(H)SPICE and Spectre results are always presented as real values, small or big values designated by an appropriate prefix or by an E notation.chichi said:the result got from thd simulation is the real value, or with unit%?
Right!chichi said:... the third harmonics increase faster than signal amplitude when increasing the input signal
No, this is a misunderstanding. See iamlearning's contribution from Thu, 18 Feb 2010 19:01, saying "IIP3 determines the input power after which gain for the 3rd harmonic is greater than that of the Fundamental". See also this wiki for a good explanation of IIP3.chichi said:so HD3 should decrease till 0 with increasing output amplitude(so called IIP3 point)
I do not quite understand your curve. From your text, it should be HD3 vs. HD1 (the Fundamental), right? Then - apart from its strange shape - how can you get an HD3 output signal between 60 and 90 dB from a fundamental signal between -70 and -20dB ? At a fundamental input signal of -60dB (1mV, in case of dbV), an HD3 output of 70dBV would mean an HD3 gain of 130dB (≈ 3e6) or an HD3 output voltage of > 3kV. There definitely something must be wrong with the size of the units.chichi said:but in my case the curve is like a wave, very bad.lz se the atattched
the result got from thd simulation is the real value, or with unit%?
but why my THD always seem to be about 8%, my specs requirement is 0.92%, what do u think is the reason?
:razz:Thanks!If you have in your transient responce current i.e I2, then you first press wave,it and then you press the waveform in transient responce so the expression is in the buffer.After that select from special functions thd.At this point you have to set as you said 4 parameters. At boxes From & To you have to write something in time, for example 3u to 5u(meaning usec).These values depends on the frequency of your output waveform.So it is good to select two periods of your signal. At fundamental choose 0 .Now for number of samples you can write 64,512,1024 but it depends on the step you have in transient analysis.Check at cadence help for calculator.I think you will find it at calc.pdf . There you will find the expression in order to select the right No of samples. If you have problem send a photo with your signal or just send the frequency of your signal.
If your waveform is voltage, press wave,vt and then the waveform
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