Common source Amplifier with source degeneration (i.e with Rs)

Hello all, this is the common source amplifier with source degeneration . As you can see the circuit has a source resistance. This resistor Rs has a big role to play.
The Rs decides the gain of the amplifier,stability etc. This is the most stable circuit than the common source amplifier.

Let's see the Gain of this amplifier.

The small signal model of common source amplifier with source degeneration is as shown above

Gain=Vout/vin

where

      vin=v1+ (gm*v1*Rs)

    vout=-(gm*v1*RD)

The gain of the amplifier is

The value of gmRs>>1 . So,the gain of the amplifier becomes

Vout/vin=-(RD/Rs)

So if RD=8k and Rs=2k

The gain of the common source amplifier will be 4.

Note: The gain of this amplifier depends totally on RD and Rs values. As long as they are constant ,the amplifier gain doesn't get affected. The amplifier is very stable and doesn't change its gain depending on the temperature as it's independent of gm. Thus Source degeneration influences the gain,stability etc.

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