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This letter presents a dual plate capacitive proximity sensor (PS) that is integrated into a single chip with high environmental noise immunity. To efficiently reject environmental noise, the proposed PS employs two noise rejection techniques: 1) the use of a switched-charge amplifier and 2) synchronous sampling/filtering technique. The proposed PS is fabricated using a standard CMOS 0.5- μm process, and it occupies an area of 0.7 mm × 0.3 mm. Experimental results show that the proposed PS can detect an object up to 8 cm away from the sensor at an average current of 370 μA with a resolution of 1% output frequency.