Abstract
In recent years, more and more MEMS sensors, especially the capacitive sensors, were used in consumer electronic products. The capacitive sensors have gained an increasing research interest in the last few years. The variance values of the capacitance are generally small, when the sensor and readout circuit are integrated together as a system on a chip (SoC). Therefore, the design of readout circuits are becoming more and more critical. The proposed sensing circuit for capacitive sensors is based on sigma-delta modulator (SDM) and can be used not only as a capacitance-to-digital convertor (CDC) but also as a analog-to-digital (ADC). The simulated results showed that the minimum detectable capacitance value and the peak SNDR are 0.1 fF and 73 dB, respectively. The chip was implemented using CMOS 0.18□m technology and occupies an area of 0.384 mm2, including I/O pads. The power dissipation is only 0.29 mW under 1.2 V voltage supply. This low power circuit is suitable for the use in portable products.