A High-Sensitivity Signal Conditioning Interface for Capacitive Touch Key Using ΔΣ Modulation

A high sensitivity signal conditioning interface for capacitive touch key is presented. Using a programmable gain amplifier, the negative feedback loop architecture with Delta Sigma modulation achieves high sensitivity and robustness. Additionally, an alternative capacitance sensing method is proposed to enhance the power supply rejection ratio and reduce the bill of material cost. A prototype that was fabricated using 0.18 mu m CMOS technology is verified experimentally using a capacitive touch key system. The measured peak signal-to-noise ratio of the Delta Sigma modulator is 98 dB at a 4 kHz data rate.