Capacitive proximity sensor with negative capacitance generation technique

An oscillator-based capacitive proximity sensor is presented. To improve the sensor's sensitivity by minimising the effect of parasitic capacitance, the proposed sensor employs a negative capacitance generation technique. The sensor is implemented with a standard 0.18 µm CMOS technology, and the measurement results show that frequency variation is about 1.4% at 5 cm distance while only consuming an 85 µA current. The die area occupies 520 by 280 µm, and the size of an external sensing plate is 0.5 by 0.5 cm.