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This paper presents a VCO-based sensor front-end utilizing differential pulse-code modulation (DPCM) to substantially reduce the amplitude of the input signal to the VCO quantizer so that high linearity is achieved. Together with a background digital gain calibration and DEM, the techniques enable a high dynamic range (DR) using only 1 ^st order noise-shaping and 32× oversampling. Fabricated in 65nm, the AFE consumes 3.2μW and achieves 1.18μV _RMS input-referred noise in 500Hz BW. It also achieves an SNDR/DR/THD of 88/94/-105dB respectively with a NEF of 4 and Schreier FoM of 170dB.