I need help with designing a bandpass filter..

[Wall-ED]

I am required to design a bandpass filter with Fl = 0.1hz and fh= 120hz and with gain 22.
I tried simulating on proteus but it doesn't seem to work, I'm beginning to think the equations I used for gain are wrong, can anyone please help me with that..
Here's a screen shot of the proteus simulation, the stage before the BPF is an instrumentation amplifier with gain 45, as the total gain is supposed to be 1000
I removed the HPF since the cut off frequency is 0.1hz, I thought it wouldn't make much of a difference..
https://i.imgur.com/hKpWC.jpg

 

[Winterstone]

Question to the instrumentation amplifier:
Why don`t you adjust the gain with R1 ? In this case you can choose 4 identical resistors for the 2nd stage. This drastically improves the CMRR.

Another question: What are the specific requirements for the filter (ripple in the pass band, attenuation in the stop band)?

 

[Wall-ED]

There wasn't any requirements or limitations or anything for the filter, just keep the band between 0.1hz and 120hz, the instrumenation part is not that important I understand it, but the filter part is the one I need help with..

 

[MrAl]

Hi,

How did you get as far as you did, what technique have you been using?

Also, the middle amp looks like it provides too much gain where the output stage already has gain.

 

[Wall-ED]

After I removed the series capacitor I used the equation fc = 1/2piRC and gain with 150/4.75 but I don't think it is working, I need to redo it as bandpass filter but I don't know how to achieve a gain of 22-30 and fl=0.1hz and fh=120hz
I need a total gain of 1000 that is why I did that..

 

[MrAl]

Hi,

Without the input capacitor to that stage the passband gain is 150/4.75 which is around 32, but at 120Hz it gets cut by 0.7071 which brings it down around 22. Is that what you wanted?
If you want less gain in the passband then simply change the resistor value(s). The gain at the corner frequency (120Hz) will then be lower.

To check the gain at any frequency you can use this:
A=sqrt(((R9+R10)^2+w^2*C1^2*R10^2*R9^2)/(w^2*C1^2*R10^2*R9^2+R9^2))

but if you put the input cap back in we'll have to change that formula.

Without the input cap though the amplifier passes DC, something that you may or may not want to happen. The input cap blocks any DC inputs.