# Questions about the definition of Z-matrix and Zin and Zout

1. ## Questions about the definition of Z-matrix and Zin and Zout

Dear,

I use ADS. I am quiet puzzling about the definition of Z-matrix and Zin and Zout.
Question:
In ADS, I use stoz(S) to get the Z-matrix of the network.
In schematic, I write the following measurement equations to get Zin and Zout.
Ztmp = stoz(S, 50)
RinEVB = real(Ztmp(1,1))*50
XinEVB = real(Ztmp(1,1))*50
RoutEVB = real(Ztmp(1,1))
XoutEVB = real(Ztmp(1,1))
Also, I use another way to get Zin and Zout:
Zin1 = sm_z1(S, 50)
Zout2 = sm_z2(S, 50)
As expected, RinEVB roughly equals Zin1 and RoutEVB roughly equals Zout2.
While there are some difference between the 2 approach. My question is, which way is more accurate.
Also, I found that XinEVB and XoutEVB differs a lot from imagines of Zin1 and Zout2. What is the reason, and which on is correct?

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2. ## Re: Questions about the definition of Z-matrix and Zin and Zout

You confuse z-parameters and Input/Output Impedances of a 2-port.
z-parameters are "open circuit parameters" and z11 is not equal to Zin ( or z22 is not equal to Zout )
Pay attention to definitions.. z11=v1/i1 while i2=0 !! similarly z22=v2/i2 while i1=0..
Zin is a measure of 2-port while 2nd port is terminated by Zo.. This is important.

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