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 How to make a bunch of diff pairs the same length??? Help! 

Last post Sat, Jun 15 2013 3:58 AM by pitbull107. 14 replies.
Started by pitbull107 13 Jun 2013 05:50 AM. Topic has 14 replies and 1463 views
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  • Thu, Jun 13 2013 5:50 AM

    • pitbull107
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    How to make a bunch of diff pairs the same length??? Help! Reply

     I have a design that has several diff pairs. I have been asked to make them the same length within .005"  (5 mil). I can't figure out how to use the constraint manager to do this.  When using the propogation delay, it says it doesn't apply to diff pairs.....  ?

     

    I am using Allegro 16.0  XL

    • Post Points: 5
  • Thu, Jun 13 2013 8:00 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     OK, looks like I found what I needed EXCEPT........how do I undock the "heads up" display?

    • Post Points: 20
  • Fri, Jun 14 2013 2:04 AM

    • oldmouldy
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply
    There is a User Preference, allegro_dynam_timing_fixedpos which is normally on, for 16.6 it is in Route / Connect section of the preferences, possibly "route" section for 16.0. Behaviour with the "not fixed" setting can be a bit dependent upon graphics card and drivers.
    • Post Points: 20
  • Fri, Jun 14 2013 3:47 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     I found that setting under "ETCH". However, it still won't fly out or display a docked heads up display........anything else I can try?

    Also, once I enabled the above, I no longer get any tuning (like trombone, etc) even though I have all those settings setup.

    When I did'nt have those heads up settings on at all, I could get the tromboning to work, but no way to see how the tuning is progressing.

    • Post Points: 5
  • Fri, Jun 14 2013 4:56 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     Just tried 16,5 XL legacy with this same brd. No flyout, no docked heads up display.I checked the user pref and it is set to be "ON".. I don't get it. Is it the type of Allegro editor affect this?  I.E.  XL vs SI, etc???

    • Post Points: 20
  • Fri, Jun 14 2013 6:38 AM

    • steve
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

    Yes but with an XL license you have enought tools. What Constraint Manager rules are set. Heads up display will only display for Total Etch Length, Static Phase and Rel Prop Delays...

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  • Fri, Jun 14 2013 7:00 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     I don't have them set.  I just set 5mil/7mil/5mil diff pair.   How/what do I set for total length? They (the diff pairs) are not a straight across routing. Some are jogged around connector pins.

    Do I have to query each pair and set for the longest wire?

    • Post Points: 20
  • Fri, Jun 14 2013 7:07 AM

    • steve
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

    Best is to set the diff pairs up correctly. Take a look at:- http://www.parallel-systems.co.uk/images/PDF/diffpairs_definition.pdf

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  • Fri, Jun 14 2013 7:21 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     Thanks for the info! BTW, there is no BGA in my design, only paired through hole connectors where video signals go between pin pairs (same pin numbers on both connectors). One connector on top and the paired one on the bottom mirrored.

    So I guess that only defining trace width and spacing for each diff pair in constraint manager is not sufficient?  (No, I have not done this type of wiring before, still learning...I am not a EE)

    So, basically, I just need to make sure each diff pair (separately) have their trace lengths macth within 5 mil.  Do I still need to do all the other setup in Constraint Manager for this?

     

    • Post Points: 20
  • Fri, Jun 14 2013 7:39 AM

    • mcatramb91
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

    Make sure you have your DRC modes ON for Propagation Delay, Relative Propagation Delay and All Differential Pair Checks.  Go to Setup > Constraints > Modes and under the Electrical Modes category to turn them On or Off.  If they are Off then it will not be DRC checked and the Dynamic Timing feedback window will not be displayed.

    It is starting to sound like you are looking to match the members of the diff pair to each other by 5mils (Phase Tolerance).  If that is the case you need to define the Phase Tolerance as 5mils to control the matching between the members of the pair.  You can do it thru Constraint Manager or attach the DIFFP_PHASE_TOL property to the diff pair nets with a value of 5 mils.

    If you need to have all the Diff Pairs match to each other you will need to use Relative Propagation Delay and add all them to a Match Group with a Tolerance. (but it sounds like you are looking for jus a Phase Tolerance).

    Hope this helps,
    Mike Catrambone

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  • Fri, Jun 14 2013 7:46 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     Yes, only to each pair, not to all pairs together.  Now, another stupid question: I have already routed the diff pairs. Can I now (after setting the constraint phase tolerance), just use the "delay tune" to adjust the diff pairs? Or do I have to delete the diff pairs and start again?

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  • Fri, Jun 14 2013 8:20 AM

    • mcatramb91
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

    No stupid questions, no need to delete/reroute - you can just use Delay Tune to adjust the Diff Pairs, just remember to check "Single trace mode" from the Right mouse button so you delay just one diff pair member.

    Mike

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  • Fri, Jun 14 2013 9:13 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     Just as a test, I set the phase tol to 5 mil on one set of diff pairs. Then I tried to tune using single trace mode, and nothing happens. If I turn off single trace mode, then I get tuning and the flyout window is bordered in red.

    I can email the brd file. So what am I doing wrong?  BTW 16.0 XL

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  • Fri, Jun 14 2013 12:37 PM

    • mcatramb91
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

    The only thing that I could think of is that the diff pair is either routed on another layer or has a dangling trace (stub) hanging of the trace somewhere.  I have seen the tool go crazy in those situations when dealing with Diff Pairs so I figured I would mention it.

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  • Sat, Jun 15 2013 3:58 AM

    • pitbull107
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    Re: How to make a bunch of diff pairs the same length??? Help! Reply

     Tried everything and I am staring to think what I am trying to do just will not work.

    A diff pair set to 5/7/5 (5mil wire width with 7mil spacing)

    One of the traces is 1008.42 mil long....the other is 1040.06

    I set the DIFFP_PHASE_TOL to 5mils  ( I think this means that both etch lengths have to be within 5 mils of each other, correct?)

    When I try to tune using the DELAY TUNE (in single trace mode), the accordian gives a drc as soon as I try to increase it's length or amplitude. In dual trace mode, no drcs, but no adjustment to make both traces "equal in length" within 5mil.

    So.....is it possible to tune this diff pair at 5 mil DIFFP_PHASE_TOL *and* containing a defined diff pair GAP of 5mil????

    If not, then what would be a reasonable tolerence of the lengths?

    • Post Points: 5
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Started by pitbull107 at 13 Jun 2013 05:50 AM. Topic has 14 replies.