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Looking for op amp that supports large gain/bandwidth

  1. Mar 5, 2014 #1
    1. The problem statement, all variables and given/known data

    I need help with finding an operational amplifier that could be cascaded with itself to produce a total gain of around 100,000, or 100dB. It also needs to be operational up to 1.5 MHz. This is for an rf amplifier for an AM radio I am building.


    2. Relevant equations



    3. The attempt at a solution

    Most amplifiers seem to amplify correctly during the first stage, but the second stage either doesn't amplify at all or it seems to drop almost back to the input values. This could be due to bandwidth issues I suppose. The most gain I've been able to achieve is 1,000. Thank you for your time.
     
  2. jcsd
  3. Mar 5, 2014 #2

    berkeman

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    Staff: Mentor

    You are not going to get 100dB gain at 1MHz with opamps on a simple breadboard. Parasitic feedback from the output stages will cause oscillations or other problems with the input stages.

    If you look at the internals of a spectrum analyzer, you will see multiple shielded modules with shielded coax connections between them. If you want 100dB gain, you will most likely need to use a similar construction technique, including a lot of power supply filtering and isolation.

    I'll see if I can find some pictures of spectrum analyzer internals. Can you say more about your application? Will you be needing AGC as part of the amplifier chain? Or non-automatic but changeable gain/attenuation like a spectrum analyzer?
     
  4. Mar 5, 2014 #3

    berkeman

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    Staff: Mentor

    OTOH, you will have fewer problems at 1MHz versus 100MHz. I don't know for sure, but I'm guessing that commercial AM radio receivers have around 60-70dB gain, with only modest isolation and shielding between stages.
     
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