Analysis of capacitive touchscreen electrodes design patterns from an EMI/EMS perspective

Abstract

Capacitive touch sensing has gained traction in modern human-machine interfaces (HMIs) due to its cost efficiency, versatility, and reliability. In parallel, the proliferation of high-speed wireless systems has spurred interest in integrating high-frequency antennas within touch screen panels (TSPs). As device dimensions continue to expand, particularly in large-screen applications, addressing challenges arising from the touch-sensing circuitry and TSP design is crucial, particularly in electromagnetic interference (EMI) and electromagnetic susceptibility (EMS). This research primarily focuses on the simulation and experimental study of various commonly used capacitive touchscreen patterns and the analysis of how these configurations influence signal coupling between touch electrodes and the surrounding environment. The results show that larger screens with complex touch electrode patterns exhibit an increased propensity to couple with undesired signals across different frequencies. While TSPs with simpler electrode design patterns can partially mitigate these effects, they might introduce additional challenges, such as higher parasitic capacitances and increased loading on the drive circuitry. However, designing TSPs with intrinsically higher immunity to EMS and lower emissions while keeping the signal-to-noise ratio (SNR) within tolerance remains vital for touch-based HMI deployment for critical systems in noise-prone environments, such as electric automotive systems.