Robust integrated shift register circuit over clock noises for in‐cell touch applications

Abstract

This paper proposes an integrated shift register circuit for an in‐cell touch panel that is robust over clock noises. It is composed of 10 thin film transistors and 1 capacitor, and the time division driving method is adopted to prevent the negative effect of display signals on the touch sensing. Two pre‐charging nodes are employed for reducing the uniformity degradation of gate pulses over time. In particular, the proposed circuit connects a drain of the first pre‐charging node's pull‐up thin film transistor (TFT) to the positive supply voltage instead of clock signals. This facilitates to lower coupling noises as well as to clock power consumption. The simulation program with an integrated circuit emphasis is conducted for the proposed circuit with low temperature poly‐silicon TFTs. The positive threshold voltage that shifts up to 12 V at the first pre‐charging pull‐up TFT can be compensated for without the uniformity degradation of gate pulses. For a 60‐Hz full‐HD display with a 120‐Hz reporting rate of touches, the clock power consumption of the proposed gate driver circuit is estimated as 7.13 mW with 160 stages of shift registers. In addition, the noise level at the first pre‐charging node is lowered to −28.95 dB compared with 2.37 dB of the previous circuit.

Review of Integrated Gate Driver Circuits in Active Matrix Thin-Film Transistor Display Panels

“…The touch sensing only in the vertical blank showed the unnatural representations of moving touch actions and there was the difficulty in achieving the higher touch reporting rate than the display frame rate. Therefore, the touch sensing intervals have been inserted in the middle of the display scanning operation as depicted in Figure 19 [115][116][117][118][119]. It is called a time division driving method (TDDM).…”