LCD 노이즈에 강인한 상호 정전용량 측정방식 저전압 구동 터치센서

Abstract

A successful touch sensing operation is demonstrated with a 0.8-V swing stimulating signal in a mutual capacitive touch sensor placed on a turned-on LCD panel. It uses the time-periodic property of the LCD VCOM noise, by setting the frequency of the stimulating signal to (n+0.5) times the fundamental frequency of the VCOM noise, where n is a positive integer. Also, an integrator is placed after the analog multiplier or the chopper, with the integration period set to twice the VCOM noise period.Two test chips are fabricated. The test chip 1 uses a differential driving technique and a single-ended sensing to extract only the difference component of the mutual capacitance. The test chip 2 uses a differential sensing and a single-ended driving to minimize the common-mode noise component at the touch sensor output. With the LCD display turned on, the minimum stimulating voltage swing of the conventional touch sensor is about 5 V, while the test chip 1 and 2 of this work showed the successful 5-touch operation with the stimulating voltage swing down to 1.2 V and 0.8 V, respectively. At these minimum stimulating voltage swings, the measured SNR of the test chip 1 and 2 are 10.4 dB and 14.7 dB, respectively.