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stability of charge pumps

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filipecbv

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charge pump ac analysis

Hi,

I'm designing a charge pump (phang topology) for memories, using a clock of 100kHz. The charge pump is working, but I'm having a difficult to analyze it in terms of stability.
I want to control the output voltage changing the amplitude of the clock signal, so I modeled my charge pump.
Then, one pole is created in the charge pump being an association of the output resistance of the charge pump (30Mohm) with the output capacitor (10pF), and resulting in a pole of 1kHz. So, the requirements of the opamp to control the system is as small as 1kHz.
The output resistance of the charge pump is given by n/c.f, where n=6, c=3p and f=100kHz.
Could be this analysis wrong?
What are good references to read about the stability of charge pumps?
I didn't found papers about this fact, mainly related to this pole that I found, and what to do with it.

Thanks
Filipe
 

stb pstb cadence

I think the difficulty that you face here is with analyzing the pole locations of a clocked loop. Do a PSS+PAC simulation to know the dc gain, loop poles and phase margin (even better is PSS+PSTB if you are familiar with stb analysis).
 

charge pump stability

hi,saro_k_82:
Could you tell the full name of PSS,PAC,PSTB? Are these tools of cadence?
 

pss pstb spectrerf

Hi,

They are analysis options avaliable with spectre

Periodic Steady State Analysis PSS
Periodic AC Analysis PAC
 

Yes., I beleive you use ADE/spectre for simulations. These are simulations just like dc, ac, tran., etc. STB analysis breaks the loop, provides all the information about the open-loop gain/phase.
PSS stands for periodic steady state. For periodic circuits (just as the one you have now) pss finds the cyclostationary steady state., which is equivalent to finding dc op point. After PSS, you can run PAC (periodic ac) analysis to find out the poles (this can help only in cases where the clock is considerably higher than the bandwidth of the loop). For PSTB, you need to connect a zero-voltage vdc source somewhere in the loop and point the instance parameter in the pstb to it and check for the loopgain plot from the directplot option.
 

    V

    Points: 2
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pss, qpss, pac, ... belong to spectreRF,
you can consult with spectreRF reference manual, user guide, theory doc
 

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