A wide dynamic range, high-resolution multi-step SAR CDC for implanted humidity sensors

This paper proposes a wide dynamic range, high-resolution multi-step successive-approximation-register-based capacitance-to-digital converter (CDC) designed for characterizing implanted humidity sensors. The CDC features three conversion phases: a coarse phase with a LSB $=100 \mathrm{fF}$ for canceling large initial capacitance, a fine phase with a $L S B=1$ fF for detecting small variable capacitance, and an optional oversampling-with-integration phase for further enhancing the measurement resolution. The fine phase operates continuously while the coarse phase is only occasionally activated, i.e., during the initial quantization of an unknown capacitor or when the fine conversion exceeds its intended range. This operating strategy not only conserves power but also reduces conversion time. The simulation results show that the CDC has an effective resolution of 13.8 bits with 5 -time oversampling and 12.86 bits without oversampling.