1 and 2 layer approach
1.5 layer approach
Cypress Semiconductor wants to usurp the low end touch arena dominated by resitive touch technology by replacing it with a single layer capacitive touch solution. The normal two layer sensor system is replaced with a single layer solution (Fig. 1) and matching electronics. Elimination of a layer has significant cost savings, as much as 30% or about $1.50. Add the better performance of a capacitive touch system to get a low cost, responsive touch solution for cellphones and other small mobile devices.
Cypress uses a single layer compared to 1.5 layer solutions (Fig. 2) also designed for lower cost. The latter actually requires a conductive bridge over an insulator to create the sensing pattern. Cypress is not revealing their pattern yet but it does not require a bridge.
A low cost sensor needs to be complemented with low cost electronics. Cypress’s CY8CTST241 provides single-touch sensing including support fo one-finger gestures. These include sliding and circular motions. The CY8CTST242 provides this as well but adds limited two-finger gestures such as “pinch” and “zoom”. It does not target the more robust sensing systems found on smartphones where cost is less of an issue but accuracy is. In this case a two layer approach makes sense. Still, there are a wide range of mobile devices where this functionality is desireable.
The TrueTouch solution targets 2- to 3.5-in screens and delivers accuracy better than 1.25 mm. It has a fast 80 Hz response time as well as excellent signal-to-noise ratios. In active mode it uses only 3.6mW. Only 100nA are needed in deep sleep mode. The chips are available in QFN as well as compact CSP (chip scale package) form factors.
