How to calculate Capacitance of a structure with extracted S-parameters?

Hi Friends,

How to calculate Capacitance of a structure with extracted S-parameters.

I want to measure capacitance of a parallel plate capacitor over a frequency range.

One more Question. For a RFIC CC1100 I am trying integrated passive capacitors. While simulating decoupling capacitors whether i should concentrate at its operating frequency or Just DC capacitance is Ok?

Thanks,
Sridhar.

plot the S11 , and place a marker , u will see the impedance
take the imaginary part , and XC=/1jwc
use this formula to get C

Khouly

hi Khouly

Ok, but the imaginary part include both inductive and capasitive part. How can i asume it as impedence because of capacitor.

Thanks,
Sridhar.

If imaginary part X is negative - is a capacitance and use C = 1/2*PI*f*X to make value in farad

If imaginary part X is positive - is a inductance and use L = X/2*PI*f to make value in Henry

Be not suprise value can vary pretty much depend of used measure frequency, this is depend of parasitic component in connection wire before cap and cap itself depend of internal structure etc.. Capacitance value near DC is not intresting if you not working in 50 Hz range...

All physic components have parasitic component so, you must measure in actual working/used frequency range. all practical capacitanse and inductance have least one resonant point (Xc = Xl) on high frequency depend of parasitic parallell/serial component and this point component only show (high or low) resistanse and frequency over this point show opposite value. ie capacitance show a inductance and inductance show a capacitance depend of parasitic component have bigger value in high frequency domain.

difference between common component and RF-component is resonance point setting much, much higher frequency to be useful in RF-world

Electrolytic and big capacitanse not working on high and RF-frequency depend of to much parasitic inductance inside.

you can use the s11 at very low frequency, in this way the parasitic inductance of leads are negligible and what you calculate is pure capacitive.

Then you can use S11 at frequency of interest , the difference between two value is mostly due to inductive effect of parasitic caused by lead.

Aslo using S21 you can ccalculate insertion loss ( series resistive part)

Mehdi