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Is it Right? How To get Capacitance?

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Jae-ho Lim

3 Posts

Posted - Apr 13 2010 : 08:00:47

I modeled tree conductor.

Width, Length, Thick of three conductors is same.

as a reulst, I got a following information.

CAPACITANCE MATRIX, picofarads
1 2 3
line1%GROUP1 1 205 -75.37 -18.98
line2%GROUP1 2 -75.37 232.7 -75.11
line3%GROUP1 3 -18.98 -75.11 205

so. I got capacitance.

C11 = 110.65
C22 = 82.22
C33 = 110.91
C12 =C21 = 75.37
C13 = C31 = 18.98
C23 = C32 = 75.11

but. I wonder why capacitance of three conductance is different?.
is it right?
please, help me.
thanks.

daver

USA
4 Posts

Posted - Jun 04 2010 : 06:13:09

Are the three conductors symmetrically positioned in space? Perhaps you should post more of the file showing the geometry.

dave

Mr.Lim

5 Posts

Posted - Jun 07 2010 : 05:59:42

0 <title>

Q line1 0.0 0.0 0.0 0.6 0.0 0.0 0.6 0.45 0.0 0.0 0.45 0.0
Q line1 0.0 0.0 0.0 0.0 0.45 0.0 0.0 0.45 700.0 0.0 0.0 700.0
Q line1 0.0 0.45 0.0 0.6 0.45 0.0 0.6 0.45 700.0 0.0 0.45 700.0
Q line1 0.0 0.0 0.0 0.6 0.0 0.0 0.6 0.0 700.0 0.0 0.0 700.0
Q line1 0.6 0.0 0.0 0.6 0.45 0.0 0.6 0.45 700.0 0.6 0.0 700.0
Q line1 0.0 0.0 700.0 0.0 0.45 700.0 0.6 0.45 700.0 0.6 0.0 700.0

Q line2 1.2 0.0 0.0 1.8 0.0 0.0 1.8 0.45 0.0 1.2 0.45 0.0
Q line2 1.2 0.0 0.0 1.2 0.45 0.0 1.2 0.45 700.0 1.2 0.0 700.0
Q line2 1.2 0.45 0.0 1.8 0.45 0.0 1.8 0.45 700.0 1.2 0.45 700.0
Q line2 1.2 0.0 0.0 1.8 0.0 0.0 1.8 0.0 700.0 1.2 0.0 700.0
Q line2 1.8 0.0 0.0 1.8 0.45 0.0 1.8 0.45 700.0 1.8 0.0 700.0
Q line2 1.2 0.0 700.0 1.2 0.45 700.0 1.8 0.45 700.0 1.8 0.0 700.0

Q line3 2.4 0.0 0.0 3.0 0.0 0.0 3.0 0.45 0.0 2.4 0.45 0.0
Q line3 2.4 0.0 0.0 2.4 0.45 0.0 2.4 0.45 700.0 2.4 0.0 700.0
Q line3 2.4 0.45 0.0 3.0 0.45 0.0 3.0 0.45 700.0 2.4 0.45 700.0
Q line3 2.4 0.0 0.0 3.0 0.0 0.0 3.0 0.0 700.0 2.4 0.0 700.0
Q line3 3.0 0.0 0.0 3.0 0.45 0.0 3.0 0.45 700.0 3.0 0.0 700.0
Q line3 2.4 0.0 700.0 2.4 0.45 700.0 3.0 0.45 700.0 3.0 0.0 700.0

Q line4 3.6 0.0 0.0 4.2 0.0 0.0 4.2 0.45 0.0 3.6 0.45 0.0
Q line4 3.6 0.0 0.0 3.6 0.45 0.0 3.6 0.45 700.0 3.6 0.0 700.0
Q line4 3.6 0.45 0.0 4.2 0.45 0.0 4.2 0.45 700.0 3.6 0.45 700.0
Q line4 3.6 0.0 0.0 4.2 0.0 0.0 4.2 0.0 700.0 3.6 0.0 700.0
Q line4 4.2 0.0 0.0 4.2 0.45 0.0 4.2 0.45 700.0 4.2 0.0 700.0
Q line4 3.6 0.0 700.0 3.6 0.45 700.0 4.2 0.45 700.0 4.2 0.0 700.0

Q line5 4.8 0.0 0.0 5.4 0.0 0.0 5.4 0.45 0.0 4.8 0.45 0.0
Q line5 4.8 0.0 0.0 4.8 0.45 0.0 4.8 0.45 700.0 4.8 0.0 700.0
Q line5 4.8 0.45 0.0 5.4 0.45 0.0 5.4 0.45 700.0 4.8 0.45 700.0
Q line5 4.8 0.0 0.0 5.4 0.0 0.0 5.4 0.0 700.0 4.8 0.0 700.0
Q line5 5.4 0.0 0.0 5.4 0.45 0.0 5.4 0.45 700.0 5.4 0.0 700.0
Q line5 4.8 0.0 700.0 4.8 0.45 700.0 5.4 0.45 700.0 5.4 0.0 700.0

This netlist is another case.
however, the result is same using this netlist.
interconnect width : 0.6um
thick : 0.45um
length : 700um

daver

USA
4 Posts

Posted - Jun 07 2010 : 22:41:58

Mr. Lim
You are modeling parallel coplanar wires. Since they are not arranged symmetrically with respect to space we would not expect their capacitances to be equal. In other words the wire at the edge only has one neighboring wire. The wire in the middle has two neighboring wires. If you want to see a symmetrical capacitance matrix you can rearrange the wires so that they are equal distance from each other (and of course they will not be coplanar).
Dave

dave

Mr.Lim

5 Posts

Posted - Jun 08 2010 : 14:59:59

Thank you daver~ :-)

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