Wither Pixel Qi (pronounced "Chi")

Introduction

Yesterday, Microsoft announced its belated response to the IPad(r) with the Microsoft Surface(r). The Surface seems targeted to those that have been considering a tablet but who still like the convenience of a keyboard. Microsoft seems to have learned something from Apple's marketing in that the announcement itself was done with a lot more flash. However, the Microsoft announcement was more engineer oriented (mentioning a vapor deposited magnesium case) whereas announcements from Apple tend to be purely consumer oriented focusing on the visual aspects of the device.

Recently, there has been much discussion about the next version of the Apple Retina screen, possibly going to an IGZO (indium/gallium/zinc-oxide) with increased resolution, lower power and greatly increased response time. Having used a tablet myself, although LCD technology can still benefit from these improvements, I find it surprising that neither Microsoft nor Apple seems to be going after the big problem with mobile device screens, sunlight viewability.

For us old codgers (meaning anyone over 30) the benefits of increased resolution start to peter-out above 200 dpi. And, the response time benefit, while important for viewing video, does not matter for those of us that rarely use our mobile devices to watch video. (Though, admittedly, mobile video is gaining in importance and my own user habits may be stuck in the old model.) However, a good part of my own mobile use, an a good part of mobile use generally, is outside usage. For that, the big deficit in LCD screen performance is the loss of contrast in direct sunlight. Indeed, I was recently using a tablet to take some photos outdoors, after pressing the button to turn on the device, it appeared to have not turned on. Shading the device with my hand, I could see that it was, in fact on, but the screen was completely useless in that location. This was reminiscent of one of the first mobile computers, the Data General One, that came with a screen that was of such low contrast, it was difficult to tell when it was on.


Pixel Qi

Sunlight, or even bright room, visibility has always been a problem with LCDs. This issue came to the fore with the development of notebook PCs for third world audiences and e-readers for the developed world. While an expedient solution for the e-reader market, where video speeds were not required, was to go to an e-paper screen, for the third world PC solution, transflective technology was developed that could be incorporated into conventional LCD manufacture.

A few years ago, I had the opportunity to see the Pixel Qi screen. Pixel Qi is a company that was formed to commercialize the screen technology that was developed for the "One Laptop Per Child" project. The screen was incredible; easily viewable in direct sunlight. When I saw it, I expected that I would start seeing this technology on notebooks within the year. Since then, although there have been a number of sample and customer announcements from Pixel Qi, the industry, in general is focusing on other areas of screen improvement with, I think, decreasing relevance to the new usage models the mobile device industry is intending to create. Again, the Pixel Qi technology has been around for some time and to my own tastes, it would have been universally implemented the very next design cycle.

Additionally, beyond the mobile market, there is an emerging Public Information Display (PID or "Digital Signage") that can make good use of the technology. PID is increasingly an outdoor technology and one of the great difficulties in engineering an LCD for outdoor usage is rejection of solar radiation. This is across the entire spectrum, UV, visible, and IR all cause problems for an outdoor LCD. Further, to make up for the washout caused by the visible light, Outdoor PIDs must be run at at-least 1000 nits and even then can have low contrast. (A Nit is a level of brightness. A conventional notebook screen probably runs at a level between 120 and 200 nits.) The LCD pictured here runs at 1000 nits and is being used to provide weather, advertising, and other information at a bus stop in Las Vegas. The display, facing north and sheltered, is readable but could be greatly improved.

The additional heat and energy required for a 1000 nit display further complicate outdoor PID design. A display that operates on reflective technology should be a natural here. So in addition to relatively small mobile displays, I would expect the Pixel Qi technology to appear in much larger PIDs. Again, I am surprised that the industry has not jumped on this technology.