[SI-LIST] Re: AW: Just a simple question
- From: "Antonis Orphanou" <orphanou@xxxxxxxxxxxx>
- To: "afu@xxxxxxxxxxxxxxxxxx" <afu@xxxxxxxxxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 25 Jul 2012 18:08:56 +0000
Hello Herbert,
Now that I understand your posting question (well, I hope I do) I could not
resist to add a couple of more comments.
In addition to the skin effect there is also the "internal" and "external"
inductance" that can influence the current through the piece of metal you
called a via. Proximity effects can indeed affect the charge distribution and
the effect of the skin effect and metal inductance. However, as inferred by the
definition, this is a proximity effect and vias far away can't have an
influence on it. I think it is safe to say that return/signal vias a few mil
away can not affect the skin effect of your via.
The way the current loop is formed now (with the via just being a part of
it).....well it is another story.....
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of afu
Sent: Monday, July 23, 2012 4:30 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: Just a simple question
Hello Steve,
first of all, I am writing in English, as I hope, and I told you, that I have
downloaded the file as PDF to the files > General Uploades VIA_SKIN.PDF !
There you can download it !!!
I know, that "The SI-LIST does not support attachments", but it allows
downloads to the file area.
If you would be so kind, and look to it, then you will agree, that the way
"how" the current will flow over the surfaces of the via will not depend on
the "far field" of the return path.
The "near field, which is working in terms of the skin effect and the ways of
current pathes forced by the magnetic field of the own forward current in
dimensions of zenth of millimeters will be by far greater in the location of
the via, as the current flowing in a distance of ca. 50 mm. The magnetic field
is decreasing with 1/r ( r is the distance from the wire) with a start
position of reltive
1 on the surface of the wire.
I think and hope, that you will not tell me that the influence of the "far
field" source is in any way relevant for the very local skin effect!
Herbert
Am 23.07.2012 23:48, schrieb steve weir:
> Herbert, there is an apparent impasse where you rely on the incorrect
> idea that in a PCB you can arrange things so that the "return path is
> far, far away from the forward path". You should review the
> presentation that Brad Brim linked to correct that wrong idea. What
> you may be thinking is that if you have conductors spaced very far
> apart that incremental increases in distance doesn't affect things
> much. That is true, but rather impractical in the context of a PCB.
>
> The SI-LIST does not support attachments.
>
> Steve.
>
> On 7/23/2012 3:11 PM, afu wrote:
>> Hello Steve,
>>
>> as I have understood the answers of both mentioned members, like from
>> the others, have all stated that the return path is a main factor in
>> the current flow. I tried to explain, that the return path is far,
>> far away from the forward path. Without a visual tool, to describe my
>> model, I used the way of verbal description, which leaded to
>> philosophical answers.
>>
>> But even the idea of Orin, to use Sinnet to answer my question, dows
>> not help because the Sonnet world is equipped with only two
>> dimensional traces in a 3D view.It shows same current densisty on
>> both viewable
>> sides ;-((( This means, that Sonnet tells the currentflow on top and
>> bottom of the trace and inside and outside the via is the same ??!!
>>
>> By the way, my original question mentioned the term of "sides of the
>> trace" and not sides or layers of a multilayer .
>>
>> So... finaly I have uploaded VIA_SKIN.PDF .... a 1:1 image of the
>> thinking model.
>> It contains a pad on top and bottom side each, a trace on the top
>> side to tze middle of the board, a via from top to bottom layer, a
>> trace to a resistor pad on the lower edge ( only for those how need
>> it to satisfy their need of a logical circuit), then traces on the
>> lower side to the sides back the edges and closing to the lower pad.
>>
>> You will agree, that the current flow in the forward path in my
>> question is not affected by the current flow and fields generated by
>> the return path and that currents on the return path.
>>
>> Herbert
>>
>>
>> Am 23.07.2012 21:55, schrieb steve weir:
>>> Herbert, with all due respect, the original question was imprecise,
>>> and included some false assumptions. There were several answers
>>> that offered very good information concerning signal transitions
>>> through multilayer boards, in particular from Brad and Orin.
