[ibis-macro] Re: a s2p example for output impedance and reflection
- From: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- To: <fangyi_rao@xxxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
- Date: Wed, 15 Dec 2010 13:02:28 -0700
Fangyi,
You are right that any modification in S-parameter values may lead to
modifying the solution.
However, there are some special cases when modifying the value does not
change the solution. Let that S-block describe resistor Rx1 to ground
(at port 1) and then controlled source: VC*S with internal resistance at
port 2 (this VC*S is controlled by port 1 voltage). Then, if you
externally attach ideal voltage source at port 1, the voltage or current
at port 2 will not depend on the resistance Rx1, even though Rx1 is
related to S11.
However, the dependence on Rx1 reappears if port 1 is connected to
something different than ideal voltage source. Hence the spec should
state that Tx S-parameters are always connected at one side to voltage
source otherwise the solution is not correct.
Vladimir
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of
fangyi_rao@xxxxxxxxxxx
Sent: Wednesday, December 15, 2010 12:18 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: a s2p example for output impedance and
reflection
I'll use the s2p of a simple resistor R to show why the handling of
touchstone file described in BIRD122 violates basic circuit equations.
To simplify the discussion let's set R=Z=Z0, then the S-parameters for R
are
S11=S22=1/3
S21=S12=2/3
Using my last equation we get expected V2
V2=0.5*V1
If we manually set S11=0, V2 will become
V2=V1*2/3
You can verify these results by DC simulation with any Spice simulator
that supports S-parameter.
Regards,
Fangyi
From: RAO,FANGYI (A-USA,ex1)
Sent: Monday, December 13, 2010 4:52 PM
To: Muranyi, Arpad; Walter Katz; Scott McMorrow; Bob Ross; Todd
Westerhoff; Dmitriev-Zdorov, Vladimir; BIERNACKI,RADEK (A-Sonoma,ex1)
Cc: RAO,FANGYI (A-USA,ex1)
Subject: a s2p example for output impedance and reflection
Hi, AMI colleagues;
Following the discussion in the last ATM meeting about S-parameter file
in AMI models, I think it might be helpful to use a simplified s2p
example to facilitate the discussion. Since I dropped out from the
meeting before it ended, I probably miss the conclusion you guys reached
at the end and my analysis here may not be relevant.
In the circuit below the reference impedance of the s2p is Z0 and the
impedance of port 2 termination is Z.
The circuit equations are
Solve for V2 we get
So V2 depends on port 2 impedance Z. When Z=Z0, S22 and S12 disappear in
the solution.
Regards,
Fangyi
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