Large Signal Behavior
Assume the input voltage Vin is reduced from a large positive value.
Assume that the channel length modulation effect is 0
If the input voltage Vin ≥ Vb - Vth, the MOS transistor is in OFF condition.
∴ Vout = VDD
For smaller values of Vin, and if the MOS transistor is operating in the Saturation region.
The output voltage Vout when the MOS transistor is operating in the saturation region is given by:
As Vin decreases, Vout also decreases, thus driving the MOS Transistor into triode region if
Let us calculate the small signal gain and is given by
Also we know,
The small signal gain can be re written in terms of transconductance and body effect as:
The body effect increases the transconductance of the stage
To increase the gain of a common Gate amplifier, do the following:
Widen the MOS transistor so that gm increases