Frequency Hopping and Parallel Driving With Random Delay Especially Suitable for the Charger Noise Problem in Mutual-Capacitive Touch Applications

Abstract

Charger noise can cause inaccurate touch points and fake touch points to appear; this can cause a device to behave incorrectly. The intensity of charger noise could be much larger than the intensities of the original touch signals. Furthermore, the frequency of charger noise varies for each different charger. Therefore, industry experts have identified charger noise as the most difficult problem in capacitive touch applications. The demand for a solution to this problem has become crucial for the mobile market. In this paper, we prove that a particular combination of frequency hopping and repeated integration is an effective method to handle this problem. In addition, we propose an efficient discrete Fourier transform-based algorithm to select an effective sensing frequency. We propose parallel driving with random delay to enhance the signal-to-noise ratio (SNR). We show an efficient hardware-software co-design that facilitates the application of our methods in touch ICs. The experimental results show that our methods can increase SNR by over 45 dB and can find an effective sensing frequency fast and dynamically.INDEX TERMS Charger noise, parallel driving, frequency hopping, repeated integration, mutual-capacitive touch.

Highly Sensitive Mutual-Capacitive Fingerprint Sensor With Reference Electrode

“…The T x electrode was connected to the touch electrode through holes, thereby causing the reference capacitance (C ref ) to be fixed, regardless of the presence of the fingertip. The FPS touch screen panel structure comprised a crossline structure with a large plate area and a mutual capacitance of the panel to maximize the fill factor (50 %) and improve touch detection, respectively [8], [15]- [17].…”

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A Mutual Capacitance Touch Readout IC with Synchronization in Touch and Mobile Display Driving for High Refresh Rate AMOLED Panels

“…Therefore, high-resolution, high-refresh-rate displays lead to an increased burden for the analog front-end (AFE) of a TSP readout system and its post processing algorithm. Several researchers [ 6 , 7 ] have proposed using a frequency hopping scheme to avoid noisy frequency bands when choosing the TSP driving frequency. However, they would suffer from an in-band noise disturbance, the amplitude and frequency of which vary according to the display contents in a high-refresh-rate display.…”

Finger and stylus discrimination scheme based on capacitive touch screen panel and support vector machine classifier

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