Conventional optical-touch systems use an array of infrared

Conventional optical-touch systems use an array of infrared (IR) light-emitting diodes (LEDs) on two adjacent bezel edges of a display, with photosensors placed on the two opposite bezel edges to analyze the system and determine a touch event. The LED and photosensor pairs create a grid of light beams across the display. An object (such as a finger or pen) that touches the screen interrupts the light beams, causing a measured decrease in light at the corresponding photosensors. The measured photosensor outputs can be used to locate a touch-point coordinate.

Widespread adoption of optical touch screens has been hampered by two factors: the relatively high cost of the technology compared to competing touch technologies and the issue of performance in bright ambient light. This latter problem is a result of background light increasing the noise floor at the optical sensor, sometimes to such a degree that the touch screen’s LED light cannot be detected at all, causing a temporary failure of the touch screen. This is most pronounced in directsunlight conditions where the sun has a very high energy distribution in the IR region.

In addition, conventional optical touch has not been adopted for small handheld touch screens (such as in cell phones and PDAs) due to a number of other technical reasons, including power consumption, mechanical packaging constraints, and resolution limitations which limit the system’s ability to detect small objects such as PDA-style pens.

However, certain features of optical touch remain desirable and represent attributes of the ideal touch screen, including the option to eliminate the glass or plastic overlay that most other touch technologies require in front of the display. In many cases, this overlay is coated with an electrically conducting transparent material such as indium tin oxide (ITO), which reduces the optical quality of the display. This advantage of optical touch screens is extremely important for many device and display vendors since devices are often sold on the perceived quality of the user display experience.

Another feature of optical touch which has been long desired is the digital nature of the sensor output when compared to many other touch systems that rely on analog-signal processing to determine a touch position. These competing analog systems normally require continual re-calibration, have complex signal-processing demands (which adds cost and power consumption), demonstrate reduced accuracy and precision compared to a digital system, and have longer-term system-failure modes due to the operating environment.

Yet another key advantage of optical touch is that there is normally no direct impact of a finger, pen, or other object with the touch recognition hardware. This reduces the possibility of failure modes typically caused by impact failure, wear, or fatigue of the touchscreen. This is also related to the requirement for low-pressure touch. In an optical-touch system, only interaction with the light beams is required – no force needs to be applied to the system for detection or activation.

Finally, optical touch is capable of implementing multi-touch, something most other touch technologies cannot easily achieve.

Neonode has taken conventional IR touch technology, using LEDs and photodiodes, and essentially miniaturized it and reduced the cost for use in handheld devices. In addition to using the technology in its own N2 cell phone, Neonode is also marketing it to other device makers.