above
Which of the push-pull amplifiers is presently the most popular form of the class B power amplifier?
Quasi-complementary
Transformer-coupled
Complementary-symmetry
Duo Quasi-complementary
nMOS and pMOS transistors can be used for class B.
True
False
Which of the following instruments displays the harmonics of a distorted signal?
Digital multimeter
Spectrum analyzer
Oscilloscope
Wave analyzer
Which of the following instruments allows more precise measurement of the harmonic components of a distorted signal?
Digital multimeter
Spectrum analyzer
Oscilloscope
Wave analyzer
What is the maximum temperature rating for silicon power transistors?
50° to 80°
100° to 110°
150° to 200°
250° to 300°
Which of the power amplifiers is not intended primarily for large-signal or power amplification?
Class A
Class B or AB
Class C
Class D
Which of the following transistors has been quite popular as the driver device for class D amplification?
BJT
FET
UJT
MOSFET
In ________ power amplifiers, the output signal varies for a full 360° of the cycle.
class A
class B or AB
class C
class D
In class B power amplifiers, the output signal varies for _______ of the cycle.
360°
180°
between 180° and 360°
less than 180°
34
39
49
54
48
56
63
70
710
790
780
760
