LCD/memory combo saves power

Liquid crystal display (LCD) pixels are relatively large, so it is possible to integrate memory in the active memory backplane at each pixel site. Sharp Corp. has done this with a miniature monochrome LCD (resolution 96 x 96 pixels) and claims a power saving factor of 130 compared to a standard LCD of the same size.

By integrating a memory cell at each pixel. location, data only needs to be sent to the display locations where the content changes from one frame to the next. With standard LC displays, the microcontroller must rewrite the complete screen content for each frame at a rate of 50 to 60 Hz, even though most or all of the image remains the same. This redundant data transmission can waste a lot of power. Sharp said that its memory LCD, with a diagonal dimension of 1.35 inches, consumes about 15 microwatts in operation, while a standard LCD of comparable size needs about 2 milliwatt to render an image.

The memory LCD was developed based on Sharp's proprietary Continuous Grain Silicon technology. As a result, and unlike other reflective displays, the new type of LCD does not need polarizers. Thanks to a special liquid crystal material, the image is generated by the status of the pixel changing from black to white with a reflectivity of 50 percent. Thanks to the low power consumption, a small solar cell can provide enough electricity to drive memory LCDs, according to Sharp. This makes the display suitable for portable applications such as wrist watches, heart-rate meters, and other fitness devices.