[SI-LIST] Re: Stripline Characteristic Impedance
- From: Ronald.De_Smedt@xxxxxxxxxx
- To: ched_chang@xxxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Wed, 04 Dec 2002 11:21:54 +0100
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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