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Diff-amp question

Discussion in 'Electronic Basics' started by Samuel Groner, Jun 20, 2004.

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  1. Hi,

    I've got a question regarding the basic diff-amp config with one opamp
    and four resistors. Does the resistor connected output and "-"-input
    load the opamp?

  2. John Larkin

    John Larkin Guest

    Sure. And it can self-heat and mess up the CMRR.

    I've added a follower opamp before the feedback resistor, inside the
    loop, to reduce the heating of the first amp, to reduce thermal
    offsets and transient hooks.

  3. Ian Bell

    Ian Bell Guest

    Yes, because it at least provides bias current for the input and depending
    on the configuration (such as a diff amp) it may be a virtual earth. Is
    this a problem. usually this resistor value is high enough for it not to
    significantly load the output.

  4. Thanks for the answers! Thought that, but nowhere read about it, so was not sure..
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