A 3.9-kHz Frame Rate and 61.0-dB SNR Analog Front-End IC With 6-bit Pressure and Tilt Angle Expressions of Active Stylus Using Multiple-Frequency Driving Method for Capacitive Touch Screen Panels

Abstract

This paper proposes an analog front-end (AFE) IC using a multiple-frequency driving method (MFDM). The proposed AFE IC achieves a high signal-to-noise ratio (SNR) by using an external noise spectrum and locating the frequencies of the excitation signals in low-noise regions. In addition, it employs the MFDM to increase the frame rate by simultaneously sending excitation signals having multiple frequencies to the touch screen panel (TSP). The proposed AFE IC extracts the coordinates of the finger as well as the coordinates, pressure, and tilt angle of the active stylus with the force gauge and gyro sensor. The proposed AFE IC and active stylus were fabricated in a 0.13-μm standard CMOS process. The measurement results show that the proposed AFE IC achieves a frame rate of 3.9 kHz, and SNRs of 61.0 and 50.1 dB when a finger and active stylus are used, respectively. In addition, the pressure and tilt angle of the active stylus are expressed with 6-bit resolution. A capacitive touch system with the proposed AFE IC is demonstrated with a 65-in 104 × 64 TSP using ten fingers and the active stylus with the pressure and tilt angle.