A 0.26-nJ/node, 400-kHz Tx Driving, Filtered Fully Differential Readout IC With Parasitic RC Time Delay Reduction Technique for 65-in 169 x 97 Capacitive-Type Touch Screen Panel

Abstract

This paper presents a readout method and circuit for large, capacitive-type touch-screen panels (TSPs). Despite the considerable amount of RC time delay of large-area TSPs, the proposed readout method 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 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-in metal-mesh TSP with 169 Tx and 97 Rx electrodes mounted on a liquid-crystal display for testing, the proposed readout method achieved 65% reduction of signal settling time within an accuracy of >= 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 of 43.5 dB was obtained for finger touch at a 120-Hz scan rate, resulting in a figure-of-merit of 0.26 nJ/node, while the overall power consumption was 76 mW.