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@01CB9C46.16C23060] The circuit equations are [cid:image002.png@01CB9C46.16C23060] Solve for V2 we get [cid:image003.png@01CB9C46.16C23060] So V2 depends on port 2 impedance Z. When Z=Z0, S22 and S12 disappear in the solution. [cid:image004.png@01CB9C46.16C23060] Regards, Fangyi