Good day.
I am trying to simulate power supply noise propagation through an amplifier stage. The amplifier is driven by a large signal, which is the PSS beat. The circuit is slightly non-linear (THD around 30dB). I use harmonic balance for PSS engine. Now I add power supply interference (small signal); I try it in two different ways:
1) Run PAC analysis, with the only PAC source being power supply voltage source, look at the output spectrum (differential voltage).
2) Run PXF (differential voltage output) and look at the transfer function from the said power supply voltage source.
I deem the two analyses should have given same spectra, but they don't. In fact, the base harmonic (i.e. number "0") is exactly identical, all the others as not.
Can anyone please explain that to me?
UPD: I have tried to verify this with transient, i.e. ran a long TRAN simulation with both the input (LO) and the power supply (SUP) active; checked the output spectrum. Thus I validate a single frequency point of the SUP. It came out very close to PAC (and very far from PXF). So I better rephrase my question: where is my understanding of PXF went wrong? The image below shows these results. Peaks are come from the transient spectrum (1st harmonic). The brown and green curves are PAC results. The two remaining curves (flat ones) are PXF.
Many thanks,
Yevgeny.