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Fully differential opamp caluculations

rakesh reddy

 

I made this schematic and I simulated this I am getting gain ~40dB and UGB 20Mhz,

I want to do stability analysis for this fully differential ckt ,

And I want to find out

--- CMRR

--- PSRR

---Loop gain (from stability analysis  )

How I should use cmdprobe to do stb analysis , please help me

  • Can't see your picture (you have to upload images using the Options tab when posting).

    For CMRR and PSRR, you can do this with an xf analysis. Set up your testbench sources for the supplies (of course), but also a source representing the common mode voltage. Then run an xf analysis and tell it where the output of the circuit. You can then plot the transfer function from every source to the differential output of the circuit.

    For stability analysis, these days you should use diffstbprobe rather than cmdmprobe. You point at that probe in the stb analysis form, and tell it whether you're analysing the differential or common mode loop gain. If using cmdmprobe (if you're using an older version - you didn't say) - then the cmdmprobe has a parameter to control whether you're analysing differential or common-mode loop gain (you set the parameter to +1 or -1; I forget which is which off the top of my head).

    Regards,

    Andrew.

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