Design of a fast capacitance sensing circuit for 16× 16 sized sensor array

This paper presents a CMOS circuit design of capacitance array sensing, including a capacitor to voltage conversion (CVC) circuit, 12-bit S-channel column-level singleslope ADCs, and a scanning circuit. The integrated circuit is implemented based on 0.35 $\mu$ m process. A high-speed scanning circuit is designed. ADC conversion speed is also improved so the conversion cycle is decreased. CVC and ADC adopt pipeline working mode to improve the speed of the proposed sensing circuit, which consumes 330 $\mu$ s for the whole frame (all 256 pixels). Simulation results show the capacitance detection range is 1pF- 5pF, and the accuracy can reach 1fF. ADC conversion time is 9.1 $\mu$ s at 450MHz clock frequency. The total power consumption of the 8-channel column-level single-slope ADCs is 32.81mW.