Yann Vernier’s Blog

2010-10-22

Around the corner – displays

Filed under: Uncategorized — yannv @ 18:26

I recently posted that I’ve ordered a so called E-reader. The particular features about that are all in the display; it needs to be readable in sunlight, and consume little power. That’s why the one I picked has an E-ink display. But as is the tendency of such things, there’s alwyas something better just around the corner – something not yet available on the market, or still just a bit too expensive. This post is a collection of the (hopefully) emerging display technologies I know of, with a focus on E-reader style displays.

E-ink

I know, not really emerging when I’ve already ordered a third generation device, is it? Still, these deserve mention at least as a point of reference. The e-ink displays are purely reflective and stable, meaning any energy to display the image comes from light bouncing off it. Changing images, on the other hand, is a lengthy process frequently involving multiple passes (at least for grayscale). New driving chips has reduced this, but it’s still suffering from flashes to black and white. E-ink Triton was recently announced, and will add color capability.

SiPix

Also on the market, and near identical to E-ink displays, SiPix claim to be the biggest in electronic paper modules. This is probably because they make custom models, only capable of showing specific segments. They do make active pixel matrix models as well.

Nemoptic Binem

This was the type I was mostly convinced to wait for. Of course, only days later the company went bankrupt, and I made my compromise. So what was so good about Binem? It came down to a few properties: Manufacturing technology as common TFTs, translucent bistable layer so it could be combined and backlit (demonstrated with OLED), and updates at video speeds without any flashing whatsoever. We never got to see what the cost might be, and I boggle at a world where this company could find investors hard to convince.

Pixel Qi

An active contender is the Pixel Qi displays. I’ve been wishing for one of these a long time, since they’re both full speed displays and feature a reflective mode. They’re proven technology, being a spin off from the OLPC project, yet they’re barely beginning to inch into the market. Currently they’ve launched a DIY kit for a few netbook computers, and we’ve heard of one tablet device that should have a Pixel Qi display. A peculiarity is that the display goes nigh monochrome when passive, which makes the subpixels more interesting for spatial separation, but this will only triple the resolution along one axis. I’d have considered making a non-square color pixel ratio to exploit the higher resolution better – video formats drop the color resolution anyway.

Mirasol

Probably the most promising development among passive displays, Mirasol uses the very property of light wavelengths to accomplish color. Not only that, it’s a bistable technology with very fast updates – although not yet at common video levels. This might have gotten me to wait, as there are now rumors that there’ll be an e-reader with their technology next year. Unanswered questions include what sort of resolution they’ve accomplished, as they’re literally bilevel and will require more subpixels per pixel to get gradual levels. On the plus side, this means they’ll be working on getting the resolution much higher than the intended pixel density, and I’m a sucker for true resolution. Let’s hope the controllers will exploit it.

Unipixel

This display is neither stable nor passive. Unipixel displays are pure active matrix, like today’s common TFTs, but operate with very rapid shutters. The idea is to perform like some color scanners, flashing whatever color base you need through the shutters (typically red, green and blue). This requires basically a distributed PWM controller, fast enough to give the desired color precision and wide enough to handle every pixel at once. It’s been done for OLEDs, but there you have the convenience to be the last visible layer. Basically it’s like a flat panel version of a DLP. The advantages of this method are that each pixel is placed in the same spot (no shifted subpixels), the shutter can pass more of the light than common panels, and since it starts with being fast there’ll be no ghosting. It’s interesting, but hardly the stuff to compete with stable displays on energy efficiency.

OLED

Another technology neither stable nor passive, but included for comparison. OLEDs use directly shining subpixels, which makes them very energy efficient for an active display; there simply is no backlight to be filtered. But it does suffer from the fact that all the picture detail has to be emitted from electrical power, meaning it’s impractical to compete with sunlight.

TFTs

A few of these are used as e-readers. TFTs are divided into a few different technologies, and the Pixel Qi display actually belongs to this group – but most of the modern ones are limited to backlit operation. The legibility when the backlight is turned off is normally negligible. Apple’s iPhone and iPad displays are of the IPS type, which have better colors and viewing angles than most – I got an IPS panel for my stationary display. The cheap panels tend to be of TN type, which has horrid viewing angles – color tends to go nuts as soon as the angle is a bit off. This is what most laptops and TVs use, and you’ve surely seen the result when you tilt the screen just a little wrong. The same effect occurs when you get close – and since it differs for horizontal and vertical angles, you can’t expect decent performance if you turn to portrait mode. And to make matters worse, a lot of displays are built glossy or shiny. Great if you need a mirror, but that’s not the purpose of my displays.

CPT

A direct competitor to Pixel Qi, CPT have a sunlight readable display that doesn’t lose color quite as much when lit strongly from the front. I don’t know much more, as all I’ve seen are a few quick video clip of a fair booth, from netbook news.

I’m sure I’ve missed a few interesting ones. Please let me know which!

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