Though not as expensive as the display or the touchscreen panel, the choice of the touchscreen controller has the most impact in terms of touchscreen system performance. The touchscreen controller incorporates capacitive sensing and processing technology to resolve finger touches and gestures by reporting their location and behavior to the host processor.
When a finger is placed on a projected capacitive touchscreen, the touchscreen controller detects a change in capacitance and converts that information into digital values. This digital conversion is further processed using sophisticated touch resolution algorithms within the touchscreen controller before passing on touch coordinates and other relevant data to the host processor.
Noise-sensitive signals are a major technical challenge for touchscreens. Controllers that employ high-quality analog front ends, built-in noise handling capabilities, and sophisticated processing algorithms is mandatory. With touch becoming the user interface of choice for many consumer electronic devices, the quality of touchscreen controllers will directly impact the end product user experience. Choosing the right touchscreen controller is integral to achieving performance and cost benefits.
A controller that provides high signal-to-noise ratio (SNR) and effective noise handling will be able to compensate for the signal strength degradation that comes from noise sources, such as a cheaper PMMA cover lens or a noisy ACVCOM display. To help optimize the performance of low-cost and multi-touch single-layer sensors, touchscreen controllers must supply compatible processing algorithms. In addition, the cost benefits of single-layer FPC routing can only be realized if the touchscreen controller pinout allows for flexible routing design.
Touchscreen controllers can also reduce system costs through some of the advanced features they support. For example, most touchscreen controllers interpret water on a touchscreen as a finger touch because the mutual capacitance signatures of water and a finger are similar. To solve this problem, touchscreen panel vendors can add an expensive layer of hydrophobic coating to the cover lens.
When drops of water land on the cover lens, the coating helps to break them apart into smaller droplets so they no longer register as touches. All the same, a touchscreen controller that enables water rejection natively through the use of its hardware and firmware features can detect and reject water on the touchscreen with built-in algorithms and can save the OEM additional coating costs.
