Low power LCDs

Later this year, Sharp also plans to introduce a 6.02in model in order to specifically address the e-books market and other portable reading devices. For this particular market segment, Sharp is aiming to supplement the range with transflective and touchscreen models. Sharp says that unlike the usual reflective memory LCDs, transflective memory LCDs offer the option of adding backlighting so that e-books or other applications can also be used in the dark. The capacitive touchscreen means e-books can be designed in such a way that readers can turn the pages almost like a paper book. The system LCDs are based on Sharp's own Continuous Grain Silicon (CGS) technology. According to Sharp, this enables it to equip each pixel with a 1bit memory that stores the image information uploaded onto the screen. Image information therefore only needs to be rewritten in those pixels in which the content has changed compared to the previous picture frame. As reflective displays, memory LCDs do not require any backlighting. According to Sharp, the combined effect means that memory LCDs only have 0.8% of the power consumption of conventional displays of the same size. In contrast, with conventional LC displays, micro-controllers have to rewrite the entire screen content from frame to frame at a speed of 50 to 60Hz, even if most of the image content remains the same. In addition, the backlight accounts for a good proportion of the power consumption. Standard LCDs, contends Sharp, therefore have a power consumption that is around 130 times greater than that of the newly developed memory LCDs. A 1.35in memory LCD uses 15µW in operation, whereas a standard LCD of comparable size requires around 2mW to display an image. The new type of LCD does not require any polarisers because of a polymer network liquid crystal (PNLC) material, and the image is generated by the status of the pixel changing from transparent to white with a reflectivity of 50%. This gives the display a silver-metallic appearance, while, with a slightly more conventional version of the memory LCDs, polarisers and high-reflective (HR) liquid crystals are used to supply a purely black-and-white image. Through their minimal consumption of power, small solar cells can supply sufficient electricity to run the new memory LCDs. Sharp suggests that the new type of display is suitable for small portable applications such as e-books, wristwatches, heart rate monitors and other fitness devices. Sharp also offers memory LCDs as 3V models so that when operated with conventional lithium ion rechargeable batteries, no charge pump is required in between. The new 6.02in display is already designed for this supply voltage and four other memory LCDs that are expected to be launched on the market in the second half of 2010 also only require the lower supply voltage. The new memory LCDs are already available in 1.35, 2.7 and 2.94in diagonals from the sales offices of Sharp in Europe and through distributors. Samples of the 6in models are anticipated to be available in Q2 2010.