SParameterChannel output transfer and rational functional data issue

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Hi,
I am facing the following strange behavioural of the SParameterChannel function in MATLAB:
  • all work fine when this function is used with TX and RX 50 Ohm impedance with 50 Ohm S-parameter ref. impedance
  • the amplification of the signal was observed when the TX impedance was less than RX impedance, TX = 40 and RX = 80 for example
I understand that amplitude of the impulse response should be more in case TX = 40 and RX = 80, as result of the RX impedance is above TX impedance and ref. S parameter impedance, but why it should be appeared in the timing simulation when transfer function and rational function are used, samples:
Obj = SParameterChannel(...);
[output,t_out] = timeresp(Obj.RationalResults(1,1),Pattern,samplingTime);
or
rationalfunc = rationalfit(SparamFreq, Obj.TransferFunction(:,1), Tolerance=-60, NPoles=150);
[output,t_out] = timeresp(rationalfunc,Pattern,samplingTime);
I can correct this mistake by:
outputNew = output / abs(Obj.TransferFunction(1,1));
but anyway, why MATLAB help doesn't describe how to use SParameterChannel for timing simulation.
What is right way for timing simulation using SParameterChannel function output object?
Thanks
Alex S

Answers (1)

Abhimenyu
Abhimenyu on 11 Feb 2024
Hi Alex,
From the information shared by you, I could infer that you are performing "timing simulation" using "SParameterChannel" object of MATLAB. The "SParameterChannel" object combines the scattering parameter (S-parameter) model of a baseband communication channel with an analog transmitter and receiver into a single S-parameter with adjustable port ordering.
From the MATLAB R2023b documentation, I found that the purpose of the object "SParameterChannel" in "RF Toolbox" is to return an impulse response object given input parameters. Timing analysis is non-trivial, and is supported by the "Parallel Link Designer EDA" tool as part of "Signal Integrity" Toolbox. I did not find the concept of "timing simulation" provided or supported by the "SParameterChannel" object of MATLAB. There is a MATLAB R2023b documentation help page that describes the functionality provided by this object at this link: https://www.mathworks.com/help/serdes/ref/sparameterchannel.html
A MATLAB R2023b example that introduces timing and mask analysis for "DDRx" (and is applicable to other systems) is available at this link: https://www.mathworks.com/help/signal-integrity/ug/ddrx-timing-and-waveform-mask-analysis.html
Also, the "Port Impedance" (TX 40 ohms, RX 80 ohms equivalent differential impedance) may be adjusted by customizing the ideal IBIS models in "Parallel Link Designer" or by importing vendor or custom IBIS/IBIS-AMI models into a project using "Parallel Link Designer". The S-parameter files may be imported to "Serial Link Designer" or "Parallel Link Designer" and incorporated into channel topologies (and also swept across simulation cases) to evaluate system performance as part of "Signal Integrity Analysis".
I hope this helps to resolve your query!
Thanks,
Abhimenyu

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