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Valued Contributor III
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Using a CARRY_SUM primitive for a TDC

Hi, 

 

I've been trying for a few days now to use the CARRY_SUM primitive to implement a delay line TDC. I am designing a circuit that looks something like this: 

 

input -> CARRY_SUM -> DFF 

 

However, during MAP the carry buffers are all ignored. I think the logic is okay, because if I replace the CARRY_SUM with the LCELL primitive, I get the circuit I wanted. So I'm a little confused about the CARRY_SUM being ignored. I searched through the forums, and quite a few people ran into the same problem, but there wasn't a solution. Any ideas? 

 

Billy
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Beginner
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​Sorry for the significant delay but I am trying to develop a delayline for a TDC. Once I have the delay steps I am happy to work with it. It seems that, no matter what I do I end up with even LAB steps (~500ps) of misaligned delays. Can you point me to some simple code for creating the delay taps required. DNL is not an issue so the simplest code will suffice. Thanks in advance.

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