[SI-LIST] Re: How to use S-parameter accurately

Terence:
   
  If I understood you correctly, you did not point out how you judge the 
waveform is accurate or not. Can you provide this information?
   
  I guess your simulation results be very accurate when you set your simulation 
length equal to 200ns, 400ns, 600ns and so on. There is a tricky parameter in 
hspice: fbase. It controls how touchstone file be interpreted by simulator. It 
should equal your touchstone file data spacing in frequency. If you do not 
specify, it will be set to 1/(simulation length). Normally, it should be fine. 
In special cases, interpolation of s-parameters will incur big error.
   
  There is also another parameter fmax, which controls how simulator do the 
inverse FFT. You should set it to be close to your touchstone file data max 
range.
   
  I hope this helps...
   
  regards,
  Han 
  IDT Corp.
   
   
   
   
  
TerenceHsieh@xxxxxxxxxxxx wrote:  Dear all
I have some s-parameter simulation problem. I have s-parameter
file extracting from board file and 
simulate it by Hspice. According to the input signal, I extracted the
s-parameter with sufficient 
bandwidth and points (input signal: 125MHz, S-parameter bandwidth : 5GHz
1000pts/linear). 
When simulating, the output waveform will vary with input rise/fall time
enormously and also 
simulation time. The most accurate waveform will occur when the input
rise/fall time set to 0.8ns
and simulation time set to some specific value. Even though the
rise/fall time set to larger or smaller 
than 0.8ns the output waveform will get inaccuracy. 
The s-parameter bandwidth is larger than knee frequency of
input signal and I also filtered out high harmonic 
component of input signal (input signal is an idea 50/50 duty pulse) by
5 order low-pass filter ( cut-off 
frequency set to 10 times the input knee frequency). Why the s-parameter
can just simulate at specific input 
condition accurately? How could I use s-parameter more accurately?
Thanks. 

Terence

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