Study of Circuit Techniques for Enhancing Display Noise Immunity in Analog Front-end of Mutual-capacitive Touch Systems

This paper evaluates circuit techniques that enhance the display noise immunity in the analog front-end of mutual-capacitive touch systems and discusses corresponding design issues. Demonstrated through behavioral-level circuit simulations based on Verilog-A with electrical modeling of a capacitive touchscreen panel, the following three points are highlighted: Firstly, a high-voltage driving scheme at the transmitter improves the signal-to-noise ratio (SNR) by directly enhancing the signal power. However, the SNR improvement could be limited by residual chopping timing errors. Secondly, the signal frequency for capacitance modulation should be properly selected to avoid the display-data-dependent fundamental tone and harmonics of the display noise interference. Lastly, a fully differential sensing scheme at the receiver has a limitation in rejecting the common-mode component of display noise interference coupled into the receiver due to the channel-to-channel mismatch in the TSP, especially capacitance mismatches.