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simulate a fully differential opamp

jacksonlu
I am a fresh ic designer, and now i am design an fully differential amplifier, but i don't know how to simulate it in spectre? such as dc gain, GBW, phase margin, CMFB stb, psrr, and so on. what are the testbenches for them? thanks!

  • For simulating the stability, you can use the  diffstbprobe component from analogLib inserted into the feedback paths, and simulate using a stb analysis. This will give you the choice of simulating either the differential or common mode loop gain, and hence the phase and gain margin of each. This is in more recent versions (it was introduced in MMSIM10.1 and in IC5141 and IC614/IC615 subversions since MMSIM10.1 was released). Prior to that you could achieve a similar thing with the cmdmprobe component in analogLib (although this is now deprecated as the diffstbprobe is superior).

    For other metrics, it's just a matter of hooking up your amplifier appropriately and using ac or xf analyses.

    Regards,

    Andrew.

  • Hi, Andrew! thanks very much for your replay. May you tell me about the test benches for them, and how to do pz analysis? Should i break the feedback loop for pz simulation? and what about the feedback circuits for other simulations? BTW, does cadence has a tutorial or workshop about simulating an fully differential opamp? thanks very much!

  • You do not need to break the loop for pz analysis - you tell it where the input and the output of the circuit are. This is covered in the documentation.

    I don't know if there's a tutorial or workshop on this, sorry (may be, but I'm not sure).

    Andrew.

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