A 70dB SNR capacitive touch screen panel readout IC using capacitor-less trans-impedance amplifier and coded Orthogonal Frequency-Division Multiple Sensing scheme

A high SNR capacitive touch screen panel (TSP) readout IC is designed. In this paper, Orthogonal Frequency Division Multiple Sensing method is proposed to enhance frame scan rate. Capacitor-less Trans-Impedance Amplifier and Direct Digital Frequency Synthesizer based on Harmonic Rejection Ratio DAC is proposed to save chip area. The prototype IC with 0.18um CMOS achieves 70dB SNR for a finger and 400Hz frame scan rate.