# Re: [SI-LIST] : Mutual Inductance between 2 Power Planes

From: Raghu ([email protected])
Date: Tue Dec 14 1999 - 18:49:08 PST

Dear Isaac

The formula you are using, I think, is the inductance L per unit lenght of a
parallel plate transmission line. The capacitance C per unit length is
(epsilon.W/d) and the inductance is calculated by using the fact that the
1/sqrt(LC) must equal the propagation velocity in the medium.

For your numbers this comes out to be 9.5 nH and is reasonable. The separtion of
12 mm between your planes seems rather high and may be causing these larger
values of inductance.

The parallel plate transmission line assumes that the plane is excited all along
the edge. More likely, you have point connections to the plane. In such cases,
the inductance can be much higher and you need specialized software to analyze
the effect of connection locations. For example, if the connection points at the
middle of both planes at the ends, you get a total inductance fo 17.48 nH. Below
are coarse grid ascii plots which show how the current spreads in the two
planes. I have shown just one plane as the other is identical.

0 0 1 1 1 2 2 2 3 4 5 6 9 9 6 5 4 3 2 2 1 1 1 0 0
0 0 0 0 0 0 0 1 1 1 1 2 3 3 2 1 1 1 1 0 0 0 0 0 0
1 0 0 0 0 0 0 1 1 1 1 1 2 2 1 1 1 1 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2
1 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 1
1 0 0 0 0 0 0 1 1 1 1 1 2 2 1 1 1 1 0 0 0 0 0 0 1
0 0 0 0 0 0 0 1 1 1 1 2 3 3 2 1 1 1 1 0 0 0 0 0 0
0 0 1 1 1 2 2 2 3 4 5 6 9 9 6 5 4 3 2 2 1 1 1 0 0

```--
************************************************************************
Raj Raghuram
Applied Simulation Technology
1641 N. First Street, Suite 170
San Jose, CA-95112.
Tel: (408) 436-9070 ext.101
Fax: (408) 436-9078
e-mail: [email protected]
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