[SI-LIST] Re: Question regarding current loop

Gee,

It seems to me you are off point.

I asked about the specific current loop (current flows in a closed loop) at 
a specific point in time, not about radiation.
You are correct that I needed to clarify where the wave form is if the 
trace is long (which I did on a follow-on post). I am assuming the point of 
interest has reached the end of the trace at the receiver.

Doug





At 01:30 PM 4/24/2006, steve weir wrote:
>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
>>
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>

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