Fully Differential Touch Screen Controller with Wide Input Dynamic Range for Thin Displays

• Published in: Sensors (Basel, Switzerland) Switzerland), 2020-02, Vol.20 (3), p.837
• Main Authors: Lee, Chang-Ju, Park, Jong Kang, Seo, Han-Eol, Huh, Junho, Chun, Jung-Hoon
• Format: Article
• Language: English
• Subjects: Capacitance; Circuits; CMOS; display noise; Displays; Dynamic range; Electrodes; fully differential charge amplifier; Interactive computer systems; Noise levels; Signal processing; Signal to noise ratio; Smartphones; thin display; touch screen panel; Transistors; wide input dynamic range
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s20030837

As today's smartphone displays become thinner, the coupling capacitance between the display electrodes and touch screen panel (TSP) electrodes is increasing significantly. The increased capacitance easily introduces time-varying display signals into the TSP, deteriorating the touch performance. In this research, we demonstrate that the maximum peak display noise in the time domain is approximately 30% of the maximum voltage difference of the display grayscale through analysis of the structure and operation of displays. Then, to mitigate display noise, we propose a circuit solution that uses a fully differential charge amplifier with an input dynamic range wider than the maximum peak of the display noise. A test chip was fabricated using a 0.35 μm CMOS process and achieved a signal-to-noise ratio of 41 dB for a 6-mm-diameter metal pillar touch when display pulses with 5-V swing were driven at 100 kHz.