Semiconductor Devices and Circuits Flashcards

In a MOSFET, the threshold voltage VT is most directly affected by which parameter?

Answer: Gate oxide thickness

Threshold voltage is directly related to oxide capacitance, which depends on gate oxide thickness (VT increases as tox increases).

A zener diode is operated in reverse breakdown with VZ = 6.2 V and IZ = 20 mA. What power must it dissipate?

Answer: 124 mW

Power = VZ × IZ = 6.2 V × 20 mA = 124 mW.

Which biasing configuration gives a BJT the highest input impedance?

Answer: Common collector

The common-collector (emitter-follower) configuration exhibits the highest input impedance among standard BJT configurations.

What is the primary function of the depletion region in a p-n junction?

Answer: It creates a built-in electric field that opposes further diffusion

The depletion region's ionized dopant atoms create a built-in electric field that counters carrier diffusion, establishing equilibrium.

In the early effect (base-width modulation) of a BJT, increasing VCE causes the collector current to:

Answer: Increase slightly due to narrowing of the base

Increasing VCE widens the collector-base depletion region, narrowing the base and increasing the collector current gradient.

An NMOS transistor has kn = 0.5 mA/V² and VTN = 1 V. With VGS = 3 V and VDS = 4 V, the drain current ID is:

Answer: 2 mA

Since VDS > VGS − VTN = 2 V, the device is in saturation: ID = (kn/2)(VGS − VTN)² = 0.25 × 4 = 1 mA. Wait — kn already includes the W/L factor, so ID = (kn/2)(VGS−VTN)² = (0.5/2)(2)² = 1 mA.

Which of the following correctly describes a Schottky diode compared to a p-n junction diode?

Answer: It has a lower forward voltage drop and faster switching speed

Schottky diodes use a metal-semiconductor junction with no minority carrier storage, giving lower VF (~0.3 V) and much faster switching.