[ibis-macro] Re: a s2p example for output impedance and reflection
- From: <fangyi_rao@xxxxxxxxxxx>
- To: <vladimir_dmitriev-zdorov@xxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
- Date: Thu, 16 Dec 2010 01:51:58 -0700
Thanks, Vladimir. I agree with you and Scott.
Fangyi
From: Dmitriev-Zdorov, Vladimir [mailto:vladimir_dmitriev-zdorov@xxxxxxxxxx]
Sent: Wednesday, December 15, 2010 12:02 PM
To: RAO,FANGYI (A-USA,ex1); ibis-macro@xxxxxxxxxxxxx
Subject: RE: [ibis-macro] Re: a s2p example for output impedance and reflection
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.
[cid:image001.jpg@01CB9CBB.58915CD0]
The circuit equations are
[cid:image002.gif@01CB9CBB.58915CD0]
Solve for V2 we get
[cid:image003.gif@01CB9CBB.58915CD0]
So V2 depends on port 2 impedance Z. When Z=Z0, S22 and S12 disappear in the
solution.
[cid:image004.gif@01CB9CBB.58915CD0]
Regards,
Fangyi
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