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Differential Stability Probe (diffstbprobe) in Stability analyses

FormerMember
FormerMember

Dear friends,

I am using the diffstbprobe to test the differential loop gain characteristics of my fully differential amplifier. I am connecting the amplifier with unity gain closed loop with inputs tied at the VCM. I put the diffstrbprobe as shown in figure below which I am sure it will break amplifier loop.

The simulation is working fine but I have two questions please,

Is the loop gain I am getting by running this simulation is the (vo1 - vo2) / (vin1-vin2) which is the true differential gain,

or it is with respect to one of the outputs, by this case I have to multiply it with 2 manually.

My second question please is when I run the STB analyses it give me two options for the diffstbprobe: differential and common. I use the differential option for the differential loop simulation, but does it it means that if I change the setting  to common then I will be able to use the same probe for simulating the common mode feedback loop  without changing the circuit configuration ?

Thank you very much in advance

Differential mode stability test

Parents
  • Andrew Beckett

    Yes, it's the differential loop gain. No need to multiply by two. Frank also (I think) answered your other question in your other post the other day. Put simply, the mode choice on the stb analysis form allows you to measure both the loop gain of a differential signal from the output of the probe back to the input, or the loop gain of a common-mode signal from the output of the probe back to the input. If that encompasses your common mode feedback loop, then the answer is yes.

    The idea is quite simple - you probe at a point where you want to measure the loop gain, and that's what it tells you!

    Oh, and by the way, when you post questions with pictures, please make them large enough to actually see.

    Andrew.

Reply
  • Andrew Beckett

    Yes, it's the differential loop gain. No need to multiply by two. Frank also (I think) answered your other question in your other post the other day. Put simply, the mode choice on the stb analysis form allows you to measure both the loop gain of a differential signal from the output of the probe back to the input, or the loop gain of a common-mode signal from the output of the probe back to the input. If that encompasses your common mode feedback loop, then the answer is yes.

    The idea is quite simple - you probe at a point where you want to measure the loop gain, and that's what it tells you!

    Oh, and by the way, when you post questions with pictures, please make them large enough to actually see.

    Andrew.

Children
  • FormerMember
    FormerMember in reply to Andrew Beckett

    Tank you Sir for your answer, Actually I am not getting a notification for my post, this is why I didn't see the post of the other day, I just replied it now

    Thank you once again

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