Symmetric Signal Reconstruction and Frequency-Division Differential Driving for High Rate Touch Screen Sensing

Abstract

As touch screens become larger, touch screen sensing techniques are facing growing demands for higher resolution and speed. While a fast touch screen sensing technique, frequency division concurrent sensing (FDCS) can provide substantial speed enhancement, its scan speed is still limited by the frequency characteristics of the touch screen and driving signals. We propose an enhanced FDCS technique to further improve the scan rate up to four times. The proposed technique drives only the first half-period of driving signals, while reconstructing the remaining half of the signals at the new fast Fourier transform (FFT) called a reconstruction FFT. This way, we can double the scan rate of the FDCS's maximum rate. In addition, we introduce a differential driving technique, which halves the number of required frequencies. This consequently allows us to increase the driving signal frequencies by two times. We also introduce a frequency shuffling technique to eliminate the multitouch cancellation problem, a common problem that makes it difficult to use differential signals for multitouch detection. Simulation experiments show that the proposed method can achieve four times higher scan rate at the cost of little overhead and SNR loss.