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Capacitive Coupling in Printed Circuit Boards

Posted Jun 14, 2010, 2:28 p.m. EDT 2 Replies

Stephen Rowe
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Hi, I'm trying to model electrical crosstalk between wires printed on a very small scale. For our model, we have four wires of about 60 microns in width with 40 microns of space between them. They are placed on a flexible circuit material (Kapton). We plan on sending signals down these lines (pulses of 100 V), but we are concerned about crosstalk between lines. Specifically, we are concerned about capacitive coupling between the lines.

www.comsol.com/showroom/documentation/model/688/
That example seems very relevant, as it discusses the issue of inductive coupling between wires on a circuit board. Is there a way for COMSOL to predict the effects of capacitive coupling? I'm not sure exactly how to calculate these effects, but if anyone could point me in the right direction, that would be great!

Thanks!
2 Replies Last Post Feb 4, 2011, 10:52 a.m. EST
Stephen Rowe
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Posted: 1 decade ago Jun 15, 2010, 1:05 p.m. EDT
I think I got somewhere on it. I found in the documentation that COMSOL 4.0 can calculate capacitance as a lumped parameter. In order to for it to do that, it needs to have terminals specified as boundary conditions. So, I set the wires to be terminals with a constant voltage of 100 on them. I have four wires, and I set each wire as a single terminal. In the data menu, I found the global variables C11, C22, C33, C44. However, I assumed I would want C12, which I believed to be the capacitive coupling between surface 1 and 2. I didn't see how to get that.

So, I changed up my model. I set the sides of two adjacent wires to be both terminal 1, with V = 100. I then ran the model (got the same potential plot) and calculated C11, thinking that since C11 is the self-capacitance, and I set the surface to be the adjacent wires, it should calculate the capacitance between the two wires. Does this make sense?

Does anyone have a better solution or am I on the right track? Thanks!
I think I got somewhere on it. I found in the documentation that COMSOL 4.0 can calculate capacitance as a lumped parameter. In order to for it to do that, it needs to have terminals specified as boundary conditions. So, I set the wires to be terminals with a constant voltage of 100 on them. I have four wires, and I set each wire as a single terminal. In the data menu, I found the global variables C11, C22, C33, C44. However, I assumed I would want C12, which I believed to be the capacitive coupling between surface 1 and 2. I didn't see how to get that. So, I changed up my model. I set the sides of two adjacent wires to be both terminal 1, with V = 100. I then ran the model (got the same potential plot) and calculated C11, thinking that since C11 is the self-capacitance, and I set the surface to be the adjacent wires, it should calculate the capacitance between the two wires. Does this make sense? Does anyone have a better solution or am I on the right track? Thanks!
Fengyuan Sun
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Posted: 1 decade ago Feb 4, 2011, 10:52 a.m. EST
Try the port boundary condition.
Try the port boundary condition.

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