From: Jim Muccioli ([email protected])
Date: Tue Feb 27 2001 - 10:13:23 PST
Lawrence,
Your theory of canceling magnetic fields, reducing the effective L of a circuit is true. If you
look at page 102 of "Capacitance, Inductance and Crosstalk Analysis"
by Charles S. Walker, he talks about how you can arrange conductors to change the mutual
inductance. The problem you face with normal capacitors is the series
parasitics will have a negative effect on performance . Also the capacitors would have to be
closely matched or balanced (expensive) to achieve maximum
field cancellation.
Instead of two capacitors, if you consider modifying the internal structure of one capacitor to
make a circuit that contains two (three if you include the X), you can achieve canceling
magnetic fields, reducing the effective L, and lowering ESR at and above the self-resonance
frequency. This is what the patented X2Y technology is all about www.X2Y.com .
When connected between two lines, currents do flow in opposite directions and the L is nearly
eliminated by the internal balance which has been measured at less
than 2.9%.
G ____________
A- - - - - - - - - - - - - -
G ____________
+ + + + + + + +B
G____________
In addition, the three shield layers are bound together with two terminations for connection to
ground. The L's, C's and R's are now all in parallel. The ESR
is lowered significantly, self resonance is pushed out and performance is dramatically improved.
As a filter, you can see measurements at this link:
http://www.x2y.com/cube/x2y.nsf/(files)/dynamictesting.pdf/$FILE/dynamictesting.pdf
Applied properly in an application, as many as seven filter elements have been replaced with
one:
http://www.tmworld.com/articles/2001/01_gtem.htm
As a decoupler, others have been investigating, at this time we lack the proper equipment for
that type of characterization.
Your theory is correct.
Best Regards,
Jim Muccioli
X2Y Attenuators, LLC
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Lawrence Butcher
Sent: Tuesday, February 27, 2001 2:29 AM
To: '[email protected]'
Subject: [SI-LIST] : Bypass Cap via placement considered. Negative L's?
A follow-up on my previous Bypass Cap via layout idea.
If it has any merit, I thought of a related idea.
You could place two same-valued caps side-to-side to try
to increase magnetic coupling, with the currents in the
two caps flowing in opposite directions.
|---| |---|
| |(+)- | Cap 1
|---\ |---|
(-) minimum safe spacing
|---| \---|
| -(+)| | Cap 2
|---| |---|
Would this result in cancelling magnetic fields, reducing
the effective L of individual components?
Would this result in a lower ESR at and above the self-resonance
frequency for individual caps for the coupled pair than
you would get with the best possible via placement for
normally separated caps?
Once I know the answer about whether this idea is simply wrong,
I think that it will take calculations or measurements to find
out whether it actually results in better cap performance.
Lawrence
I don't know how far apart components can be to stay coupled.
Frequency-dependent, I assume. But caps don't work as bypass
devices to very high frequencies. Giga-Hzs are feet, so there
might still be hope.
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