An incremental ADC sensor interface with input switch-Less integrator featuring 220-nVrms resolution with ±30-mV input range

An incremental ADC for Wheatstone CMOS stress sensor systems is described. A switched-capacitors integrator without switches toward virtual ground avoids spur signals, clock feed-through, residual offset and glitches. The circuit, fabricated in a 0.35-μm CMOS technology, consumes 42 μW at 500-kHz clock and 2.8-V supply. Low speed chopping cancels offset and limits the 1/f noise contribution. The signal-to-noise ratio with measures lasting 2²⁰ periods is 114 dB at ±100 mV full-scale range. The active area is 0.32 mm².