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Electronic Design

Capacitive Sensors Squeeze Versatile Touch Into Tight Quarters

Probably the greatest demand for highly featureridden touchscreens comes from the portable market, with the iPhone and similar communications products as ripe examples. But while it’s one thing to integrate a simple touchscreen accepting single-touch input to control the basic functions of a device, simple touchscreens are few and far between these days.

Give or take a few millimeters, the typical area for input on a cell phone is about the size of a credit card, which is barely enough room for an average finger to maneuver. In addition to basic numeric input for phone dialing, the touchscreen designer needs to squeeze into this space a plethora of other functions that often need to operate simultaneously, like cameras, address books and calendars, Internet and e-mail activities, video, music, and texting, with more yet to come.

As if shrinking space and expanding functionality weren’t big enough challenges, the manner in which end users address the touchscreen goes way beyond a single tap of the finger. Various gestures, i.e., sweeping, scrolling, rocking, variable pressure, and even shaking, are now the norm. The input area must be able to recognize each novel input type, associate it with the desired function, and enable the execution of that function accurately every time.

Naturally, this critical responsibility rests primarily on the shoulders of the touchscreen sensor. Synaptics says it has these concerns under control with its ClearPad sensors. According to the company, these high-resolution capacitive components for cellular phones, smart remote controls, digital cameras, and other devices provide an easy-to-use, discoverable interface for screen navigation, selection, and interactive input.

Custom designed for fit, a ClearPad sensor lays over the LCD providing the GUI. The sensor supplies the touch-activated interface buttons and controls (see the figure). Supporting design flexibility, the size and placement of the GUI controls can vary, accommodating a specific application or user mode.

RoHS-compliant with additional green-manufacturing options available, the sensors’ size and shape are customizable. Sensitivity is tunable for operation under a casing or plastic coversheet measuring up to 1.2 mm thick. Touch panels can be designed with a glass or polyethylene-terephtalate (PET) substrate. The sensors also save power via doze, sleep, and deep-sleep modes and are ready for use in as little as 100 ms from device power-up.

Unlike resistive topologies, the capacitive components don’t create wells or valleys around the sensor, enabling a smooth appearance. ClearPad sensors also promise to minimize internal reflections and specify resolutions beyond 500 dpi. They don’t require calibration, and they don’t have any moving parts. And, they’re highly resistant to contaminants and moisture.

One of the sensors’ most notable features is their ability to recognize and accurately translate gestures, or the manner in which users interface with the touchscreen. Functions relevant to a particular gesture are customizable for a specific device or application, and the sensors support a wide variety of gestures for enhancing usability.

These gestures include flicking to scroll through photos and lists, two-finger pinching to zoom in and out, finger presses to display information, taps to launch or close an application, taps and slides to move files or icons, and double taps to activate other functions. Since all of these inputs are customizable, they’re just a few examples of what a particular gesture can activate within a particular device.

ClearPad sensors are gaining significant ground in the market as well. For example, NTT DOCOMO/Sharp’s SH906i clamshell handset debuted in June as the first ClearPadenabled touchscreen in Japan’s mobile handset market.

In addition to gestures, the handset employs ClearPad technology to enable finger-input character recognition capabilities for Japanese character entry. According to Synaptics, the combination of the SH906i’s character recognition software and its ClearPad technology will pave the way for greater usability in regions with even more complex alphabets.


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