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Whats the difference between active and passive filters?

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electron_boy

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active filters

what is the difference between active and passive filters. why in active filters an opamp used at the end of the RC passive filter section.
 

Re: active filters

Passive filters do not require any external power like +-15V DC They are made from R L C and transmission lines for the 'electric wave filters' as they were once called. There are many types of passive acoustic and optic filters. I once saw a mechanical acoustic low pass filter for use with telephone handsets. It was for the case of a PWM drive for the earphone for higher efficiency. Only the lower, desired audio frequency got through.
 

Re: active filters

Hi !

We use op amps in active filters because we can simulate the characteristics of RLC elements used in passive filters, using only resistors and capacitors and not inductors (no one kind of active filter uses inductor). More advantages are that we can give a gain to the stage (we can cascade several stages to increase and sharp the slope of the filter), isolate the signal source from the load (as op amp has high input impedance and low output impedance).
 

Re: active filters

active filter is good because you can have it in ic form. however it is limited in terms of bandwidth. at high frequency, you have to depend on passive filters, ie those with inductors and capacitors instead of opamps and capacitors.

at high frequency, inductors becomes more manageable. op amps roll off at high frequency.
 

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