Low Power and Low Noise Shift Register for In-Cell Touch Display Applications

Abstract

This paper proposes a shift register circuit integrated in in-cell touch display panels that achieves low power operation, low coupling noise, and high long-term reliability with 11 thin film transistors (TFTs) and two capacitors. A time division driving method is utilized to prevent the crosstalk of display signals into touch circuits, and two pre-charging nodes are employed to relieve the uniformity degradation of output signals caused by different stresses on pull-up TFTs. The proposed circuit activates a drain of the first pre-charging TFT only at display scanning periods, which reduces coupling noises and power consumption. In addition, an internal inverter is turned off for touch sensing operations, resulting in a wide range of threshold voltage shift compensation and low power consumption. SPICE simulation results with a low temperature poly silicon TFT model show that the proposed circuit compensates for the threshold voltage shift up to 17 V. In a 60 Hz full-HD display with a 120 Hz touch reporting rate, the noise level of the first pre-charging node is −16.78 dB in between 2.37 and −28.95 dB of two previous circuits, and the total power consumption for 160 stages is substantially reduced to 4.44 mW compared to previous approaches.