Mismatch sometimes is a important error source of circuits such as differetial amplifier. In order to get better match,we need to use big transistors,but how can i kwon the size i use is big enough but not too big.
how big is your transistors is a function of how much matching do you need(in terms of variance(sigma) parameters.
there are some formulas relating matching to some technology dependent factors such as AvT and transistors' W*L