help, how to simulate output impedance of balun with cadence

[stachel]

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

[/img]

 

[BigBoss]

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.

 

[stachel]

Re: help, how to simulate output impedance of balun with cad

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

 

[BigBoss]

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

 

[stachel]

Re: help, how to simulate output impedance of balun with cad

BigBoss,

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

regards,
stachel

 

[sharethewell]

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

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