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To get the PM and GM from stb analysis for a parameter sweep

Jaikrishnan

I have a basic opamp with input capacitance (Cin), feedback capacitance (Cf) and  feedback resistance (Rf). Initially I did a stability analysis (stb) with fixed values for all the design variables mentioned. I swept the frequency in a range and got the Phase margin (PM), Gain margin (GM) for the analysis. 

Now I want to sweep the Rf for a range and analyse the stability of the system. For this I have to use a specific frequency (eg. 100MHz) and select the range of Rf. The simulation is running ok and I have the plots for the Loop Gain and Phase. The plots are wrt Rf and not wrt Frequency

But, I am not getting the PM and GM for each Rf. This is because the simulation has not been swept based on frequency. 

How can I get the Stability summary for each iterations from the cadence itself?

Parents

  • Thanks Frank for the information and the link for further reading.

    Yes you are right regarding the analysis for a single frequency. 

    What I figured out was, first we have to perform the normal frequency sweep in the stb analysis for a rough fixed value for the Rf (parameter you want to sweep), then in the ADE -L environment go to Tools -> Parameter Sweep

    In the Parameter sweep, choose the variable we want to sweep and fix the range of it and then run the Parametric sweep. Since the sweep wrt frequency was already performed first, this parametric sweep will give the LoopGain, Phase, PM, PM frequency with respect to Rf .

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  • Thanks Frank for the information and the link for further reading.

    Yes you are right regarding the analysis for a single frequency. 

    What I figured out was, first we have to perform the normal frequency sweep in the stb analysis for a rough fixed value for the Rf (parameter you want to sweep), then in the ADE -L environment go to Tools -> Parameter Sweep

    In the Parameter sweep, choose the variable we want to sweep and fix the range of it and then run the Parametric sweep. Since the sweep wrt frequency was already performed first, this parametric sweep will give the LoopGain, Phase, PM, PM frequency with respect to Rf .

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