Sujet : Re: transmission line z
De : jl (at) *nospam* glen--canyon.com (john larkin)
Groupes : sci.electronics.designDate : 22. Jun 2025, 00:21:46
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <8ife5kt06pc7qk21sjuk020scaam9miopi@4ax.com>
References : 1 2 3 4 5 6 7
User-Agent : ForteAgent/8.00.32.1272
On Sat, 21 Jun 2025 21:31:11 +0100, JM
<
sunaecoNoChoppedPork@gmail.com> wrote:
On Tue, 10 Jun 2025 20:06:13 -0700, john larkin <jl@glen--canyon.com>
wrote:
>
On Tue, 10 Jun 2025 21:00:37 +0100, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
>
On Tue, 10 Jun 2025 07:53:38 -0700, john larkin <jl@glen--canyon.com>
wrote:
>
On Tue, 10 Jun 2025 13:33:57 -0000 (UTC), "Don" <g@crcomp.net> wrote:
>
JM wrote:
john larkin wrote:
>
Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
>
air
__________________ copper
.........................................fr4
__________________ copper
>
air
>
>
>
What's that called?
>
Does anyone know of a calculator that handles this case?
>
It's just a parallel plate waveguide.
>
For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w).
>
ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip
>
Formulas for the higher modes also exist.
>
But I'd have to look them up.
>
Your free space impedance is easier for me to comprehend than the one
contained in Chemandy's calculator:
>
<https://chemandy.com/calculators/microstrip-transmission-line-calculator.htm>
>
Danke,
>
And that one assumes an infinite ground plane.
>
I suspect that all such formulas are wrong, except in a few rare cases
like a coax. EM simulation is better.
>
Get Cadence to come along and demonstrate Alllegro + Clarity to you.
>
The days of using formulas to calculate these things are long gone.
>
We have lots of programs and web sites that use the formulas!
>
I'm having to do some EM simulations at the moment for some fast stuff
(13ps rise time) so thought I'd also check the accuracy of that
equation I gave.
>
Although it agrees with the one posted by Leo Baumann from his
reference book (for sensible trace widths and heights) the impedance
it calculates is nowhere near that given by simulation. If I do a
parametric sweep on the width of the return conductor, by the time
it's x10 or so that of the trace conductor the resulting impedance
agrees with that given by the likes of the Saturn toolkit, or the
website linked to by Don, so my simulation is probably correct.
>
If I have time I'll bend some copper tape over some Kapton tape and
cut off a few slices of varing widths to do a TDR measurement on as a
reality check.
Where do you get a 13 ps rise time?
transmission line z
Re: transmission line z
