between 10-100KHz, depending on inductance, or the lack of self-inductance. 1MHz is where most if not all current follows the signal path.
and my stab at the Bonus Question:
Return path is the return path. If the power for the signal is the return path, then yes. If ground is the return path, not as good, if at all. Think loop area...
Roger
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of
Brooks,Bill
Sent: Thursday, December 02, 2004 2:17 PM
To: [log in to unmask]
Subject: Re: [DC] Return Current Path vs. Frequency
Hi Jack... (safety tip... don't say that on an airliner)
If I remember correctly... the RF return currents will always follow the
path of least impedance... :) Wherever that path is... on the ground plane,
or power plane or even if it's radiated through the air I would imagine...
I must admit though, I do not remember at what freq it stops following under
the 'U' shape... I would guess it would be around a megahertz...
Best regards,
Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
http://www.dtwc.com
http://pcbwizards.com
-----Original Message-----
From: Jack C. Olson [mailto:[log in to unmask]]
Sent: Thursday, December 02, 2004 10:55 AM
To: [log in to unmask]
Subject: [DC] Return Current Path vs. Frequency
Return Current Path vs. Frequency
-=-=-=-
Easy question:
Imagine a "U"-shaped trace above a solid ground plane,
with a connection at each end.
Inject a signal through the "U", and vary the frequency.
At what frequency will you see the return current
follow the shape of the U rather than the shortest path?
-=-=-=-
Bonus question:
What if I replace the ground plane with a power plane?
(I say it makes no difference. )
thanks,
Jack (the "arguing with a new engineer" guy)
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