Introduction of DMD chip display principle-2016.5.13

DMD subtle reflective mirror is a kind of integrated microcomputer electric superstructure circuit unit (memssuperstructure cell), which is made by using CMOS SRAM memory cell. DMD superstructure is manufactured from the full CMOS memory circuit, and then through the use of the mask layer, the aluminum metal layer and hardened photoresist layer (hardenedphotoresist) alternating upper structure, aluminum metal layer including address electrode (addr electrode), Twisted chain ( Hinge), yoke (yoke) and mirrors, the hardened photoresist layer acts as a sacrificial layer (sacrificial layer) to form two air gaps. The aluminum metal is treated with sputter deposition (sputter-deposited) and plasma etching (plasma-etched), and the sacrificial layer is treated with plasma ash (plasma-ashed) to create an air gap between the layers.each micro-mirror can reflect light from two directions, and the actual reflection direction depends on the state of the underlying memory cell.；when the memory cell is in the "on" state, the mirror rotates to +12 degrees, the memory cell is in the "off" state, and the mirror rotates to 12 degrees. As long as the combination of DMD and the appropriate light source and projection optical system, the reflector will reflect the incident light into or away from the projection lens of the transparent hole, so that the "on" state of the mirror looks very bright, "off" state mirror looks very dark.Gray-scale effect can be obtained by using two-bit pulse width modulation, and color display will be obtained if fixed or rotary color filter is used with one or three DMD chip.。DMD input is the electronic character represented by the current, the output is an optical character, this optical modulation or switching technology, also known as the two-bit pulse width modulation (binary pulsewidth modulation), it will send 8 characters to each of the DMD Digital light switch input terminal, Produces 28 or 256 gray levels. The simplest address sequence is to divide the available character times (field time) into eight parts, from the most significant bit (MSB) to the least significant bit (LSB), sequentially using an address sequence at each bit time. When the entire optical switch array is addressed by the highest bit, the individual pixels are then enabled (reset) to react to the state of the most significant bit (1 or 0) at the same time. At each bit time, the next bit is loaded into the memory array, and when the bit time ends, the pixels are reset so that they react to the next address bit at the same moment. This process repeats until all the address bits are loaded with memory. When the incident light enters the optical switch, it is switched or modulated by the light switch into a pack (light bundles), and then reflected out, the light packet time is determined by the individual bits of the electronic character. For the Observer, the light packet time is much smaller than the integrated response (integration) time of the eye, so they will see a fixed luminance of light.

Description of the work process of DMD

             DLP technology is based on optical semiconductors, digital micro-mirror Chip (DMD) by the Texas Instruments company Larryhornbeck invented in 1987, DMD chip can be digitized modulation of the light , The digital micro-mirror device consists of a rectangular array composed of microscopic mirrors, the array corresponding to the light in the projection image, these mirrors and digital signals, light sources and projection lens work together, the image, the most faithful to reproduce, the digital signal will activate the micro-electrodes of the lens, This electrode pushes the lens toward or away from the light source, and when the lens is facing the light source (on), a white pixel is reflected through the lens, onto the screen, and when the mirror avoids the light source (off), the specular pixels appear darker in the position on the screen. Fine Wei Mirror rotation speed is 5,000 times per second (these DMD mirror can, switch thousands of times per second), exchange each mirror switch time, you can produce different levels of gray, open time and close time, the gray pixels produced by light, close the time and the opening time, the resulting gray pixel depth, DMD mirror can reflect 1024 gray level, to produce gray image, gray image plus color most of the DLP system, the light source and the mirror seat plate plus a color wheel of the light filter, with the rotation of the color wheel, red, green, blue three light in turn will fall in, DMD Mirror, the opening of each mirror, The off state will adjust with the flashing of colored light, through this method, a typical DLP projection system, can produce 16 million kinds of colors for example, when the red or blue light falls on the mirror to open the mirror, through our eyes can produce purple pixels, purple image. The use of DLP technology projector, TV, home theater system using a single DMD structure, single DMD chip system, including a DMD chip, a cast lamp a color wheel and a set of projection lens, the resulting image than any other display technology should be more clear. More colorful, movies and large-screen projectors are using 3-piece DMD chip system, white light through a             prism, is broken down into red, Green, blue Three colors, each DMD chip dedicated to a color, reflected red, green, blue light is mixed up, through the lens projection to the screen,dlp  cinema projection system can produce 35 trillion colors.

After spending a lot of effort to understand the color wheel, let's look at another big core--DMD chip of DLP projector.
If the development of the color wheel, projector manufacturers can also be based on their actual needs to produce different products, then the DMD chip is fully in the hands of Texas Instruments. After more than 10 years of development, DMD chip not only size from 0.55 "to 0.95", technical also from the SDR DMD chipset developed to the DDR chipset, while the highest resolution can reach 4K (the first DMD resolution is only 16x16), Texas Instruments even the DMD chip called the world's most sophisticated optical components.

