An 18.5nF-Input-Range PM-SAR-Hybrid Capacitance-to-Digital Converter Achieving 6.1μs Conversion Time at 18.1pF Input Capacitance

Capacitive sensors are widely used to acquire various types of physical information. A wide-input-range fast-conversion capacitance-to-digital converter (CDC) with high resolution and energy efficiency can accommodate such diverse applications. Among prior CDC topologies, SAR [1]–[4] and $\Delta\Sigma{M}$ CDCs [5]–[10] show high energy efficiency, but their input range is limited by the voltage saturation in analog blocks. Although period-modulation (PM) CDCs [11]–[13] can achieve a wide input range thanks to their time-domain operation without saturation, they consume a long conversion time to count many oscillation periods, resulting in poor energy efficiency. Moreover, all these topologies inevitably suffer from a trade-off between resolution and conversion time (Fig. 28.1.1 (top)).