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First, you got to design a perfectly symetric opamp to eliminate systematic opamp that may exist in some architecture.
The remaining of, which is random offset, will vary infunction of your device's dimensions. So, you've got to have large transistors to significantly reduce offset, but be aware that an exact zero offset opamp is just not feasible. But with big transistors area, you may reduce bellow your desired offset value.
However, if you really need an extremely low offset voltage, some technics exists to compaste for the amplifier offset, which are namely the input offset compensation, and output offset compensation. Both consists in using capacitors to remove the offset voltage at the input (resp. output) of the amplifier.
These technics are described in Design Tech. for High Speed High Resolution Comparators - IEEE JSSC vol 27 n12, Dec 1992 by Behzad Razavi.
But, once again, even with these techniques, there will still remain a slight offset in you amplifier. Moreover, some time is necessary for the offset compensation to be carried out, when your amplifier won't be available for amplifiyin. And, last drwaback, some conditions are required on the amplifier to allow input/output offset compensation.
Can you upload me the paper "Design Tech. for High Speed High Resolution Comparators - IEEE JSSC vol 27 n12, Dec 1992 by Behzad Razavi" as you mentioned in the forum.
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