In-cell Capacitive Touch Panel Structures and Their Readout Circuits

Abstract

This paper proposes an in-cell capacitive touch panel structure and a readout circuit (ROIC) to sense the variation in self-capacitance using a small number of sensing lines. The proposed touch panel structure sequentially senses the variation in self-capacitance by adding a thin-film transistor and a scan signal line into each touch sensor so that the number of sensing lines can be reduced. In addition, the proposed ROIC enhances the signal-to-noise ratio (SNR) by compensating for the stray capacitance. The simulation results show that the proposed ROIC achieves an SNR of 57 dB. Moreover, the number of sensing lines per inch is 6.7 and 230.8 using the proposed active self-capacitive sensing method and the advanced in-cell touch (AIT) technology, respectively. Therefore, the proposed active self-capacitive sensing method reduces the number of sensing lines by 97.10 % compared with the AIT technology, while maintaining high sensitivity and multi-touch sensing capability.