Whether you work with or without gloves, Capacitive touch panel performance behind protective cover glass is now exceptionally good. Getting the most out of your touch screen under these circumstances does take a bit of thought though. In a two-part blog, we look at the key issues to think about:
1. Touchscreen controller
2. Interdependencies between the components
3. EMI and noise issues
1. Which touchscreen controller should I choose?
Moore’s Law improvements in processing performance enable the latest touchscreen controller ICs to deliver a better combination of sensitivity and response time than older generations of devices. This is particularly important in the medical device environment where accurate touches and quick recording of data is essential.
The latest know-how for laying-out ITO (indium-tin oxide) electrode patterns, also allows design tools to determine patterns that are better-optimised for touchscreens to be placed behind thick cover glass or to accommodate users wearing gloves. It may soon be possible to create touchscreens that can be tuned for optimum performance with a certain type of glove, such as application-specific industrial gloves.
2. Managing inter dependencies
Whether engineers designing touch-enabled user interfaces into their latest projects can satisfy application requirements for thick cover glass, or end-user demand for a response when wearing gloves depends on achieving a suitable combination of ITO pattern, controller performance, and cover-layer properties including optical clarity and thickness. There are several inter dependencies between the components, materials, and settings, and these should be considered from a system perspective to optimise touchscreen performance in the context of the application.
The ITO pattern that forms the array of sense and drives nodes, which sets up the capacitances for touch detection, influences the signal-to-noise ratio and, together with the touch-controller firmware, determines the touch threshold. Both factors influence the permissible cover-glass thickness, and potential performance if the user is wearing thick gloves.
3. How do I overcome EMI and noise issues
The graphical display behind the touch sensor can couple noise into the capacitive touch-sensing layers and therefore the ITO pattern can determine the sensor's susceptibility to EMI. Including a ground shielding layer in the touch-sensor stack-up can reduce noise emanating from the LCD and entering the sensor’s circuitry.