# How to deal with the AC capacitor in a serial link?

Question asked by bruce_qin on Sep 3, 2009
Latest reply on Nov 29, 2016 by aleksandr.kupchik@oracle.com

Hi Guys,

I'm really confused by the AC capacitor in a serial link, who can detail its function?  In our simulation,how to deal with it?

I want to use the S parameter model, which can be found from its supplier. But when the upper frequency of the model is only 6G Hz, i can't use it in my 6G Hz simulation again. I also found another option to deal with this problem, its main thought is model the ESL and ESR of a capacitor, not directly use it but divide ESL/ESR value to some small inductor/resistor, as below showing. But how does this model working?

(ESpice ".subckt Cap2 1 2

C1 1 0  0.15p

R1 1 3a  0.001

L1 3a 4a  0.2n

R1a 4a 3  0.001

L1a 3 4b  0.2n

R1b 4b 3ab  0.001

L1b 3ab 4ab  0.2n

R1ab 4ab 3b  0.001

L1ab 3b 4  0.2n

* CB 4 5  100n  * uncomment to use 100nF series cap

R2 4 6a  0.001  * change node 4 to 5 when using cap

L2 6a 2a  0.1n

R2a 2a 6  0.001

L2a 6 4c  0.1n

R2c 4c 6ac  0.001

L2c 6ac 2ac  0.1n

R2c 2ac 6c  0.001

L2c 6c 4b  0.1n

R2b 4b 6ab  0.001

L2b 6ab 2ab  0.2n

R2ab 2ab 6b  0.001

L2ab 6b 2  0.2n

C2 2 0  0.15p

RS 1 2  100k

.ends Cap2

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