It wasn't long ago when "Pong" was the most popular electronic household game. At that time, moving two white vertical lines while hitting a square back-and-forth on a black screen kept consumers staring at their TVs for hours. Since then, today's households are home to electronic games that have video graphics that rival blockbuster movies. These high-tech video games have mobile versions that are just as capable of providing high-quality video performance in the palm of your hand. Today, high-performance semiconductor components provide enabling technology that allows system designers to bring mobility back to the big screen. Aside from the highly integrated SoCs, there are many "accessory" components that provide the means to switch, drive and display the audio and video seen (and heard) on the most cutting-edge electronic videogaming units. This article will examine how integrated video filter drivers enable portable electronic games to achieve high-definition quality video performance, integrate the capability of driving larger displays, and yet maintain their popular, compact size. PORTABLE DEVICE MARKETCOMES INTO PLAY Handheld gaming devices are an emerging market for integratedvideo filter driver accessory ICs. An integrated video filter driver provides reconstruction filtering that eliminates undesired noise on a video signal. The filtering capability is coupled with an output driver that is capable of driving video off the portable gaming device, ultimately allowing the consumer to view the game on a larger monitor and share the gaming experience with others. Many integrated video filter drivers on the market provide much-needed electrostatic discharge (ESD) protection, helping to protect the handheld from electrical stress that may be introduced via the external cable. More and more consumers now want the capability of watching movies on their gaming units. Tiny, low power integrated video filters enable portable units to display standard definition (SD) or high definition (HD) video on larger monitors. As the quality level of the video increases, the effect of noise becomes more visible. This increases the need for video filtering. When consumers connect their handheld gaming device to a larger display, they want to view a crisp, clean video signal. The SOC drives the unit's display, but it does not have the capability to filter and drive video off the handheld device. The SOC handles the digital processing of the video signal, and it also converts this signal back into the analog domain with a DAC; this process is called reconstruction. The analog video signal can then be used to drive an external display. High frequency artifacts are introduced during the reconstruction process, which distorts picture quality. A reconstruction filter removes these artifacts through low pass filtering. The filter's reconstruction performance is based on how well the artifacts are removed without distorting the video signal within the passband. Noise from the digital-to-analog conversion process causes many adverse affects on a video signal, such as Moiré, herring bone patterns and flashing streaks. All of this can be categorized as "fuzzy" or "noisy" video. DEFEATING UNWANTED VIDEO SIGNALS An output reconstruction (or image rejection) filter removes the clock and sideband components that are present after the sampling and analog reconstruction process (Figure 1). The video signal is between zero and 5MHz; the Nyquist limit is at ½ the clock frequency; and the lower/upper sidebands or images are centered around the clock frequency. As the figure illustrates, the reconstruction filter removes much of the unwanted signal while passing thedesired video signal. Today's consumers are also continuously looking for more compact units with more mobile play time, making the main requirements for video filter drivers size and power consumption. Fairchild's FMS6151 meets these requirements with its 1.45mm× 1mm × 0.55mm package andcombination of the reconstructionfilter function with a fixed gainof 6dB video drive capability and6kV of ESD protection. For consumers who want to display HD quality video on a larger television, a high-definition filter is required. A high-definition YPbPr video signal uses three channels. As shown in (Figure 2). The video signal is , a typical third-order discrete LC filter requires four components: 12 components for three channels. Additional components are required to add drive or gain capability, bringing the component count to above 25. In addition to the space consumed by this discrete approach to filtering, the wide tolerances of passive components cause frequency variations in the filter response. For consistent video performance, filter frequency adjustment or tweaking is required when using discrete components. This timeconsuming task is eliminated when using an integrated device. The integration into one silicon chip lowers part count, decreases board space and improves filter reliability. Integrated video filter drivers offer ±10 percent variation in frequency response - a sharp contrast to the standard ±20 percent tolerance on discrete capacitor and inductor components. If left unscreened, the discrete LC filter can have frequency variations of over ±20 percent. LC filter performance varies over time, whereas an integrated filter offers a consistent filter frequency that does not change over time. About the author DebbieBrandenburgisMarketingEngineer, Signal Conditioning Products, for Fairchild Semiconductor. Before joining Fairchild, Debbie was Marketing/Applications Engineer at KOTA Microcircuits. She has also been an Applications Engineer at both National Semiconductor and Comlinear Corp. Debbie has a BSEE from Colorado State University. For more information, contact Fairchild Semiconductor, 82 Running Hill Rd., Portland, ME 04106;(800) 341-0392; www.fairchildsemi.com. |
