Re: [SI-LIST] : Ground gap problem

Douglas McKean (dmckean@corp.auspex.com)
Wed, 24 Mar 1999 13:09:49 -0800

Hi Sangil,

The return current of a trace that crosses a gap

in the ground plane will excite the gap as a slot

antenna. The area of most radiation will be out

at the ends of the gap. That's due to the current

being the most dense and taking the most complete

change in direction. This is of course assuming

that the gap does not completely dissect the

ground plane.

My own interpretation is that the return current

smears itself out from the trace to the perimeter

of the gap inversely according to frequency, i.e.

the higher freq, the more the return current tries

to follow in the *shadow* of the trace until the

gap completely interrupts a return path. The return

currents of all the frequencies will focus, though,

at the ends of gap.

Forgive the following ASCII art but ...

High Speed Trace

|

|

|

Area +--------|--------+ Area

of | Gap | Gap | of

most +--------|--------+ most

radiation | radiation

|

|

This has been demonstrated and empirically measured

for seminar purposes by my manager Doug Smith.

Regards, Doug McKean

At 02:09 PM 3/23/99 -0800, you wrote:

>>>>

<excerpt><fontfamily><param>Arial</param><smaller>Hi all,

I am trying to find the effects of the gaps on the ground plane for the
high-speed circuits.

Even though I have a couple of references about the via, which has the
ground gap problem, I need more specific data about the ground gap
problem regarding the gap size, gap location.....

Either measured data or simulated data will be fine ( papaers or refernce
book...)

Looking forward to your answers.

</smaller></fontfamily>

<fontfamily><param>Arial</param><smaller>Thanks

Sangil Lee

</smaller></fontfamily>



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