The integrated video filter was very expensive when it first came out. It was an extremely high-performance component mainly for video broadcasting applications. Later, it gradually developed into a cost-sensitive consumer electronics solution such as set-top boxes. The first mainstream integrated video filter came out in the early 1990s and was first used in direct broadcast satellite set-top boxes and cable set-top boxes. So, what is the role of the video filter? First, it can be used as a reconstruction filter after the digital-to-analog converter on the output of the video processor; second, it is used as the input of the video processor in set-top boxes and DVD devices. Anti-aliasing filter (anTI-aliasing filter).
In the past, the selection of video filters was very easy, just consider the number of outputs: the general composite video (CVBS) uses one filter, the S-video uses two filters, and the DVD player uses a three-component video output scheme, marked separately For Y, Pb and Pr, these have become the standard configuration on the back of the video device. In this way, the total number of analog outputs that users and designers of video equipment must consider up to 6 (ie CVBS, S-video (Y, C), component video (Y, Pb, Pr)).
However, with the emergence of higher-definition video and acceptance by consumers due to the continuous cost reduction, the situation has begun to change. 480, 720, and 1080 (and other non-US standard videos) the letters "i" or "p" begin to appear after these numbers. This strange number / letter combination has also become one of the increasing terms in the video field. So what do they mean? Number / letter combinations such as 480i, 1080p refer to the number of display lines of video scanning, and whether to use interlaced scanning (i) or progressive scanning display (p). Interlacing means that each line is scanned alternately and displayed, and progressively means that each line is scanned sequentially and displayed sequentially.
Interlaced scanning is a technology inherited from the old CRT screen design. Its purpose is to make the phosphor layer on the glass panel glow, let the top fade out, and replace the bottom, so that the phosphor layer will not be before the image is completed. Blanking. The phosphor must emit light for a long time so that it does not affect the next image. Progressively, pixels sequentially emit light. This scanning method has higher spatial resolution and better visual effects. Obviously, this is too complicated for consumers who just want to watch videos and do not intend to become video engineering experts. Therefore, in order to facilitate understanding and at the same time facilitate sales, it is necessary to create a short and easy-to-understand terminology. Therefore, under the term "sharpness", a variety of number / letter combination categories are formed, which are mainly used to describe the detailed performance of the image: the higher the definition, the better the image quality, because more lines mean more More pixels make the color and detail level of the image more vivid and realistic.
Regarding the naming of signals and the classification of definition categories, they can be written into a thick monograph, and may become a hot topic for video engineers for a long time. In view of the discussion of the actual video filter purpose, here is roughly divided as follows: 480p is the standard definition (SD), 480p is the enhanced definition (ED), 720p and 1080i are high definition (HD). For convenience, only American standards are discussed here. In addition, when using the term high-definition (HD), many video equipment suppliers began to loosen up. In order to be more precise, various video industry associations have proposed terms such as HD ready, HD ready 1080p, and Full HD, but the success and failure of this move may even cause more confusion. For this reason, the video filter manufacturer decided to use the terms SD, ED, HD, and 1080p HD to classify the filter according to the filter's cutoff frequency (passband for low-pass filters): the SD filter cutoff frequency is at Around 8MHz, ED is around 20MHz, HD is around 30MHz, and the 1080p cut-off frequency is between 65 and 70MHz. Using cut-off frequency to classify is very straightforward.
So, what is the relationship between all these video definitions and the selection of video filters? Understanding these new definition standards actually reveals that the selection of video filters must consider two factors: designers must consider both the number of channels Clarity. In addition, there are two ways to implement integrated circuit filtering: one is to use a combination of filter ICs, and the other is to use a single filter IC that can handle all different channels and resolutions. How should designers choose? One of the methods is to find a variety of filters that can meet various requirements. For example, Fairchild Semiconductor can provide a wide range of filter combinations to meet different requirements.
When you start to choose, you can refer to the example in this article. Figure 1 shows Fairchild's filters suitable for different channel / resolution combinations. In the figure, one axis represents the number of channels, and the other axis represents the type of sharpness, which can help designers more easily select the appropriate filter. Filter selection is just the beginning, and there are other issues to deal with next. But this is a good start.
As long as the number of channels and clarity are determined, designers should begin to consider other key factors in product selection, such as ESD protection, standby power requirements, voltage rail requirements, and package types, especially in the rapidly growing trend of mobile video applications. Device size is also critical.
As for ESD, set-top box manufacturers have standardized BAV99 protection diodes for discrete filtering. But on the other hand, the integrated video filter can not only save a lot of discrete filtering components, but also reduce the number of diodes used. For specific products, integrated filters can provide ESD protection up to 12KV. ESD protection is indeed a notable problem. In order to avoid damage to expensive TV core processing chips, designers should not bring unprotected video output products to the market.
There is also a growing concern about reducing standby power consumption. Standby power consumption is sometimes referred to as "vampire power" and it has become a major environmental issue. For example, California, USA recently promulgated regulations on reducing the standby power consumption of LCD TVs, which require that such products must comply with the "Energy Star" standard. Fairchild Semiconductor will provide filters with relevant off-modes to better meet ENERGY STAR requirements.
WLCSP and MicroPak MLP and other mobile product packages are now also used in video filters. For mobile applications, size is critical, so these small packages are particularly useful. In fact, their size is small enough to easily pass through the small mesh on the salt shaker lid.
For video filters, designers should adhere to the principle of careful design. For example, you should ensure that the wiring is as short as possible and close to the actual output port to reduce circuit board parasitics. This concept is explained in more detail in Fairchild's "Application Note AV-6041: PCB Layout Considerations for Video Filters / Drivers".
As long as you know which products are available and which are important considerations, choosing the right filter has become quite easy. Fairchild Semiconductor is always happy to provide engineers with all the assistance they need. After all, helping customers succeed means the success of video filter suppliers themselves, and video engineers also like to discuss the topic of video. As you plan your next design, Fairchild Semiconductor will gladly provide you with timely and detailed support.
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