# what does this op amp circuit do?

#### Gerelectronic

Joined Mar 3, 2021
15
Hi everyone, could anyone tell me how the circuit works with the op amp that I have attached?

I wish I could find the formula that allows me to find Vout as Vin varies.
Thank you all.
Sorry for the poor English.
Long live electronics!

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#### Papabravo

Joined Feb 24, 2006
20,404
It looks like a bandpass filter, with an inverting gain stage.
Is that what you expected?

#### atferrari

Joined Jan 6, 2004
4,701

#### Gerelectronic

Joined Mar 3, 2021
15
It looks like a bandpass filter, with an inverting gain stage.
Is that what you expected?
Yes it is, thanks. Do you have any idea how to find the Vout?

#### Gerelectronic

Joined Mar 3, 2021
15
Do you mean a gain that varies as the frequency changes automatically? Do you have any idea how to find the Vout?

#### AnalogKid

Joined Aug 1, 2013
10,591
It is a 3-pole lowpass filter with a non-inverting gain stage. The gain is variable between 1 (0 dB) and 21 (26.4 dB). Note: upward-pointing ground symbols are a *very* poor schematic practice. Ground symbols *always* point downward.

That is not a good way to do a the filter. It has a very gradual transition from the passband to the attenuation slope. IOW, the passband - the signal bandwidth below the cutoff frequency - is not very "flat". The input signal attenuation at the corner frequency will be 9 dB, as opposed to only 3 dB with a proper filter design.
Do you have any idea how to find the Vout?
Yes.

Do you?

Is this school work?

ak

#### atferrari

Joined Jan 6, 2004
4,701
Do you mean a gain that varies as the frequency changes automatically? Do you have any idea how to find the Vout?

#### Gerelectronic

Joined Mar 3, 2021
15
It is a 3-pole lowpass filter with a non-inverting gain stage. The gain is variable between 1 (0 dB) and 21 (26.4 dB). Note: upward-pointing ground symbols are a *very* poor schematic practice. Ground symbols *always* point downward.

That is not a good way to do a the filter. It has a very gradual transition from the passband to the attenuation slope. IOW, the passband - the signal bandwidth below the cutoff frequency - is not very "flat". The input signal attenuation at the corner frequency will be 9 dB, as opposed to only 3 dB with a proper filter design.

Yes.

Do you?

Is this school work?

ak
Yes, I know that the earth symbols must face downwards, but in this case it is not an earth symbol, but a symbol that represents a voltage.
I can't find the formula of the Vout, if you are capable could you please tell me the formula?

It is a school assignment.

Thanks a lot in the meantime.

#### crutschow

Joined Mar 14, 2008
32,934
Do you have any idea how to find the Vout?
Yes.
But since this is homework we don't do that for you here, however we can help you find the answer.
To solve the problem analytically you need to write the transfer function of the circuit using Laplace Transforms (here's an example).
For your circuit that's gives a fairly complex function.

Or you can simulate it with a Spice type simulator.

#### Papabravo

Joined Feb 24, 2006
20,404
Hint: Divide and conquer
Consider the operational amplifier and the RC network as separate problems.
Solve them separately and then combine the results.