Odd Order Active Filter Calculator

[T3sl4co1l]

Most calculators only show 1st and 2nd order stages.  This is a waste: in a synthesized filter (Bessel/Butterworth/etc.), odd order filters always have one real pole, which means you can simply throw in an RC pole somewhere.  So if you find that you need, say, a 4th or 6th order filter, you can sweeten it to a 5th or 7th with no problem whatsoever.   Of course, the RC values for the 3rd order stage aren't simply R and C, so you need a calculator to figure that out.

http://beis.de/Elektronik/Filter/Act3PoleLP.html

Tim

[moffy]

Nice! Thanks for the info, it is always handy to have a means of calculating the filter component values.
Also the first input RC reduces the BW that the opamp sees, nice if you have a high BW input signal.