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DC-DC Converter/ Feedback/ Verilog-A

Pyroblast

Hi  dear fellows,

I am trying to design a DC-DC converter using Cadence/Spectre environment.

That said, what I want to do is to measure the feedback loop. I've been told that HSPICE has a simulation option that allows one to break the feedback loop and measure it. The person who told me that didn't knew if the same would be possible with spectre.

After searching around the web, I found a website where they were talking about the stb analysis. From what I've understood and read on the spectre manual this stb analysis allow:

"The loop-based and device-based algorithms are available in the Spectre circuit simulator for small-signal stability analysis. Both are based on the calculation of Bode’s return ratio. The analysis output are loop gain waveform, gain margin, and phase margin."

"Linearizes the circuit about the DC operating point and computes loop gain, gain margin, and phase margin for a specific feedback loop or an active device. The stability of the circuit can be determined from the loop gain waveform. The probe parameter must be specified to perform stability analysis."

On that website they did this analysis with a Single-ended Opamp simulation. To perform this analysis, a iprobe component was needed.

I haven't tried this yet.

 So what I'd like to ask is if someone here as used this kind of analysis and if it was successful.

Based on this, I was wondering if it is possible to do the same thing but in a feedback loop of a dc-dc converter? Break it on a particular part, block th AC signal and let the DC pass.

Taking the advantage of this post, I'd like to as anoter thing.

I don't know if some of you guys that are reading this post are familiar with DC-DC Converter. Picking the Basso's book, where he teaches how to simulate DC-DC Converters using PSPICE, he uses a switch model to model the power devices. He uses a transformer, current sources, etc.

It is possible to implement such models in Cadence? Transformers, current sources, etc.

Please feel free to comment, give an opinion, share experiences. If you can give some tips too I would appreciate.

Sorry for the long post.

Kind regards

 

EDIT: Can someone tell me where can I find some good Verilog-A models for comparator, ramp generator, PWM, etc?

Parents
  • Pyroblast

    Hi Andrew and thanks for the quick reply.

    To be honest I didn't understood the point 1.

    I have used PSS analysis, in fact I kind use this PSS analysis to make almost all my simulations, instead of transient (more fast).

    In the paper that you gave at UK NMI event you have analysed the stability of the DC-DC Converter? Can you send me a private message and tell me where can I find that or maybe you could send me that paper?

    Returning to the question of the STB, PSTB, PSS, when you say PSS/PSTB means that one should perform those two simulation at the same time?

    Here: http://www.lumerink.com/courses/ece5411/Handouts/Loop%20Stability%20Analysis.pdf you can find the slides from what I was talking about.

    As you can see, they put the iprobe at the OPAMP output.

    If we grab what you said,  "Instead it injects a signal at the probe point and measures it returning around the loop (it's a bit more complicated than that, but that's the principle)" and look at the schematic on that slides I showed above, slide 4, this means that the iprobe, that has an arrow pointing from "left to right", located at the output of the OPAMP and before the feedbac, is injecting a signal there, that will be going to the load and to the feedback loop? Is that it?

    You said "The stb analysis is geared up for when you have a DC operating point and then does a small signal analysis around that. For a switching circuit, you're more likely to need to analyse a period of operation of the circuit and use this time-varying operating point to analyse the time-averaged stability using pstb."

    In this case, because we are dealing with a switching circuit,  we're in the presence of a time-varying operating point and what you said in bold is totally right (of course!).

    Let me see if I can explain myself and expose my doubt clearly. This means that we can analyse the stability of the DC-DC Converter directly through simulation using the PSS/PSTB, even though knowing that the power devices are non-linear and the circuit is time-varying? There is no need build a linear model, like that one that Mr. Basso's uses in his book using a transformer, current source, etc?

    Thanks for your time.

    Regards.

Reply
  • Pyroblast

    Hi Andrew and thanks for the quick reply.

    To be honest I didn't understood the point 1.

    I have used PSS analysis, in fact I kind use this PSS analysis to make almost all my simulations, instead of transient (more fast).

    In the paper that you gave at UK NMI event you have analysed the stability of the DC-DC Converter? Can you send me a private message and tell me where can I find that or maybe you could send me that paper?

    Returning to the question of the STB, PSTB, PSS, when you say PSS/PSTB means that one should perform those two simulation at the same time?

    Here: http://www.lumerink.com/courses/ece5411/Handouts/Loop%20Stability%20Analysis.pdf you can find the slides from what I was talking about.

    As you can see, they put the iprobe at the OPAMP output.

    If we grab what you said,  "Instead it injects a signal at the probe point and measures it returning around the loop (it's a bit more complicated than that, but that's the principle)" and look at the schematic on that slides I showed above, slide 4, this means that the iprobe, that has an arrow pointing from "left to right", located at the output of the OPAMP and before the feedbac, is injecting a signal there, that will be going to the load and to the feedback loop? Is that it?

    You said "The stb analysis is geared up for when you have a DC operating point and then does a small signal analysis around that. For a switching circuit, you're more likely to need to analyse a period of operation of the circuit and use this time-varying operating point to analyse the time-averaged stability using pstb."

    In this case, because we are dealing with a switching circuit,  we're in the presence of a time-varying operating point and what you said in bold is totally right (of course!).

    Let me see if I can explain myself and expose my doubt clearly. This means that we can analyse the stability of the DC-DC Converter directly through simulation using the PSS/PSTB, even though knowing that the power devices are non-linear and the circuit is time-varying? There is no need build a linear model, like that one that Mr. Basso's uses in his book using a transformer, current source, etc?

    Thanks for your time.

    Regards.

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