HDTV TECH

It may not sound very exciting, but Advanced Super In-Plane Switching (AS-IPS) is a pretty neat technology. It is yet another improvement in the world of LCD, brought to you by Hitachi, as well as Panasonic and Toshiba.

A top-down illustration of two methods of LC manipulation

Hitachi created IPS in the mid-1990s, in an attempt to widen LCD's viewing angle. To understand it, you need to understand LCD. If you read our April 2006 GearWorks (also online), the following overview will be a recap. For everyone else, here's a brief description on how LCDs work.

Like Crystal; Like Liquid
At the back of an LCD is a light source, usually something similar to the fluorescent lamps you'd find in an office, only a lot smaller. This light passes through a polarizing filter. The filter forces the light, which would otherwise scatter everywhere, to march in a straight line. While the next steps vary a little, depending on how the LCD is made, they basically work like this. If a pixel is supposed to be lit, the light passes through a liquid-crystal (LC) layer unmolested, through another polarizing filter (at the same orientation as the first), and out toward your eyes. (There's a color filter in there too, but don't worry about that.) If the pixel is supposed to be dark, an electric current is supplied to the LC, and it twists. The light twists with it, and now all the light is marching 90 degrees from where it left the first polarizing filter. When this hits the next polarizing filter, it blocks the light like a good pair of sunglasses. It's in this twisting that IPS differs.

IPS, on the Other Hand
With a regular LC panel, there is an electrode on the front glass and one on the back glass. When current is applied, the tube-shaped LC molecules pivot so that they're perpendicular to the screen. One end faces the front, one the back. With IPS, there are two electrodes on the front screen, so the LC molecules rotate parallel to the screen. The ends face the sides of the screen, or the top and bottom.

The original IPS had problems with motion (more so than regular LCDs) and also took a hit on contrast ratio. Then came Super IPS. It was fine with motion and improved the contrast ratio. Now there's the mouthful of Advanced Super In-Plane Switching, which improves everything across the board.

The Good and the Bad
The advantage of AS-IPS, according to the designers, is better control over the LC. This means a faster response time and better light control. The most noticeable difference with an IPS-type LCD is a vast improvement over one of my biggest pet peeves about LCDs—their viewing angle. There is nearly no fall-off in color accuracy or contrast ratio at wide angles. So, the people in the cheap seats can still have a watchable image. The viewing angle is still not as good as that of plasma or CRT, but it's close enough that any normal seating position will be fine.

The downside is that, because there are twice as many electrodes on the front glass, overall light output is reduced, necessitating a brighter backlight.

To aid in response time, AS-IPS uses what the makers call Motion Overdrive. Many companies in the LCD business now use similar methods. LCDs are fastest when turning all the way on and off. This is the number manufacturers most often quote in response-time measurements (and is therefore fairly useless). LCs are much slower transitioning from one partial brightness to another partial brightness (which is pretty much all video). To combat this, the pixels are overdriven. So, if the video calls for a pixel at 45-percent brightness to go to 55 percent, it is momentarily jolted with about 25 percent more power than it would typically need and is then brought down to the 55 percent it was told. The result, believe it or not, is a faster overall response time, which means less blurry video. It also means a slightly brighter image, which is great for the show floor.