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OP-amp and transistor

  1. Sep 1, 2011 #1
    What is the meaning of differential gain?
    Iam studying a document that says, opamp can provide differential gain unlike transistor. I don,t know what does it mean. Can some clear me out.

    More, what is meant by bias volatge in case of op-amp. I am very beginer to electronics.
  2. jcsd
  3. Sep 1, 2011 #2
    Differential gain means that your op-amp's output is related to the difference between it's positive and negative inputs.

    So if you had an differential amplifier with a gain of 1 and applied +5V to the + input and +3V to the - input you would get a +2V output.

    Bias voltage on an op-amp is the output value with no inputs applied to the op-amp. Generally it will be about zero but you can construct your circuit so that it has a different value.
  4. Sep 1, 2011 #3


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    Staff: Mentor

    The input of most opamps uses a differential transistor gain stage, and there are more gain stages after that. So you get high effective differential gain with opamps -- the output is a function of the difference of the two inputs, multiplied by a very large number.


    The bias voltages on an opamp are the input quiescent voltages. You will generally set the bias voltage at the + terminal explicitly, and use negative feedback to set the bias voltage at the - terminal.
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