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CMOS OpAmp Design

Discussion in 'Electronic Design' started by [email protected], Dec 16, 2008.

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  1. Guest

    Hi,
    I was looking for a CMOS OpAmp circuit which doesnt need need any
    special Common Mode Feedback circuit for stabilizing the bias point.
    Anybody has come across a circuit like that ?

    Please let me know
    regards
    Jean
     
  2. MooseFET

    MooseFET Guest

    Take a look at some of the CMOS op-amps that RCA made back in the
    stone age. They had a very low transistor count.
     
  3. Guest

    Do you mean fully differential CMOS opamp?
     
  4. Guest

    Yes,
    I was looking for fully differential design.

    Jim,
    which is the textbook you are talking about ? GHLM ?

    regards
    Jean
     
  5. Guest

    Unless you have something really lame such as accurate resistor loads
    and a diff pair driven by an accurate bias current, I don't see any
    way to do such a design without common mode feedback. Basically, to do
    such a circuit without common mode feedback, you need to be able to
    look at the circuit and predict the bias conditions, specifically the
    voltage at the high impedance nodes (gain nodes).

    You can do common mode with switch cap, but that doesn't mean you
    don't have common mode feedback.
     
  6. Guest

    Even with a ground pin, I don't see a way to establish a common mode
    at the outputs of the op amp without some sort of feedback, with the
    one exception I stated in my previous post, i.e. well known current
    and resistor loads. High impedance nodes tend to go to a rail without
    feedback.

    I suspect the original poster isn't phrasing the question properly.
     
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