Articles and whitepapers

D-ILA Projector Technology (3/3/2005)

By Iain Ambler, JVC Professional Europe

When people think of home projection, they generally consider only two technology options - DLP and LCD. Although CRT projection is still available, small fixed-panel projectors account for the vast majority of the market place. However, there is another projection technology option of which, for a variety of reasons, few people are aware. This technology is D-ILA (Direct-drive Image Light Amplifier) and it belongs exclusively to JVC.

Since early 1998, JVC Professional has been producing high-end projectors to suit very specific and specialist professional/industrial applications. In markets such as medical, post-production and simulation, JVC has enjoyed particular success in establishing a strong customer base for its projectors. The reason for this is that its D-ILA projectors intrinsically have the ability to very accurately reproduce the source material without introducing any colour changes or artefacts to the image.

Although D-ILA projectors have been chosen by some home cinema users, this has been the exception rather than the rule until now. The reason for the relatively slow uptake of D-ILA projectors for home use is two-fold:

1. Cost
Due to their specialist applications and relatively small production runs, D-ILA projectors have always carried a higher price tag than their DLP and LCD competitors.

2. Black level
For domestic use, traditionally, the home cinema user has been particularly concerned about the black level or off-state of projectors. Basically, this relates to the amount of light that falls onto the screen from the projector when the projector is not projecting anything, or is simply trying to project a black raster.

Although in far less demand these days, CRT projectors have had a distinct advantage in this respect. When a CRT device is projecting a full black raster, no light at all will come from the projector. Conversely, all fixed-panel projectors are driven by a lamp which is constantly running. This lamp will spill light onto the screen even when the projector is trying its hardest not to. This is the black level or off-state.

The market for D-ILA

Even though D-ILA projectors were widely regarded in the projection industry as the best around for accurate image reproduction, the home market would not accept them so readily because they could be beaten on black level by lower-cost single-chip DLP projectors.

Over recent years however, as production of the D-ILA chips has increased, resultant economies of scale have led to the gradual fall in the price of D-ILA projectors, while the market itself has changed. Additionally, as a result of further improvements in D-ILA projection technology and the development of new, higher-resolution projectors, the latter half of 2004 saw the introduction of D-ILA projectors that displayed a vast improvement in black levels and contrast ratios. To accommodate the increasing demand for display and projection devices that will show true high-definition images, the first of these was the DLA-HD2K. This was introduced in September 2004 as the world's first compact, native high-definition projector - with a native resolution of 1920 x 1080 and a contrast ratio of 2000:1. A second D-ILA projector, model DLA-HX2, made specifically for the home cinema market, will be released shortly. With a native resolution of 1400 x 788, a contrast ratio of 1500:1 and at a price that will suit the discerning home enthusiast, the rise of D-ILA for home cinema use is inevitable.

The D-ILA panel

How D-ILA works

Technically, the D-ILA differs substantially from its rivals LCD and DLP. Although it is a reflective device (similar to DLP), rather than having separate mirrors that reflect a pixelated image, it uses a silicon layer to project a very natural, pleasing analogue image. I should mention at this point that D-ILA is only used in three-chip devices.

While the D-ILA device is made up of many layers, it can be simplified to three distinct layers:
1. The silicon layer.
2. The reflective surface.
3. The CMOS chip.

Cross section and front view of the D-ILA chip

The reflective surface is sandwiched between the silicon layer and the chip. The image is produced on the CMOS chip, which is linked electrostatically to the silicon layer. Light passes from the lamp through the silicon layer, and is then reflected off the reflective surface, back through the silicon layer and away. The silicon layer can modulate the light depending on the charge in the CMOS chip.

Basic structure of D-ILA projector

The above image shows, in more detail, how a D-ILA projector operates. The natural light from the light source is separated into RED, GREEN and BLUE by the PBS (Polarised Beam Splitter) into P wave light (light vibrating parallel to the surface) and S wave light (light vibrating perpendicular to the surface). The P wave light passes straight through the PBS and the S wave light is reflected off the PBS and reaches the D-ILA elements. The S wave light passes through the silicon onto the pixelated reflective layer and is bounced back out again through the silicon towards the PBS. At this time the light waves that have been modulated into P wave light will pass through the PBS, into a combing prism, through the projector lens and onto the screen. Light that is not modulated and remains as S wave light will be reflected back off the PBS towards the light source to be re-used.

The benefits of D-ILA

Since images from the D-ILA projector are produced on an analogue device, they appear very natural and are perfect for viewing video images. Add to this the fact that D-ILA technology generates the smallest pixels and smallest pixel gaps currently on the market, and the result is on-screen images that display a very high pixel density which, in turn, create smooth, clear viewing.

Installing D-ILA projectors has been simplified as the product line-up has developed. Large projectors with bulky Arc Xenon lamps have been replaced by considerably more compact units that use smaller NSH (high-pressure mercury) lamps. These lamps enjoy the beneficial characteristics of Arc Xenon combined with the cost and running life advantages of more standard UHP- (Ultra High Pressure) type lamps. Consequently, the projectors are quieter and lamp changes are simpler.

The range of D-ILA projectors has undergone considerable changes in its lifetime. While it continues to offer higher-cost systems for the professional/industrial user, where true colour rendition and image consistency are of paramount importance, the line-up of compact, lower-cost units for home cinema use will undoubtedly contribute significantly to the consumer's viewing options and pleasure in the future.

Iain Ambler is an Area Sales Manager and projection specialist for the UK branch of JVC Professional Products Europe Ltd, manufacturer of broadcast presentation and AV equipment.

www.jvcproeurope.com