A 20 μ W, 0.05mm2 Duty-Cycled Resistor and Frequency-Locked-Loop-based Wheatstone Bridge Interface for Low Resistance Sensing Systems

The growing need for ubiquitous, ultra-low-power sensors has driven continuous advancement in low-power performance and energy efficiency for read-out circuits, with broad applications in environmental sensing of temperature/humidity [1,2] and barometric pressure [3]. In these sensor architectures, a Wheatstone bridge circuit provides balanced readout. While this approach is efficient for large sensor resistance $(5k \Omega - 500k \Omega)$, measuring small resistance $(\lt 1k \Omega)$ with low power consumption presents a fundamental challenge that is increasingly necessary for a growing class of sensors for strain [4] and force [5] in wearable devices and robotics.