[sdiy] Analysing 4-stage RC filters without the hot air

[Neil Johnson]

Oh, yeah, I forgot:

> Well, firstly it would help to add more to your filter specification -
> how much ripple in the passband and in the stop band, whether
> preserving phase is important or not, and so on.  Once you have that
> info then I think your choices fall into two options:
>
> 1) the easy way is to grab a copy of a standard filter tables
> handbook, look up the filter type you need, pull out the coefficients,
> and frequency and impedance scale to your specific needs.
>
> 2) the harder way is to go back to basic theory, slog through the
> maths (in essence repeating what the authors of the filter tables
> books did) to arrive at the same, or near enough the same, answer.

3) Easiest of them all: either download a filter CAD tool (e.g.
Linear's FilterCAD) or use one of the many online resources to design
the filter for you.

The real question is: do you want to spend brain cycles designing a
filter from first principles, or do you want something good enough so
you can get on with solving the real technical details of your
project?

Although of course it is good to have a grasp of what the tools are
doing so you check if they are lying to you!

Neil
--
http://www.njohnson.co.uk