Touchscreens being integrated inside LCDs
R Colin Johnson
6/10/2011 2:51 PM EDT
PORTLAND, Ore.—Current touchscreens are add-ons that are overlaid atop a standard display, but display manufacturers are gearing up to add touchpads inside the stack of standard LCD materials. Samsung and Nokia already have already integrated touch into the the OLED displays on their Galaxy S and N8 smartphones, respectively.
But doing that for OLED displays was easier than it will be for LCDs. OLEDs are much less noisy than conventional LCDs, which generate interference that foils conventional touchscreen techniques. Now, touchscreen controller makers like STMicrosystems NV (Geneva), Cypress Semiconductor Corp. (San Jose, Calif.), Atmel Corp. (San Jose) and Synaptics Inc. (Santa Clara, Calif.) are solving the noise problems so that touchscreens can become standard-equipment on LCDs.
If the touchscreen controller makers are successful at converting LCD manufacturers into touchscreen makers, they will effectively eliminate the need for the three dozen companies—and the billion dollar industry—that specializes in making add-on touchscreens today.
ST, for instance, announced Friday (June 10) what it claims is a breakthrough noise-rejection technology for integrating touchscreens inside LCDs, either by adding an extra layer to their existing LCD stack—called "on-cell"—or by multiplexing electrodes on the same layer as those which write pixels on the LCD—called "in-cell."
ST claims its FingerTip technology is unique by virtue of eliminating interference from noise at its source, by using a proprietary analog-front-end originally designed for MEMS that is capable of detecting atto-Farads of capacitance, but which ST claims is virtually immune to noise.
"Analog capacitive interface IP, developed for MEMS sensors, allows us to achieve higher noise rejection prior to digital filtering," said Benedetto Vigna, general manager of ST's MEMS, Sensors and High Performance Analog division.
However, the other touchscreen controller makers claim to also have proprietary technologies that nix noise—not with special analog IP, but with clever algorithms that sense the presence of noise, then switch to modes that are naturally immune.
"Touchscreens have to operate in a very noisy environment, most of which comes from the LCD itself," said Ed Grivna,a touchscreen architect at Cypress. "But we have been solving these noise issues for four successive generations of controllers."
Touchscreens today are a separte overlay that is added onto a display, but LCD makers are quickly tooling up to integrate them inside the LCD itself. Source: Cypress Semiconductor.
Cypress's unique noise solution for touchscreens combines two projected capacitive methods that they can alternate between on-the-fly to nix not only noise from the LCD, but environmental "noise" such as moist fingers. In normal mutual capacitance mode—which the other projected capacitive controller makers use exclusively—multiple touches can be detected without ghosting, but environmental noise can sometimes cause it to fail. In these situations, Cypress controllers automatically fall back to surface-capacitive mode, which can only detect single touches, but which can recognize the proximity of a finger even before it touches down, supports an ultra-small millimeter-sized passive stylus for writing Chinese characters, and can even operate in light rain.
Cypress is currently working with major LCD vendors to build their noise-immune touchscreens technology directly into displays, rather than as a separate add-on. But Synaptics and Atmel are also seeking design wins with LCD makers, claiming they have cleverly sidestepped the LCD noise issue—rather than meet it head-on like Cypress—by synchronizing their touchscreen controller with the LCD's refresh period. By only reading out touch information when the LCD is "quiet"—not writing pixels—they claim noise becomes a non-issue.
"We offer controllers that will work with conventional touchscreen suppliers, but which can also be integrated directly into an OLED display or, with the proper timing, even a conventional LCD which is usually too noisy to add touchpads," said Andrew Hsu, technology strategist at Synaptics.
One of the first LCD makers to offer integrated touchscreens will likely be Taiwan's AU Optronics Corp., which reported on a novel method of adding touch sensors into the stack of a standard-sized display at the Society for Information Displays' Future of Touch conference last month. AU Optronics also reported related progress with adding sensors directly into the thin-film transitor TFT cell, without the need for an extra layer, albeit only for the smaller screens used in digital cameras, portable navigation devices, and low-end mobile phones.