Touch Screen Sensing Circuit with Rotating Auto-Zeroing Offset Cancellation

• Published in: Journal of Information and Communication Convergence Engineering, 13(3) Vol. 13; no. 3; pp. 189 - 196
• Main Authors: Won, Dong-Min, Kim, HyungWon
• Format: Journal Article
• Language: English
• Published: 한국정보통신학회JICCE 01.09.2015; 한국정보통신학회
• Subjects: 전자/정보통신공학; Auto-zeroing offset cancellation; Frequency division concurrent sensing (FDCS); Touch screen sensing; Amplifier
• ISSN: 2234-8255; 2234-8883
• DOI: 10.6109/jicce.2015.13.3.189

In this paper, we present a rotating auto-zeroing offset cancellation technique, which can improve the performance of touch screen sensing circuits. Our target touch screen detection method employs multiple continuous sine waves to achieve a high speed for large touch screens. While conventional auto-zeroing schemes cannot handle such continuous signals properly, the proposed scheme does not suffer from switching noise and provides effective offset cancellation for continuous signals. Experimental results show that the proposed technique improves the signal-to-noise ratio by 14 dB compared to a conventional offset cancellation scheme. For the realistic simulation results, we used Cadence SPECTRE with an accurate TSP model and noise source. We also applied an asymmetric device size (10% MOS size mismatch) to the OP Amp design in order to measure the effectiveness of offset cancellation. We implemented the proposed circuit as part of a touch screen controller system-on-chip by using a Magnachip/SK Hynix 0.18-µm complementary metal-oxide semiconductor (CMOS) process. KCI Citation Count: 1