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real model capacitors in amplifier design

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patra4ever777777

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hello everyone,

im building a power amplifier 5-6 ghz bandwidth and i had to put one capacitor at the input and one at the output to make the imaginary part of impedance zero and then with a multisection chebysev l/4 i matched the inut and output impedances to 50 ohms..
my ideal capacitors have ideal values of 3.1 pf at the input and 9.67 at the output.. but when i try to replace them with the real models from Murata the whole thing goes down.. i tried many values but they dont seem to fit..and some fit but only for a frequency like for example 5 ghz but for the others i have bad results..
any suggestions?
thnx a lot!!
 

I think you can try to model each of the two capacitors with a spice equivalent, that is an RLC model. Then do the optimization with fixed R, L and variable C. Once the ideal C has been found, replace the whole RLC model with the s-parameters of the real capacitor. Probably R will be negligible, so you can try with just an LC series. You could estimate the L value from the self-resonance frequency of the capacitor.
I hope it works.

Another approach that is better, but probably longer to implement, is to ask your simulator to optimize using capacitors taken by a list of s-parameter models.
 
yeah, you see i already have the libraries with all the capacitors that Murata provides.. ok then ill try to make some optimization as you proposed thanks a lot!!
 

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