[ibis-macro] Re: a s2p example for output impedance and reflection
- From: Jianhua Gu <jianhua.gu@xxxxxxxxx>
- To: fangyi_rao@xxxxxxxxxxx, ibis-macro@xxxxxxxxxxxxx
- Date: Wed, 15 Dec 2010 14:25:31 -0500
Another way to say it is the 4 entries (S11, S21, S12, S22) altogether
characterizes the physical network, not 3 (S21, S12, S22).
Jianhua
*From:* ibis-macro-bounce@xxxxxxxxxxxxx [mailto:
ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *fangyi_rao@xxxxxxxxxxx
*Sent:* Wednesday, December 15, 2010 2:18 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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