Question

Which is not a difference between active and passive filter?

(a) A passive filter does not use op-amp while an active filter uses an op-amp

(b) A passive filter can’t use an inductor while an active filter can

(c) A passive filter performs only filtering while an active filter amplifies too

(d) A passive filter is used at audio frequency and an active at radio frequency

The question was asked at a job interview.

My doubt stems from Frequency Filters topic in portion Op-amps and its Applications of Analog Circuits

Answer 1

Right choice is (d) A passive filter is used at audio frequency and an active at radio frequency

Best explanation: A passive filter can consist of all R, L and C elements. An op-amp is used in an active filter, and it also provides amplification along with filtering. There are no inductors used in active filters because they are bigger in size and bulky. Active filters are used at audio frequency and passive filter at radio frequency.