Sights and sounds in our world are analog, yet when we electronically acquire, store, and communicate these analog phenomena, there are significant advantages in using digital technology. This was first evident with audio as it was transformed from a technology of analog tape and vinyl records to digital audio CDs.
Video is now making the same conversion to digital technology for acquisition, storage, and communication. Witness the development of digital CCD cameras for image acquisition, digital transmission of TV signals (DBS), and video compression techniques for more efficient transmission, higher density storage on a video CD, or for video conference calls. The natural interface to digital video would be a digital display. But until recently, this possibility seemed as remote as developing a digital loudspeaker to interface with digital audio. Now there is a new MEMS-based projection display technology called Digital Light Processing (DLP) that accepts digital video and transmits to the eye a burst of digital light pulses that the eye interprets as a color analog image.
Digital Light Processing technology provides all digital projection displays that offer superior picture quality in terms of resolution, brightness, contrast, and color fidelity. This paper provides an overview of the digital light processing that have been developed by Texas Instruments for the all-digital display.
1.1 INTRODUCTION TO DLP:
Digital Light Processing is a revolutionary new way to project and display information. Based on the Digital Micro mirror Device developed by Texas Instruments, DLP creates the final link to display digital visual information. DLP technology is being provided as subsystems or "engines" to market leaders in the consumer, business, and professional segments of the projection display industry. In the same way the compact disc revolutionized the audio industry, DLP will revolutionize video projection.
DLP has three key advantages over existing projection technologies. The inherent digital nature of DLP enables noise-free, precise image quality with digital gray scale and color reproduction. Its digital nature also positions DLP to be the final link in the digital video infrastructure. DLP is more efficient than competing transmissive liquid crystal display (LCD) technology because it is based on the reflective DMD and does not require polarized light. Finally, close spacing of the micro mirrors causes video images to be projected as seamless pictures with higher perceived resolution. For movie projection, a computer slide presentation, or an interactive, multi-person, worldwide collaboration—DLP is the only choice for digital visual communications, today and in the future.
The world is rapidly moving to an all-digital communications and entertainment infrastructure. DMD and DLP technologies are introduced in the context of that infrastructure.
1.2 INTRODUCTION TO DMD:
Figure 1 The DMD microchip lies at the heart of the DLP system. It consists of an array of digital light Switches that accept electrical words as their inputs and output optical words. Surrounding the DMD are the necessary functionalities to take a digital source and project its undegraded image to a projection screen or hardcopy surface. These functionalities include image processing, memory, Reformatting, timing control, a light source, and projection optics. The input to the DLP system is a digital source (e.g., from a computer or DBS satellite receiver) or it may be NTSC video converted to digital.
The basic building block of DLP technology is the DMD pixel, a reflective digital light switch. It is the equivalent of the electrical switch or gate in memory or microprocessor technologies. Unlike its electrical counterpart, however, the DMD light switch involves not only the electrical domain but also the mechanical and optical domains. Responding to an electrical input signal, the DMD light switch uses electromechanical action to interact with incident light and to switch that light into time-modulated light bundles at its output. This switching scheme is called binary pulse width modulation and is used to produce the sensation of gray scale to the observer's eye.
In the near future, most of the technologies necessary to achieve an all-digital communications and entertainment infrastructure will be available at the right performance and price levels. This will make an all-digital infrastructure chain such as the one shown in Figure 3commercially viable. The All-Digital Infrastructure
The links in this chain include capture, compression, transmission, reception, decompression, hearing, and viewing. But the final link is missing-an all-digital display. Digital images received today must be translated into analog signals for viewing on today's analog televisions. The digital display block shown in Figure 1 accepts a digital signal, but unlike analog displays of today, it outputs to the eye of the viewer an optical signal that is also digital. The viewer Perceives the digital signal as an analog signal, in essence performing the digital-to-analog (D/A) Conversion physiologically. An all-digital display possesses a degree of image stability and noise immunity that is inherently attributable to its digital nature. Consider a digital word that is input electronically to the display. That word is converted into an optical word that is nearly immune to environmental, aging and manufacturing influences. DLP provides the all-digital projection display solution, accepting a digital electrical input and outputting a digital optical image. Figure 2 shows the functional elements of such a system. The Missing Link in the All-Digital Infrastructure
2. DIGITAL MICRO MIRROR DEVICE
The world is rapidly moving to an all-digital communications and entertainment infrastructure.
DMD and DLP technologies are introduced in the context of that infrastructure.
2.1 The Mirror as a Switch
The address circuit and electromechanical superstructure of each pixel support one simple function, the fast and precise rotation of an aluminum micro mirror, 16 μm square, through angles of +10 and p;10 degrees. Figure 4 illustrates the architecture of one pixel, showing the mirror as semitransparent so that the structure underneath can be observed.