[SI-LIST] Re: DC-blocking transmission-line - noting a lack of hi-lites I added in response

I don't see the fancy color hi-lites I added to my inline comments below 
--sorry.
  
Bill Owsley <wdowsley@xxxxxxxxx> wrote:
  The original Q'er still want to AC couple the T-line instead of a transformer 
coupled DC-block. And in one package no less. With more information, this might 
not be as easy as the first impression.
ps. Does a discussion in the list count as a technical disclosure and thus 
prevents a subsequent patent?
Terry Fox wrote:
At risk of being stoned...the "differential impedance" has very little to 
do with anything.
The key issues is the impedance of the individual lines to their reference.
As long as the individual lines above are confined to a PCB or other structure 
that contains a reference? Let's not include a twisted pair floating in space 
for this discussion, unless the reference is the other line?

The number "differential impedance" comes from 2 X Z0 which is the 
characteristic impedance of each of the individual lines.

If these lines are balanced mirror images, the current through each of the 
That indeed is a really big if. These balance mirror images exist in simulation 
software and textbooks, but in an actual circuit???

two Z0 50 ohm resistors cancels and there is no net current out the 
reference...hence you can use a single 100ohm resistor rather than two 50 
ohm resistors.
For DC analysis or short transmission lines? 
For long lines, The edge that 'sees' the Z0 has not yet arrived at the 50 ohm 
terminations, or 100 ohm one, and is using either the reference plane/s or the 
other line to 'use' Z0?

The out fall of this is that everyone thinks differential imp[edance is 
some magical thing.
ElectroMagicalCompatibility of course! 

In my experience it is not.

He has touched the holy thing...let us now begin the stoning.

TFox

At 07:59 AM 6/28/2007, George Korony wrote:

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>BlankHi All,
>I am not a board designer, but I do design parts that other people put on
>boards. We are working on a new (patent protected) concept: the "
>DC-blocking transmission-line".
>Basically the idea is to build a pair of capacitors that can be intercalated
>on the differential signal traces, having a controlled characteristic
>impedance between the two capacitors, the obvious scope is to reduce the
>reflections that may show up due the DC-blocking capacitors.
>One request, we have, is that the characteristic impedance between the two
>capacitors (treated as a simple transmission line) should be 100 Ohm.
>Of course things are not so simple; and my question is: does anyone have a
>different approach to this problem?
>Thanks for any suggestion, George.
>
>
>
>
>
>------=_NextPart_002_0008_01C7B973.5B78CED0
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>Hi All,
>I am not a board designer, but I = do design=20 parts that other people 
>put on boards. We are working on = a new =20 (patent protected) concept: 
>the " DC-blocking = transmission-line".
>Basically the idea is to build a = pair of=20 capacitors that can be 
>intercalated on the differential signal = traces,=20 having a controlled 
>characteristic impedance between the two capacitors, = the=20 obvious 
>scope is to reduce the reflections that may show up due the = DC-blocking 
>capacitors.
>One request, we have, is that the=20 characteristic impedance between the 
>two capacitors (treated as a simple = transmission line) should be 100 Ohm.
>Of course things are not so = simple; and my=20 question is: does anyone 
>have a different approach to this = problem?
>Thanks for any suggestion,=20 George.
>
>
>
>
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>
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