Touch Sensors Press For Low Costs, Streamlined Design

Jan. 15, 2009
In terms of overall integration, touch sensors and their related components are probably the most seamless technologies. Touchscreens have evolved beyond the simple, single-button-entry format to incorporate new interface functionalities.

In terms of overall integration, touch sensors and their related components are probably the most seamless technologies. From automated teller machines (ATMs), cell phones, and video games to test-and-measurement and medical equipment, touch interfaces can be found nearly everywhere. And unless they’re confusing or inoperable, they’re taken for granted by most users.

In a brief period, touchscreens have evolved beyond the simple, single-button entry format. State-of-the-art components offer multifunction buttons, sliders, scrolling, simultaneous inputs, and unique human gestures. With each new interface variation offering more functionality, some users may ask where we go from here and what’s next.

Price Slice Like every sector, lowering future costs is a top priority in the touch-sensor arena. “In the area of touchscreens, performance and cost reduction are the two areas where customers are driving most aggressively for innovation,” says Eric Itakura, director of marketing and business development at Leadis Technology.

“Fundamentally reducing the cost of the touch sensor itself by simplifying its construction or reducing the number of required ITO (indium tin oxide) layers, without giving up functionality and performance, is a potential game-changer in this market,” adds Itakura. 

“Most consumer electronics companies are subject to the current economic downturn, thereby driving the search for competitive technologies,” says Chris Ard, director of marketing at Atmel’s touch technology division. “The main challenges are differentiating products and price. We are finding that the demand for low-cost and reliable touch-sensing controls remains strong.”

Present economic circumstances and resolutions aside, the quest for the lowest-cost yet highly reliable and functional touch sensors continues unabated.

Room For Innovation Where will we see the greatest focus of touch-sensor innovation in 2009? Size reductions? Greater functionality? According to Ard, achieving a richer user interface will come out of innovations in X-Y touchscreens, especially multi-touch interactions.

For this, Ard sees capacitive touch-sensing technology surpassing resistive touchscreens in terms of reliability. Compared to resistive components that install on the front of a panel and require multiple layers with air gaps, he says, “Capacitive sensing controls situate behind a cover and are consequently more resilient across all operating environments.”

In addition, when it comes to reducing size and weight, Ard said the thinner structure of a single-layer capacitive sensor makes it easier to implement the structure and requires less backlighting. In contrast, Leadis’ Itakura foresees enhanced robustness against LCD electromagnetic interference (EMI) and multi-touch gesture recognition as just two examples of performance-related innovation in the capacitive-touch segment. 

“Even though the consumer market has only recently started to adopt capacitive touch technology, the competition among end products is still fierce,” says Itakura. “For touch-button, slider, and scroll applications, the innovation will come in the form of functionality integration.”

Markets And Challenges The market for touch sensors is pretty wide, and predicting where the greatest demand will come from may be tricky. “Every touch-sensor market is interesting right now, basically everywhere there is a button. The technology is spreading quickly into automotive designs, children’s toys, and games, and the design criteria are very similar across most segments. But cost drivers vary, particularly in high-volume applications,” says Ard. 

“Buttons and scrollers are ubiquitous in consumer and mobile applications. Touchscreens in any volume have only been in mobile devices to date, but are moving very fast at the moment and are likely to become the interface of choice for over-display applications in the coming years,” adds Ard. “Manufacturers are now working with smaller engineering teams, so we (Atmel) find ourselves increasingly supporting prototype developments.”

“For touchscreens, the consumer market, mobile handsets in particular, is the most aggressive in driving innovation. With lower barriers to consumer adoption and faster product cycle times, there’s little doubt in my mind that the consumer market has the great potential for innovation and growth for touchscreens in 2009,” says Itakura. 

“Customers are not satisfied with the touchscreen solutions available now. This provides a challenge and opportunity for touch-sensor designers and manufacturers,” continues Itakura. “What’s necessary is a solution that takes into consideration the requirements of the entire system and addresses the full range of performance parameters, including resolution, accuracy/linearity, data rate, and multi-touch, all in the most cost-effective and streamlined way.”

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Some Examples Building richer user interfaces, Atmel’s AT42QT family of charge-transfer, capacitive touchscreen controllers enables two-touch gestures for intuitive interfaces with the ability to track and report one or two simultaneous touches as separate X and Y positions. Gestures include tap, double tap, flick and drag, as well as two-touch actions, i.e., zoom in/out and rotate.

Initial family members, the AT42QT5320 and AT42QT5480, support screen sizes up to 8 in. with a 16:9 aspect ratio. The AT42QT5320 comes in a 5- by 5-mm quad flat no-lead (QFN) package while the AT42QT5480 is available in 5- by 5-mm ball-grid array (BGA), 7- by 7-mm QFN and a 10- by 10-mm thin quad flat pack (TQFP). The RoHS-compliant (Restrictions on Hazardous Substances) controllers will arrive in the first quarter of 2009.

To boost functionality in space-limited designs, Leadis offers the 5- by 5- by 0.8-mm LDS6040 PureTouch capacitive touch controller with integrated LED and VibeTonz-ready haptics drivers (see the figure). For touch-based input controls including sliders, scroll wheels, and buttons, the device provides 15 sensor inputs, configurable as LED drivers delivering up to 8 mA. It operates with a 1.8-V touch supply, and LED and haptics supply voltage ranges of 3 to 5 V. Typical power consumption is 150 µW in full-power mode.

Leadis’ TapTouch 15-channel capacitive touch controller supports up to 56 independent touch zones, lowering the cost of adding capacitive touch in high-button-count designs. The technology’s two-layer sensor array allows each sensor to support multiple touch zones, eliminating the need for multiple touch controllers. According to the company, it minimizes experience-inhibiting first-touch latency by enabling continuous scanning of touch zones without the high power consumption common to low- or no-latency implementations.

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