[SI-LIST] Re: Stripline Characteristic Impedance
- From: Martyn Gaudion <martyn.gaudion@xxxxxxxxxxxxxxxxxxxx>
- To: "Ched-Chang Chai" <ched_chang@xxxxxxxxxxx>
- Date: Wed, 04 Dec 2002 15:15:48 +0000
Dear Chai,
I agree with Dr. De Smedt. You may find these
application notes also explain how to take into
account copper thickness. Also the arithmetic
gets a little more interesting when you take
into account etch taper and differential impedance.
www.polarinstruments.com/support/cits/AP160.html
www.polarinstruments.com/support/cits/AP161.html
The notes are written around the Polar Si6000, however
the information holds true for any field solver or calculator
that takes copper thickness into account.
Kind regards
Martyn Gaudion
Polar Instruments
www.polarinstruments.com
T +44 1481 253081
F +44 1481 252476
M +44 7710 522748
E martyn@xxxxxxxxxxxxxxxxxxxx
At 10:21 04/12/2002, you wrote:
>Dear Chai,
>
>I have re-calculated your configurations (see Annex).
>
>Reversing the configuration upside down, must give
>you the same results (as NO preference is attributed
>to any of the reference planes). This is illustrated
>by comparing case #1 with #2, ... in the table below.
>
>It seems that the discrepancies that you have found
>in your results are mainly due to the unclear
>definition of the heights h1 and h2 and whether the
>thickness of the conductor must be subtracted from
>one of them or not (which simulates the effect that
>the conductor is embedded inside the epoxy layer).
>I have illustrated this with case #3 to #8.
>In case #3 and #4 the conductor is embedded in both
>parts. In case #5 and #6 the conductor is embedded
>in the 0.2mm layer only. In case #7 and #8 the
>conductor is in the 0.4mm layer only. The resulting
>characteristic impedances seem to confirm your
>values.
>
>Sincerely yours,
>
>Dr. Ronald De Smedt
>Alcatel Bell - Physical Design / EMC & SI
>Francis Wellesplein 1, B-2018 Antwerpen (Belgium)
>Tel: +32/3/240-4650, Fax: +32/3/240-9845
>mailto:ronald.de_smedt@xxxxxxxxxx
>
>
>Annex : Characteristic impedance calculations
>^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>Reference plane ---------------
> ^ ^
> | h2
> | v v
>Conductor H ===== t width w
> | ^ ^
> | h1
> v v eps_r
>Reference plane ---------------
>
>The following characteristic impedances Zc are found,
>with the fixed parameters :
> w=0.15mm, t=0.035mm, eps_r=4.5
>
>Case H h1 h2 Zc
> # [mm] [mm] [mm] [Ohm]
>----------------------------------
> 1: 0.6350 0.4000 0.2000 54.71
> 2: 0.6350 0.2000 0.4000 54.71
> 3: 0.6000 0.3825 0.1825 52.72
> 4: 0.6000 0.1825 0.3825 52.72
> 5: 0.6000 0.4000 0.1650 51.11
> 6: 0.6000 0.1650 0.4000 51.11
> 7: 0.6000 0.3650 0.2000 54.01
> 8: 0.6000 0.2000 0.3650 54.01
>----------------------------------
>
>Ched-Chang Chai wrote:
> >
> > Dear all,
> >
> > I have a question regarding the stripline characteristic
> > impedance Zo. I have the following stack-up:
> >
> > Reference plane -------------
> > a
> > Trace ---
> >
> > b
> >
> > Reference plane -------------
> >
> > where a<b.
> >
> > When I used impedance calculator to get Zo, I have 2 ways to
> > key in a and b values:
> > (1) Use the stack-up shown above.
> > (2) Reverse it upside down, as shown below:
> >
> > Reference plane -------------
> >
> > b
> >
> > Trace ---
> > a
> > Reference plane -------------
> >
> > I got different values for Zo.
> > For example, a=0.2mm, b=0.4mm, trace width=0.15mm, trace
> > thickness=0.035mm, and dielectric constant=4.5, approach (1)
> > gives 51ohm while approach (2) gives 54ohm.
> >
> > Can someone tell me which one is the correct value?
> > Thank you very much in advance.
> > --
> > Regards,
> > Chai
> >
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