Eye-diagram simulation when S21 result of touchstone file isn't enough

Hi. Nowadays I am testing Eye-diagram simulation using S21 touch stone file.
My target data rate is 20Gbps.

But I've found that my S21 file has the result upto 15GHz.

As you know, S21 result should have the result of frequency upto 30GHz(3rd Harmonics of the target data rate, 3*10GHz)
when we want to to 20Gbps Eye-diagram simulation

Even though my file has the result only upto 15GHz, simulation completed with some result. (Maybe imperfect Result)


So, I wonder what kind of algorithm ADS is using to compensate those lack of information (S21 of frequency from 15GHz)
Does ADS assume that every S21 value of frequency which is higher than 15GHz is the same value of 15GHz?
Or does ADS use some special algorithm to compensate the lack of S21 information?


Thanks a lot.

If you are using the S2P component, it uses constant extrapolation, by default. However, there are other options. Refer to the documentation on tihs component for details. You could run an S-parameter simulation of just your S-parameter data, and sweep the frequency out to 30 GHz and see what happens as you change the extrapolation method.

The S-parameter simulation will default to constant extrapolation, however, in the Transient and Channel Simulators ADS uses a patented causal transformation based on the Hilbert transform and enforcement of the Kramer's-Kronig relationship. The simulation messages also provides information on the bandwidth used in the time domain simulation for each of the S-Parameter blocks. I would suggest taking a look at the following DesignCon papers on the topic and then experiment with bandlimiting the S-Parameter to even smaller bandwidths to see the relative impact on your design. A lower bandwidth is basically a low pass filter, but if the channel already has other components slowing down the edge rate it may not be a significant impact and 1.5 x Nyquist might still be sufficient.

../img/keysight/ADS2020-455-5991-4084.pdf Look in the Fixture Design Analysis section.

../img/keysight/ADS2020-456-DC2008_CM2.pdf

Regards,
Heidi

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