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Differences between HB and Transient simulations

Question asked by NEWPORTY on Dec 10, 2007
Latest reply on Dec 13, 2007 by NEWPORTY

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I am simulating a power amplifier (single FET modeled with an SDD, microstrip lines, LC bias tee), sweeping the input power. The ouput power results reasonably agree at lower power values but start to differ when reaching saturation. Do you know what the main cause could be? IÂ´ve tried different number of harmonics and oversample in the HB analysis, and different trasients settings, the results donÂ´t change. I am using the markers to delimit time start and stop time for the fs function.

Thanks,

Yolanda

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wrivas Dec 11, 2007 12:08 AM
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I presume that your power sweep is for a single tone. If we call the HB order N then you should set the timestep for the transient simulation to 1/(2*N*Ftone), where Ftone is the frequency of you input tone. From your question I think you are allowing for the traneient signal to reach steady state so that is a positive but you may have to collect more data so that the fs() function give you a small RBW. I would also try no windowing or different windows in the fs() function.
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NEWPORTY Dec 13, 2007 9:17 PM
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Thanks, MaxStep was set according to that, but the problem was that it was not reaching steady-state at high power levels at the times that I had set. Still, there is about 0.8 dB difference at low powers (where HB output power is lower than transient) and 0.9 dB at high poweres (where HB pout is higher), not sure how to explain that. Also, the fs function is extremely sensitive to the start and stop time and itÂ´d give completely wrong results if more than one period is included. Is that the way it is supposed to work?
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Differences between HB and Transient simulations

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