A 1 pF-to-10 nF Generic Capacitance-to-Digital Converter Using Zero-Crossing \Delta\Sigma Modulation

• Published in: IEEE transactions on circuits and systems. I, Regular papers Vol. 65; no. 7; pp. 2169 - 2182
• Main Authors: Li, Bing, Wang, Wei, Liu, Jia, Liu, Wen-Jun, Yang, Qian, Ye, Wen-Bin
• Format: Journal Article
• Language: English
• Published: IEEE 01.07.2018
• Subjects: Calibration; Calibration scheme; Capacitance; capacitance-to-digital converter; Capacitors; Linearity; Modulation; oversampled ΔΣ modulation; Sensors; Switches; zero-crossing-based circuits
• ISSN: 1549-8328; 1558-0806
• DOI: 10.1109/TCSI.2017.2777872

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 avoid these limitations, a 13-b 1 pF-10 nF generic CDC is presented. In the proposed CDC with the oversampled <inline-formula> <tex-math notation="LaTeX">\Delta \Sigma </tex-math></inline-formula> 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. In addition, for the purpose of making the proposed CDC sufficiently intelligent to adapt to a wide capacitance-sensing range, an adaptive auto-range mechanism is proposed. The above three techniques complement each other and work as a whole leading to the proposed CDC with wide range, high resolution, high linearity, and low power consumption. A prototype fabricated using 0.18-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> CMOS technology is experimentally verified using a MEMS capacitive humidity sensor. The measurement results show that the CDC achieves a 13-b root-mean-square noise equivalent resolution with a 128-<inline-formula> <tex-math notation="LaTeX">\mu \text{s} </tex-math></inline-formula> conversion time and a 230 fJ/conversion-step figure of merit. The calibration scheme enhances the linearity from 7 to 11.4 b in the 1 pF-10 nF compatible capacitance range.