Re: [SI-LIST] : differential impedance calculations

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From: chasgra (chasgra@email.msn.com)
Date: Wed Nov 01 2000 - 21:03:48 PST


RE: [SI-LIST] : differential impedance calculationsHi Larry - Thanks for your comments.

If you are referring to slides 45 & 46 I think you misunderstand the intent.

Dr Bogatin was, I believe, trying to show comparisons between Ist order
approximations and a field solver. I do not belive any assumptions were
being made. Indeed as I recall he did nake the statement that one should
not always trust approximation BECAUSE of the assumptions.

Charles Grasso

  ----- Original Message -----
  From: Larry Miller
  To: Charles Grasso ; Gary Peterson ; si-list
  Cc: eric
  Sent: Wednesday, November 01, 2000 2:04 PM
  Subject: RE: [SI-LIST] : differential impedance calculations

  Unfortunately, the piece by Dr Bogatin makes and refers to the very assumptions that Dr Johnson refers to.
  All roads lead to the National App Note AN-905.
  (I have been battling this same fight myself.)

  Larry Miller

    -----Original Message-----
    From: Charles Grasso [SMTP:chasgra@msn.com]
    Sent: Wednesday, November 01, 2000 2:23 PM
    To: Gary Peterson; si-list
    Cc: eric
    Subject: Re: [SI-LIST] : differential impedance calculations

    Hello - There is an excellent presentation available for download called
    "Differential Impedance finally made Simple" authored by Dr Bogatin that
    should help answer this question.

    Please goto http://www.ewh.ieee.org/rmcemc Click on Last Meeting and
    follow the instructions for the presentation download.

    Enjoy!!

    Charles Grasso
    Ansoft Corporartion
    p: 303-666-1400
    f: 303-666-1499
    ----- Original Message -----
    From: "Gary Peterson" <Gary_Peterson@Emcore.com>
    To: <si-list@silab.eng.sun.com>
    Sent: Wednesday, November 01, 2000 12:50 PM
    Subject: [SI-LIST] : differential impedance calculations

>
>
> I seem to recall Dr. Howard Johnson mentioning that impedance calculation
> formulas made assumptions (since closed-form solutions aren't possible).
>
> Can someone comment on assumptions made for the equation for differential
> impedance shown below? Seems to me that as traces get closer together,
    the
> single ended impedance would be affected. When I calculate single-point
> values for differential impedance using Hyperlynx LineSim, I do see the
> single-ended impedance change when the spacing between the pair gets
    small.
>
> Thanks,
>
> Gary Peterson
>
>
>
> (Embedded image moved to file: pic27894.pcx)
>
>

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