A new type of portable video projector that can fit in the palm of the hand is rapidly growing in popularity with business professionals. These small devices, commonly called Pico Projectors, use new projection technologies to display still or moving images on any convenient flat surface.
They are a popular alternative to mobile phone, digital camera, and PDA LCD screens, which can be difficult to use with multiple viewers. With a Pico Projector, a business presentation, short video, or just pictures of the family can be shared easily with an audience.
An example of a Pico Projector being used to display pictures of real estate properties to a client is shown in Figure 1.
At the time of this writing, Pico Projectors are still expensive enough to be most popular with businesses. As prices start to fall, however, a host of consumer applications will emerge, and Pico Projectors will become a pervasive display technology for convenient, medium resolution image display. FPGA devices are uniquely capable of enabling the transition from costly business-oriented devices to more cost sensitive consumer products.
Recent forecasts have estimated Pico Projector shipments in 2009 at 500,000, with shipments in 2011 to be over ten times that of 2009. Over 200 companies are currently developing products with improved quality and lower costs.
Figure 1: Example Pico Projector useCurrent Pico Projector technologies
There are several competing technologies currently used in Pico Projector systems. Four of the most popular are Digital Light Projection (DLP), Liquid Crystal on Silicon (LQoS), Laser Beam Steering, and Holographic Laser Projection (HLP).
DLP uses a light source and tiny mirrors that direct the light. Each mirror controls the amount of light for each pixel on the target picture. The mirror has two states, on and off, and it refreshes continually. Brightness is controlled by modulating the mirror state. If it is off 50% of the time, then the pixel appears with the brightness at 50%. Color is achieved by using a color wheel between the light source and the mirrors that splits the light in red/green/blue, and each mirror controls all thee light beams for its pixel.
An LCoS projector employs a method similar to DLP, but uses a liquid-crystal instead of mirrors to control how much light each pixel gets. To achieve color, three different chips are used, one for each color (red/green/blue). The light beam is directed through filters or by using dichroic mirrors (mirrors that only allow certain wavelengths to pass through). The light source can be either an LED or a diffused laser.
An LBS projector creates the image one pixel at a time. It uses three different laser beams (red/green/blue), each at its required brightness. The beams are combined using optics that guide them using a mirror. By scanning the image fast enough (usually at over 60Hz), the eye does not notice the pixel-by-pixel creation of the image.
HLP systems use a laser to illuminate a hologram that diffracts the laser to create the original image. A diffraction pattern of the desired 2D image is calculated and displayed on an LCoS micro-display. When illuminated by a coherent laser light, the desired 2D image is projected, remaining in focus at all distances.Types of Pico Projectors
There are currently three main types of Pico Projectors: Stand Alone, Media Player and Embedded:
- Standalone Projectors: These devices are essentially a traditional projector. They receive the input via a cable (A/V, USB, etc) and cannot display anything unless another device is used to stream the video signal.
- Media Players: These devices are a projector with on-board memory or a memory-card slot, and can play files directly from the memory. The projector must support the file types in the memory- photos, videos or audio files. Some projectors even support office documents, PDFs and other file types.
- Embedded Projectors: These devices add the projector to an existing device (or as an accessory) to provide an alternative (or in addition to) an LCD display. Mobile phones, cameras, laptops, photo frames and PDAs are a few possible applications.
Each of the previously described technologies has advantages and disadvantages when implementing one of the three main types of Pico Projectors. For example, with Media Players, resolution and response time are important. With Embedded Projectors, size and low power are important. Table 1 shows the various advantages and disadvantages of each technology for each type of player.
Table 1: Pico Projector technology comparison tableExample Pico Projector description
During the transition to integrated devices, many Pico Projectors will first be available as accessories for existing devices. An accessory for a digital camera that can show stills, slide shows or videos by plugging directly into the camera is a likely transition device.
A system block diagram for this example design is shown in Figure 2. The Light Engine (the optics and an interface circuit) portion of the system is shown at the top of the diagram and the controller is shown at the bottom. A standard 7:1 LVDS (Camera Link) interface is used to transfer image data from the Controller to the Light Engine (although this is not a standard interface today, as the Light Engine comes down in cost, an interface such as the Camera Link is a probable option so it is used for the Light Engine in our target design).
Figure 2: Example Pico Projector design for a digital camera accessory
The LatticeECP3 FPGA, shown in detail in Figure 3 below, combines the algorithmic processing to process the image pixels for display while managing the various interfaces in the system. A LatticeMico8 microcontroller controls the data flow and various commands from the user interface. It communicates with the rest of the FPGA functions via a Wishbone system bus.
