Active in-cell touch circuit using floating common electrode as sensing pad for the large size in-plane-switching liquid crystal displays

In this paper, we propose an in-cell active touch circuit using the concept of floating common electrode for large size in-plane-switching liquid crystal displays. Compared with the conventional passive in-cell touch circuit, the proposed method can greatly reduce the readout channel numbers by sharing the sensing bus for one column. Because the touch signal is amplified in the pixel, the touch panel can be easily scaled up in size. Simulation results show that the difference between touch and no-touch signals can be as large as 10 μA even with threshold voltage shift of ±1 V. The possible issues of the proposed method are experimentally verified.