# Linear Integrated Circuit Questions and Answers – DC and AC Amplifiers

This set of Linear Integrated Circuit Multiple Choice Questions & Answers (MCQs) focuses on “DC and AC Amplifiers”.

1. An inverting amplifier that amplifies dc input level is called
a) DC and AC amplifier
b) AC amplifier
c) DC amplifier
d) None of the mentioned

Explanation: In a DC amplifier, the output signal changes it response to changes in its dc input level. A DC amplifier can be inverting, non-inverting or differential.

2. Find the DC differential amplifier with offset null circuitry?
a)

b)

c)

d)

Explanation: The mentioned circuit is the DC differential amplifier, since DC voltage is applied to the differential inputs of the amplifier.

3. Why DC amplifier uses offset null circuitry?
a) To reduce the distortion in output
b) To improve the accuracy of amplifier
c) To get large output gain
d) All of the mentioned

Explanation: A DC amplifier uses offset null circuitry to reduce the output offset voltage to zero, that is , to improve the accuracy of DC amplifier.

4. Why are coupling capacitor used in audio receiver system?
a) All of the mentioned
b) Thermal drift
c) Component tolerance
d) Variation in signal

Explanation: An audio receiver system consists of a number of stages because of thermal drift, components tolerance and variation, which introduces a dc level. To prevent the amplification of such dc level, the coupling capacitors are used.

5. Find the AC inverting amplifier from the circuits given below?
a)

b)

c)

d)

Explanation: AC amplifier consists of external offset voltage compensating network. Therefore, the external offset voltage is connected to the non-inverting input terminal of the amplifier.
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6. Determine the bandwidth of the AC inverting amplifier for high cut-off frequency of 15 Hz?

a) 4.321Hz
b) 8.356Hz
c) 7.056Hz
d) 2.334Hz

Explanation: Input resistance RIF=R1=100Ω (for ideal inverting amplifier).
=> The source resistance RIN=RO=5kΩ.
Therefore, Low frequency cut-off, fL=1/2πCi(RIF+RO) = 1/ [2π×4.7µF×(5kΩ+100Ω)] = 6.64Hz. and the bandwidth is calculated as, BW= fH-fL = 15Hz-6.64Hz = 8.356Hz.

7. When does the offset voltage compensating network must be used in inverting configuration?
a) When the input is AC voltage
b) When the input is DC voltage
c) When the input is either AC or DC voltage
d) None of the mentioned

Explanation: To reduce the output offset voltage to zero, the offset minimizing resistor is used to minimize the effect of input bias currents on the output offset voltage. However, when the inputs are DC voltages, the offset compensating network must be used.

8. State the application in which summing, scaling or averaging amplifiers are used?
a) Multiplexers
b) Counters
c) Audio mixers
d) All of the mentioned

Explanation: Summing, scaling or averaging amplifiers are commonly used in audio mixers, in which a number of inputs are added up to produce a desired output.

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