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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

    Hello guys, Hope everything is going well.

    Frank, I appreciate your availability and kindness for the answers to my questions.

     

    In attached, Frank and all can see the circuit schematic, that for the time being it is presented like that to keep it simple and transmit the idea of what I am trying to get. Nothing special and it is the well know DC-DC Buck Converter, composed by:

    - VPULSE, which is simulating a fixed duty cycle (the duty-cycle that the converter will be working to get achieve the voltage conversion);

    - Non overlap circuit, which devides the PWM signal (obtained by the VPULSE source) and connects to the Drivers;

    - Drivers (mentioned before), fed by the VDC source;

    - Power Devices, fed too by the VDC source;

    - and the LC Filter, Load;

    Now frank, when you say to connect a PAC source between the ground and the input of the circuit that I want to examine, you mean what by that? Because I want to get the frequency response of the converter in open loop (as you can see by the schematic), you say I need to add that PAC source. Well I assume that the PAC source that you're referring can be either a VSIN, VPULSE or even a VDC source provided that any of them has the field PAC MAGNITUDE to be filled.

    (in this image you can see the PAC AMPLITUDE field. The VPULSE has that same field. 

    To keep things simple, lets just consider the VSIN SOURCE.

    Now, regarding the question on where I must connect the VSIN source working as a PAC SOURCE, it will depend where I want to examine (that is, where is the input of the circuit that I want to examine).

    From what I have been reading, we can have 3 types of transfer functions on the converter: VLINE (I think it is the Vin) to VOUT, the CONTROL to OUTPUT and the INPUT IMPEDANCE. To be honest I am not sure what transfer function should I analyze, so that one can study which controller to use. I would say that the transfer function that really matters for the design of the controller is the Control-to-Output transfer function?

     If so, I need to insert the VSIN SOURCE in series with the VPULSE SOURCE? Which is the point where the control signal is?

    Kind regards. 

     

    EDIT: Mark I tried to run a simulation using VSIN source in series with the VPULSE as well as using the VPULSE it self with the AC Magnitude @ 1V but an error occured:

    "Error found by spectre during pac analysis .. There is no AC source in the circuit." Here: (I didn't used the DC Analysis at the same time - don't know if it's needed):

    Then I remember to use the PSIN source. I tried that in series with the VPULSE and in parallel (with a capacitor separating the VPULSE to PSIN) but the same error appeared. Here:

     

    After that I have added a DC analysis and now a new error appears (but the other one desappeared) saying that the PAC analysis was skiped because PSS analysis must be performed first. But I have the PSS analysis configured, as you can see here:

     

    On the PAC analysis, he detected the PSS beat frequency, I start the sweep @ 100MHz an stop @ 3GHz (step size 10MHz). Maximum Maximum sideband I put 2.

    Any idea of what I am doing wrong? I appreciate all the help.

     

    Regards. 

Reply
  • Pyroblast

    Hello guys, Hope everything is going well.

    Frank, I appreciate your availability and kindness for the answers to my questions.

     

    In attached, Frank and all can see the circuit schematic, that for the time being it is presented like that to keep it simple and transmit the idea of what I am trying to get. Nothing special and it is the well know DC-DC Buck Converter, composed by:

    - VPULSE, which is simulating a fixed duty cycle (the duty-cycle that the converter will be working to get achieve the voltage conversion);

    - Non overlap circuit, which devides the PWM signal (obtained by the VPULSE source) and connects to the Drivers;

    - Drivers (mentioned before), fed by the VDC source;

    - Power Devices, fed too by the VDC source;

    - and the LC Filter, Load;

    Now frank, when you say to connect a PAC source between the ground and the input of the circuit that I want to examine, you mean what by that? Because I want to get the frequency response of the converter in open loop (as you can see by the schematic), you say I need to add that PAC source. Well I assume that the PAC source that you're referring can be either a VSIN, VPULSE or even a VDC source provided that any of them has the field PAC MAGNITUDE to be filled.

    (in this image you can see the PAC AMPLITUDE field. The VPULSE has that same field. 

    To keep things simple, lets just consider the VSIN SOURCE.

    Now, regarding the question on where I must connect the VSIN source working as a PAC SOURCE, it will depend where I want to examine (that is, where is the input of the circuit that I want to examine).

    From what I have been reading, we can have 3 types of transfer functions on the converter: VLINE (I think it is the Vin) to VOUT, the CONTROL to OUTPUT and the INPUT IMPEDANCE. To be honest I am not sure what transfer function should I analyze, so that one can study which controller to use. I would say that the transfer function that really matters for the design of the controller is the Control-to-Output transfer function?

     If so, I need to insert the VSIN SOURCE in series with the VPULSE SOURCE? Which is the point where the control signal is?

    Kind regards. 

     

    EDIT: Mark I tried to run a simulation using VSIN source in series with the VPULSE as well as using the VPULSE it self with the AC Magnitude @ 1V but an error occured:

    "Error found by spectre during pac analysis .. There is no AC source in the circuit." Here: (I didn't used the DC Analysis at the same time - don't know if it's needed):

    Then I remember to use the PSIN source. I tried that in series with the VPULSE and in parallel (with a capacitor separating the VPULSE to PSIN) but the same error appeared. Here:

     

    After that I have added a DC analysis and now a new error appears (but the other one desappeared) saying that the PAC analysis was skiped because PSS analysis must be performed first. But I have the PSS analysis configured, as you can see here:

     

    On the PAC analysis, he detected the PSS beat frequency, I start the sweep @ 100MHz an stop @ 3GHz (step size 10MHz). Maximum Maximum sideband I put 2.

    Any idea of what I am doing wrong? I appreciate all the help.

     

    Regards. 

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