Single-layer sensor cuts capacitive touchscreen cost

Traditional capacitive touchscreens use a two-layer sensor to deliver the accuracy and linearity required for today's user experience. Cypress has developed proprietary algorithms that interface with a true single-layer sensor with no bridges to deliver two-layer performance for an unparalleled combination of user experience and cost sensitivity.

Available for glass and film, the removal of this second sensor layer can save mobile device manufacturers 30 per cent or more on sensor costs.

According to John Carey, director of touchscreen marketing at Cypress, what has been described as single layer technology up until now has been based on a manufacturing technique that uses diamond and snowflake patterns, and requires a layer of insulator and an expensive bridge (see Figure 1).

Cypress says that even with only one sensor layer, the TrueTouch solution delivers accuracy better than 1.25mm, good SNRs, a response time of 80Hz and active power of 3.6mW.

The technology is used in the Cypress CY8CTST241 (single-touch with one-finger gestures) and CY8CTST242 (adds limited two-finger gestures such as 'pinch' and 'zoom'), and delivers improved performance touchscreen accuracy of around 1mm and responsiveness with a true single-layer sensor panel, reducing the cost of the most expensive component of the touchscreen.

The controllers should enable manufacturers of handsets, cameras, GPS systems and other mobile systems to use capacitive touchscreens at lower resistive touchscreen costs.

Capacitive touchscreens' advantages over resistive touchscreens include a more intuitive user experience, better transmissivity, lower power, increased reliability and better durability. According to Carey, many lower-priced feature phones do not offer capacitive touchscreens today because of the cost. "The new TrueTouch single-layer sensor opens up new feature phones and lower-cost smartphones to capacitive touchscreens, especially in major markets such as China and India."

The controllers are suitable for screen sizes of 2 to 3.5inches while multiple devices could be used for larger touchscreens, according to Carey. Cypress has a history of moving from multi-controller implementations to single-device solutions. The company's CY8CTMA884 is a single-chip tablet solution for touchscreens up to 11.6inches.

The CY8CTST241 and CY8CTST242, which both provide QWERTY keyboard support, are available today for lead customers in QFN and CSP packages. The CSP measures 2.2mm x 2.32mm and has 30 balls. Active power is 3.6mW, low power current is 0.7mA, deep sleep current is 100nA and the refresh rate is 110Hz.

- Colin Holland
  EE Times