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?

 

The circuit is a Sallen-Key second order lowpass filter.

 

The circuit is a Sallen-Key second order lowpass filter.

Many thank for your replay,
Could you please explain more about this kind of configuration this my first time to see it?

 

The circuit is a Sallen-Key second order lowpass filter.

By the way this is the real circuit
I just send the first part but this is the full one.

 

Since I am not a teacher then you should look it up in Google.
A good second-order filter has a Butterworth response which is flat in the passband then a sharp cutoff. A Bessel response has a droopy and slow cutoff but has less phase shift than a Butterworth.
Usually a Butterworth filter with a gain of 1 like the circuit you showed has equal values for the resistors and the first capacitor value is double the second capacitor value.

 

Since I am not a teacher then you should look it up in Google.
A good second-order filter has a Butterworth response which is flat in the passband then a sharp cutoff. A Bessel response has a droopy and slow cutoff but has less phase shift than a Butterworth.
Usually a Butterworth filter with a gain of 1 like the circuit you showed has equal values for the resistors and the first capacitor value is double the second capacitor value.

Many thanks for you.

 

This might be useful -

http://www.ti.com/lit/an/sloa024b/sloa024b.pdf

Regards, Dana.

 

This might be useful -

http://www.ti.com/lit/an/sloa024b/sloa024b.pdf

Regards, Dana.

Thank you

 

The input to R1 is normally an AC signal, not DC as shown.

 

The input to R1 is normally an AC signal, not DC as shown.

Thanks for that hint