Small-Signal Amplifiers MCQs

Practice Small-Signal Amplifiers MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Analog ElectronicsSmall-Signal Amplifiers

A BJT has beta = 120 and gm = 60 mS. Its hybrid-pi input resistance r_pi is approximately?

A500 ohm
B1 kOhm
C2 kOhm
D7.2 kOhm

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Correct Answer: C. 2 kOhm

Explanation: r_pi=beta/gm=120/0.06=2000 ohm=2 kOhm.

Reference: Standard analog electronics: hybrid-pi model

Question 2

Analog ElectronicsSmall-Signal Amplifiers

A common-emitter stage has gm=40 mS and an effective collector load of 2 kOhm. Neglecting ro and emitter degeneration, its approximate small-signal voltage gain is?

A+20
B-20
C+80
D-80

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Correct Answer: D. -80

Explanation: For the simplified CE stage, Av≈-gmRC=-0.04×2000=-80.

Reference: Standard analog electronics: common-emitter gain

Question 3

Analog ElectronicsSmall-Signal Amplifiers

An unbypassed emitter resistor in a common-emitter amplifier generally causes the voltage gain magnitude to?

AIncrease without limit
BDecrease while improving linearity
CRemain exactly unchanged
DBecome exactly unity in every case

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Correct Answer: B. Decrease while improving linearity

Explanation: Emitter degeneration introduces local negative feedback, reducing gain but improving linearity and bias stability.

Reference: Standard analog electronics: emitter degeneration

Question 4

Analog ElectronicsSmall-Signal Amplifiers

A bypass capacitor placed across an emitter resistor is intended mainly to?

AReduce AC emitter degeneration over its effective frequency range
BIncrease DC emitter resistance
CBlock all collector current
DCreate positive DC feedback

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Correct Answer: A. Reduce AC emitter degeneration over its effective frequency range

Explanation: The capacitor provides a low-impedance AC path around the emitter resistor while leaving the resistor available for DC bias stabilization.

Reference: Standard analog electronics: emitter bypass capacitor

Question 5

Analog ElectronicsSmall-Signal Amplifiers

For a BJT biased at IC = 2 mA at room temperature, using VT approximately 25 mV, the small-signal transconductance gm is closest to?

A20 mS
B40 mS
C80 mS
D200 mS

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Correct Answer: C. 80 mS

Explanation: gm=IC/VT=2 mA/25 mV=0.08 S=80 mS.

Reference: Standard analog electronics: BJT transconductance