A Noise-Immune High-Speed Readout Circuit for In-Cell Touch Screen Panels

Delta-Integration, a novel readout method, is introduced in an effort to solve the noise and speed issues impeding the performance of in-cell touch screen panels. In the proposed method, a differential sensing scheme effectively cancels common noise components and locally occurring noise is spatially low-pass filtered. Due to the consequently enhanced Signal- to-Noise Ratio, the proposed scheme is simply implemented by a comparator and a counter only in place of a complex ADC. The comparator is designed to have a `dead-zone´ for noise-immune characteristics. In addition, a new global charge amplifier that has much wider bandwidth and higher current-driving capability than the conventional one is proposed for high speed operation. The prototype chip consumes a static power of 1.15 mW and the total chip area without panel loads is 2.5 mm².