Frequency Selection Concurrent Sensing Technique for High-Performance Touch Screens

Abstract

In this paper, we present a frequency selection concurrent sensing (FSCS) technique for multi-touch detection of the projected mutual capacitance touch screens. The proposed technique improves the signal-to-noise ratio (SNR) and the frame scan rate of large touch screens. With the proposed technique, the controller concurrently applies sine waves with different frequencies to all drive lines. It converts the output signals of each sense line to the frequency domain using a Fast Fourier Transform, and measures the touch signal strength at the frequency corresponding to each touch position. We show that the proposed method can substantially improve the SNR by properly selecting the frequencies for the excitation signals to avoid the ambient noise. We also demonstrate that the FSCS technique can significantly increase the frame scan rate by concurrently driving all lines. Experimental results show that the proposed technique provides a frame scan rate of 128.2 Hz and an SNR of 70.5 dB with a large touch screen of 23 in.