Noise cancellation techniques based on frequency selection OFDM and instrumentation sensing circuit for large touch screens

摘要

This paper presents efficient double-noise suppression techniques for large form-factor mutual-capacitance touch screen panels (TSPs). Different carrier frequencies are applied to TSP concurrently using orthogonal frequency division multiplexing (OFDM), while the sensing lines are sensed sequentially. The proposed technique ensures a high frame scan rate by using simultaneous driving signals, and it provides a high signal to noise ratio (SNR) by avoiding frequency band with high noise power. The proposed instrumentation sensing circuit employs the recycling folded cascade (RFC) instrumentation amplifier, which has the benefits of rail-to-rail input and output swing, lower power consumption, with high DC gain compared to conventional FC. We designed and implemented the proposed sensing circuit in a 65 nm CMOS process technology. The experimental results show that the proposed technique improves the SNR of TSP by 28 dB compared to the conventional integrator based sensing circuits. Also, we show that the design consumes 6.9 mA with a supply voltage of 1.8 V.