Hi,
Both methods are approximation to ideal situation....
Quote:FYI, I found different result for different VDS voltage.
Obviously, you will find different results for different vds voltages...MOS current has a loose dependence on vds too....But until the vds is too low, the change in the figures of merit of a MOS is very less.
If you want such accurate matching, sweep both VGS and VDS voltages and generate data for different vgs / vds permutations & you are good to go.
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Mayank.