help, how to simulate output impedance of balun with cadence

hi everyone,

i'm designing a RFPA. At the input side a balun is used to convert single-ended signal to differential signal.

i have two questions:

1. i think the input impedance Zin of transistor should be conjugate matched to source impedance Zs, am i right?

2. to get Zs, i must know the output impedance of balun Ztr. i wanna make a AC-simulation and Ztr=V/I.
but when a input signal is added to PORT and a resistence R is added at the right side of balun, the simulated impedance is always equal to R (i.e. the impedance looking to right side, but what i want is the impedance looking to left side). How should i setup the testbench?


regards,
stachel

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Why don't you make a s-paameters simulation instead of AC to get the reflection coefficient and then impedances ?
If you know the reflection compare to characteristic impedance, after that you can get the real impedance.

hi BigBoss,

good advice, thanks

if i understand correctly, each of differential terminate is connected with a port(port number =2 and 3) and i make a SP-simulation,
impedance can be computed according to Ztr_1=Z0*(1-S22)/(1+S22); Ztr_2=Z0*(1-S33)/(1+S33), is it right?

but i'm confused it is the impedance looking to left or right, have i the correct S-parameter selected?

regards,
stachel

I have attached a pdf file that explains the simulation setup in ADS.All you should do is to make a s-parameters simulation independent of RFPA..
I have put the transformation ration as 2 and you can easily observe that impedances are transformed by this ratio for each Sxx

BigBoss,

your example is very helpful for me, it validates the equations i attached, now i konw the method.
thanks again.

regards,
stachel

How do you do the SP analysis in Cadence? Is Z11 is the input impedance or the Zin equation?