about op amp

Discussion in 'General Electronics Chat' started by blue6x, Apr 28, 2005.

  1. blue6x

    Thread Starter Active Member

    Apr 6, 2005
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    Good day to everyone....

    As an electronics student, I was fascinated by the numerous application of an op amp. I've been trying to study this particular active device for quite sometime now, looking at their configuration. (there were lots of them though). I was just wondering why in cases that it is being applied in acircuit, being its primary purpose is amplification, tends not to do that amplification at all. Take the case of a unity-gain op-amp. How could i possibly know that this op amp is actually functioning as a unity gain op-amp by looking at its configuration alone. How about integrators, comparators, differentiators and inverting ang non-inverting op amp. This could be a long topic, but if you could share your thought most especially on the above configurations, I would appreciate your help.


    The most important is, of course how could you easily identify the purpose of the op-amp in a particular schematic diagram by just looking on their configuration. please share your thoughts by stating your knowledge. Thank you very much to everyone...

    This could be of great help to everyone who would read this....
     
  2. pebe

    AAC Fanatic!

    Oct 11, 2004
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  3. hgmjr

    Moderator

    Jan 28, 2005
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    The website link that pebe provided is a terrific place to begin your exploration of opamps.

    You will also find some good basic information on opamps in the tutorial section of this website.

    You asked how you can look at the circuit and determine what opamp topology or configuration it is. That is just a skill that you will have to develop with experience.

    I recommend that you familiarize yourself with the basic characteristics of an opamp.

    For example:

    - high input impedance looking into its positive and negative input terminals
    - low impedance at its output terminal
    - high open loop gain

    These are a few of the major characteristics. There are several more but these are a good place to start.

    Also you will need to acquire a basic understanding of feedback theory since many if not all opamp topologies use feedback techniques to stabilize their operation.

    In summary, opamps are fundamental elements in analog circuit design and a strong grasp of how they operate is an important tool to be included in any aspiring electronic engineer's tool box.

    hgmjr
     
  4. blue6x

    Thread Starter Active Member

    Apr 6, 2005
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    thanks, I asked this topic mainly because though I really have studied op-amp characteristics even before, unfortunately, there were some configurations that when I try looking at books, it says that the configurations is like would say inverting op amp, or non inverting op amp. so what follows is I study their characteristics as inverting or non-inverting but to some dissapointment, the actual circuit is acting not like that.....
     
  5. mozikluv

    AAC Fanatic!

    Jan 22, 2004
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    hi

    just to add a few things. study the basic feedback topology and you will readily understand how the op-amp is used for a certain function. there are only 4 basic feedback topology, 1. shunt-shunt, 2. shunt-series, 3. series-shunt 4. series-series :D

    likewise study feedback stability. :p
     
  6. blue6x

    Thread Starter Active Member

    Apr 6, 2005
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    thanks, do you have any links to pages which discusses this things???
     
  7. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Hi,

    You should look at Microelectronic Circuits (Sedra and Smith) Chapter 8, for a detailed analysis of feedback. It starts looking at generalised feedback structures, the 4 basic topologies mozikluz mentioned above, moving onto more advanced topics such as feedback stability and feedback analysed in terms of poles/zeros and Bode plots.

    Some of this may be a little to "indepth", but its worth learning the basic feedback theory, not just for analysing op amps, but also in broader areas such as Control Theory (of which op amps play a significant part).

    Can I also point you to the section here on All About Circuits dedicated to op amps and feedback: http://www.allaboutcircuits.com/vol_3/chpt_8/index.html

    Hope this helps a little.
     
  8. duqamoq

    New Member

    Mar 23, 2005
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    I'm glad to see the ref. to Sedra-Smith. It's not all on the WWW, newbies! Gotta crack an actual book now and then.
     
  9. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
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    hi blue6x,

    this is just an addendum to what i have posted about feedbacks.

    1. a series-shunt feedback topology is what we usually call a voltage amplifier

    2. a shunt-series feedback topology is a current amplifier

    3. a series-series feedback topology is a transconductance amplifier

    4. a shunt-shunt feedback topology is a tranresistance amplifier

    am posting here the series shunt circuit diagram, its equivalent circuit and bjt equivalent.

    of course there are other aspects but this will suffice for now.
     
  10. blue6x

    Thread Starter Active Member

    Apr 6, 2005
    38
    0
    guys thanks, i appreciate all of your help....
     
  11. shreyas_bhat

    Active Member

    Jul 26, 2004
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