In this TI DLP Labs training module, we will cover some of the common optical terms found in DLP Digital Micromirror Device, or DMD, datasheets. DLP DMDs are qualified over a specific wavelength range. Standard display DMDs assume a white light spectrum where the light is between 420 and 700 nanometers. Operating the DMD outside this range can lead to a reduced lifetime. DLP also has specific DMDs that use illumination sources in the Ultraviolet, or UV, and Near-Infrared, or NIR, range.

It is important to note that different light sources have unique thermal loads for a given lumens value. Lamps, LEDs, and laser phosphor sources provide a heat load of approximately 310 lumens per watt. With the increased usage of RGB direct lasers, the laser spectrum is 230 lumens per watt, which increases the thermal load on the DMD. For specific information on this topic, watch the Thermal Management of DMDs DLP Labs module linked immediately below this video.

The diagram above shows illumination of a 12-degree tilt as well as a 17-degree tilt device. Marginal ray is defined as the widest angle from normal of the illumination design. For a standard telecentric design, the following applies. Using our 17-degree tilt device, the marginal ray is the sum of 34-degree illumination angle plus the 17-degree half-angle cone of an F/1.7 design. The specifications for this device defines the max allowable as 55 degrees. Keeping the light bundle less than 55 degrees will prevent shadowing due to the window aperture.

Non-telecentric designs illuminate the device at angles higher than 2x the tilt angle. It is recommended to model the DMD and window apertures to ensure that light rays incident on the active array clear the window aperture on the incoming light side.

The DMD mirror array is composed of active addressable mirrors that rotate from on state to off state. For the sample DLP4710 DMD shown, the tilt angle is plus or minus 17 degrees. There is a border of non-addressable mirrors surrounding the active array called the Pond Of Mirrors, or POM. They are landed in the off state to provide a black transition border to the active array.

DMD pixel designs offer three different illumination directions depending on the device-- bottom, side, and corner. The 5.4-micron pitch devices have a 17-degree tilt angle. The illumination options are designed for optimum efficiency while providing the smallest optical volume possible.

Total transmission through the windows is calculated by the square of 97% transmittance or 94% transmission. The coding transmission will roll off outside the visible range. Our UV and NIR devices have window transmissions optimized for those applications.

There are many options for an optical design. It is recommended to start with a telecentric projection design and set the illumination and projection F number to match the F number as defined by the tilt angle of the device. For example, a 17-degree device will have an F number of F/1.7 and an illumination angle of 34 degrees. These choices should eliminate flat-state light artifacts and provide a pupil-matched system design.

Controlling illumination overfill is important for increasing the optical efficiency, reducing thermal loads, and eliminating window-induced optical artifacts. Full system design examples are available on TI.com and in the link below this video.

This presentation has covered the optical terminology and guidelines contained in the DMD datasheet. This included illumination, DMD mirror function, and window characteristics. Following these guidelines, combined with good optical design practices, should result in an optical system with excellent image quality. Full system design examples are available on TI.com to get you started on a successful DLP projection system. Be sure to visit TI.com/DLP for more information. Thanks for watching.