Highly Reliable a-Si:H TFT Gate Driver With Precharging Structure for In-Cell Touch AMLCD Applications

Abstract

This paper presents a novel bidirectional gate driver circuit based on hydrogenated amorphous silicon thin-film transistors (TFTs), especially for use in active-matrix liquid-crystal displays with in-cell touch technology. The proposed circuit exploits the time-division driving method to implement the in-cell touch panels with a high report rate and prevent the distortion of touch signals. The proposed structure employs a highly reliable precharging circuit to ameliorate the degradation of the driving TFT during the long-term touch-sensing stages. The output TFTs in the precharging structure are activated only once at the end of the touch-sensing stage in a frame, effectively extending the lifetime of the circuit. The experimental and simulated results illustrate that the proposed gate driver circuit generates uniform output waveforms regardless of whether the circuit operates in forward and backward transmission or stops in any row. To verify the high reliability of the proposed gate driver circuit, long-term stress tests at 85 °C are conducted. After the proposed circuit is operated for 720 h, the falling time of the output waveforms after the touch-sensing stage slightly varies by only $0.51~\mu \text{s}$ , confirming that the output TFT in the proposed precharging structure with a low duty ratio of 0.15% can achieve the high reliability of the proposed circuit. Therefore, the proposed gate driver circuit is highly feasible for use in high-report-rate in-cell touch panels.