Measurement and Analysis of Current Noise in Chopper Amplifiers

This paper presents a theoretical analysis and measurements of the current noise of several chopper instrumentation amplifiers, which demonstrate that the charge injection and clock feed-through associated with the MOSFETs of the input chopper give rise to significant input current and current noise. In combination with high source impedances, this “chopper noise” is converted to voltage noise, which may then be a significant contributor to the amplifier´s total input-referred voltage noise. Chopper noise has a white power spectral density, whose magnitude is roughly proportional to the chopping frequency. Design guidelines are proposed to reduce chopper noise, as well as the use of a clock-bootstrapped chopper, which generates significantly less noise than a traditional chopper.