Design of interference-resilient touch controller IC using hybrid spread spectrum and multiple sensing techniques

Abstract

An interference-resilient, power- and area-efficient capacitive touch screen controller IC is designed for multi-touch recognition in mobile handset’s applications. In this paper, the hybrid spread spectrum scheme, or direct sequence spread spectrum (DSSS) cascaded with chirp spread spectrum (CSS), suppresses interferences coupled to TSP by more than 24dB. In respect of designed circuits, newly designed Trans-Impedance Amplifier (TIA), in which large feedback capacitor can be removed, is proposed in receiver circuit. On the other hand, in transmitter, Direct Digital Frequency Synthesizer (DDFS) based on Harmonic Rejection Ratio (HRR) digital-to-analog converter (DAC) are proposed to save the chip area and power con-sumption. The prototype IC with $0.18\mu m$ CMOS achieves 58dB SNR and capacitance resolution of 271aF for horizontal one layer 7-inchs’ touch screen panel (TSP). The chip area is $0.8 \times 2 mm^2$ for transmitter and $1.8 \times 1.8 mm^2$ for receiver, respectively. Total power consumption is 25.2mW with 1.8-V supply.