Op amp circuit identification

Discussion in 'Homework Help' started by notoriusjt2, Dec 14, 2010.

  1. notoriusjt2

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    Feb 4, 2010
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    [​IMG]
    I am thinking that circuit #1 is a low-pass filter because of the cap and resistor in series on the feedback leg
    [​IMG]

    #2 I am thinking that is a high-pass filter

    [​IMG]
    I am thinking this one is also a low-pass filter based on this article
    [​IMG]
     
  2. t_n_k

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    Looks like a Wien Bridge Oscillator.
     
  3. thatoneguy

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    Since both inputs are tied to ground, and there are two capacitors in the positive feedback path for phase shift, I would guess the top circuit to be an oscillator.
     
  4. notoriusjt2

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    is this one (#2)

    [​IMG]

    a bandpass filter because it has both a low pass and a high pass filter within it?
     
  5. thatoneguy

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    LM102 Datasheet, Page 5 shows examples of high pass and low pass filters.

    You might recognize a circuit on that page as well. :D
     
  6. notoriusjt2

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    haha one of those looks awfully familiar

    so circuit #2 has both a high-pass and a low-pass filter in it
    which makes it a band-pass filter right?
     
  7. Wendy

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  8. notoriusjt2

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    the second one is neither a band-pass filter or a high-pass filter.

    I have failed at op-amp circuit identification. LOL
     
  9. Jony130

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    The second diagram show AC-coupling audio-band non-inverting amplifier.
     
  10. t_n_k

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    Presumably you refer to that somewhat blurry colored figure?

    I would have thought 'effectively' a high pass filter.

    There are two poles at ω=1 rad/sec and ω=10 rad/sec. There are two zeros at ω= 0 rad/sec (i.e. DC) and ω=0.1 rad/sec.

    So DC gain is zero. Gain rises from 0 to 0.1 rad/sec at 20dB per decade. From 0.1 rad/sec to 1 rad/sec the gain rises at 40dB per decade. From 1 rad/sec to 10 rad/sec the gain rises at 20 dB per decade and from 10 rad/sec the gain begins to level out to a final high pass value of 20dB.

    What is the correct answer according to your teacher?
     
  11. notoriusjt2

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    Prof says that it is an AC noninverting op amp
     
  12. t_n_k

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    As Jony130 correctly indicated.

    Interestingly, if one were presented only with the Bode plot (magnitude / phase frequency response) rather than the circuit diagram itself, then it would be equally valid to state the response as being consistent with that of an active high-pass filter.
     
  13. thatoneguy

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    I agree.

    Should have gotten partial credit.

    notoriusjt2: Sorry Jony130 didn't reply in time. :D
     
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