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EETE FEB 2014

MOEMS & MEMS How to design an efficient MEMS-based pico-projector By Carlos Lopez Over the last few years, millions of products incorporating pico projection have shipped, and developers are innovating new applications for this rapidly growing display category. Applications for pico projection include near eye display, interactive digital signage, head mounted display, ultra short throw TV, standalone portable projectors and embedded projection in smartphones, tablets and laptops as illustrated in figure 1. New uses continue to emerge; for example, imagine a thermostat using an on-demand display with interactive touch. After a developer formulates a great idea on how to use pico technology in their application, they are faced with several factors to be considered. As noted in the block diagram of figure 2, these include selection of the display technology, light source, optics and software. A well-chosen selection of these variables can result in an end product with optimal power and light efficiency capable of delivering bright, high quality images. So what are the considerations for designing a pico projector that will maximize power efficiency and yet deliver large, bright and crisp images? We will next address each one of these variables. Imaging technology Designers are faced with imaging technology options. Selecting the imaging device that most efficiently utilizes light is most important. There are two different optical path architectures in the market place: transmissive and reflective. Most pico Fig. 1: A smartphone embedding a DLP Pico MEMS projector. projectors use Texas Instruments’ DLP Pico technology, which is reflective. It utilizes an array of microscopic mirrors to create the image which utilizes reflection to maximize light efficiency – see figure 3. In contrast, other technologies employ transmissive or a hybrid of transmissive and reflective systems, requiring polarization of light to control the intensity of each pixel – both of which incur significance light loss thus reducing optical efficiency. Another consideration for the selection of the display technology Fig. 2: A typical DLP display. is the ability to tilt the micromirrors. DLP technology uses a microelectromechanical system (MEMS) superstructure to tilt the micromirrors toward or away from the optical path to create each display pixel see figure 4. Tilting mirrors allows the device to more efficiently capture light without worrying about polarization, resulting in higher brightness at lower system power. Switching speed is another consideration for the selection of the display technology. For this case, the developer should consider a technology that can switch as fast as possible as this will allow the design to quickly control the light path and colour sources for the system. The faster switching speed not only provides better colours but also better image quality as there is less motion blur, resulting in a better viewing experience. As a reference, DLP Pico devices can switch each pixel / micromirror at up to 3000 times per second – making it the fastest solution available. Carlos Lopez is the Strategic Marketing Manager for Pico Products at Texas Instruments – www.ti.com - www.dlp.com Fig. 3: Typical DLP pico display system. www.electronics-eetimes.com Electronic Engineering Times Europe February 2014 25


EETE FEB 2014
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