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Need help about this OP AMP Configuration

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Programmer.C

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Hi guys,
Can anybody tell me what's this configuration please?
I have found this strange configuration on a strange circuit & i need to know what's the purpose of that?

OPAMP.png
 

Hi,

To safe time...please tell us where this circuit is from. Why do you want to know about this circuit.

Klaus

Btw: from the wiring it's a (sallen key) low pass filter circuit....but the 5V DC input makes no sense.
 

Many thanks for your reply,

This's the real circuit image
I'm trying to analyse this circuit coz it's damaged & i'm trying to make a new one with the same functions,
So i'm analyzing every thing i can just to make a new equivalent one but with some new modifications

OPAMP2.jpg
 

Hi,

You show a semi professional PCB layout where the parts are hand soldered.
Did you do this on your own? Tell us the complete truth.

Klaus
 

Okay,
It was made by another engineer not by me it takes an analog signal and convert it to VOLTS
I'm asking coz i have to fix it or create another one like it & really don't know what the real purpose of it so i'm asking! about it's function
 

Hi,

So I guess the input is not 5V DC. But what is the input? Sensor? Audio?

convert it to VOLTS
The input is Volts .... and the output is Volts...

Klaus
 

I'm still not sure about the input signal type coz the signal coming from another board connected to a group of sensors so i'm so confused the signal may be just a frequency coz i think the above image looks like a Sallen-Key second order low pass filter !!! any suggestions
 

Hi,

coz i think the above image looks like a Sallen-Key second order low pass filter !!!
That's what I've wrote in post#2...


Klaus
 

looks like you'll have to trace the wiring carefully back to the source of the signal that goes to this device.

you might in the process trace out other circuits to see what their source is and how they are
connected to some sort of analog processing.
it is a lot of effort, but it can give hints about what's going on
and about how the original designer was thinking

it isn't particularity old - is there any documentation?
 

Thanks for your replay & that's what i'm trying to do i'm tracing everything
Unfortunately there's no documentation :-(
 

It's a basic Sallen Key low pass, you can calculate the transfer function. What are you missing?
 

I noticed that the PCB on the photo implements two cascaded second order low passes, the schematic in post #1 only showing the first stage. How did you arrive at the capacitor values, 20 nF doesn't belong to a standard series.
 

Hi man
I just guess the capacitor capacitance coz it gives me random readings
But thank you for your hint about the cascaded second order low passes coz it's like what i guess too.
If you know anything about the default capacitor values or how can i get it please help coz there's no code written on it.
 

No chance for conclusions. Need to measure the capacitors. Or the transfer function.
 

Thanks for your help

- - - Updated - - -

This's the final drawing after measuring the capacitance could anybody please explain what kind of filter is this ?
In the first part i can see a low pass filter but i don't know what the other part exactly do?

LOW Pass Filter.png

- - - Updated - - -

I think the other part is a high pass filter. is that true ?
And the all circuit is just to to read a certain Band width?
Could anybody just assure that

- - - Updated - - -

Okay again i'm sure it's a band pass filter but what kind of band pass filter and how to calculate the output ?
 

So What about this red branch
I'm really confused in this circuit
LOW Pass Filter11.png

- - - Updated - - -

And why it's a two stage filter ?

- - - Updated - - -

Note :
I'm still a beginner in the electronics field, basically i'm a programmer.
 

Hi,

The first circuit and the second circuit are identical but the second circuit includes an additional gain stage.

Each is a second order LPF, in combination it is a 4th order LPF.

Klaus
 

The red "branch" is no relevant signal path. U1.1 is driving C1.

It's a common implementation of a 4th order filter.
 
this is your circuit redrawn in a more usual form

filter11sch.png

the blue circled section is the first filter stage while the green circled section is the second filter stage stage
the red circled section is the gain setting on the second stage

each filter stage is a second order filter, so together, you get a 4th order filter

the gain setting on the first stage is 1 as the output of U1 is fed back to the inverting input, like a follower.

this is the analysis in LTSpice XVII

filter11plt.png

the gain is the smoother curve with the minimum at about 10kHz
the phase is the curve that starts in the upper left corner and goes to the lower right corner
 
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