DMD is the role of the color wheel through the three primary colors of light mixed together, and through the data control to convert to color image. Although seemingly simple, but the technical content is very high , then how does DMD achieve this function? The
DMD is an integrated microprocessor-based electrical superstructure circuit unit made of COMs SRAM memory cells. The manufacture of DMD superstructure is from the complete CMOS memory circuit, and then through the use of the mask layer, the aluminum metal layer and the hardened photoresist layer can be fabricated in an alternating upper structure, the aluminum metal layer includes the address electrode, the Strand (hinge), the yoke (yoke) and the reflector, the hardened photoresist layer as the sacrificial layer ( Sacrificiallayer), used to form two air gaps. Aluminum metal through the sputtering deposition and plasma etching treatment, the sacrificial layer is processed by the ion-plasma-ashed, to create the air gap between the layers.
If from a technical point of view, the structure of DMD chip includes electronic circuit, mechanical and optical three aspects. Part of the electronic circuit is the control circuit, the mechanical part is the structure of the control lens rotation part, the optical part is refers to the lens part. When the DMD normal work, the light through the DMD chip, DMD surface covered with small volume of rotating lenses will be rotated to reflect the light, each lens rotation is controlled by the circuit. Each mirror rotates only one color at a time (for example, a micro mirror that casts purple pixels is only responsible for reflecting red blue light on the projection surface, whereas a micro mirror projecting an orange-red pixel is responsible for proportionally reflecting the red and green lights on the projection plane (the red ratio is high and the green ratio is low), the mirror rotates at a speed of thousands So many mirrors are changing so fast that the light is projected onto the screen after the lens, causing the illusion of the human visual organ, the human eye is wrong to quickly flashing three-color light mixed together, so in the projection of the image to see the mixed color.
If you simply want to understand how DMD works, the last paragraph of the text is enough. If you want to disquisitions, let's come up with a comprehensive and detailed understanding of the structure and working methods of DMD chip.

On the top of the DMD chip is composed of hundreds of thousands of areas of 14x14 micron, smaller than the hair section of the micro-lens, increase the number of micro-lens in DMD, you can improve the product resolution, without changing the size of the micro-lens (such as 1024x resolution 768 of the projector DMD chip has 786,432 small lenses), these mirrors through the following is called "Yoke" device link, and by "torque hinge" control, can flip left and right. Prior to the lens of the flip angle of only 10°, and then Texas Instruments to the lens below the link part of the improvement and simplification, the lens of the flip angle to the 12°. Although it only increased by 2 degrees, the effect of stray light in the imaging process was greatly reduced and the contrast index increased. When the memory cell is in the "on" state, the mirror rotates to +12 degrees, and if the memory cell is in the "OFF" state, the mirror rotates to 12 degrees. As long as the combination of DMD and appropriate light source and projection optical system, the reflector will reflect the incident light into or away from the projection lens of the transparent hole, so that the "0N" state of the mirror looks very bright, "0FF" state of the mirror looks very dark. The gray scale effect can be obtained by using two-bit pulse width modulation, and the color display effect is obtained if the fixed or rotary color filter is used with one or three DMD chips. Equipped with a DMD chip DLP projection system called "single-chip DLP projection system", after the color wheel filtered light, can generate at least 16.7 million colors. DMD input is the electronic character represented by the current, the output is an optical character, this optical modulation or switching technology, also known as two-bit pulse width modulation, it will send 8-bit characters to each of the DMD digital optical switch input, resulting in 28 or 256 gray levels.
At present, the optical effective area of DMD itself is also greatly enhanced, has been able to account for more than 90% of the entire chip surface area, effectively enhance the optical utilization. There is also a need to understand: through the storage unit under each lens is electronically addressed by the binary planar signal, each lens on the DMD array is tilted in an electrostatic manner to open or close the state. The technique for determining how long each lens tilts in which direction is called pulse width modulation (PWM).
The "yoke" and "torsion hinge" under the lens are made with the method called "Surface micromachining (surface micromachining) polycrystalline silicon", which has the characteristics of strong mechanism, flexibility and low cost. The concrete realization step is chooses the aluminum alloy material for the mechanical unit, and uses the traditional light resistance as the sacrificial space. All work is done under 200 ℃, so adding MEMS to the wafer does not affect metallization processes or transistors, nor does it affect the completed CMOS circuitry. This method is the standard basis for MEMS micro-mirrors. At the same time, it solves the problem of the mutual damage between the semiconductor process, the mechanical process and the energy of the optical process. This approach is completely different from other MEMS manufacturing methods, and TI is the only company that is still using this approach.
DMD chip is the main mode of operation is based on the back-end circuit transmitted to the CMOS chip of the different signals, control the rotation of each micro-mirror on the chip, so that the light irradiated on the micro-mirror has a choice of reflective channel in different directions. As a micro-digital optical processing device, DMD is not only the core of DLP projector, but also widely used in printing, can be studied and many other needs of digital optical switch field, has become one of the most successful microelectronics mechanical MEMS products.
darkchip--Many projection industry people are familiar with this word, we can often see some high-end 1080pDLP projector using the DARKCHIP4 chipset, then what is the matter? There are some projectors deliberately nominal products are "data projector" or "video projector", they are using DLP technology, why do they call different?
Using the first generation DMD DLP projector is only for business applications, the resolution is 848x600, can take into account 800x600 SVGA computer Standard and 848x480 480p (16:9) video standard. This generation of DMD micro-mirror deflection angle of 10 degrees, contrast ratio of 400:1 to 800:1. DLP projector after the second generation of DMD chip began to enter the home theater market (before the home theater projector mostly using CRT technology), the second generation of chip lens deflection angle to 12 degrees, the resolution has been raised to 720p.
That is, from the second generation of DMD chip start, DLP projector began to be divided into data projection (commercial) and video projection (home) in accordance with the application of the direction of the development of the route. Texas Instruments also on the DMD chip has been the biggest technological change-the micro-mirror non-optical surface of the metal all processed into black, the move greatly reduced from the metal reflected stray light, unprecedented increase the contrast of DLP projector, this technology is called "Darkchip 1". Of course, darkchip also in the continuous development, September 2007 Texas Instruments released the latest generation of "ultra-Black" technology darkchip 4, can increase the original contrast of up to 30%.

Introduction of DMD chip display principle-2016.5.13