MOSFET Transconductance and MOSFET Small Signal Model Explained

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 Small-Signal 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 non-linear. But when the input signal is very small, then under small-signal 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 small-signal 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 small-signal model.

The drain current is a linear function of Vgs and can be represented as a voltage-controlled current source in the small-signal model.

This small-signal 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 small-signal model of the MOSFET

The link for the other useful videos related to MOSFET:

1) Enhancement Type MOSFET:
https://youtu.be/l9LBIy9Ioxo

2) MOSFET Biasing: Enhancement Type MOSFET Biasing Explained
https://youtu.be/Ae8L9-WOiVE

3) MOSFET Channel Length Modulation
https://youtu.be/qFbdsLm5mvI
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#MOSFET
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