So I had an experiment (few weeks ago) where I had to measure certain things of an opamp used as an active filter. One of the questions was to measure the bode plot by measuring the ratio of the AC peak to peak values and the phase shift between two signals for a certain set of frequencies (50 Hz - 10MHz). I also had to explain this measured bode plot with the one from my preparation.
There are two problems now.
1) I didn't manage to draw the bode plot for my preparation.
2) My measured bode plot is nowhere close to the one from the spec sheets or the one that I expect from my preparation. I'm afraid it isn't even close to being a bode plot of any kind. Can't be helped much I guess.
Bode plot from my preparation
So to draw the bode plot, I figured I'd have to start with the transfer function.
In the picture I included are two opamps visible. If I remember correctly, the second one could be ignored as it was only used as a buffer or something. So I'll only focus on the setup indicated by the red rectangle.
Via KCL & ideal opamp I get:
I made the substitution s= jw. I've got a zero for s = -R1/C1 and two poles s = 0 and s = 1/C2R2. Can anyone confirm if I'm correct here. If not, where's my mistake? Probably something stupid. When I fill in the values for my resistors (R1 = R2 = 22k) and capacitors (C1 = 220pF, C2 = 100pF), I get absurdly high values. Nothing that resembles the bode plot from the spec sheet.
I should be able to draw the bode plot following the instructions here. But the above results need to be correct first.
I'll edit my post to take a look at the (possible) problem with my measurements once the above issue is cleared. It might give me inspiration on how to solve the problem.
There are two problems now.
1) I didn't manage to draw the bode plot for my preparation.
2) My measured bode plot is nowhere close to the one from the spec sheets or the one that I expect from my preparation. I'm afraid it isn't even close to being a bode plot of any kind. Can't be helped much I guess.
Bode plot from my preparation
So to draw the bode plot, I figured I'd have to start with the transfer function.
In the picture I included are two opamps visible. If I remember correctly, the second one could be ignored as it was only used as a buffer or something. So I'll only focus on the setup indicated by the red rectangle.
Via KCL & ideal opamp I get:
I made the substitution s= jw. I've got a zero for s = -R1/C1 and two poles s = 0 and s = 1/C2R2. Can anyone confirm if I'm correct here. If not, where's my mistake? Probably something stupid. When I fill in the values for my resistors (R1 = R2 = 22k) and capacitors (C1 = 220pF, C2 = 100pF), I get absurdly high values. Nothing that resembles the bode plot from the spec sheet.
I should be able to draw the bode plot following the instructions here. But the above results need to be correct first.
I'll edit my post to take a look at the (possible) problem with my measurements once the above issue is cleared. It might give me inspiration on how to solve the problem.