A Compact Self-Capacitance Sensing Analog Front-End for a Touch Detection in Low-Power Mode

Abstract

A novel self-capacitance transition sensing method is presented for low-power touch detection using a capacitive touch-screen. While maintaining a voltage level, an additional electric charge is additionally required when a touch-input is newly added; the amount of charge is used for detection. Accordingly, the proposed current mirroring voltage-level regulation (CM-VLR) circuit senses the transition of self-capacitance of the touch-screen and detects motions of the touch-object. Only one CM-VLR cell is used to scan the entire touch-screen. Thus low-power readout and high integrated-circuit area efficiency are achieved. Moreover, the proposed self-capacitance sensing method does not require an offset-calibration step through a charge-sharing-based voltage generation and the offset-coverage capacitor. Fabricated in a 180-nm CMOS process, and the CM-VLR cell occupies 0.12 mm(2). At a 120-Hz report rate, the proposed analog front-end (AFE) detects touch-input at a 32-dB SNR while dissipating 2.1 mW.