A Reconfigurable 40-to-67 dB SNR, 50-to-6400 Hz Frame-Rate, Column-Parallel Readout IC for Capacitive Touch-Screen Panels

Abstract

This paper describes a capacitive touch-screen panel (TSP) readout IC that provides a reconfigurable SNR and frame rate with high noise immunity and touch sensitivity. The readout IC mitigates severe noise interference with a lock-in sensing architecture. In addition, a band-pass filtering effect by the TSP and charge amplifier further improves the noise immunity. A differential sensing scheme is employed to enhance the touch sensitivity and to reject a common-mode noise. A column-parallel incremental ΣΔ ADC is adopted to provide a high resolution and frame rate. Furthermore, a multiple sampling and averaging effect of the ADC enhances the noise immunity. The readout IC reconfigures its SNR and frame rate by adjusting the configurable resolution of the employed ADC. The test chip is fabricated in a 0.18 μm CMOS process and occupies a 2.2 mm 2 active area. The test chip achieves a 60 dB SNR and 200 Hz frame rate with a 12×8 TSP. The SNR can be adjusted from 40 dB to 67 dB, while the frame rate is then inversely scaled from 50 Hz to 6.4 kHz. The test chip supports a supply voltage range from 2.1 V to 3.3 V and consumes 6.26 mW from a 3.3 V supply.