An Ultra-Compact Low Power Self-Capacitive Touch Screen Readout IC Embedding Reconfigurable Noise Immunity and Current-Driven Capacitance Compensation

Abstract

This brief presents the design of a readout IC for dot-matrix, self-capacitive touch screen system. To accommodate only a capacitive change with large base capacitance of electrodes, it employs an encoded multiple sensing method as well as current-driven offset compensator (OC), that strike circuit complexity, power consumption and handling range of the base capacitance. The current-driven OC can provide compensation current up to 300 μA with a 4-bit tunable magnitude and mismatch calibration between source and sink currents. It can also perform adaptive noise rejection for in-band as well as out-band interferences by introducing hybrid touch screen panel (TSP) drive scheme. The measurement results show that it achieves 47.2 dB signal-to-noise ratio and 31 dB in-band noise rejection with 220 kHz TSP drive frequency and 330 Hz scan rate when a 4 mm metal pillar is used. The proposed front end circuit, fabricated on a 130-nm CMOS technology, occupies an area of 0.128 mm2 and consumes 1.04 mW of power for 16 channels 1.3-in, dot-matrix On-cell TSP for rigid OLED.