Toshiba Matsushita Display Technology Co. Ltd. (TMD) exhibited a LCD panel equipped with a touch-panel function as a reference presentation at Wireless Japan 2007 (July 18-20, 2007; Tokyo Big Sight).
It is reported that the latest product features higher touch-panel sensitivity compared with the existing LCD with a touch-panel function the company presented so far at other exhibitions.
The photosensors are integrated with the pixels of the LCD panel using a low-temperature poly-Si TFT. In bright places, the LCD panel detects the shadow cast by the finger caused by external light, whereas, in dark places, it detects the light from the backlight reflected by the finger.
For touch-panel functionality, a photosensor is installed for every three pixels to detect a finger.
In order to enhance operability, the company has reportedly modified the algorithm used to read out the detected signals. The modification includes the optimization of conditions such as difference in contrast between before and after touching the LCD panel as well as the sensor area.
When used in a bright place, the latest product can be operated with sensitivity almost comparable to that of a standard touch panel. Sensitivity, however, decreases when the panel darkened, such as when it is completely covered with a hand.
TMD explains that the algorithm control is difficult in the detection by reflected light because the difference between the contrasts before and after touching the LCD panel is small. Targeting the applications in mobile phones and PDAs, the company plans to focus on the improvement of sensitivity in a dark place.