[SI-LIST] Re: Question regarding current loop

Doug:

All of your assumptions are fine.  I am also happy to band limit the 
wave form rather than make it trapezoidal.  Either arrangement is fine for me.

I propose:  8mil lines 24mils center to center, 30" long, symmetric 
stripline construction with plenty of stitch vias plane to 
plane.  Assume an eR of anything you like from 1.0 to 5.0 and we will 
set the dielectric thickness as needed for 100 Ohms odd mode.  We 
center the pair in a 10" wide board.

We consider X the 30" axis, Y the 10" board width, and the thickness 
of the board Z.

Now, lets also add a free standing antenna along the side of the 
board in the X-Z plane and locate that 10" along the X axis from the 
transmitter.

Finally, let's test with two plane arrangements.

A.  The image plane is solid
B. We cut a 0.100" wide slot in the plane end to end in the Y 
direction 10" along the X axis from the transmitter.  ( Dead center 
of our antenna. )

Let's drive with 50ps rise times, and 500ps bit intervals.

I submit that under A, our antenna will be nice and quiet.

I submit that under B, our antenna is going to light right up from 
the big slot wave we excite crossing over the gap.

Please comment:

Do you agree that the slot wave will be there?
For the dimensions cited, do you think the slot wave be a little 
50-100ps pulse, or will it be a really messy thing with much lower 
frequency content mixed in?
How does what you expect correlate with your original statements?
How does the fact that the line is much longer than the bit interval 
relate to your statements concerning current loops?

Regards,


Steve.
At 12:36 PM 4/24/2006, Doug Brooks wrote:
>Assume we have a differential pair, driven in odd mode with no timing offsets.
>Assume the pair is terminated with a single resistor between the two traces.
>Assume the signal is purely trapezoidal.
>Assume there is an underlying plane (but assume what you want about the
>spacing to the plane.)
>Assume what you want about the spacing between the traces.
>*If* current flows in a closed loop and *if* current is constant everywhere
>in the loop, and *if* current is a point (as opposed to an average) concept
>in time....
>
>What is the definition of the current loop at the instant when the current
>wave form is at the middle of the constant part of the wave form (between
>the rise and fall times)?
>
>Doug Brooks
>
>____________________________________________________________________________-
>Check out UltraCAD's differential impedance and skin effect calculators at
>http://www.ultracad.com
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>http://www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>List FAQ wiki page is located at:
>                 http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
>List technical documents are available at:
>                 http://www.si-list.org
>
>List archives are viewable at:
>                 http://www.freelists.org/archives/si-list
>or at our remote archives:
>                 http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
>                 http://www.qsl.net/wb6tpu
>

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: