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How to calculate of the requirements of Op-am when designing a filter?

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yorande

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Hi,
How to calculate of the requirement of Op-am when designing a filter?
It seems the wrong OP-amp might quite likely to fail the filter.
But how could we know what kind of Op-amps do we need?

Thanks!
 

Re: OP-AMP in filter

it mainly depends on the 3db frequency of the opamp.... the opamp shouldnt attenuate the input signal beyond a particular level...
 

OP-AMP in filter

But......how will the 3dB bandwidth of the opamp affect the performance of the active filter?

Thx in advance!
 

Re: OP-AMP in filter

beyond that the opamp gain wouldnt help that much... i'm talking about the closed loop gain....
 

OP-AMP in filter

just assume your opamp has a limited bandwidth and limited DC gain, probably a one-pole system and then plug that in your filter's transfer function, you will see the impact
 

Re: OP-AMP in filter

You may want to consider looking at TI's Active Filter designer software. If you are using a rail-to rail opamp. I recently used this software to design a 10Hz LP filter for sensors interfacing into a microcontroller. The software also does band-pass filters. I like it better than Microchips filter designer software.
 

Re: OP-AMP in filter

yorande said:
Hi,
How to calculate of the requirement of Op-am when designing a filter?
It seems the wrong OP-amp might quite likely to fail the filter.
But how could we know what kind of Op-amps do we need?

Thanks!

the op bandwidth should 10 times larger than filter bandwidth
 

Re: OP-AMP in filter

for example the 741 has a 1MHz BW - gain product.. and u can use it only to design filters in the range of max some 100 KHz...
 

Re: OP-AMP in filter

Take a look at TI's "active filter design techniques", google it.

the op bandwidth should 10 times larger than filter bandwidth
 

Re: OP-AMP in filter

windmillkity said:
Take a look at TI's "active filter design techniques", google it.
the op bandwidth should 10 times larger than filter bandwidth

After reading this I'm still a bit confused about that bandwidth/gain stuff. I'm planning to build up a lowpass filter with a corner frequency of 100kHz with gain=1.

If I use a 741, which has a bandwith of 1MHz, this should be working, right?

But what happens if my filter has to have a corner frequency of 200kHz and gain=1. Would I have to look for another op amp then?
 

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