A Power-Aware Chopper-Stabilized Instrumentation Amplifier for Resistive Wheatstone Bridge Sensors

This paper presents a power-aware instrumentation amplifier (IA) based on differential difference amplifier (DDA) dedicated to a resistive Wheatstone bridge sensor system. The design incorporates a proposed current source replica (CSR) circuit that facilitates the pair matching layout for all critical pairs in DDA input stage. This is in contrast with the conventional design where the stated layout technique can only be applied to the input transistor pairs. Besides, a new analysis on common-mode signals and differential common-mode signal in chopper-stabilized DDA is given. It has shown that the differential common-mode signal is not modulated in chopping DDA. The relationship between dc offset and differential common-mode rejection ratio (CMRRd) is illustrated. Enhancing CMRRd will lead to reduction of dc offset and offset drift in DDA. Fabricated by a 0.18-μm CMOS process, the experimental results have shown that the maximum input-referred offset for the injection-nulling switch chopper DDA with CSR circuit is 3 μV, while the input-referred dc offset is 1.78 μV (mean + standard deviation) at a chopping frequency of 10 kHz from eight fabricated samples. For a closed-loop gain of 40.17 dB, its output ripple is reduced by three times with respect to itself without CSR. The IA powered with a high-power supply rejection regulator has been tested with a resistive Wheatstone bridge. The transducer achieves an input-referred noise of 3.76 μVrms for 2-kHz bandwidth.