Low-Noise Current-Mode Bridge-to-Digital Converter Based on ΔΣ ADC with Ratiometric Feedback DAC and Dynamic Element Matching

This work discloses an innovative current-mode readout chain for piezoresistive full-bridge sensing. Without introducing any analog front-end stages, the differential bridge current is directly digitized through a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta \Sigma$</tex> ADC, with the aim of lowering noise and power consumption. Towards this goal, the critical part of the design becomes the feedback DAC, whose noise, in absence of analog amplification, directly compares with the bridge current. The circuit, tailored as a case study for the sensing chain of a MEMS micro-mirror, eliminates the consumption of the front-end stage. Besides, by deriving the DAC tail current from the bridge, and using dynamic element matching, no noise worsening is observed. Thus, the architecture represents a key solution, in line with recent mixed-signal design trends.