This document contains 30 multiple choice questions about analog and digital electronics concepts like transistors, amplifiers, feedback, and operational characteristics. The questions cover topics such as transistor modeling, amplifier configurations, feedback fraction calculations, effects of feedback on gain and impedance, and applications of common circuits like the emitter follower.

1. NEC-409: ANALOG AND DIGITAL ELECTRONICS
MCQ for unit 2
1. The current ib through base of a silicon npn transistor is 1+0.1 cos (1000πt) ma. At 300K, the rπ in the
small signal model of the transistor is
1. 250Ω
2. 27.5Ω
3. 25Ω
4. 22.5Ω
2. The amplifier circuit shown below uses a silicon transistor. The capacitors CC and CE can be assumed
to be short at signal frequency and the effect of output resistance r0can be ignored. If CE is disconnected
from the circuit, which one of the following statements is TRUE?

2. 1. The input resistance Ri increases and the magnitude of voltage gain AV decreases.
2. The input resistance Ri decreases and the magnitude of voltage gain AV increases.
3. Both input resistance Riand the magnitude of voltage gain AV decrease.
4. Both input resistance Riand the magnitude of voltage gain AV increase.
3. In an ideal differential amplifier shown in the figure, a large value of (RE).
1. Increases both the differential and common-mode gains.
2. Increases the common-mode gain only
3. Decreases the differential-mode gain only
4. Decreases the common-mode gain only
4. The cascode amplifier is a multistage configuration of
1. CC-CB
2. CE-CB
3. CB-CC
4. CE-CC
5. Assuming VCEsat = 0.2 V and β = 50, the minimum base current (IB) required to drive the transistor
in the figure to saturation is
1. 56 μA
2. 140 μA
3. 60 μA
4. 3 μA

3. 6. Generally, the gain of a transistor amplifier falls at high frequency due to the
1. Internal capacitance of the device
2. Coupling capacitor at the input
3. Skin effect
4. Coupling capacitor at the output
7. The current gain of a BJT is
1. gmr0
2. gm / ro
3. gmrπ
4. gm / rπ
8. The current gain of a bipolar transistor drops at high frequencies because of
1. Transistor capacitances
2. High current effects in the base
3. Parasitic inductive elements
4. The Early effect
9. In the differential amplifier of the figure, if the source resistance of the current source IEE is infinite,
then common-mode gain is
1. Zero
2. Infinite
3. Indeterminate
4. (Vin1 + Vin2) + 2VT
10. In the cascode amplifier shown in the figure, if the common-emitter stage (Q1) has a trans
conductance gm1 and the common base stage (Q2) has a trans conductance gm2 then the overall trans
conductance g(=i0 / Vi) of the cascode amplifier is

4. 1. gm1
2. gm2
3. gm1 / 2
4. gm2 / 2
11. the unit of q / KT are
1. V
2. V-1
3. J
4. J / K
12. A multistage Amplifier has a low-pass Response with three real poles at s = -ω1, –ω2 and ω 3 The
approximate overall bandwidth B of the Amplifier will be given by
1. 𝐵=ω1+ω2+ω3
2. 𝐵=1ω1+1ω2+1ω3
3. 𝐵=(𝜔1+𝜔2+𝜔3)1/3
4. 𝐵=√𝜔12+𝜔22+𝜔33
13. When negative voltage feedback is applied to an amplifier, its voltage gain
……………….
1. Is increased
2. Is reduced
3. Remains the same
4. None of the above
14. The value of negative feedback fraction is always …………….
1. Less than 1
2. More than 1
3. Equal to 1
4. None of the above
15. If the output of an amplifier is 10 V and 100 mV from the output is fed back to the
input, then feedback fraction is ………..
1. 10
2. 1
3. 01
4. 15

5. 16. The gain of an amplifier without feedback is 100 db. If a negative feedback of 3 db
is applied, the gain of the amplifier will become …………..
1. 5 db
2. 300 db
3. 103 db
4. 97 db
17. If the feedback fraction of an amplifier is 0.01, then voltage gain with negative
feedback is approximately………..
1. 500
2. 100
3. 1000
4. 5000
18. A feedback circuit usually employs ……………… network
1. Resistive
2. Capacitive
3. Inductive
4. None of the above
19. The gain of an amplifier with feedback is known as ………….. gain
1. Resonant
2. Open loop
3. Closed loop
4. None of the above
20. When voltage feedback (negative) is applied to an amplifier, its input impedance
………….
1. Is decreased
2. Is increased
3. Remains the same
4. None of the above
21. When current feedback (negative) is applied to an amplifier, its input impedance
…………..
1. Is decreased
2. Is increased
3. Remains the same
4. None of the above
22. Negative feedback is employed in ……………..
1. Oscillators
2. Rectifiers
3. Amplifiers
4. None of the above
23. Emitter follower is used for …………
1. Current gain
2. Impedance matching
3. Voltage gain
4. None of the above

6. 24. The voltage gain of an emitter follower is ………..
1. Much less than 1
2. Approximately equal to 1
3. Greater than 1
4. None of the above
25. When current feedback (negative) is applied to an amplifier, its output
impedance ……..
1. Is increased
2. Is decreased
3. Remains the same
4. None of the above
26. Emitter follower is a ……………….. circuit
1. Voltage feedback
2. Current feedback
3. Both voltage and current feedback
4. None of the above
27. If voltage feedback (negative) is applied to an amplifier, its output impedance
…………..
1. Remains the same
2. Is increased
3. Is decreased
4. None of the above
28. When a negative voltage feedback is applied to an amplifier, its bandwidth……….
1. Is increased
2. Is decreased
3. Remains the same
4. Insufficient data
29. An emitter follower has ………… input impedance
1. Zero
2. Low
3. High
4. None of the above
30.The output impedance of an emitter follower is ……….
1. High
2. Very high
3. Almost zero
4. Low