Low Pass Filter basics

[toyo22r]

I have a question about low pass filters. I am designing a 2nd order lo
pass LC filter. What determines the response type? (ie. butterworth
bessel, etc.)

Many thanks,
Paul

 

[Pooh Bear]

I have a question about low pass filters. I am designing a 2nd order low
pass LC filter. What determines the response type? (ie. butterworth,
bessel, etc.)

Active or passive ?

Graham

 

[James Douglas]

Search google for filter software, there is a ton of it which may help
with your design stuff. Some of it if very good and best most that I
recall was F R E E!

 

[BobG]

toyo22r:
What determines the response type? (ie. butterworth,
bessel, etc.)
====================
Response has to do with damping... this is controlled by Q of the coil
Q=omegaL/R,
f=1/(2*pi*R*C)

 

[BobG]

Sorry. Too early. that f was for an RC filter. For the LC filter
f=1/(2*pi*sqrt(LC))

 

[Pooh Bear]

toyo22r:
What determines the response type? (ie. butterworth,
bessel, etc.)
====================
Response has to do with damping... this is controlled by Q of the coil
Q=omegaL/R,

Not alone. The load on the filter affects the damping too. ( in the case
of an active filter the gain ).

Graham

 

[john jardine]

I have a question about low pass filters. I am designing a 2nd order low
pass LC filter. What determines the response type? (ie. butterworth,
bessel, etc.)

Many thanks,
Paul

The various response types emphasise certain filter features, such that one
chosen style may offer a little extra benefit in a particular filtering job.
(You) make the choice based on knowing what flavours are available (there's
about half a dozen kicking about) and the particular properties that they
each advertise.
Feature wise, there's not a great deal to mug up on but I can't offhand
suggest a [useful] filter website as I've not seen one and most filter
textbooks lose the plot after about page 1.
At the end of the day, a LP filter is a LP filter and a design that gives
components calculated for a Butterworth style response (feature: flat
response upto it's cutoff) can be OK for maybe 90% of all day to day
filtering needs.
All the rest is just niceties
regards
john

 

[Bob Monsen]

I have a question about low pass filters. I am designing a 2nd order low

pass LC filter. What determines the response type? (ie. butterworth,

bessel, etc.)

Look here:

http://www.dspguide.com/pdfbook.htm

Chapter 3 has a nice explanation of antialias filters, and gives a good
description of the different types of filters.

--
Regards,
Bob Monsen

A great discovery solves a great problem, but there is a grain of discovery
in the solution of any problem. Your problem may be modest, but if it
challenges your curiosity and brings into play your inventive faculties,
and if you solve it by your own means, you may experience the tension and
enjoy the triumph of discovery.
- George Polya