Understanding MOSFET mismatch for analog design

Abstract

This paper addresses misconceptions about MOSFET mismatch for analog design. V/sub t/ mismatch does not follow a simplistic 1/(/spl radic/area) law, especially for wide/short and narrow/long devices, which are common geometries in analog circuits. Further, Vt and gain factor are not appropriate parameters for modeling mismatch. A physically based mismatch model can be used to obtain dramatic improvements in the prediction of mismatch. This model is applied to MOSFET current mirrors to show some non-obvious effects over bias, geometry, and multiple unit devices.