Design of noise immune readout IC with panel parasitic RC time delay reduction technique for large size capacitive-type touch screen panel

Abstract

An effective readout method and circuit adopting the method for large size capacitive-type touch-screen panels (TSPs) is presented in this thesis. Despite the considerable amount of RC time delay of large-area TSPs, the readout method of this thesis with a receiver (Rx) input series-capacitor improves the settling speed of signals transferred from the transmitter (Tx) to the Rx, by reducing the RC time delay. Combined with the Rx input series-capacitor, a capacitive-input fully-differential filtered charge integrator (CI-FDFCI) effectively cancels out the display noise and reduces the self noise in capacitive-type TSPs. The proposed Rx circuit was implemented using 0.35-$\mu$m CMOS. Using a 65-inch metal-mesh TSP with 169 Tx and 97 Rx electrodes mounted on a liquid-crystal display (LCD) for testing, the proposed readout method achieved 65% reduction of signal settling time within an accuracy of $\ge$ 3$\tau$ for the longest signal path of the TSP. Using the RC time delay reduction technique, the Tx driving frequency could be boosted by as much as 400 kHz, and the measured signal-to-noise ratio (SNR) of 43.5 dB was obtained for finger touch at a 120 Hz scan rate, resulting in a figure-of-merit (FOM) of 0.26 nJ/node, while the overall power consumption was 76 mW.