A 65nm CMOS ping-pong auto-zero resistance-to-frequency converter for resistive bridge sensors

A low energy-noise switched-capacitor (SC) interface with low offset for resistive bridge sensor in 65nm CMOS technology is presented. It converts the resistance imbalance of the bridge sensor into a saw-tooth frequency using current-mode sensing technique. Auto-zero (AZ) technique incorporating with ping-pong architecture is proposed to reduce the offset and low-frequency noise of the amplifier. The AZ SC amplifier achieves a temperature coefficient of 0.016 µV/°C from −40 °C to 90 °C whilst the input offset displays less than 100µV. Compared to conventional counterpart without the AZ technique, it offers significant lower offset and offset drift at the tradeoff for the increase of power. The sensor interface consumes 337 µW at a 1.2 V single supply and displays excellent energy-noise FOM with respect to other representative reported works.