non-inverting summing amp

Discussion in 'Homework Help' started by fran1942, Sep 3, 2010.

  1. fran1942

    Thread Starter Member

    Jul 26, 2010
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    0
    Hello, my tutor has asked me to sketch a non-inverting summing amp with three inputs.
    I understand all the other common amp configurations, but I am unsure how to sketch this one.
    Can someone please show me a basic example with some figures so I can clearly see how the individual gains are calculated with three inputs ?

    Thanks kindly for any help.
    (I have searched the web, but most examples just have formulas rather than actual figures)
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Are you allowed to use two opamps? If so, then add an inverting unity gain opamp to the output of your inverting summing amplifier.

    hgmjr
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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  4. fran1942

    Thread Starter Member

    Jul 26, 2010
    58
    0
    thanks, great advice,
    Would this attached sketch work.
    I need gains of 4, 10 and 15.

    Thanks kindly
     
    • amp.jpg
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  5. hgmjr

    Moderator

    Jan 28, 2005
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    Sorry that will not do the trick. You have used a non-inverting unity gain buffer. What you need is an inverting unity gain amplifier.

    hgmjr
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    [​IMG]

    I didn't bother checking gains, you should be able to do that.

    .
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    Thanks Bill. That is what I was suggesting.

    hgmjr
     
  8. fran1942

    Thread Starter Member

    Jul 26, 2010
    58
    0
    thanks guys, I really appreciate your help.
     
  9. fran1942

    Thread Starter Member

    Jul 26, 2010
    58
    0
    excuse my ignorance, but can I just ask why the two 2x 1K ohm resistors are in place ?

    Thanks kindly.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    It is a unity gain inverter circuit. Which is why converts the first inverting circuit into a non inverting circuit per your requirements.

    The exact resistors values aren't important, they need to be the same values for unity gain.
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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