Correction - the YouTube link below should be
https://youtu.be/ke9ZQTVHB7U ;
Yuriy
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Yuriy Shlepnev
Sent: Thursday, May 7, 2020 8:47 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AC current return path
Hello Everyone,
I did a quick investigation (numerical experiment) of AC current return path
on PCB - it is #2020_23 at
https://www.simberian.com/ScreenCasts.php ;(see "How interconnects work"
section, YouTube version is at https://youtu.be/qeJ2EqaiBdc).
It is about a curved trace over large plane and attempt to force current to
"return" directly between input and output. At DC current follows the path
of least resistance (no inductance effect) - about straight line between
input and output or direct path. At high frequencies (or AC) current follows
the path of least impedance - mostly below the trace, as you can see. The
resistance of such path is larger, but inductance is much smaller comparing
to the loop inductance. When frequency goes down, the total impedance of the
straight line path becomes smaller and the return current flows directly.
The question is at which frequency AC current switches to the direct path?
It is relatively easy to estimate the crossover frequency, but not so easy
to simulate and visualize for PCB geometries. My conclusion is that it
happens at Hz frequencies (depends on stackup), rather than at KHz or MHz
frequencies - can it be true? As usual, I will appreciate any feedback.
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
www.simberian.com
Simbeor THz - Accurate, Productive and Cost-Effective Electromagnetic Signal
Integrity Software to Design Predictable Interconnects!
Simbeor SDK - The Industry-First Signal Integrity Analysis Automation Kit!
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