A 105 dB Effective Dynamic Range Self- Capacitance Proximity Sensing System With Consecutive Double-Sided Conversion Technique

This article presents a self-capacitance sensing system for proximity sensors with a wide offset capacitance range. Auto-calibration technique is adopted to compensate for the large sensor offset capacitance and achieve high sensitivity and dynamic range (DR). Sensor capacitance is converted to a voltage by a capacitance-to-voltage (<inline-formula> <tex-math notation="LaTeX">${C}/{V}{)}$ </tex-math></inline-formula> converter that performs conversions during both the charge and discharge phases of operation, which we call consecutive double-sided conversion (CDSC). The conversion technique doubles the number of conversions compared to a conventional structure to improve the power efficiency. The adjustment of an appropriate duty cycle for the clock signal applied in the <inline-formula> <tex-math notation="LaTeX">${C}/{V}$ </tex-math></inline-formula> converter and delta-sigma modulator reduces the power consumption. A prototype chip has been fabricated in a 0.13 <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS technology. The analog circuits occupy an area of 0.264 mm2, dissipating 4.04 mW. It achieves an effective DR of 105 dB in a conversion time of 4.1 ms when the offset capacitance is 215 pF.