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Inverting op-amp with too much gain ?

Trying to build a multi-stage 120kHz bandpass filter... decided to
use multi-feedback topology...

Seems that it amplifies the desired signal alright, but ends up full-
swing output (after just one stage) and since it's inverted, the full-
swing output feedback ends up cancelling out the input and it
collapses back on itself.

I'm no op-amp expert but am ernestly trying to learn.... and I'm
stumped on how to procceed...

thanks!
...dane
 
A

Anthony Fremont

Jan 1, 1970
0
Trying to build a multi-stage 120kHz bandpass filter... decided to
use multi-feedback topology...

Seems that it amplifies the desired signal alright, but ends up full-
swing output (after just one stage) and since it's inverted, the full-
swing output feedback ends up cancelling out the input and it
collapses back on itself.

I'm no op-amp expert but am ernestly trying to learn.... and I'm
stumped on how to procceed...

Schematic? Maybe you could shoot for unity gain in the filter stage and do
your amplifying seperately. The filter stage will still provide gain, but
only to what you want to hear. Download TI FilterPro, you won't regret it.
I've built active filters using it, it works. :)
http://focus.ti.com/docs/toolsw/folders/print/filterpro.html
 
D

dane

Jan 1, 1970
0
Schematic? Maybe you could shoot for unity gain in the filter stage and do
your amplifying seperately. The filter stage will still provide gain, but
only to what you want to hear. Download TI FilterPro, you won't regret it.
I've built active filters using it, it works. :)http://focus.ti.com/docs/toolsw/folders/print/filterpro.html

Thanks Anthony. I tried it out and it's working great...

I used some filter design tool the first time around (can't remember
which), but I think I may have 'tweaked' it too much and broke it...
Going back to FilterPro helped a lot and I'm now back-on-track.

thanks!
...dane
 
A

Anthony Fremont

Jan 1, 1970
0
dane said:
Thanks Anthony. I tried it out and it's working great...

I used some filter design tool the first time around (can't remember
which), but I think I may have 'tweaked' it too much and broke it...
Going back to FilterPro helped a lot and I'm now back-on-track.

I told ya you'd like it. :)
 
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