For the power engineers among us, the lower limit should include 50/60 Hz
and handle thick copper traces.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf
Of Yuriy Shlepnev
Sent: Saturday, May 09, 2020 10:55 AM
To: hubing@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AC current return path
Hi Todd,
Thank you for the feedback and explanation.
Looks like for DC convergence we need to push the algorithm down to at least
100 Hz :-)
Best regards,
Yuriy
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Todd Hubing
Sent: Friday, May 8, 2020 7:32 AM
To: si-list@xxxxxxxxxxxxx
Cc: shlepnev@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AC current return path
Yuriy,
Nice simulation! Thanks for sharing it! Note that even if you had terminated
the loop on the top plane (forcing all the signal current to flow in the
trace), there would still be a current in the plane under the trace. At kHz
frequencies, the magnetic field induces an eddy current that attempts to
cancel the magnetic flux passing through the plane. The current flowing in
the trace loop would be approximately the signal voltage divided by the load
impedance. At kHz frequencies, the current flowing in the disconnected plane
would be approximately equal to that. Now if we terminate the source and
load in the plane (as in your simulation), the signal current flowing
directly between the source and load is canceled in the plane by the eddy
current and we get the current distribution you are observing (i.e. the
signal current returns in the plane under the trace).
Of course, the rule that's often quoted is:
"At kHz frequencies and below, currents take the path(s) of least
resistance. At MHz frequencies and above, currents take the path of least
inductance."
This is generally correct for circuit board and system geometries. For a
straight trace over half-ounce copper, I believe the currents in the plane
will spread out significantly at 1 kHz and be basically the same as the DC
distribution at 100 Hz.
Thanks again for sharing this! Your simulations have really helped to
visualize fields and currents in a variety of important situations.
Best regards,
Todd
---------------------
Todd Hubing
LearnEMC, LLC
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf
Of Yuriy Shlepnev
Sent: Thursday, May 7, 2020 10:47 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!
------------------------------------------------------------------
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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
------------------------------------------------------------------
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:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
