vivkr
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For a given current value, the maximum possible Gm is fixed. This is the Gm of a BJT.
Gm/Id(MOS) < Gm/Id(BJT) = (q/kT) (At 300 K, this is around 38)
The MOS Gm/Id is typically constrained to be less than that of the BJT by a factor approx. 1.3 or so (think of the MOS as a BJT but with a capacitively coupled input divided by the cap divider formed by Cox and Cinversion.
That being said, you can use positive feedback to increase the Gm of the MOS. Please search the forum. I remember having asked the same question and having received an answer a few months ago.
Regards Vivek
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