Op amp circuit identification

Thread Starter

notoriusjt2

Joined Feb 4, 2010
209

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
 

thatoneguy

Joined Feb 19, 2009
6,359
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.
 

t_n_k

Joined Mar 6, 2009
5,455
the second one is neither a band-pass filter or a high-pass filter.

I have failed at op-amp circuit identification. LOL
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?
 

Thread Starter

notoriusjt2

Joined Feb 4, 2010
209
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?
Prof says that it is an AC noninverting op amp
 

t_n_k

Joined Mar 6, 2009
5,455
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.
 

thatoneguy

Joined Feb 19, 2009
6,359
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.
I agree.

Should have gotten partial credit.

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