Originally Published EMDM January 2006
Technology News: Electronics
Single-Conductive-Layer Technology Brightens Outlook for Touch Screen Sourcing
 |
| Because it uses a single conductive layer of indium-tin oxide, QField technology enables the cost-effective production of touch screens without panel openings, seals, or bezels. |
To operate, resistive touch screens typically require the user to apply physical pressure to force two layers of indium-tin oxide (ITO) to come into contact with each other. Although the technology is not known for its durability, its low cost has led to widespread adoption. Quantum Research Group Ltd. (Hamble, Hants, UK) has developed a single-conductive-layer design that reduces wear while improving brightness and contrast at a cost comparable to traditional touch screens, according to the company.
QField touch screens are based on the company’s proprietary charge-transfer sensing technology. It involves charging a sensor electrode—in this case, the ITO layer—and transferring that charge to a detector composed of a fixed capacitor. Charge transfer acquisition is carried out in burst mode using microprocessor-controlled switching of MOSFET transistors. The presence of the external capacitance of a finger affects the charge flow to permit sensing. The so-called spread spectrum sensing reduces radio-frequency emissions and susceptibility, and results in low power consumption.
The technology eliminates the need for panel openings, seals, and bezels because the ITO layer can be printed directly under the touch panel surface. This may be of particular value to medical device manufacturers seeking to design products with a sealed surface that can be easily cleaned. The use of a single layer also makes the screen more transparent, thus improving light transmission, and because less backlighting is required, energy consumption is reduced. The technology renders obsolete most resistive-type touch screens up to 4 in. diagonal, according to the firm. It also expects QField products to make significant inroads into touch screens measuring up to 10 in. diagonal.
Touch panels can be up to 3 mm thick. The technology can be applied to flexible or curved surfaces, and the company will introduce a family of integrated circuits that can be used to implement QField in various devices. Product features include x-y-coordinate output, gloved-hand operation, 256 X 256 pixel resolution, a 20-millisecond response, and microamp current consumption in low-power mode. The technology also allows the creation of opaque, arbitrary position, x-y reporting, capacitive touch keypads. Numerous other control features can be integrated on a low-cost, single-sided printed circuit board that adheres to the back of the plastic or glass touch screen panel.
Copyright ©2006 European Medical Device Manufacturer
