Re: Low pass filter, cut off 500 Hz, short response time...

From: Don Lancaster (don_at_tinaja.com)
Date: 02/11/05 

Date: Fri, 11 Feb 2005 09:11:26 -0700

bill.sloman@ieee.org wrote:
> Viram wrote:
>
>>I'm trying to design a LP-filter with a cut off at around 500 Hz. My
>>problem is getting a short response time and low/no resonance peak.
>
> What
>
>>order should the filter be? I'm currently trying with a simple
>>LC-filter...
>
>
> You need to get hold of a decent text on filter design - I use the
> "Electronic Filter Design Handbook" by Arthur B. Williams and Fred J.
> Taylor - ISBN 0-07-070434-1. Since then there has been a third edition
> (ISBN 0-07-070430-9) which is supposed to be even better, but it seems
> to be out of print - www.amazon.com offers three second hand copies for
> about $130. You should be able to find it - or something very like it -
> in a university library.
>
> The usual choice for what you seem to want to be doing is a
> "linear-phase" or "Bessel filter", though a "synchronously tuned"
> filter (consisting of identical multiple poles) actually gives fastest
> settling for a given number of poles, with the step getting to better
> than 99% after five time constants. Adding more poles makes the step
> steeper at the 50% point, and pushes the 50% point back from around one
> time constant at one pole to closer to three at ten poles.
>
> A simple LCR filter is two poles ...
>
> ---------
> Bill Sloman, Nijmegen
>

Do it digitally.
Distortionless digital filters are superb because they can look
backwards as well as forwards in time.

More on my website.

But if you must go analog, use my Active Filter Cookbook. 

-- 
Many thanks,
Don Lancaster
Synergetics   3860 West First Street  Box 809  Thatcher, AZ 85552
voice: (928)428-4073 email: don@tinaja.com
Please visit my GURU's LAIR web site at http://www.tinaja.com

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