what is current mirrors-errors
Hi jiachang ,
It is very good to use to have cascode mirror for this precise replication .even though it is a feeble difference due to diff in VDS between actual and mirrored (or finite op impedance ) it may be noteworthy in some cases. I think cascode with more stacks(>2) can multiply the op. resistance thereby bringing down the difference
p.s :If supply voltage is a constraint .WIDE SWING CASCODE will help u .
Added after 4 minutes:
Jiachang ,
You can use longer L(also W by same factor) but maintaining the same W/L ratio so that op resistance is increased .