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Determining Inductance/Capacitance from S-Parameters

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asubraman

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s-parameter inductance

Hi,

I'm trying to determine the inductance and capacitance of chip inductors/capacitors at 1-2 GHz from the S-Parameters (S11 & S21) measured on an VNA. Does anyone know what equations/methods I should use to get these values. Thank you for your help!
 

capacitance from s parameters

1. Find an appropriate model including the most important parasitics
2. Find some good starting component values for the I/C and their parasitics
3. Optimize the component value and parasitics (preferrably automatically) to the S-parameters match the model as good as possible.

A good starting point for inductors would be the Spice models of the Coilcraft inductors. You should be able to find something similar for the caps, but usually a series RLC circuit works fine.

https://www.coilcraft.com/models.cfm
 
s parameter inductance

Hello asubraman,

Import or read your S-pareameter file to any simulator (AWR MWO or Sonnet EM)
then plot the Y parameters Then use the following equation to get the Capacitance & Indutance values

Y11 = Im(Y(1,1))

C1=1.0E12 / ( 2 * _PI * _FREQ * ( 1 / Y11 ) )

Where
L1=1.0E9 * ( 1 / Y11 ) / ( 2 * _PI * _FREQ )

L1: Effective Inductance (in nH) of a series RL network

C1: Effective Capacitance (in pF) of a series RC network

_FREQ: is project frequencies in GHz

Note: Sonnet has direct measurement option for the above...


---manju---
 
dear manju,

thank you so much for the above post, it really helped me. can u tell me whether in this case, the resistance would be Re(Z(1 1)) or Re(1/Y(1 1))?
 
hello,


I hope this helps you...see the attached document...

---manju---
 
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Dear Manju,

In the calculation of L1, the formula you have used.... is it 1/imag(Y(1 1)) or should it be imag(1/Y(1 1))? Please reply soon... Thanks so much!

Kas
 

Hello acekas,

it is imag(1/Y11)...

Also Note that on your query Resistance calculation;
If you are looking for the equivalent series resistance then

Z11 is only equal to 1/Y11 for a one-port (or if you short circuit port 2 device).
When you have a two-port, Y and Z are matrices and you cannot just take the reciprocal of each element in the matrix.

so whatever kspalla told was theoretically not true...

I hope this helps you...!!!


---manju---
 
Thanks Manju, yeah, that helped!

Regarding what you said about short circuiting port 2, can you please tell me how I can do that on cadence?

Further, isn't the expression imag(1/Y(1 1))... valid only for circuits with the second port short-circuited? If not, I would appreciate it tremendously if you could throw some light on how we are arriving at the expression!

Thank you once again!
Kas
 

Thanks Manju, yeah, that helped!

Regarding what you said about short circuiting port 2, can you please tell me how I can do that on cadence?

Further, isn't the expression imag(1/Y(1 1))... valid only for circuits with the second port short-circuited? If not, I would appreciate it tremendously if you could throw some light on how we are arriving at the expression!

Thank you once again!
Kas

can i do it in cadence?
 

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