Large-Area Capacitive Active Touch Panel Using the Method of Pulse Overlapping Detection

In this paper, we propose a novel active touch panel circuit using the RC time constant changes when the panel is touched to induce pulse overlapping. The transient ON current of the pixel thin-film transistor (TFT) is to be detected for the judgment whether panel is touched or not. The proposed circuit has many advantages, such as simple structure, multi-touch, low operating power, as well as significant current to be read out easily by low cost ICs. Especially, it provides excellent stability since the circuit is hardly influenced by variation of TFTs. Discrete TFTs are used to build the proposed circuit to verify its function and the function is further demonstrated in a 2-inch 9×9 array. The potential for large area applications is proven by simulating a 42-inch touch panel with proper assumptions.