DC offset is for

Discussion in 'General Electronics Chat' started by DexterMccoy, Apr 5, 2014.

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  1. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    What is DC offset for?

    Having extreme DC offsets for each stage is for what purpose?

    A lot of times, multiple stages of op amps don't even have a DC offset on the input or output

    What Purpose is having DC offset on the input or output of op amps?

    I thought DC offset was to not distort or clip off the positive or negative cycle of the waveform
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
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    Dc offset, if designed in, is there to make the circuit work the way it should. Without it, the circuit will not provide the desired function. It all depends upon the next stage and what it expects as a proper signal. This has been discussed before.
     
  3. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    Yes true i know this

    But why would a stage need a very high DC offset and the next stage need a very low DC offset or change Polarities of the DC offset , one stage is positive DC offset and next stage is Negative DC offset

    I thought DC offset was to not clip off the positive and negative cycles, isn't this true?

    What else is it used for?
     
  4. BillB3857

    Senior Member

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    It makes the design engineer a valuable asset to his company. He is the only one that knows how and why the circuit is made the way it is. Job security.
     
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  5. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    A DC offset voltage is used for
    1.) To change the Input threshold of the op amps input?
    2.) To change the Zero crossing point of when the input?
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
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    1.) yes, unless there is a problem with that stage or earlier stages.
    2.) yes, unless there is a problem with that stage or earlier stages.
     
  7. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    Cause most Op amps inputs and outputs are at ZERO BIAS and start at Zero crossing

    When Op amps that have a DC offset , it changes the starting of the zero crossing point and the inputs threshold

    When you change the inputs threshold voltage , the Input signal won't TURN ON the Op amps input unless it " Exceeds or Crosses" this threshold voltage/dc offset voltage
     
  8. BillB3857

    Senior Member

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    You are describing a comparator when you talk of Turning ON and Turning OFF. In an analog amplifier with moderate gain, the output will rise and fall to values less than saturation levels as the input changes.

    The offset can be used to center the output about zero or to either a positive or negative value depending upon the need of the following stage or the status of the input signal.

    Frequently, since no circuit is perfect, an offset control will be installed as part of the design. That control will allow compensation for component tolerance variations that cause the output to be something other than optimal.
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I think you are mixing up comparators and opamps. Opamps are NOT turned on or off, the should behave linear all the way. Sometimes it is convenient to have base level be at zero, sometimes its not. Could be beacause of the available choice of resistors, or the lack of added resistors in other stages, or a billion other reasons.

    You really need to stop thinking that by analyzing a few ovely complex circuits (that are already severly optimized) down to the very last detail you can suddenly understand everything. It just doesn´t work like that, and the kind of questions you keep asking suggest that you still don´t understand that.

    Start with simple circuits, not with aircraft avionics. Even though those circuits come from the seventies they are really a product of many years of fiddling and optimization, they contain almost nothing that is straightforward and easy to explain and understand.
     
    Last edited: Apr 13, 2014
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