I would like to ask one question about Charge pump loop stability

[yixiusky]

Dear all, i would like to ask one question:

As we can see from schematic, there is one loop existed from output to FBP (feedback point).

I would like to run AC simulation to check the loop stability. However, the part in white box is discrete signal, so i need modeling it, and then i can run AC simulation.

The white part is two diode with one cap, and input to cap is pulse ^^

Do any of you have experience to do it? Or do you have any book to recommend in order to modeling it?

Thank you so much ^^

 

[varunkant2k]

I guess out put of your white box ramps up from VREG to Vpeak (pulse) and the down from Vpeak to VREG.
Your gain is Average voltage of ramp signal devided by VREG. I hope this should work.

Again Pulse duty cycle again have to take in account once you calculate average output voltage.

 

[yixiusky]

Thank you so much ^^
You are right, out put of white box ramps up from VREG to Vpeak (pulse) and the down from Vpeak to VREG.
After load cap, it will have DC output VGH.

Pulse duty cycle is 50%.

I would like to know how can i do modeling for it to run AC simulation? Could you please help me?

Thank you so much ^^

 

[varunkant2k]

you need not to do any thing, just add one ideal gain block with constant gain of VGH/VREG.
Thats all for AC analysis.

---------- Post added at 16:49 ---------- Previous post was at 16:45 ----------

Remove the resistnace from VFB to ground. Open the loop from VGH and apply unit amp. AC signal. It should give correct result.

 

[yixiusky]

thank you very much ^^ I attach the new schematic here, i replace the white box with one gain stage. And i run loop stability by using the iprobe. However, the result is very strange. And i would like to know whywe need to remove the resistor at FBP to ground?

could you please help me? Thank you so much. ^^

 

[varunkant2k]

If you use Iprobe/stb analysis, you need not to remove resistance thats so I told. Sorry for that.
That was basic method , we have followed from beginning.

Anyways, please check the stb analysis. There also you can know the correct gain and phase.
The Wave form shape is correct but they are attenuated, may be various reasons. I am interested to know the gain from STB analysis.

---------- Post added at 17:59 ---------- Previous post was at 17:57 ----------

At which point you are capturing gain and phase plot?

 

[yixiusky]

Thank you very much ^^ when we put iprobe in the loop, the result is independent of which point we capture. My test bench it same as the attachment ^^