Good afternoon! I am trying to impliment a bandpass filter using the Multiple feedback topology with fo = 19khz, q=20, and Resonant Gain = 40 dB:
Theoretical circuit simulated with a filter design tool, ac magnitude response above.
I used a DC supply of 1.2V for Vref, I replaced ADA4661-2 (GBW of 4 MHz) with TI LM7301 that has a GBW of 4 MHz also. I used 1% capacitors and .5% tolerant resistors. I simulated the circuit with TI TINA and got close to a 1V pp output with an input voltage of 10mv pp, 19khz input voltage. This TI TINA simulation respresents a 100x gain (same as theoretical results above).
However, when I impliment the exact circuit above on the breadboard and force 10mv pp, 19khz with a function generator on the input, I get only a 200mv pp scope reading on the output. If I sweep the frequency from 1khz to 30khz, I do see the bandpass frequency response I would expect.
My main question is what would cause the resonant frequency gain to be so much lower then the simulated and theoretical results? I would think TI TINA already compensates if the GBW is insufficient, which I don't believe it is. Any ideas?
Regards,
George