How to choose Vds in analog design based on 2id/gm methodology

If the transitor appears in the small signal model of an amplifier and is required to contribute to the DC gain of the amplifier, the best Vds is about 2 or 3 times greater than Vov. In my study about 2id/gm methodology, I find the intrinsic gain of a transistor only relates to the L and the ratio K of Vds and Vov (or V* mentioned in EE240 from UCB), and only when the ratio reaches to 2 to 3, there is a certain intrinsic gain of a transistor.
Fig. 1 shows the relationship between the intrinsic gain and the ratio K as well as L, which could prove the above arguments. All data are mesured in TSMC 130nm technology.
Note that the expression of DC gain of a amplifier could convert into the expression of the correspondent intrinsic gain of Mosfets, which could be found in EE214 from stanford.

Copyright 2013 by Joy Shockley

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