Hi Raj,

The issue I was pointing out is that if you design the source follower such that 1/gm=50 ohms and the load is also 50 ohms then half of the output voltage has to be dropped across the 1/gm resistance of the source follower (-6dB gain). The gain will be closer to 1 when 1/gm is much less than 50 ohms which means the output is no longer matched to the load.

You can't have the output impedance of the source follower be the same as the load resistance unless you can tolerate the gain being -6dB.


Alternatively, a common source amplifier can have gain because you can set the amplifier output impedance with a resistor and compensate the gain by designing gm high enough to drive the total load.


I hope this clarifies my comment.

Best regards