A Wide Measurement Range and Fast Update Rate Integrated Interface for Capacitive Sensors Array

A CMOS Capacitance-to-Digital Converter (CDC) for capacitive sensors array applications is presented. It consists of a 16: 1 multiplexer, a capacitance-to-voltage front-end and a 16-bit voltage-to-pulses converter. The proposed capacitance-to-voltage front-end circuit extends the dynamic range by charging or discharging the measured capacitive sensors indirectly. For low power consumption and short conversion time, hardware reuse technique and multi-steps quantization method have been applied in voltage-to-digital pulse converter design. This 16-ch CDC's maximum absolute input capacitance is 350 pF under a non-uniform distributed sampling interval of 0.15-0.75 ms with 90 mu A current consumption under +/- 0.9 V voltage supply. This prototype chip has been designed and fabricated in 0.18-mu m 1P6M CMOS process with active area of 640 x 630 mu m(2)