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Re: [802.3_COM] Correction: Question about equation in function get_TDR

Hi Norman,

The function on line 63 of TDR_RL is the renormalized return loss (Sdd11' or Sdd22') where one is changing the differential reference impedance from sdd.Impedance to (2*ZT). Does this help answer the quesiton?

The function TDR_RL on line 63 is called by the following on line 71.
RL(i)=TDR_RL(sdd.Impedance,2*ZT,sdd.Parameters(param.RL_sel,param.RL_sel,i) ,sdd.Parameters( 1,2 ,i), sdd.Parameters( 2,1 ,i),sdd.Parameters( other_port,other_port ,i) );

Attached is a presentation that derives the formula on line 63, starting from the renormalization of a 2×2 S-matrix. It leads to an _expression_ for the renormalized return loss in terms of the original (unrenormalized) S-parameters and the input/output reference impedances.

Regards,
Hansel D'Silva
From: Norman Swenson <norm.swenson@xxxxxxxx>
Sent: Saturday, July 19, 2025 11:10 AM
To: STDS-802-3-COM@xxxxxxxxxxxxxxxxx <STDS-802-3-COM@xxxxxxxxxxxxxxxxx>
Subject: Re: [802.3_COM] Correction: Question about equation in function get_TDR
 
CAUTION: EXTERNAL EMAIL

Correction: The name of the function (and corresponding .m file) is get_TDR.



From: norm.swenson@xxxxxxxx <norm.swenson@xxxxxxxx>
Sent: Friday, July 18, 2025 10:30 PM
To: STDS-802-3-COM@xxxxxxxxxxxxxxxxx
Subject: Question about equation in function TDR_results



Hello all



I am trying to reverse engineer the current version of COM in the main
branch.  Lines 62 and 63 of the function get_TDR define a pure function:



% re-normalize reference of s-parameterss: this seems correct for a s4p
input file [sic]

TDR_RL
=@(Zin,Zout,s11,s12,s21,s22)(Zin.^2.*s11+Zin.^2.*s22+Zout.^2.*s11+Zout.^2.*s
22+Zin.^2-Zout.^2
<mailto:=@(Zin,Zout,s11,s12,s21,s22)(Zin.%5e2.*s11+Zin.%5e2.*s22+Zout.%5e2.*
s11+Zout.%5e2.*s22+Zin.%5e2-Zout.%5e2> +
Zin.*Zout.*s11.*2.0-Zin.*Zout.*s22.*2.0+Zin.^2.*s11.*s22-Zin.^2.*s12.*s21-Zo
ut.^2.*s11.*s22+Zout.^2.*s12.*s21)./(Zin.*Zout.*2.0+Zin.^2.*s11+Zin.^2.*s22-
Zout.^2.*s11-Zout.^2.*s22+Zin.^2+Zout.^2+Zin.^2.*s11.*s22-Zin.^2.*s12.*s21+Z
out.^2.*s11.*s22-Zout.^2.*s12.*s21-Zin.*Zout.*s11.*s22.*2.0+Zin.*Zout.*s12.*
s21.*2.0);



In typeset form, TDR_RL is given by :





Or, expressing the numerator and denominator as polynomials in Zin and Zout,
TDR_RL is:





I am wondering what this is.  Is this an _expression_ of the return loss when
Zin and Zout are the source and load impedances, respectively, when they
differ from the reference impedance Z0 used to calculate the s-parameters?
(If so, this would be along the lines of the presentation I made last Monday
to the interim working group meeting, but I would like to be sure.)



Thanks for any guidance anyone can provide.



Regards,

Norm






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Attachment: Sparameter_Renormalization_COMTool__REVISED.pptx
Description: Sparameter_Renormalization_COMTool__REVISED.pptx