You might want to try using a piecewise linear approximation rather than tanh(), and use cross functions at the corners so that you know the simulator spends some time within the linear region.

-Ken

Hope this article on EDN helps.

Periodic steady-state and small-signal analyses of switching regulators
http://www.edn.com/article/CA6579651.html

It compares the results between averaged model and PSTB simulation.

Hi, I know that this thread is old but right now I am trying to do the same thing that Richard did and Jason too.

I am trying to get the frequency response of my dc-dc converter with the loop closed. I have inserted a VSIN with the PAC field at 1V and I have connected the positive terminal do the VSIN to the output of the converter and the negative to the input of the error amplifier.

After running the PSS + PAC analysis, I ask for the amplitude in dB20 on the left side of the VSIN and what I get is this:

http://postimg.org/image/b7d4v1mt3/

This result is strange because the response starts at 0dB and that shouldn't be right?

After that I tried to use the PSS + PSTB analysis replacing the VSIN source by the iprobe and the result that i got, asking for the loop gain option in the PSTB separator was this:

http://postimg.org/image/4lsqcxpr5/

If we go back to the PSS + PAC analysis, instead of selecting the left side of the VSIN source, selecting the right side I get almost the same shape and values of the PSS + PSTB analysis but inverted.

From what I have read all over the place I think that I am placing the PAC and/or iprobe in the correct place, I think I am configuring in the right way the analysis and I get this different results.

Can anyone help me out here? I am out of ideas and I don't have a clue on how to solve this.

Thanks in advance.

Kind regards.

EDIT: I forgot to tell that my converter is operating at very high frequency > 300MHz.