A general description of common-mode feedback in fully-differential amplifiers

Abstract

Fully-differential amplifiers and their common-mode feedback (CMFB) loops are described, and the impact of CMFB loop mismatching on common mode rejection ratio (CMRR) noise and distortion is discussed. A set of gain parameters which are suitable for predicting the actual performance of such a balanced amplifier is defined. The presented formalism takes mismatching and nonlinearity in the CMFB loop into account. The gain parameters can easily be calculated or simulated for different circuit configurations. It is concluded that the common-mode sense circuits can have a major impact on the accuracy of the differential mode signal processing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>