High-Resolution Auto-Balancing Wheatstone-Bridge with Successive Approximation of $\Delta \Sigma$-Modulated Digitally Controlled Variable Resistor

This paper describes a high-resolution, highly linear, low power amp-less sensor interface. A Wheatstone-bridge with $\mathbf{\Delta} \mathbf{\Sigma}$ -modulated digitally controlled variable resistor is proposed. The proposed bridge is automatically balanced by successive approximation (SA) of the digitally controlled resistor, which can eliminate power consuming amplifiers and ADCs. To overcome conversion speed limitation caused by settling time of each SA step, the output differential voltage of the bridge is shorted in advance to the comparison phase of each SA step. A developed prototype system achieved 9.68 bit resolution in target resistance range of three orders of magnitude and conversion speed improvement by 66%.