Analog Electronics MCQ – 6 previous year questions with solutions

A BJT used as a linear amplifier is biased in the active region: the base-emitter junction is forward biased and the collector-base junction reverse biased. In saturation both junctions are forward biased and the transistor behaves approximately as a closed switch, not an open switch.

Exam focus: Active region for amplification; cutoff/saturation for switching. Common trap: Saturation corresponds to ON/closed-switch behavior.

In CE configuration the input junction is the forward-biased base-emitter PN junction, so I_B rises non-linearly with V_BE exactly like a forward-biased diode.

It conducts strongly in forward bias after its knee/cut-in region and ideally blocks reverse current; practical reverse current includes a small minority-carrier leakage until breakdown. For a silicon diode, the familiar constant-drop approximation is about 0.7 V. Key relation: Shockley form: I≈I_S(e^(V_D/nV_T)−1).

Exam focus: Use 0.7 V only as a practical silicon approximation. Common trap: A diode is not a linear element over its full operating range.

A — Very fast, low. A Schottky diode is a majority-carrier (metal–semiconductor) device with almost no stored minority charge, so it switches very fast and has a low forward drop (about 0.2–0.4 V).

The ideal op-amp model assumes infinite open-loop gain and input resistance, zero output resistance and—within the ideal model—unlimited bandwidth. Real devices have finite gain-bandwidth, slew rate, input bias currents and output-current limits. Key relation: For ideal negative feedback: V+≈V− and input currents≈0.

Exam focus: Use the virtual-short rule only when negative feedback keeps the amplifier linear. Common trap: Infinite voltage gain does not mean infinite output current.

D — By converting the output of a sine-wave generator. A passive square-wave generator shapes (clips/squares) a sine-wave output into a square wave.