A 40-μV Offset 130-dB CMRR Analog Front End With Automatic Offset Calibration and Common Mode Cancellation for High-Precision Instrumentation Measurement

This article presents a fully integrated high-precision analog front end (AFE), consisting of a three-opamp instrumentation amplifier (IA) followed by a 24-bit $\Sigma \Delta $ analog-to-digital converter ( $\Sigma \Delta $ -ADC). Automatic-offset-calibration (AOC) and common-mode-cancellation (CMC) techniques are proposed to improve the measurement accuracy. The prototype has been fabricated in a 180-nm BCD process, which achieves an input offset of $40~\mu $ V, an input impedance of 3.8 G $\Omega $ , and a common mode rejection ratio (CMRR) of 130 dB. The peak SNR and SNDR are 106.2 and 95.4 dB, respectively, while obtaining a dynamic range of 110.5 dB. In a three-lead resistance-temperature detector (RTD) temperature measurement experiment, the prototype achieves an accuracy of $0.03~^{\circ } $ C within a temperature range of $- 40~^{\circ } $ C to $160~^{\circ } $ C, whereas in a full-bridge pressure measurement using strain gauges, the relative error ranges from −12.6 to 39.0 ppm. The experimental results demonstrate the potential capability of the prototype to be widely adopted in high-precision instrumentation measurement.