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Impedance inconsist

Wild
 1. Just finished a design, updated the stack up by refreshing materials.

2. Re-enetered the thickness's required for each layer (dielectric and conductor).

All the routes that I have a 50 Ohm constraints on the bottom layer have DRC's, while the routes on the top do not.

The stackup is symetrical.

Both top and botom traces are 6 mil traces, Parastic calculator shows top traces are 49.2 Ohm, bottom traces are 59.8 Ohm (impedance).  The capacitance

The Xscetion table  predicts 5.8 mil wide trace as 50.05 on both top and bottom.

Very confused, any suggestions?

Attached are pictures of the  stck up, parastic calculation and cline width information.
  • tltoth

    I have the very same problem. see http://www.cadence.com/community/forums/T/25128.aspx

    The calculated impedance is far from what it should be ...

  • BillZ

    Hi,

    What version and ISR level are you at? There were some updates related to impedance in some of the ISR's.

    BillZ

    EMA Design Automation

  • Wild

    Was at hot fix 38, updated to hot fix 40.

    Issue still exists.  

    Note: Opened same database on 2 other computers, issue disappears.  1 computer is a windows based with hotfix 40 applied, other computer is a linix base at hotfix 17.

    Could this be hardware (PC) related?

    Opened a Sr, and the Cadence team does not see this issue.

     

    Thanks for feedback

     

  • Dennis Nagle

    If you are getting different results on different machines, try:

    - deleting your local cache for the field solver (delete the file interconn.iml and then reopen the design)

    - see if you have anything solver related in your env file (like trapezoidal_angle_in_degree)

    -Dennis 

  • Wild

    Thanks for the reply:

    The database is on a network drive, which I open from all 3 machines (2 windows based - 1 linix based).

    I deleted the interconn.iml file in the network drive, made no differnce.

    Where would the local chache be located?  Doing a search on my local disc, lots of interconn.iml files......

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