The DDR2 Memory Controller provides the interface to the external DDR2 memory and has two ports- one from the Wishbone bus (for general purpose system control functions and when image data is received over the DVI/HDMI interface), and one from the JPEG Decoder and Pixel Processor (for high priority image processing functions).
The SPI Memory Controller interfaces to the non-volatile memory, where many of the image processing tables and code are stored. Image data, encoded using the JPEG format, comes from the camera over the DVI/HDMI Interface and is stored in the DDR2 memory.
The JPEG Decoder converts JPEG Encoded image data into the separate red, green and blue pixel data needed by the projection optics. This pixel data can also be operated on by the Pixel Processor and other custom algorithms to improve image quality. Once the pixels are ready to send to the optics, the 7:1 LVDS Video Interface packetizes the pixel data and transfers it to the optics interface using a standard video protocol.
The USB Interface connects to the external USB 2.0/3.0 Phy. The General Purpose IO block controls the external functions responsible for power management, user interface (buttons and switches) and configuration control. Many of these key function blocks are readily available as IP Cores from FPGA manufacturers or their partners, and free the designer to focus on the value- added portion of the design.
Figure 3: Example Pico Projector FPGA controller block diagramLeveraging FPGA capabilities
An FPGA brings several key capabilities to the design that will help expand the market for these small projectors. Given the high growth rate of the market there will be unexpected shifts and changes in the features that users will demand. Competitive pressures will also grow along with the market, and companies that can respond to market and technology shifts should be able to grow at a faster rate. FPGAs provide a key advantage in these markets because of the ease with which feature changes can be implemented, even after devices have been purchased by customers. Downloadable updates can improve existing features, respond to competitive introductions and quickly adapt to changing interface requirements. Additionally, image processing algorithms can evolve, based on customer feedback or new research, and be distributed quickly to units already in customers’ hands.
One example where the ability to make changes to the image processing algorithms could be utilized is in the de-speckle algorithms used in laser-based systems. Laser speckle makes the image “sparkle” when coherent light is scattered from a rough projection surface and then subjected to interference at the retina. The ability to reduce speckle is important because users find the artifact a distraction, it impacts the perceived image quality and reduces the effective resolution. The various algorithms used to combat speckle can involve controlled variations in the laser modulation frequencies (to vary the coherent nature of the light), modifying the intensity of the pixel brightness from image to image or applying algorithms similar to anti-aliasing used in traditional displays. As research into new methods is likely to spawn new breakthroughs in these algorithms, a design that can adapt to a wide variety of possible changes, like those based on an FPGA, will enjoy a competitive advantage.
Modern FPGAs like the LatticeECP3 provide several advanced hardware capabilities useful for Pico Projector designs. Digital Signal Processing (DSP) functions can be used to implement complex image processing algorithms like color space conversion and JPEG Encode/Decode, as well as more general purpose DSP algorithms like FFTs and Filters. Dedicated on-chip block memory can be used as image buffers, FIFO buffers and data or code storage for embedded processors. High speed SERDES blocks can be used to implement popular serial video interfaces like DVI, HDMI, DisplayPort and the 7:1 LVDS-based standards like CameraLink or ChannelLink, as well as computer interfaces like PCI-Express, Serial Rapid I/O, and Ethernet (GbE, XAUI, and SGMII).
Perhaps the most compelling FPGA advantage for high-growth markets is faster time to market. FPGAs have a significant development and deployment cycle time edge over ASIC implementations in fast growing markets, where weeks of development time instead of months can make the difference between product success and failure. ASICs may still be a viable design choice for established, high volume markets where technology migrates in a predictable timeframe, but quickly growing and fast evolving markets are the sweet spot for today’s FPGAs.
FPGA manufacturers have been investing more in market segment targeted development kits, where FPGAs and peripheral devices are combined with segment-specific IP Cores to give the designer a starting point for creating differentiated content. In many cases, all the external components and interfaces required by the application are available on the board and have drivers and operating systems available for rapid deployment. These kits further enhance the FPGA’s time to market advantage over ASIC-based designs.About the author
Niladri Roy is Senior Manager, Product Marketing at Lattice Semiconductor, where he is responsible for product marketing in the Cameras and Displays markets.
Mr. Roy holds a bachelor's degree in electrical engineering from the Bengal Engineering & Science University, India.