Semiconductor Devices and Circuits Flashcards

In a full-wave bridge rectifier with a transformer secondary voltage of 12 Vrms and ideal diodes, what is the average DC output voltage?

Answer: 10.8 V

Vpeak = 12√2 ≈ 16.97 V; Vavg = (2/π)Vpeak ≈ 0.637 × 16.97 ≈ 10.8 V.

The transconductance gm of a MOSFET in saturation is proportional to which of the following?

Answer: (VGS − VT)

In saturation gm = ∂ID/∂VGS = kn(VGS − VT), so gm is proportional to (VGS − VT).

Which parameter of a BJT is defined as the ratio of collector current to base current?

Answer: β (beta)

β (hFE) = IC/IB is the common-emitter current gain of a BJT.

A CMOS inverter draws maximum power during which condition?

Answer: During input signal transitions

CMOS draws significant current only during transitions when both transistors are momentarily on, dissipating dynamic power.

In a p-n junction, the diffusion capacitance is dominant under which bias condition?

Answer: Moderate to strong forward bias

Diffusion (storage) capacitance arises from minority carrier charge stored during forward bias and dominates in forward-biased junctions.

An emitter-follower (common-collector) amplifier is primarily used for:

Answer: Impedance buffering with unity voltage gain

The emitter-follower has voltage gain ≈1, very high input impedance, and low output impedance, making it ideal as a buffer.

In a JFET, pinch-off voltage VP is the gate-source voltage at which:

Answer: The channel is completely depleted and ID approaches zero

At VGS = VP (pinch-off), the depletion regions fully close the channel and the drain current drops to essentially zero.