amplifier plus a filter feedback

[AZALBE1975]

I have design an amplifier with a bandwidth of 10kHz. now I want to set a lower cut off frequency at 50hz. So I designed a lowpass fliter that I placed between the output and the input. But the simulation is not showing a bandpass like structure in the bode diagram. I am pretty at lost to combined these two structures that are working perfectly.

 

[tyassin]

Hi

I dont know how you have designed your filter. But you have to be aware that if you make a simple lowpass structure like RC. Then making a simulation of this isolated will give you a certain cut off frequency. But when you insert this filter in another circuit it could be loaded by other circuitry. This will definitely change your cut off frequency.

If you place a lowpass filter before your amplifier then it will be a low pass like response you get.

I hope this helps.

Regards