How to use OrCAD P-Spice to simulate TIM and Distortion correctly???

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Hello All
Sorry for bother everybody
I have a quaestion about distortion simulation.
My procedure is
1: Spice run transient simulation
2: Use probe to measure Power AMP output voltage
3: Use "voltage unit" waveform to convert to FFT (Trace->Fourier)
4: And shown the result, change to log or linear scale

but now I have one problem, that is the Y-Axis of FFT waveform is voltage unit,
but in others result, it is always dB unit. I use a way to change to dB,
but I feel that is strange, maybe it's wrong, could you help me to check this way is right or not??

I only change step 3:
in step 3. the waveform unit is voltage, so I use P-spice DB() function, to change
the waveform Y-Axis to DB, then convert to FFT, that will make the FFT result
Y-Axis to DB.
Does this method is correct??, I doubt if this is workable.

Thank you very much, appreciate!!!!!
 
I'ld like to help but I use a Freeware product of their's called Schematics. In my terms I think you neglected to mention something along the lines of nameing the node your measuring and entering that variable as the source for the fourier.
In the sim window I use a Log/Lin button on the toolbar to get DB???
Schematics is basically easier to use, for me ;)
 
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