Differentiator based sensing circuit for efficient noise suppression of projected mutual-capacitance touch screens

This paper presents a new technique to improve noise immunity of the RX sensing circuit of mutual-capacitance large touch screen panel (TSP). A differentiator circuit is incorporated to effectively suppress the high frequency noise. The proposed architecture provides low-pass and high-pass filter functions to reduce the noise and improve SNR. It uses square wave as a driving signal and integrates the output signal after filtering out the noise. The sensing circuit is small enough so that we can duplicate it to achieve target frame scan rate. We implemented the proposed technique using a 65 nm CMOS process and evaluated its operations in response to various touch events. The experimental results shows that the proposed technique improves the SNR of TSP by 9.5 dB compared to the conventional integrator based sensing circuits. We show that the design consumes 2.7 mA per each sensing circuit with supply voltage of 1.2 V.