I have a particular problem.
I want to design a lowpass filter which would have passband freguency = 80 Hz and passband frequency 100 Hz. Stopband attenuation should be 30 dB or something like that.
Obviously I need this filter for microcontroller :)
I have designed sucha filter and it consist of 4 stages. N=8 Overall gain is 60 [v/v]
It is Chebshev filter.
Unfortunately on the second stage there are high oscillations!
I don`t know why they are occuring but even if I don`t provide signal to the input they are existing.
I really need your help cause I am not very proficient in designing filters. I used special program for designing filters.
Below I am enclosing filter characteristics and circuit designs:
Why oscillations occur on the second stage ??
I join each stage in series.
Is this design is wrongly designed ??
What should I take into consideration ??
I supply each op-amp MC4558 +-5 [V]
Please help me any clues and maybe other designs are welcome :)
Thanks in advance