A CMOS Low-Noise Instrumentation Amplifier Using Chopper Modulation

This paper describes a low-power, low-noise chopper stabilized CMOS instrumentation amplifier for biomedical applications. Low thermal noise is achieved by employing MOSTs biased in the weak/moderate inversion region, whereas chopper stabilization is utilized to shift 1/f-noise out of the signal band hereby ensuring overall low noise performance. The resulting equivalent input referred noise is approximately 7 nV/\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sqrt{\rm Hz}$$\end{document} for a chopping frequency of 20 kHz. The amplifier operates from a modest supply voltage of 1.8 V, drawing 136 μA of current thus consuming 245 μW of power. The gain is 72.5 dB over a 4 kHz bandwidth. The inband PSRR is above 90 and the CMRR exceeds 105 dB.