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EDN Europe's Editor Graham Prophet posts a selection of comments and insights prompted by the many items of industry news and rumour that cross the editorial desk or are gathered on his frequent travels to interviews, press conferences and events around Europe - and further afield - and somehow never find their way to the magazine or the web site, recovering some of the information otherwise lost in the noise level...

Tuesday, April 22, 2008

Ready for an LCD speedo?

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When we go shopping for LCD monitors or televisions, one of the parameters that the sales pitch includes is contrast ratio. It’s a figure that is subject to considerable manipulation. As a subtractive technology (LCDs start with white light and filter out all but the colour you want in every pixel) there is an inherent problem in producing black. To make a bright image you need to start with a bright white light (which is why the power consumption of big LCD TVs is so high): to get black you need to shut it all out. To get the contrast ratios of many-thousands that some products claim, manufacturers turn to tricks such as active control of the backlight; in areas where the image is meant to be black, you not only drive the pixels accordingly, but you turn down the backlight as well. Sharp has come up with a screen that it says has the highest contrast ratio – 2,500:1 – currently available for automotive displays: and, it would seem from the details in the press release that this is a native figure, a real contrast ratio with no tricks involved.
Why does it matter? As well as applications such as providing screens for the kids to watch Winnie-the-Pooh in the back seats (or play Grand Theft Auto, depending what sort of kids they are) designers would like to replace the driver’s instrument panel with an LCD. As well as having to be affordable (despite being tricky electromechanical assemblies with lots of parts, volume manufacture of conventional instruments makes them really cheap) such a display needs to be convincing – your speedometer has to look like a sharp white needle on a really black, black ground. And no, the market doesn’t really seem to want digital readouts. Here’s some of what the Sharp Press release says (edited a bit);
“The 2,500:1 High Contrast Automotive TFT LCD takes the development towards fully digitalised vehicle instrument clusters a significant step ahead. The contrast ratio enables improved readability and deep, rich blacks of the display. Operating temperature range is -30°C to 85°C. The 8-inch, 480x800-pixel screen uses optimised pixel design in the LCD panel and improved performance of components such as colour filters. These LCDs are intended to display read-outs from gauges such as the speedometer, as well as simultaneously display images that enlarge the driver’s field of vision and provide visual guidance and safety warnings via connections with cameras and various sensors mounted on the vehicle.”
I guess that means that, with a lesser requirement for the accurate full-gamut colour rendition you need for a TV or monitor, they can work with the colour filters to make a blacker black. I’m still not sure that black can be “rich”, though. It would be interesting to see a BoM comparison fully worked out between conventional and LCD-panel options, especially if you could figure in the extra freedom for the cabin designer when the instrument panel needs minimal depth.

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