Enhancement of touch screen sensing based on voltage shifting differential offset compensation

Abstract

In this paper, we present an offset compensation technique to enhance the performance of differential sensing circuits for capacitive touch screens. Accurate offset cancellation of differential circuits is regarded as a difficult problem, especially when the offset changes depending on the input signals. The proposed technique can improve the touch detection SNR by compensating both the input and output offset voltage of the differential integrator. It pre-stores the differential offset voltage and corrects both the positive and negative outputs by shifting them by the ½ of the pre-stored offset voltage. We implemented the proposed technique in a touch screen driving and sensing chip using 65 nm CMOS process. Experiments with three different sensing circuit techniques show that the proposed technique provides an SNR improvement of up to 11.17 dB over conventional sensing circuits.