High Q value bandpass filter circuit diagram

As shown in the figure is a high-Q bandpass filter circuit. This circuit uses two high input impedance operational amplifiers SF356. The first stage is an ordinary single-stage filter with a low Q value, a small value of R3, large signal attenuation, and small amplification factor. However, the second-stage inverting proportional amplifier has an amplification factor of 10 times, and a certain amount of positive feedback is introduced through R2 to the first-stage input terminal, which increases the Q value of the entire circuit, so the filter has better Frequency selection characteristics.

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