>>>
>>> Steve.
>>>
>>> On 7/23/2012 10:16 AM, hws wrote:
>>>> Hello Wolfgang,
>>>>
>>>> I before asked a not so simple question, and the answering people
>>>> were answering to quite a different question ( "vias and current
>>>> pathes" ), at least it seamed to be like this.
>>>> Therefore this simple and stupid question was a way for me to find
>>>> out, if here are people that read and think and .... then answer.
>>>> I do not want to unpolite against the others... but I am a little
>>>> bit frustrated from their answers.
>>>> Maybe you have an opinion to the "vias and current pathes" question
>>>> ???
>>>>
>>>> Herbert
>>>>
>>>>
>>>> Am 23-07-2012 9:14, schrieb Wolfgang.Maichen@xxxxxxxxxxxx:
>>>>> Well, at least as long as it is an ideal, homogeneous transmission
>>>>> line (or at least pretty close to ideal, homogeneous and lossless
>>>>> at the frequency range of interest), and if your "simple
>>>>> multimeter" can measure capacitance and inductance (many better
>>>>> units today can), then
>>>>>
>>>>> - measure total capacitance Ctot between center conductor and
>>>>> shield
>>>>> - measure total inductance Ltot between center conductor and
>>>>> shield, with center conductor and shield shorted together at the
>>>>> far end (then end NOT connected to the multimeter)
>>>>> - calculate the characteristic impedance as Zo = sqrt (Ltot/Ctot)
>>>>>
>>>>> Or if your "simple multimeter" can measure resistance in less than one
>>>>> round trip delay of your cable then you can simply use the Ohmmeter mode
>>>>> and get the result directly. With typical DMMs producing 2-3 reading per
>>>>> second, a cable from here a quarter the distance to the moon is just
>>>>> about sufficiently long for that.
>>>>>
>>>>> Otherwise, you will always measure the termination resistance (inifinite
>>>>> if the cable is open at the end) plus the Ohmic resistance of the cable,
>>>>> not the characteristic impedance.
>>>>>
>>>>> May I now ask what the reason for the question is?
>>>>>
>>>>> Wolfgang
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: si-list-bounce@xxxxxxxxxxxxx
>>>>> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Havermann, Gert
>>>>> Sent: Monday, July 23, 2012 9:56 AM
>>>>> To: afu@xxxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
>>>>> Subject: [SI-LIST] AW: Just a simple question
>>>>>
>>>>> I'd say: first verify that the statement is correct and present
>>>>> the data to proof it , or call it an unproven assumption
>>>>>
>>>>> BR
>>>>> Gert
>>>>>
>>>>>
>>>>> ----------------------------------------
>>>>> Absender ist HARTING Electronics GmbH& Co. KG; Sitz der Gesellschaft:
>>>>> Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596;
>>>>> persönlich haftende Gesellschafterin: HARTING Electronics Management
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>>>>> HRB 8808; Geschäftsführer: Edgar-Peter Duening, Torsten Ratzmann, Dr.
>>>>> Alexander Rost
>>>>>
>>>>> -----Ursprüngliche Nachricht-----
>>>>> Von: si-list-bounce@xxxxxxxxxxxxx
>>>>> [mailto:si-list-bounce@xxxxxxxxxxxxx] Im Auftrag von Herbert
>>>>> Gesendet: Samstag, 21. Juli 2012 16:48
>>>>> An: si-list@xxxxxxxxxxxxx
>>>>> Betreff: [SI-LIST] Just a simple question
>>>>>
>>>>> When I would say that I can measure the impedance of a coaxial cable with
>>>>> a simple multimeter, would you think that I am wrong under all
>>>>> circumstances or would you onle begin your answer with the words :
>>>>> " But only when... " ?!
>>>>>
>>>>> How free is your brain from fixed thinking pathes ?!
>>>>>
>>>>> Herbert
>>>>>
>>>>>
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