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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.

 

  • redwire

     What Specctra license level is this?

     

  • pcbeng25

    redwire said:

     What Specctra license level is this?

     

     

     

    Not sure what you mean as I don't buy the licenses here, I am just a user.  We don't have a complete Cadence package, just the router as we have our own PCB design tools and just write rules files to use the router.  I can tell you what the "About Allegro PCB Router" window says about it:

     You are running...

    Allegro PCB Router

    and have the following feature licenses checked out ......

    SPECCTRA_256U; SPECCTRA_ADV; SPECCTRA_DFM; SPECCTRA_HP

  • lcanx2
    Try this: “rule class dac_data (phase_tolerance_delay .04)”  Bill

     

  • pcbeng25

    lcanx2 said:
    Try this: “rule class dac_data (phase_tolerance_delay .04)”  Bill

     

     

    No difference in functionality.  It just routes it and the pair is still mismatched by a significant enough amount to matter in our design.  I can always fix it manually, but I really want to figure out why this router isn't breaking the coupling to create a small trombone...

  • lcanx2

    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

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