High Definition TV (HDTV) represents the new frontier for Liquid Crystal Display (LCD) technology, requiring higher resolution than previous LCD standards, which, in turn, increase data rate and power consumption. As the data rate accelerates, faster moving video requires special image processing algorithms. This article describes how algorithms can be implemented into FPGAs in order to properly convert and map the digital video signal onto the display panel.
Flexibility is the key
FPGAs give LCD designers the flexibility required to reconfigure image-processing algorithms, accommodating the increasing data rate for different LCD sizes while maintaining the same hardware platform for all products. Specifically in the digital consumer market, FPGAs can provide an effective blend of cost, performance, and flexibility for digital televisions and displays. Manufacturers of LCD TVs leverage FPGAs for time-to-market benefits, as the competition to get products into retail outlets quickly is particularly fierce.
An LCD system can be designed around an FPGA in which the FPGA coprocessor, running a real-time embedded operating system, controls the complete display apparatus. Besides the central control of the display, designers can use FPGAs in the data path for specific processing. For instance, FPGAs are ideal for optional display features, where they perform real-time image scaling on the video stream.
The newer generations of FPGAs include optimized hard-coded DSP blocks, which form the basic elements of video and image processing. DSP blocks possess high-speed parallel processing capabilities ideal for implementing DSP applications, such as image processing, that require high data throughput.
The most commonly used DSP functions include Finite Impulse Response (FIR) filters, complex FIR filters, Fast Fourier Transform (FFT), Discrete Cosine Transform (DCT), and correlators. These functions are the building blocks for HDTV and other complex LCD applications.
System designers also benefit from incorporating FPGAs into their LCD systems because they can be reprogrammed throughout the life of the product. This critical ability allows designers to add features from one generation to the next without having to redesign the whole system.
New technologies overcome HDTV obstacles
As HDTV continues to move into the mainstream of commercial television, key industry players have introduced specialized technologies that help incorporate LCD technology into the HDTV application.
National Semiconductor introduced Low Voltage Differential Signaling (LVDS) to reduce the amount of power and Electromagnetic Interference (EMI) associated with the high-speed LCD interface. Flat Panel Display (FPD) is a National Semiconductor-defined LVDS-based link between a host panel and display panel in an LCD HDTV and monitor platform.
Reduced Swing Differential Signaling (RSDS) is also a National Semiconductor-defined signaling standard primarily used for display applications with resolutions between VGAs and Ultra Extended Graphic Arrays UXGAs.
Texas Instruments also introduced a similar interface standard called mini-LVDS with the same objectives of reducing power and EMI. Flat link is a TI-defined LVDS-based link between a host panel and display panel in an LCD HDTV and monitor platform. The requirements for mini-LVDS interfaces are identical to that of RSDS, except that mini-LVDS assumes a center-aligned output clock under the AC timing requirements.
This interface is similar to that of the FPD link and is primarily used by LG, Philips, and Thomson for their LCD HDTV products. With the consumer appetite for larger and larger TV displays, current interface technology may still have its limitations when designers try to design circuit boards and traces in order to meet signal integrity. The latest interface called PPDS by National Semiconductor is aimed at the larger LCD display.
Consider a typical digital LCD TV block diagram. The tuner module can be a satellite, terrestrial, or cable demodulator, followed by an MPEG2 decoder. Besides the signal from the digital TV tuner, a typical LCD TV also provides external video input such as Digital Visual Interface (DVI) or High Definition Multimedia Interface (HDMI), analog RGB, CVBS, S-video, and component video.
The LCD HDTV monitor must be able to handle various video input formats. Some formats may directly be mapped into the display while others must be rescaled for proper viewing.
The heart of the LCD HDTV is its image processing and timing control block. The image processing block typically includes functions such as scan rate conversion, frame rate conversion, color decoding, motion detection, scalar, and de-interlacing.
The color response time of the LCD is slower and depends on the color content, which presents a challenge in designing an image-processing algorithm that can eliminate any viewing artifact. FPGAs offer a critical time-to-market advantage with their design flexibility, allowing designers to redesign the algorithm within the device without having to reprogram it.
Display manufacturers can differentiate from their competitors’ products by adding their own proprietary algorithms for true color and motion performance. There are two methods of proprietary video enhancement used for creating a true video performance from an LCD panel.
The first, a technique called temporal dithering, generates a true gray scale for different colors by rapidly switching the pixels between on and off over a certain time period. The second, spatial dithering, generates the exact amount of color intensity scale. Spatial dithering can cause spatial noise, or error diffusion. Further filtering and fine-tuning are required to correct this type of noise.
FPGA flexibility supports dynamic image processing
LCDs, originally designed for steady computer data text and graphics, now display fast moving video content over much larger display panels. This capability requires special image-processing algorithms that can be implemented with FPGAs. LCD designers using FPGAs can also reconfigure these algorithms based on panel size within a standard hardware platform, which can help reduce manufacturing cost and speed time to market.
Major manufacturers have introduced technologies that help incorporate LCDs into HDTV commercial applications by overcoming power and electromagnetic obstacles. National Semiconductor’s low voltage differential signaling and reduced swing differential signaling, and Texas Instruments’ mini-LVDS, are two such technologies.
By utilizing FPGA flexibility for dynamic image processing and new technologies to help overcome power and EMI obstacles associated with HDTV, designers are well equipped to take LCD even further into leading edge commercial TV and display applications.
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