DLP projectors: How the technology works

The basic operation of a 1-chip DLP projector


3-chip


Exactly twenty years ago, Larry Hornbeck developed the first DMD chips (Digital Mirror Device) in the labs of Texas Instruments. In 2017, he received a technology Oscar for this technology, which now supplies almost 90% of digital cinemas, as well as surplus of home appliances with DLP images (digital light processing).


Single-Chip


The brilliant idea was to build chips with small mirrors, which could be tilted mechanically by a few degrees. Each mirror becomes a filmed pixel when it directs the light of a projection lamp to be reflected either onto the screen or into nothingness. However, since these pixels only know the "On" and "Off" states, the mirrors have to be flipped thousands of times per second, each of varying lengths in order to represent all the different brightness levels. So you got a messy black-and-white image, but to get color into play, two approaches were developed that require either three or a DMD chip.


These expensive devices are similar to LCD projectors. The light of the bulb is divided into three basic colors, each of which receives its own DMD chip. After the pixelization, the partial images are again directed together onto the screen. With 3-chip DLPs the colors are generated at the same time and there are no rainbow artefacts. And the mirrors have a long time to build up all the brightness levels without generating quantization noise. For this, it is visually complex to bring the basic images back to the canvas.


New Technologies


In the case of 1-chip DLP lasers, the light is not split spectrally, but the basic colors are generated one after another. This is accomplished by a rotating color wheel, or recently by fast-switching RGB LEDs as a light source. The DLP chip produces red, green, and blue basic images that mix in the eye.


This is made possible by the very high tilting speed of the mirrors. Nevertheless, many people see rainbow effects with these DLP-Beamers. They are created by movements of the eye. If it scrawls across the screen, it does so within milliseconds and gets thereby variously colored partial images. The effect disturbs the viewer to a greater or lesser extent.


A further disadvantage of the 1-chip solution is, of course, that less time can be used to generate fine brightness gradations by multiple mirror tilting. It usually produces noise in dark colors.


The DLP technology can be enormously improved by new light sources. On the one hand, colored high-power LEDs replace the projection lamp with the mechanical color wheel. They last longer and switch so fast that the basic color can be changed more often during image setup, which reduces the rainbow effect. The same applies to lasers as light sources. In the future there will be considerable innovations. One could also imagine integrating quantum dot material into the color wheel, doubling the light output and enabling HDR. And then come now also the first 4K DLPs for the home cinema.


Texas Instruments brings the ultra-HD resolution in affordable price regions. The new 4K chip, however, instead of the eight million micro-mirrors, which are actually natively necessary, has only four. Using a shift technique, each mirror alternately generates two separate pixels. Due to the fast switching time of more than 9000 cycles per second, the full Ultra-HD resolution is to be visible. How well all pixels on the screen can be sharply and precisely separated from each other, tests still have to show.


In demos, the chip is said to have demonstrated its abilities with impressive detail - in direct comparison to the e-Shift variants of the competitors and even native 4KBeamern. And so we are very excited about the first Ultra-HD DLPBeamer announced for the end of 2017.


DLP in Ultra HD