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LMH1297: Allegro: How to set the differential pair gap in "Constraint Manager"?

Part Number: LMH1297

Hi team

I have encountered a strange question when setting the differential pair parameter in Allegro:

I need to modify an existing PCB design that is based on LMH1297 and the first three differential lines in the table are the existing differential pairs, their distance parameters were set to four numbers separated by colons like "8.500:11.700:11.700:8.500" in "Prim.Gap"?

However, when I enter or copy the same four numbers for the two added new differential pairs setting, it informs me of an error shown below.

Due to the impedance match, I need to keep the distance parameters of newly added differential pairs to be the same with the existing three old differential pairs.

Hence my question is that what is the meaning of four numbers in the chart like "8.5:11.7:11.7:8.5" in "Prim.Gap"? and How to set these four numbers as the setting value instead of a single number? 

I really need your help. Thank you.

Shawn Wang

  • Hi Shawn,

    I am not familiar with pcb layout tool good enough to comment on this. Please consult with the pcb layout tool vendor if possible. Perhaps there could be other E2E member which may be more familiar and will respond to this case.

    Regards,, Nasser