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Going through the mill
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09/02/2006
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Going from digital to analogue and from analogue to digital is unavoidable in most designs. But with the decline in analogue tv sets, one might be tempted to think that, for one sector at least, d/a conversion would be required less frequently. With the move away from analogue in displays being reflected in entirely digital set top boxes, is the d/a converter on the way out of the bill of materials for video applications?
Reconstructing the value of an encoded analogue signal at a given point in time – the job of the perfect d/a converter – is no mean task. It involves applying techniques to ‘fill in’ the blanks between samples – invariably this means producing an imperfect analogue signal and then filtering it.
For a video d/a, the task of ‘filling in’ the blanks might require it to consult conversion tables, which provide a reference for the likes of gamma correction, contrast and brightness. In this case, the d/a might integrate some form of memory to store the conversion tables. But in any case, its construction is typically more complex than that of an a/d converter.
LB Fowler, video applications engineer with Texas Instruments, confirms: “There’s not a lot of ‘smarts’ on the video a/d side. The a/d simply removes information, such as the sync, and packetises it into VT656 (the digital video standard). However, the d/a conversion process is a bit more challenging.”
Mobile applications and high performance consumer devices, such as dvd players and dvd recorders, are driving video d/a evolution. And with mobile applications proving such a driving force, it will be no surprise that the integration trend is alive and well in the d/a conversion world.
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Author
Vanessa Knivett
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