A -24 dB in-Band Noise-Immunity Mutual Capacitance Readout System for Variable Refresh Rate of Active-Matrix OLED Display

This paper describes the design of a touch screen panel (TSP) readout IC having an in-band noise immunity. The proposed IC employs a cascaded spread spectrum TSP driving scheme combining chirp spread spectrum (CSS) and pseudo-random (PR) orthogonal sequences. The CSS shows the 12-dB spread gain prior to an application of PR sequences, resulting in total -24-dB in-band noise immunity. The proposed IC adopts trans-impedance amplifier (TIA) with differential current scaler (DCS), providing dynamic range of an analog front-end (AFE) only for a capacitive change from touches. The IC was fabricated in a 0.13-μm standard CMOS. The measurement result shows that the proposed AFE achieves 54.2-dB SNR and 240-Hz scan rate with 11.5-mW power consumption. The readout IC was demonstrated with 5.3-inch 31 × 16 TSP.