An Energy-Efficient 13-bit Zero-Crossing ΔΣ Capacitance-to-Digital Converter with 1 pF-to-10 nF Sensing Range

Conventional capacitance-to-digital converters (CDCs) suffer limitations either on narrow capacitance range or low resolution for jitter-induced noise and high power consumption. In order to overcome these limitations, a 13-bit 1 pF-to-10 nF generic CDC is presented. In the proposed CDC with the oversampled Delta Sigma modulation, the zero-crossing-based circuits (ZCBCs) are used to replace the operational transconductance amplifier to avoid feedback loop stability issues. However, the ZCBCs inevitably incur the non-idealities and thus a novel calibration scheme is presented for efficient non-ideality-error cancellation. A prototype fabricated using 0.18 mu m CMOS technology is experimentally verified using a MEMS capacitive humidity sensor. The measurement results show the CDC achieves a 13-bit rms noise equivalent resolution with a 128 mu s conversion time and a 230 fJ/conversion-step figure of merit. The calibration scheme enhances the linearity from 7 bits to 11.4 bits in the 1 pF-to-10 nF compatible capacitance range.