A 70-μW 1.35-mm2 Wireless Sensor With 32 Channels of Resistive and Capacitive Sensors and Edge-Encoded PWM UWB Transceiver

Abstract

This article presents a wireless multi-channel sensor interface circuit for emerging e-skin applications. The proposed interface circuit uses a CDMA-like sensing method to simultaneously record 16-channel resistive sensors and 16-channel capacitive sensors. The code-modulated multi-channel signals are conditioned and wirelessly transmitted through an edge-encoded pulsewidth-modulation ultra-wideband (PWM UWB) transmitter in the time domain. The PWM UWB transmitter eliminates the need for digitization on the sensor node, reducing the number of data to be sent. This improves the sensing and wireless transmission efficiency. With the proposed edge-encoding technique, the PWM UWB transmitter can recover the sensor data with SNR above 70 dB despite 20% data loss under a lossy environment. Fabricated in 130-nm technology, the wireless multi-channel sensor node occupies a die area of 1.35 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and consumes a power of 70 μW. It achieves an energy efficiency of 0.87 pJ/Conversion-step per channel.