What is DLP projection system

In: Industry information On: Tuesday, December 31, 2019 Hit: 2155

Since the first DMD chip appeared in 1987, DMD has become the core part of DLP projector. What role does DMD chip play? You may have a clear answer after reading this article!

In 1987, the first DMD (Digital Micromirror device) chips, soon after the dmo is DLP (Digital Light Processing) is the core component of the projector, after years of development, DLP projector is becoming the leading projector products, won the beautiful news, mitsubishi, Acer support of a number of projector manufacturers, TI is the monopoly with DMD chip production to reap profits and guide the development of the projector.

In appearance, DMD chips are very similar to semiconductor chips of CPU, GPU, etc. DMD chip is the product of MEMS (Micro Electro Mechanical systems) technology, which integrates hundreds of thousands or even millions of Micromirror Pitch on its chip surface. The Micromirror is the physical pixel of its DMD chip. The more the Micromirror, the higher the display resolution of DMD chip.

DMD is not displayed by changing the polarization state of the incoming light or by emitting its own light, but by controlling the reflected direction of the light with numerous micromirrors. Therefore, in addition to the number of microreflectors, the performance of the microreflector also has a decisive influence on the DLP projector -- the larger the deflection Angle of the microreflector, the higher the contrast of the image, the faster the deflection speed, and the lower the delay of the image. After years of development, the microreflector has developed from an early deflection of plus or minus 10° to a deflection of plus or minus 12°, with a refresh frequency of up to 200MHz. It is worth mentioning that the microreflector is not controlled by a mechanical arm or a hydraulic device to adjust the deflection Angle, but by electrode voltage control, so in theory, DMD's life is unlimited if there is no external force damage and no aging of its own. In addition, because the DMD chip spacing is very small, the middle spacing of each pixel is very small, the image still appears very fine after zooming through the lens, which is very suitable for the projector.

Because of the DMD chip is small, the human eye to be able to watch directly DMD reflected image, thus introducing a lens to enlarge images of DMD (with the camera lens plays an opposite role), in order to ensure the optical effect, the lens must be as close to the DMD chip, so in DMD chip is placed behind the lens became a common layout, DLP projector manufacturers will tend to change the light source position constitute different optical system. The optical system of DLP projector is mainly divided into two structures: telecentric and non-telecentric. From the naming, it can be roughly understood that "heart" refers to DMD chip, and "far" and "flying far" refers to the distance between the light source and DMD chip. Their specific structure is as follows.

                                                                         Telecentric DLP projector optical system

In telecentric structure, the light source is often UHP point lights, metal halide, DMD chip can not directly use the light, so will use one and a half elliptic reflector converge to gather light and projection light Integrator (Rod), poly (light will make the original direction of the light into parallel rays, but parallel light DMD far distance and Angle is not appropriate, still need to be with the help of folding mirrors (a Fold Mirror) and a series of optical lenses can help reach the surface of the DMD chip. After a long marathon, the light still doesn't hit the DMD chip directly, but must pass through a TIR prism to separate the incoming light from the reflected light (image).

                                                          Non-telecentric DLP projector optical system

The telecentric structure is simple, the optical path does not need to go through many turns to reach the DMD chip surface, the optical structure is relatively simple, but the system can not be made small, not suitable for miniaturized DLP projector. The complex optical path of the non-telecentric structure reduces the volume of the optical system, but causes the problem that the incident Angle of the incident light is too large, and the lack of TIR prism makes it impossible to reduce the incident Angle to the level of the telecentric structure, resulting in the mutual convergence of light on the micro-reflector and the destruction of brightness uniformity.

 TIR (Total Internal Reflection) prism is a lens made by using the phenomenon of Total Internal Reflection of light. When light passes through two media with different refractive indices, some of the light will be refracted at the interface of the media, and the rest will be reflected. However, when the incident Angle is larger than the critical Angle (the light is away from the normal line), the light will stop to enter the other interface, and will instead all reflect to the inner surface. The projector's optical system USES TIR prism to separate incident light from reflected light to avoid interference.

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