Why there is a difference between transmission line models

Thread Starter

kintaro

Joined Jun 1, 2022
16
I have a transmission line with characteristic impedance of 75Oohm.
I model it with both TLIN (electrical) and MSUB (physical) model.
using a 5GHZ data generator to check the signal quality. I found that the result with TLIN model is ok. But the result with MSUB model is bad, still got some ringing.
Both model has Z0=75Ohm and the load is also 75Ohm, which should be impedance matched.
but why there is the difference? why the MSUB model has ringing even though impedance matched?


linecal.jpg

MSUB2.jpg

TLIN2.jpg

msub.jpg

TLIN.jpg
 

MrAl

Joined Jun 17, 2014
9,633
Do you have the model statements?

They must be different so you have to compare. You can get 75 Ohms with different line specs as well.
 
In your schematic the substrate is defined as MSub1 whereas the line width calculator is using MSUB_DEFAULT. I'm no ADS expert, but that might be the cause if MSub1 and MSUB_DEFAULT are not the same.
 

WesBrodsky

Joined Dec 27, 2019
13
For the MSUB1 case, all the dimensions of the transmission line are specified, and the characteristic impedance is also. There are three parameters, K Eff = 5.946; A DB = 1.006; SkinDepth = 0.043; which appear to be calculated. What are they.
One cause of "ringing" can be the "Gibbs phenomenon"; when the frequency response of the analysis is not high enough. Maybe you need to specify a higher frequency of the ADS Fourier Transform or, alternative, a smaller step size if a purely time analysis.
 
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