Whats the function of approximate filters?

Filters approximation ?

I have studied the active filters and the passive filters. But i could not understand on the function of approximate filters such as

1)Butterworth
b)Bessel
3)Eleptical

Can anybody explain to me how they function to the filters..

Re: Filters approximation ?

I suggest you to read the book : Digital Filter Designers Handbook, McGraw-Hill.
You can find the book here:

Re: Filters approximation ?

zahrein said:

I have studied the active filters and the passive filters. But i could not understand on the function of approximate filters such as

1)Butterworth
b)Bessel
3)Eleptical

Can anybody explain to me how they function to the filters..

Click to expand...

1)Butterworth is the filter results in flat pass band and a moderate group delay. Phase is somewhat linear. You must understand all filters without exception their output is delayed.

2)Bessel is the most complicated filter in my opinion. The amplitude is horrendous. Forget the flattest thing you get in butterworth. Good thing about Bessel filter are the best for linearity which mean if you plot their transfer function phase of an active bessel filter you will see nearly a straight line comming from origin 0. Rule of thumb. Any straight line that comes from origin is linear.

3)Eleptical are somewhat like Chebychev filters. Ripple in passband but with only difference I guess in my opinion is high attenuation in stopband.

Now where do you want these? All have their roles. You can not use only one kind of filter. If you need a filter for precission in linearity I would pick Bessel. If I am not that much over-concerned about linearity but amplitude I would pick Butterworth etc etc.

Once you face with projects where you need compromises offered by one filter you would pick that kind of filter. You will see it in future. You wanna bet 1milion dollars?