The touch-sensing HMI in wearable and IoT devices

December 05, 2023

Whitepaper

The touch-sensing human-machine interface (HMI) in wearable devices is a key element of their consumer appeal, providing a responsive, intuitive way to interact via touch buttons and sliders in devices such as earbuds and smart glasses, or via a small touchscreen in a smart watch. 

Competition in the market for these types of wearable device continually drives innovation. Manufacturers battle for superiority in two features that particularly matter to consumers: 

• Battery run-time between charges (the ‘recharge cycle time’)
• Form factor – OEMs have to balance comfort, convenience, and the abundance of features such as sensors with the demand for a sleek and attractive design

This market pressure affects design decisions about the touch HMI: with every new generation of a wearable product, manufacturers want to achieve substantial improvements in the touch system’s:

• Average power consumption, to conserve the battery’s energy
• Impact on the device’s mechanical design and form factor. The goal is to improve touch sensor functionality and features while reducing size and weight of the product
• Liquid tolerance, to maintain high performance in the presence of rain, sweat, etc.

And any such improvements must of course do nothing to detract from the device’s pleasing user experience. To enable manufacturers to achieve these two goals, Infineon has introduced a new touch-sensing controller, the PSoC™️ 4000T, for any type of wearable device, as well as small IoT devices. Based on the new 5th generation of Infineon’s famous CAPSENSE™️ capacitive sensing technology, the PSoC™️ 4000T reduces average power consumption by 10x com-pared to the previous generation PSoC™️ touch controller for wearable devices. It also enables designers shrink size of touch sensors and denser placement of components around a smaller touch-sensing element without compromising performance thanks to a 10x higher signal-to-noise ratio (SNR). 
 
At the same time, new multi-sense capability enables a single sensor to perform multiple sensing functions – not only touch buttons and sliders, but also force, proximity, and touchscreen sensing. And improvements to the touch technology result in very high liquid tolerance, giving superior touch-sensor performance in the presence of liquids such as rain or sweat. 
 
This white paper describes the Infineon engineering breakthroughs that have produced these dramatic improvements.