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Ask for help: how to do the ac stability simulation for fully-differential Op-Amp using with switched-capacitors?

chensiw12

Hi, there,

I am designing a pipelined ADC, and it's my first time to design a fully differential Op-Amp with CMFB & switching-capacitor, it's a little bit difficult for me. In the pipelined stage, the MDAC uses a fully differential (differential-input and differential-output) Op-Amp, so there is a CMFB circuit. My questions are:

1) how to simulate the ac stability of this whole circuit? there are two kinds of feedbacks: diff-mode feedback and cmfb, how do I simulation its ac gain, phase margin, unity gain frequency?

2) can you provide me some documents on this kinds of simulation? my email: chensiw12@yahoo.com

Thanks

 

  • Hi, there,

    I am designing a pipelined ADC, and it's my first time to design a fully differential Op-Amp with CMFB & switching-capacitor, it's a little bit difficult for me. In the pipelined stage, the MDAC uses a fully differential (differential-input and differential-output) Op-Amp, so there is a CMFB circuit. My questions are:

    1) how to simulate the ac stability of this whole circuit? there are two kinds of feedbacks: diff-mode feedback and cmfb, how do I simulation its ac gain, phase margin, unity gain frequency?

    2) can you provide me some documents on this kinds of simulation? my email: chensiw12@yahoo.com

    Thanks

  • Simulating the stability of the amplifier can be done using the pstb analysis. You can use the diffstbprobe component inserted in the loop, and then run a PSS analysis of a period of the clock, and then pstb analysis pointing at the diffstbprobe component.

    There is an application note on using pstb in the MMSIM installation, although this is focussed on an oscillator. Search in <MMSIMinstDir>/tools/bin/cdnshelp and search for "pstb" to find out more about it.

    Regards,

    Andrew.

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