Home > Community > Forums > PCB Design > Cross section tool and impedance calculations

Email

* Required Fields

Recipients email * (separate multiple addresses with commas)

Your name *

Your email *

Message *

Contact Us

* Required Fields
First Name *

Last Name *

Email *

Company / Institution *

Comments: *

 Cross section tool and impedance calculations 

Last post Tue, Dec 25 2012 10:41 AM by redwire. 18 replies.
Started by TH Designs 05 Dec 2012 06:10 AM. Topic has 18 replies and 2962 views
Page 1 of 2 (19 items) 1 2 Next >
Sort Posts:
  • Wed, Dec 5 2012 6:10 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Cross section tool and impedance calculations Reply

    I ran into something the other day and have been working with tech support on, but thought I might get some answers here.

    Four layer board, two inner layers set to planes (and shield) FR4 material.

    In the Setup - cross section tool, when I try to calculate the trace width based on a given impedance and stack up, the impedance is always 60 ohms. For example, I open the cross section tool and select Show Single Impedance.  The default impedance shows as 60 ohms. If I try to change it to 50 ohms by manually editing the cell, it resets to 60 as soon as I click out of the cell.

    If I try to change it by using the drop down boxes at the bottom of the window; Layer Type - Conductor; Material 1oz cu; Field set to - Impedance; Value Set to - 50; then select "Update Fields", nothing happens.

    We tried multiple things yesterday. I even sent the board file to tech support and it works just fine for them (figures.....)

    I tried it on a different computer at my home office and the impedance is displayed in exponential format, not in ohms.

    A couple of screen shots:


    • Post Points: 5
  • Wed, Dec 5 2012 6:21 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    Second picture


    • Post Points: 35
  • Wed, Dec 5 2012 6:33 AM

    • oldmouldy
    • Top 10 Contributor
    • Joined on Tue, Jul 15 2008
    • Woking, Surrey
    • Posts 1,408
    • Points 24,030
    Re: Cross section tool and impedance calculations Reply
    Which exact version are you running Help>About in PCB Editor? I don't think that you are going to see the values update if you don't have any conductor layers that match, also the default materials.dat has 0 for some of the conductor thicknesses. When the "Update Fields" runs, you should see the "Field Solver bem2d" messages in the Command Window. It seems OK when I try this....
    • Post Points: 20
  • Wed, Dec 5 2012 6:35 AM

    • budnoel
    • Top 50 Contributor
    • Joined on Tue, Aug 12 2008
    • Rochester, NY
    • Posts 129
    • Points 2,100
    Re: Cross section tool and impedance calculations Reply

    Hi TH - For whatever it's worth, I'm running 16.5 and here's a screen shot of my results.


    • Post Points: 20
  • Wed, Dec 5 2012 6:46 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    I'm at the latest ISR. Just spent some time on the phone with tech support. We tried many things, he is going to forward it to Cadence. Stumped..........

    I do not see anything run in the command window when I hit update fields.

    • Post Points: 5
  • Wed, Dec 5 2012 6:48 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    Bud,  

    Your results are exactly what I would expect to see and what they see at tech support. I wonder if something went amiss with my install..........

    Tom

    • Post Points: 5
  • Wed, Dec 5 2012 6:52 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    Another tid bit, I do get a warning saying the the default impedance and propvelocity values are being used.

    I don't know where these "defaults" are located or come from and neither did tech support. 

    • Post Points: 50
  • Wed, Dec 5 2012 6:57 AM

    • budnoel
    • Top 50 Contributor
    • Joined on Tue, Aug 12 2008
    • Rochester, NY
    • Posts 129
    • Points 2,100
    Re: Cross section tool and impedance calculations Reply

    Interesting.  Keep us posted.  Thanks.

