New FFT design with enhanced scan rate for frequency division concurrent sensing of mutual-capacitance touch screens

As the touch screens become larger and demand higher resolution, various concurrent sensing methods have been developed for higher scanning speed and performance. One of such fast detection methods called the frequency division concurrent sensing (FDCS) employs an FFT to distinguish concurrent driving sine waves of different frequencies. In this paper, we propose a new FFT architecture and design, which can further improve the speed of the FDCS based controller for large mutual capacitance touch screens. The proposed FFT is used to increase the frame scan rate without duplicating sensing circuit. It uses only half the cycle of the driving signals to reconstruct the complete cycle of the signals, and so it can convert the signals to the complete frequency domain data. This paper shows that the proposed FFT architecture can double the frame scan rate with negligible loss in signal to noise ratio (SNR) and small area overhead.