BEE Semiconductor Devices and Circuits 5

Question 1

In a differential amplifier with a tail current source ITAIL, increasing ITAIL primarily affects which parameter?

Accepted Answer

Transconductance gm and thus differential gain

Answer

Each transistor's bias current is ITAIL/2, so increasing ITAIL raises gm = IC/VT and therefore increases the differential voltage gain.

Question 2

The Miller effect in an inverting amplifier stage causes the input capacitance to appear as:

Accepted Answer

Cgd × (1 + |Av|)

Answer

By Miller's theorem, a feedback capacitance Cgd appears at the input multiplied by (1 + |Av|), significantly increasing effective input capacitance.

Question 3

What type of semiconductor material results when silicon is doped with phosphorus?

Accepted Answer

n-type, with electrons as majority carriers

Answer

Phosphorus has five valence electrons; donating one to the lattice creates a free electron, making the silicon n-type.

Question 4

In a cascode amplifier topology, placing a common-gate (or common-base) stage above a common-source (or common-emitter) stage primarily provides:

Accepted Answer

Increased output resistance and reduced Miller effect for wider bandwidth

Answer

The cascode's common-gate stage shields the input transistor from drain voltage swings, suppressing the Miller effect and raising output resistance, extending bandwidth.

Question 5

A tunnel diode exhibits negative differential resistance (NDR) because of which quantum mechanical phenomenon?

Accepted Answer

Quantum tunneling of carriers through a very thin junction barrier

Answer

In heavily doped tunnel diodes, electrons quantum-mechanically tunnel through the thin junction, producing a current peak followed by an NDR region.

BEE - Bachelor of Electrical Engineering Practice Test

BEE - Bachelor of Electrical Engineering Practice Test

BEE Semiconductor Devices and Circuits 5