# Op amp circuit identification

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

1. ### notoriusjt2 Thread Starter Member

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

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

I am thinking this one is also a low-pass filter based on this article

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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Looks like a Wien Bridge Oscillator.

3. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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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 Thread Starter Member

Feb 4, 2010
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is this one (#2)

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

5. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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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.

6. ### notoriusjt2 Thread Starter Member

Feb 4, 2010
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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?

Mar 24, 2008
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8. ### notoriusjt2 Thread Starter Member

Feb 4, 2010
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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 AAC Fanatic!

Feb 17, 2009
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The second diagram show AC-coupling audio-band non-inverting amplifier.

10. ### t_n_k AAC Fanatic!

Mar 6, 2009
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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.

11. ### notoriusjt2 Thread Starter Member

Feb 4, 2010
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Prof says that it is an AC noninverting op amp

12. ### t_n_k AAC Fanatic!

Mar 6, 2009
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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 AAC Fanatic!

Feb 19, 2009
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I agree.

Should have gotten partial credit.

notoriusjt2: Sorry Jony130 didn't reply in time.