Is it possible to use an op amp bandpass filter in a FM radio circuit instead of a capacitor and Inductor?

Question

Is it possible to use an op amp bandpass filter in a FM radio circuit instead of a capacitor and Inductor?

Answer 1

I think you can... the fact is that it's cheaper to do it with passive components and you will get a better response. I say because I had a project of radiocommunications and I tried an amplifier with an opamp which supposedly was for RF (the datasheet published a bandwidth of 1 GHz) for a band-pass centered a 220 MHz. The amplifier was not cheap but the response was very bad... I ended with a RLC filter that did the job very good. That's my experience, and based in it I strongly recommend passive filters for RF applications.

Answer 2

depends on frequency. Upto 1MHz, one can certainly do without inductors. With high bandwidth amplifiers, one can do without them even upto 10 MHz. See "op amps for every one, 3rd edition fig 22.6 for example showing a 10.7MHz bandpass. Active filters is a very good subject to learn and has usefulness in all other bramches of electronics. At very high frequencies, inductors are preferred. Do you know? Inductors behave as capacitors and vice versa at very very high frequencies.

Answer 3

Short answer, yes. Just make sure that your op amp selection has adequate performance characteristics, in particular, frequency response and gain bandwidth product. They should be at least some multiple of the upper cut-off frequency of your filter design.



First answerer is correct however in stating that it can be done simpler with passive components.