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

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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