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How to measure phase margin through deepprobe.?

VIRAJ PANCHAL

Hello community,

I am doing the verification of one block. I want to measure the phase margin(PM) though stability analysis. 

I know the method to measure the phase(i.e connect iprobe in feedback path). But my this circuit is complex, so I want to measure the PM from top level testbench so I am using the deepprobe and cds_thru to connect the signal. 

but I am unable to measure PM. In maestro view I got error message in PM expression. 

So my question is that is this a right method to measure PM. if it is right then which probe should I select in stability form.?

 

  • ULPAnalog

    I do not see what IPRB3 is in the figure posted. Generally, how I would approach this is by placing a small metal resistor in the circuit where you would have normally inserted iprobe. Then, in config view, I would bind the metal resistor to open.

    In the testbench I would create two instances of deep probe that are setup to probe either side of the metal resistor and connect them across an iprobe.  This is the probe that would be specified in stb analysis.

    Alternatively, you could specify the instance terminal instead of adding an iprobe.

    I am assuming that your pdk has metal resistors.

  • VIRAJ PANCHAL
    in reply to ULPAnalog

    Thank you for your suggestion and respond, now it worked. 

    I've another little doubt then, if we ignore the resistance while doing simulation then why do we keep the resistance in feedback path.? 

    Thank you. 

  • VIRAJ PANCHAL
    in reply to Andrew Beckett

    Thank you Andrew, now it worked. your article has information regarding this thread. 

    Thank you. 

  • Andrew Beckett
    in reply to VIRAJ PANCHAL

    A small metal resistor is likely to have a very small resistance and unlikely to be significant; given that it's no different from the parasitic resistance of a tiny part of the routing, and you are omitting a small part of that interconnect, even if you include the parasitics from extraction you wouldn't be missing much...

    Andrew

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