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    cmfb - creation cm voltage

    hi
    how can we create in cmfb amplifier circuit a CM voltage?
    explenation that CM voltage is ideal( or desired) common mode output voltage.
    i am reading Gray & Mayer book and in chapter 12 (about cmfb) has been used CM voltage , but in this chapter does not have explained how to create this voltage
    i think with an inverter that its output tied to its input ,maybe can be create desired voltage but the mismatch and thermal effect will change this value.
    thanks

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    Dominik Przyborowski's Avatar
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    Re: cmfb - creation cm voltage

    Before chapter 12 is a chapter 4 in this book. Read it, there is an answer for your question.



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    Re: cmfb - creation cm voltage

    The CMFB compares between your "output common mode" and "desired common mode" and feeds back a negative signal for regulation. The desired CM voltage you can generate by using a resistive divider from rail-to-rail, assuming your rails are already robust.
    Your life is all about ΔΣ, the narrow you estimate it, the precise it is ...



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  4. #4
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    Re: cmfb - creation cm voltage

    hi ashrafsazid
    itis in first glance, but then below problem are raised:
    large area
    power consumtion
    matching thermal effect

    i think can create with inverter that output connected to input, but then thermal effect and mismatch are leaved



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