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Differential Pair Phase Tolerance matching error

pcbeng25

I cannot seem to get my differential pairs to phase match, and the router is not creating tiny tuning trombones on half of the pair to match the pair either.  Is there a constraint that needs to be set for the router to allow tuning trombones to be created for pair phase matching?  I define the pair as follows:

  define (pair (nets %R3008<1> %R3009<1>))

define (class dac_data (add_net %R30*<1>))
rule class dac_data (phase_tolerance_length 0.04)
rule class dac_data (limit_way 20)
circuit class dac_data (priority 200)
circuit class dac_data (use_layer L2)
 

All I get is a phase mismatch error, but the router does not add a small trombone or meander even when I have a PCB rule set to allow trombone and meanders.  Anyone have an idea what would cause the router to NOT fix the pair?

I am using Allegro PCB Router v16.3.

Thanks in advance.

 

  • pcbeng25

    lcanx2 said:

    Perhaps it is the value you have assigned to phase_tolerance_length which I believe should be specified in length units.   I use (phase_tolerance_length 5) for 5 mils.  .04 may be small enough a number so that the router treats it as a goal that cannot be achieved. 

    Wishing you success. 

    Bill

     

    Well I have the units set to inch, so .04 is actually 40 mils.  I can't tolerate anything larger than that.  I have a couple of pairs that after routing are 0.1" different, which is 100 mils. I don't think it is a units thing...but I am quickly running out of ideas.  I'm wondering if one of the other rules in the file is conflicting with this and causing the router to think that 0.1 is fine.  This is the only thing left to figure out on this particular PCB, then I can finish up the artwork and get this thing built...

     The devil is in the details here somewhere...just have to find where.

     Thanks for the help, and if you think of any other ideas, I'm all ears.

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