Electronic Design

Unique Touchscreen Tech Gets Ready To Enter Portable Markets

Enlisting semiconductor sultan AMI Semiconductor, Tyco Electronics’ Acoustic Pulse Recognition (APR) touch technology may be appearing on a cell phone near you soon. AMI has agreed to develop a silicon solution that will allow the integration of APR touch technology from Tyco’s Elo Touch- Systems group with handheld and mobile devices.

Normally associated with larger touchscreen installations in the commercial and industrial spaces, the APR technology may soon find a home in portable consumer products like cell phones, PDAs, navigation units, portable gaming, and signature capture, as well as in handheld industrial and medical devices. According to Ken North, director of engineering at Elo, the partnership will extend the boundaries in which APR technologies operate (Fig. 1).

HOW APR WORKS
APR combines the features of existing touch technologies within a single package while offering an alternative to capacitive and resistive topologies. A basic implementation consists of a display with a glass overlay and a small USB control board (Fig. 2). An audio-based technology, APR recognizes the sound created when the glass is touched at a preset position, which can vary depending on the application.

This audio approach enables touch input via finger, fingernail, gloved hand, or stylus. The technology also includes palm rejection functionality. The screen is scaleable in size from that of a PDA up to a 42-in. diagonal. The glass overlay offers durability in its resistance to liquids and other contaminants, including chemicals that do not affect glass such as acetone, toluene, methyl ethyl ketone, isopropyl alcohol, methyl alcohol, ethyl acetate, ammonia-based glass cleaners, gasoline, kerosene, and vinegar.

APR touch activation force is in the realm of 55 to 85 g with a maximum positional accuracy of 1%. Touch-point density depends on a controller resolution of 4096 by 4096 with a light transmission figure of 92% ±2%. Operating temperature ranges from –20°C to 60°C, with a storage temperature range from –40°C to 71°C. Other environmental operating limits include a relative humidity of 90% maximum at a maximum of 50°C for 240 hours non-condensing and a maximum operating altitude of 3048 m. Its storage and transport limit is 15,240 m.

The technology provides electrostatic-discharge protection as per EN 61000-4-2, 1995 and meets Level 4 based on 15-kV air and 8-kV contact discharges. It also carries UL, cUL, TUV, CE, and FCC Class A approvals and is sealable to meet NEMA 4 and 12 and IP 65 standards.

APR’s surface durability, specified as that of pure glass, offers a hardness rating of 7. As the technology relies on no moving parts, coatings, or layers, life expectancy exceeds 50 million touches in a single location using either a finger or stylus. For certain applications, impact resistance can meet UL-60950 and CSA 22.2 No. 60950 ball-drop test requirements, which entails dropping a 0.5-kg/50-mm diameter ball from a height of 1.3 m on the design.

THE SEMICONDUCTOR CHALLENGE
APR technology is native to PDA-size and larger touchscreens, but not the tiny displays common to cell phones and other palm-sized electronics. It also relies on recognizing the audible characteristics of touching the screen in whatever manner.

Considering how and where most consumers use cell phones and other devices, grooming an audio chip that will reliably allow accurate, uninterruptible input with instant user gratification is a formidable task. Also, smaller screens increase the chance for proximity errors since the closeness of preset input points is extremely high.

AMI Semiconductor has some difficult work ahead. The company isn’t giving up much information on this proprietary project for now, but as the year progresses, we’ll follow up on the results of those labors. “The development of an APR IC has the potential to enable Kanji writing and to scale screen size more effectively than other touch technologies, potentially accommodating displays from 1.8 in. to over 65 in.,” North said. We shall see.

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