Measurement and analysis of input current noise in chopper amplifiers

Abstract

This paper explains how the charge injection and clock feed-through of MOSFET switches causes significant input currents and current noise in chopper amplifiers. The current noise can be modeled as a form of shot noise with a white power spectral density (PSD). Both the input current and its noise PSD increase linearly with the chopping frequency. This has been verified by measurements on identical chopper amplifiers with different types of input choppers. Some design guidelines are proposed, as well as a low-noise input chopper based on a reduced-swing (V dd /2) bootstrapped clock driver.