# Determining Inductance/Capacitance from S-Parameters

1. ## 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!

2. ## 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.

http://www.coilcraft.com/models.cfm

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3. ## 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---

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4. ## Re: Determining Inductance/Capacitance from S-Parameters

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))?

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5. ## Determining Inductance/Capacitance from S-Parameters

both should be equal by theory.

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6. ## Re: Determining Inductance/Capacitance from S-Parameters

hello,

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

---manju---

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7. ## Determining Inductance/Capacitance from S-Parameters

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

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8. ## Re: Determining Inductance/Capacitance from S-Parameters

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---

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9. ## Determining Inductance/Capacitance from S-Parameters

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

10. ## Re: Determining Inductance/Capacitance from S-Parameters

Originally Posted by acekas
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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