A Fully-Differential Correlated Doubling Sampling Readout Circuit for Mutual-capacitance Touch Screens

Abstract

A fully-differential touch-screen sensing architecture is presented to improve noise immunity and also support most multi-touch events minimizing the number of amplifiers and their silicon area. A correlated double sampling function is incorporated to reduce DC offset and low-frequency noises, and a stabilizer circuit is also embedded to minimize inherent transient fluctuations. A prototype of the proposed readout circuit was fabricated in a 0.18 mm CMOS process and its differential operation in response to various touch events was experimentally verified. With a 3.3 V supply, the current dissipation was 3.4 mA at normal operation and 140 mA in standby mode.