A Touch Prediction and Window Sensing Strategy for Low-Power and Low-Cost Capacitive Multitouch Screen Systems

Abstract

A new multitouch sensing strategy, named the Touch Prediction and Window Sensing (TPWS), is proposed and realized in this paper for projected capacitive touch screens. The detection procedures of TPWS are divided into two stages: a pre-sensing stage for predicting the possible touched regions, and a window sensing stage for obtaining the accurate touched positions. Since the measurements of the untouched sensing cells are reduced significantly, the TPWS strategy needs lower efforts on signal readout and data processing than the traditional strategies. A prototype system was designed and realized, which consists of three identical 48-channel readout chips, a 15-in capacitive touch screen, and a commercial host processor. The readout chip is specially designed for the TPWS strategy using $\hbox{0.13}~\mu\hbox{m}$ 1.8 V/5 V CMOS process. The measurement results show that, the total power consumption of the system is only about 65 mW with a power supply of 5 V, and the reporting rate of the system achieves 500 Hz for no touches and 83 Hz for ten touches. The area of the readout chip is only 0.087 $ ~\hbox{mm}^{2}$ per sensing channel. The proposed TPWS strategy can be used to realize low-power and low-cost multitouch screen system, and it is especially efficient for large-sized screen.