[SI-LIST] Re: DC-blocking transmission-line
- From: Bill Owsley <wdowsley@xxxxxxxxx>
- To: tfox@xxxxxxxxx, gkorony@xxxxxxxxx, Si-List <si-list@xxxxxxxxxxxxx>
- Date: Thu, 28 Jun 2007 14:07:04 -0700 (PDT)
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 <tfox@xxxxxxxxx> 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.
>
>
>
>
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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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