    • Post Points: 5
  • Wed, Dec 5 2012 7:36 AM

    • oldmouldy
    • Top 10 Contributor
    • Joined on Tue, Jul 15 2008
    • Woking, Surrey
    • Posts 1,408
    • Points 24,030
    Re: Cross section tool and impedance calculations Reply
    Where is you TEMP directory set to? The SI related stuff can be a bit picky about spaces in paths but, having said that, my TEMP is set to "docs and settings" in XP and it still calls the bem2d as expected. We have also tried a standard license and that calculates OK as well. You can also "just type" the numbers in the field, like "width" and the impedance will "just update".
    • Post Points: 35
  • Wed, Dec 5 2012 7:42 AM

    • oldmouldy
    • Top 10 Contributor
    • Joined on Tue, Jul 15 2008
    • Woking, Surrey
    • Posts 1,408
    • Points 24,030
    Re: Cross section tool and impedance calculations Reply
    OK, another thought. Any chance at all that the User Preference for the materials.dat locations has changed or that you have a custom, but incomplete, materials.dat in the local directory. Possibly the required values are not in the materials.dat being found and the calculations bail out from there. I have found that the first materials.dat found is used in isolation and not merged with other materials.dat files, so an incomplete one could potentially wreck things.
    • Post Points: 20
  • Wed, Dec 5 2012 8:17 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    oldmouldy:
    Where is you TEMP directory set to? The SI related stuff can be a bit picky about spaces in paths but, having said that, my TEMP is set to "docs and settings" in XP and it still calls the bem2d as expected. We have also tried a standard license and that calculates OK as well. You can also "just type" the numbers in the field, like "width" and the impedance will "just update".

    OM,

    My temp path is C:\Users\Tom\AppData\Local\Temp.

    Either way of entering the numbers,  directly into the cells or using the update field cells at the bottom of the window, does not yield the correct results.

    Tom

    • Post Points: 5
  • Wed, Dec 5 2012 8:17 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    oldmouldy:
    Where is you TEMP directory set to? The SI related stuff can be a bit picky about spaces in paths but, having said that, my TEMP is set to "docs and settings" in XP and it still calls the bem2d as expected. We have also tried a standard license and that calculates OK as well. You can also "just type" the numbers in the field, like "width" and the impedance will "just update".

    OM,

    My temp path is C:\Users\Tom\AppData\Local\Temp.

    Either way of entering the numbers,  directly into the cells or using the update field cells at the bottom of the window, does not yield the correct results.

    Tom

    • Post Points: 5
  • Wed, Dec 5 2012 8:19 AM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    oldmouldy:
    OK, another thought. Any chance at all that the User Preference for the materials.dat locations has changed or that you have a custom, but incomplete, materials.dat in the local directory. Possibly the required values are not in the materials.dat being found and the calculations bail out from there. I have found that the first materials.dat found is used in isolation and not merged with other materials.dat files, so an incomplete one could potentially wreck things.

    Tech support sent me a new materials.dat file that we tried in a few locations with no effect.

    • Post Points: 20
  • Wed, Dec 5 2012 1:09 PM

    • oldmouldy
    • Top 10 Contributor
    • Joined on Tue, Jul 15 2008
    • Woking, Surrey
    • Posts 1,408
    • Points 24,030
    Re: Cross section tool and impedance calculations Reply
    This calculator depends upon the SI tools. Any chance that you installed "only" the licensed products? (Maybe from a control file during product installation) The "defaults" come from Analyze>Preferences, you should be able to view them from the menu. BUT I am pretty confident that the calculator behind this is some "SI magic", possibly Java from the SI install, it might be possible that a restricted install does not include this, likely an oversight on the part of the installer. See what you have in <Install_dir>\share\pcb\signal - I have over 200 items in there, cds_interconnect.iml is of interest here, it is the interconnect models and <install_dir>\share\pcb\etc\context, there are some tlcalculators files, it's possible they do the actual calculations for the cross-section. I would have thought that you would have got "at least" some "missing files" messages in the Command Window for any missing "stuff" though.
    • Post Points: 20
  • Wed, Dec 5 2012 4:59 PM

    • TH Designs
    • Top 25 Contributor
    • Joined on Fri, Apr 13 2012
    • Warminster, PA
    • Posts 269
    • Points 4,370
    Re: Cross section tool and impedance calculations Reply

    OM, thanks for continuing to dwell on this, I know I have been also.

    As for the install, I don't remember exactly what selections I made, but all of the files / directories you mentioned are there along with plenty of other files.

    I might try an uninstall - reinstall later. I have some things to keep working on and I can't have much down time right now.

    Tom

    • Post Points: 35
Page 1 of 2 (19 items) 1 2 Next >
Sort Posts:
Started by TH Designs at 05 Dec 2012 06:10 AM. Topic has 18 replies.