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Old 11th Jul 2004, 6:47 pm   #7
ppppenguin
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Join Date: Dec 2003
Location: North London, UK.
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Default Re: New Multi-Standards Converter

Fortunately the SAA7113 decoder that Darryl uses at the input of his converter will accept almost any modern standard and deal with it well. It will lock to poor quality VCR output without problems. Since Darryl is using a framestore there should be no timebase errors at the output.

My view, which may be different from Darryl's, is that the output clock should be free running, unrelated to the input clock. This is true on the Domino converter and also on my own experimental design. (My design is never going into production, it's purely for my own amusement, using a spare card left over from a design for one of my clients. It could probably do 819 fairly easily though I have no real intention to do that.) The separate output clock ensures that the output timebase is completely stable regardless of input.

A further thought on decoder chips. I have used many of the Philips devices over the years. The SAA7113 is a decent design but does not have a luminance comb filter. I use the SAA7118 (which does have a comb) but I can't say I actually like it very much. And it's a ball grid package. For ultimate quality on composite inputs the comb may be worthwhile. I am looking at the latest parts from Analogue devices (ADV7181, 7183A and 7189). The last of these is expensive and not needed in most applications. I will most likely use the ADV7183A (note that this is very different from the earlier ADV7183) and hope to borrow an evaluation kit from the local AD distributor.

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