In this video, the MOSFET Transconductance and MOSFET Small Signal Model is explained.

Timestamps for the different topics covered in the video:

0:00 Introduction
0:37 What is Transconductance?
2:06 Different MOSFET transconductance equations
5:47 MOSFET SmallSignal Model

What is MOSFET transconductance?

The MOSFET transconductance is the ratio of change in the drain current to the change in the voltage Vgs. (Gate to Source Voltage)
It signifies that, for the given change in the gate to source voltage, what is the change in the drain current.

The transconductance (gm) = ΔId / ΔVgs
Unit Siemens

MOSFET Small Signal Model and Small Signal Approximation:
In the saturation region of operation, the relation between the drain current and the voltage Vgs is nonlinear. But when the input signal is very small, then under smallsignal approximation, the relation between the change in the drain current is linearly proportional to the AC input signal.
Under small signal approximation, the change in the drain current id = gm * vgs
And for the AC analysis, the MOSFET can be replaced by the smallsignal model.
Since the gate current is almost zero, the impedance seen between the gate and the source terminal is very high and can be represented as an open circuit in the smallsignal model.

The drain current is a linear function of Vgs and can be represented as a voltagecontrolled current source in the smallsignal model.

This smallsignal model of MOSFET is particularly useful for the AC analysis of the MOSFET when the MOSFET is used as an amplifier.

This video will be helpful to all the students of science and engineering in understanding the concept of transconductance and the smallsignal model of the MOSFET

The link for the other useful videos related to MOSFET:

1) Enhancement Type MOSFET:
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2) MOSFET Biasing: Enhancement Type MOSFET Biasing Explained
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3) MOSFET Channel Length Modulation
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