OFDM and TDM based sensing method for large projected mutual-capacitance touch screens

This paper presents a new technique for reading out projected mutual capacitance touch screen panels. It models touch screen panel as a communication system. Orthogonal frequency division multiplexing (OFDM) is used along with time division multiplexing (TDM) to read out all channels of touch screen panels. Different carrier frequencies are applied to touch screen panel concurrently using OFDM, while the sensing lines are sensed sequentially using TDM. The proposed technique ensures a high frame scan rate by using simultaneous driving signals, and it provides high signal to noise ratio (SNR) by avoiding frequency band with high noise power. Simulation results demonstrate a SNR improvement of 8.2 dB by selecting adequate carrier frequencies.