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. Experimental results show that the proposed technique provides a frame scan rate of 128.2Hz and an SNR of 70.5dB with a large touch screen of 23 inches.Īs touch screens become larger, touch screen sensing techniques are facing growing demands for higher resolution and speed. We also demonstrate that the FSCS technique can significantly increase the frame scan rate by concurrently driving all lines. 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. It converts the outpqut signals of each sense line to frequency domain using Fast Fourier Transform (FFT), and measures the touch signal strength at the frequency corresponding to each touch position. With proposed technique, the controller concurrently applies sine waves with different frequencies to all drive lines. The proposed technique improves the signal to noise ratio (SNR) and frame scan rate of large touch screens. In this paper, we present frequency selection concurrent sensing (FSCS) technique for multi-touch detection of projected mutual capacitance touch screens. Experimental results show that our methods can increase SNR by over 45 dB and can find an effective sensing frequency fast and dynamically. We show an efficient hardware-software co-design that facilitates the application of our methods in touch ICs. We propose parallel driving with random delay to enhance signal-to-noise ratio (SNR). In addition, we propose an efficient discrete Fourier transform (DFT)- based algorithm to select an effective sensing frequency. In this paper, we prove that a particular combination of frequency hopping and repeated integration is an effective method to handle the problem.
The demand for a solution to this problem has become crucial for the mobile market. Therefore, industry experts have identified charger noise as the most difficult problem in capacitive touch applications. Furthermore, the frequency of charger noise varies for each different charger. The intensity of charger noise could be much larger than the intensities of the original touch signals. We implemented the proposed circuit as part of a touch screen controller system-on-chip by using a Magnachip/SK Hynix 0.18-?m complementary metal-oxide semiconductor (CMOS) process.Ĭharger noise can cause inaccurate touch points and fake touch points to appear this can cause a device to behave incorrectly. We also applied an asymmetric device size (10% MOS size mismatch) to the OP Amp design in order to measure the effectiveness of offset cancellation. For the realistic simulation results, we used Cadence SPECTRE with an accurate TSP model and noise source. Experimental results show that the proposed technique improves the signal-to-noise ratio by 14 dB compared to a conventional offset cancellation scheme. While conventional auto-zeroing schemes cannot handle such continuous signals properly, the proposed scheme does not suffer from switching noise and provides effective offset cancellation for continuous signals. Our target touch screen detection method employs multiple continuous sine waves to achieve a high speed for large touch screens. In this paper, we present a rotating auto-zeroing offset cancellation technique, which can improve the performance of touch screen sensing circuits.