Mismatch?

Hi Marc,

I believe output current vs output voltage corresponds to the output conductance/resistance you also mention. I would add that noise may be an issue in some cases. I would also mention that Iout/Iin both includes static offset and mismatch.

Paul

Hi Marc,

I would say that systematic mismatch is an issue if you want precise currents, because you may know the
systematic mismatch at one corner (process, voltage, temperature), but it is unlikely to be the same
across all (P,V,T) corners.

Whether the mismatch is critical or not is largely dependent on the application. For instance, it would
be fatal in a current-steering DAC, but may be a little less serious in an opamp.

However, a significant amount of systematic mismatch is a sign of a poorly designed mirror, and may
be an indirect sign that your output impedance etc. are poor. You should ask yourself why there is systematic
mismatch. You have the same VGS, same (W/L) or a fixed ratio. The only variation comes from the VDS
variation, and if this causes significant deviation in the mirror ratio, then you will run into trouble with
some other critical parameter such as gain or PSRR.

So pay attention to the mismatch is what I would say.

Regards
Vivek

hi vivkr
 how to analyze the systematic  mismatch of a current mirror?

can U give a example?