Active bandpass filter experimental measurements different from simulation results

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confuseddesigner

Joined Mar 14, 2017
9
I designed an active bandpass filter (circuit diagram and data shown in the PDF). I took measurements in the lab and also did a frequency sweep using Cadence PSpice.
The experimental measurements agree with my calculation on paper, and also agree with the simulation on most points except on the gain at the high frequency cutoff(5296Hz). What could have caused this difference? If it's simply the normal discrepancy between actual and theoretical, why is it that my calculation agrees with the experimental results?
 

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crutschow

Joined Mar 14, 2008
26,969
The experimental measurements agree with my calculation on paper, and also agree with the simulation on most points except on the gain at the high frequency cutoff(5296Hz). What could have caused this difference?
Did you include the gain-bandwidth-product of the op amp in your calculations?
That value may be lower in the simulation op amp model, then you have in the actual device.

You can check the model GBW by doing a simulation of it as a follower (+1 gain) and see the frequency of the -3dB gain point.

Edit: My simulations confirm yours and it's not related to the GBW of the op amp.
 
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crutschow

Joined Mar 14, 2008
26,969
Did you calculate the gain from the equations for the circuit response?
I calculate a rolloff of -17.23dB at 52964Hz, the same as the simulation.

What is the tolerance of the parts you used?
That could likely account for the difference between simulated and measured.
 
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