MOSFET AMPLIFIERHIGH FREQUENCY ANALYSIS OF CS MOSFET AMPLIFIER

FACTORS AFFECTING HIGH FREQUENCY RESPONSE

Internal capacitances of MOSFET affects its high frequency response

2 Types of internal capacitances

1. Gate capacitanceIt is formed by a gate electrode with the channel. Oxide layer acts as dielectric. Denoted by Cox.

2. Junction capacitance

i) Source diffusion capacitance (between n+ source and p-type substrate)

ii) Drain diffusion capacitance (between n+ drain and p-type substrate)

FACTORS AFFECTING HIGH FREQUENCY RESPONSE

1. Gate capacitances: There are 3 gate capacitances

i. Cgs

ii. Cgd

iii. Cgb.

2. Junction capacitances: There are 2 junction capacitances

i. Source diffusion capacitance (Csb)

ii. Drain diffusion capacitance (Cdb)

MOSFET-HIGH FREQUENCY MODEL

MOSFET-HIGH FREQUENCY MODEL

The capacitance Cdb can be neglected to simplify the analysis

UNITY GAIN FREQUENCYThe fT is the frequency at which the short circuit current gain of the CS MOSFET amplifier becomes unity.

Input – Current source Ii

Output terminals are shorted

UNITY GAIN FREQUENCY

UNITY GAIN FREQUENCY

Current Gain =

FREQUENCY RESPONSE OF CS AMPLIFIER

FREQUENCY RESPONSE OF CS AMPLIFIER

FREQUENCY RESPONSE OF CS AMPLIFIERLOW FREQUENCY RESPONSE

FREQUENCY RESPONSE OF CS AMPLIFIERLOW FREQUENCY RESPONSE

FREQUENCY RESPONSE OF CS AMPLIFIERLOW FREQUENCY RESPONSE

FREQUENCY RESPONSE OF CS AMPLIFIERHIGH FREQUENCY RESPONSE

FREQUENCY RESPONSE OF CS AMPLIFIERHIGH FREQUENCY RESPONSE

FREQUENCY RESPONSE OF CS AMPLIFIERHIGH FREQUENCY RESPONSE

FREQUENCY RESPONSE OF CS AMPLIFIERHIGH FREQUENCY RESPONSE

FREQUENCY RESPONSE OF CS AMPLIFIERHIGH FREQUENCY RESPONSE