A Mutual Capacitance Touch Readout IC With 64% Reduced-Power Adiabatic Driving Over Heavily Coupled Touch Screen

• Published in: IEEE journal of solid-state circuits Vol. 54; no. 6; pp. 1694 - 1704
• Main Authors: Park, Jiheon, Hwang, Young-Ha, Oh, Jonghyun, Song, Yoonho, Park, Jun-Eun, Jeong, Deog-Kyoon
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Adiabatic; Adiabatic driving; Adiabatic flow; analog front end (AFE); Capacitance; capacitive sensor; charge recycling; CMOS; Coupling; Couplings; Demodulation; Detection; Energy conversion efficiency; Interactive computer systems; Interference; modulation; Modules; Noise; Noise levels; Noise sensitivity; Power consumption; Power efficiency; Sensors; Signal generation; Signal generators; Signal processing; stepwise charging; switched-capacitor; Switches; Touch screens; Touch sensitive screens; touch-screen controller (TSC)
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2019.2898344

This paper presents a touch sensing analog front end (AFE) for capacitive touch-screen integrated into an ultra-thin display. Reduced distance between the touch screen and display causes large capacitive coupling, resulting in increased parasitic capacitance and reduced touch sensitivity. Display noise interference is worse due to the large coupling capacitance. Hence, it is a challenge to design an AFE capable of accurate and energy efficient sensing of a touch input in the integrated touch-screen panel. An adiabatic multi-driving method based on charge recycling is proposed to provide power-efficient stimulation of the touch-screen panel. Furthermore, in order to cancel out the display noise interference through the large parasitic capacitance, a fully differential touch sensing module is incorporated in the AFE. A correlated noise sampling (NS) is employed in the decoder stage for the multi-driving demodulation process. To further improve power efficiency, the sensing module is multiplexed in four ways while achieving an optimal conversion time per sample. The proposed AFE was implemented in a 180-nm CMOS process. The fabricated AFE shows 57.0-dB signal-to-noise ratio (SNR) at 120 fps while consuming 17.8 mW. Compared with power consumption of 19.9 mW expected with a conventional signal generation, the proposed adiabatic signal generator dissipates only 7.1 mW, exhibiting a power reduction of 64% due to the adiabatic driving method.