A SNR-Enhanced Mutual-Capacitive Touch-Sensor ROIC using an Averaging with Three Specific TX frequencies, a Noise Memory, and a Compact Delay Compensation Circuit

Abstract

Three methods are proposed to enhance signal-to-noise ratio of a mutual-capacitive touch-sensor read-out integrated circuit (ROIC). The first one isan averaging method with three specific transmitter frequencies of (n+0.5) times the frequency of a gate driving signal (GCLK) of LCD with integer n which are the dips of a display noise magnitude.The second one is a noise memory method that eliminates the DC and low frequency noise by subtracting the noise data from the measured data.The third one is a compact delay compensation method. A digital dual-loop phase-locked-loop generates the three specific frequencies automatically from the GCLK. The noise memory method is applied to the beginning of every frequency period. The compact delay compensation method was implemented with 11 flip-flops, a 4-to-1 multiplexer, and two clock signals (8.66 MHz, 4.33 MHz). The proposed ROIC applied to a 14x16 touch-sensor panel on a 7.9” LCD achieves the SNR of 52.9 dB with the frame rate of 367 Hz. The ROIC chip with a 0.35-m CMOS process takes an area of 5.64 mm2 and consumes power of 29.7 mW.