[SI-LIST] The case of 3 planes
- From: "xsirfr" <rtso1@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Sat, 08 May 2004 18:47:43 -0000
Suppose I have 3 planes. I wish to create a LCR mesh element model for
a square section of the 3 planes. Now the inductance per square of
plane is the loop inductance per square, which can be expressed as a sum
of Partial inductances: self inductances - mutual inductances,
assuming currents flow
in opposite directions, which for a return path is a valid assumption.
Total Effective Inductance: L_loop = L11 + L22 - 2M (where M=L12=L21)
For a section comprised of 2 planes, the loop inductance is split in
half and applied to each "layer" of the schematic for the LCR model
section. By
doing this, we don't need to use "K" factors for coupled inductors - we
simply model the net loop inductance as isolated inductors.
Now what is the correct inductance value for modeling plane#2 in a 3
plane stack? Intuitively, the sandwiched layer should be modeled as
having
a reduced value of inductance/sq, IF it uses both plane#1 and plane#3 as
return paths. But for a circuit that is powered between plane#1 and
#2 only,
it seems the inductance in plane#2 would be too small, since the circuit
does not use plane#3. My conclusion is that for a 3-plane system, I
CANNOT use
isolated inductors, but have to use "K" factors to represent the
physical effect
of coupled mutual inductance. This way, the total effective loop
inductance of either
adjacent pair (#1, #2) or (#2, #3) can be affected by the direction of
current in the other
plane (#3 or #1). I believe I need to model K12 and K23, but can
ignor K13.
Is there a modeling expert out there that would concur with my conclusion?
Thanks,
-xsirfr
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