Reply To: S-parameter causality issue

[Dan Dvorscak]

Hi Alex,

The short version is that shap discontinuities in the s-parameters appear as being numerically non-causal. The point of the two tiered sweep, log at low frequency and linear at high frequency, is the best way we've found to capture the resonances withouth grossly oversampling. PDN effects are best captured by the log sweep and signaling (and other strutures interesting at higher freqeuncies) by the linear sweep.

If we try to do just one sweep, say log, you would have to add 100s of points per decade to not undersample the higher frequencies, and that would add way, way more points you need a low frequencies. 

This sampling is about more than just causality but a general best practice. So it does more than just help preserve the causaliyt in the model.