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  1. #1
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    Novel method in Compensation for Op-amp

    Hello,
    I was reading through compensation methods for 2 stage CMOS op-amps which include 3 methods:
    1. Nulling resistor
    2. Put Source follower with Miller Cap
    3. Common Gate with Miller Cap (aka Ahuja Compensation http://ieeexplore.ieee.org/stamp/sta...number=1052012)

    My question is -To Block the FeedForward path why not simply use a diode, say instead of Souce Follower? See the pic for more clarity...Any reasons why it won't work?Click image for larger version. 

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  2. #2
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    Re: Novel method in Compensation for Op-amp

    FeedForward path means a signal path, an ac path!



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  3. #3
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    Re: Novel method in Compensation for Op-amp

    Hi analog_wiz,

    Quote Originally Posted by analog_wiz View Post
    2. Put Source follower with Miller Cap
    I think you meant Common Source stage with Miller Cap.

    Quote Originally Posted by analog_wiz View Post
    My question is -To Block the FeedForward path why not simply use a diode, say instead of Souce Follower? See the pic for more clarity...Any reasons why it won't work?Click image for larger version. 

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    I think the goal (in Ahuja Comp) was to remove the feed forward path from 1st stage to 2nd stage but still have a miller compensation (or Cap multiplication).

    In you circuit isn't the diode blocking the Miller Cap ? The diode small signal equivalent model can be drawn when it is forward biased, how do you ensure in your ckt that the diode is DC forward biased ? Also it's small signal (ac) equivalent is nothing but a resistance so its'n it same as normal Miller (if at all one can keep it in forward bias)?

    What small signal (ac) behavior are you expecting from the diode ? Could you elaborate or show any result/derivation ?

    Let me know your comments.

    Thanks,
    Siddhartha



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