I have asked a similar question but I did not get an answer, as it was too specific. So I will build on it but make it a bit more broad spectrum.
I would like to make a digitally selectable BPF using transistors to select a component in the filter; resulting in the center frequency being changed.
I have used FilterPro to generate quick second order filters and get a rough filter response.
For all the designs, a Multiple-feedback was selected:
In the first picture, a center frequency at 108KHz with a bandwidth @ -3dB of 103K to 113KHz is given.
For the second, a center frequency at 117.5KHz with a bandwidth @ -3dB of 112.8K to 122.2KHz is given.
The only difference between these two circuits is R3.
If I were to implement a circuit as shown below, would it work and what transistor would be recommended? I have selected the TL082ID as the Opamp in the circuit design as that is what was used for the ST7590 RX gain amplifier.
For the transistors, I was thinking of using the MOSFETs (2N7002) used in the ST7590 design as well.