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Fig. 4: DLP MEMs mirror array. Light sources When considering light sources, there are three primary options: lamps, LEDs and lasers. Lamps are commonly used in conference room and home theater projectors, where high lumens levels (1000L to 2000L) are required. For pico projectors, the most common light sources used are LEDs, specifically individual red, green and blue LEDs. The benefit of LEDs is that they provide the best tradeoff between cost, size, brightness (lumens per watt) and reliability. Laser illumination has the benefit of high flux density (lumens) from a small volume, and highly saturated colors. Laser illumination is an attractive option for pico projector applications requiring 100s of lumens and where the cost of lasers can be accommodated. Optical engines Creating an Optical Engine design involves making numerous trade-offs, each of which has an effect on size, cost, and optical efficiency. DLP has developed a mature network of Original Equipment Manufacturers (OEMs) that can supply fully tested, off-the-shelf (OTS) designs. Using an OTS design is the fastest way to get to market. If there isn’t an OTS design that meets a developer’s needs, DLPs OEMs are fully capable of creating semi-custom or custom designs such as shown in figure 5. Typical DLP optical engine For most pico projectors, achieving efficiencies for battery operation is critical. An important part of managing power is by utilizing algorithms to analyze the image on a frame-by-frame basis. By doing so, the intensity of each LED can be optimized for each frame. For example, a blue sky will not need much red MOEMS & MEMS Fig. 6: Effects of the content-adaptive illumination control algorithm. and green, while a red sunset won’t need much blue and green. This can provide a savings in power consumption of up to 50% without compromising image quality or brightness - and in many cases actually improving both. TI’s DLP IntelliBright suite of algorithms can be tuned by the device manufacturer to intelligently provide the optimal brightness, power consumption and contrast according to the specific usage of the device. The first algorithm in the suite is called Content-Adaptive Illumination Control (CAIC). This algorithm operates by adjusting red, green and blue illumination strength on a frame-by-frame basis. The algorithm can be configured to maintain “constant image brightness” (which results in lower power consumption) or to maintain “constant illumination power” (which results in higher image brightness). This enables developers to select their desired amount of brightness boost versus power savings. The second algorithm is Local Area Brightness Boost (LABB) which identifies ‘dark areas’ and ‘light areas’ within a frame. The gain is then adjusted for the darker parts of the image to give a more balanced realistic picture. Furthermore, adding an ambient light sensor to a pico-projector enables the algorithms to adjust the image brightness to suit varying ambient light conditions. This further maximizes the battery life and optimizes the viewing experience. Through careful selection of image technology, light source, optics and software implementation, developers can create innovative world-class applications incorporating pico projection. Fig. 5: A compact off-the-shelf DLP optical engine. Fig. 7: Effects of the local area brightness boost algorithm. 26 Electronic Engineering Times Europe February 2014 www.electronics-eetimes.com


EETE FEB 2014
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