Small Signal Analysis of Common Drain (CD) MOSFET Amplifier

This CalcTown calculator calculates the small signal voltage gain of a Common Drain (CD) MOSFET amplifier, working in the saturation mode. A Common Drain MOSFET Circuit is also called a Source Follower circuit because any change in the Drain voltage is reflected in the Source Voltage.

Its small output resistance makes it desirable when the circuit is to act as an ideal voltage source and drive a load circuit
without suffering any loading effects.

* Please note that body effect has been taken into consideration only for calculating the small signal output resistance and not for the current calculation in DC analysis.

Small Signal Analysis of Common Drain (CD) MOSFET Amplifier

R₁

K-Ohm

R₂

K-Ohm

R_si

K-Ohm

R_S

K-Ohm

DC Bias Drain current (I_D)

Calculate Drain Bias current here

MOSFET constant (K_n)

uA/V²

V^-1

Result

r₀

K-Ohm

Small signal transconductance (g_m)

uA/V

Small signal Voltage gain

V/V

Click here to view image

where

K_n=1/2(k`W/L)=MOSFET constant

g_m=Small signal transconductance

λ=V_A^-1 =Inverse of Early Voltage

and the corresponding small signal equivalent circuit is