Dynamic Current Mirrors

Abstract

Based on a simple idea, the dynamic current mirror (or current copier) eliminates the main limitations of standard current mirrors, that are due to offset and 1/f noise. A new problem is created by the charge injected from the switches but the resulting error can be kept very low by adequate design procedures, especially when speed is not a limitation. Except in very special cases, the cascode configuration (or equivalent means) is needed to avoid spoiling the excellent intrinsic precision by errors due to the nonzero output conductance and to the gate-to-drain capacitance. The basic cell, which provides a single one-to-one discontinuous copy of the input current, can be extended to obtain continuous multiple copies as well as current multiplication or division by integer numbers. The principle of dynamic mirrors can probably be extended to a variety of different circuits, to create very precise analogue CMOS building blocks.