hello, everyone. I need to calculate the filter circuit like this(first passive stage R1/C1+second active MFB):
http://sim.okawa-denshi.jp/en/MultipleFB3Lowkeisan.htm
The link above, I can get the circuit, but I can not change the values of resistors and capacitors for my needs.
Maybe there is a program which allows to consider such a scheme and to change the values of resistors and capacitors?
Or it may be the formula for the calculation of the manual?
WEBENCH Filter Designer good solution, but there's no calculation of this scheme MFB:
Vitalij,
Actually this filter is realized with a standalone first order filter followed by a second order. A lowpass, 3rd order, Butterworth, cut-off frequency 1 kHz, MFB circuit looks like this:
The reason that your starting R/C pair is replaced with a 1st order amplifier lowpass circuit is because we found there was interaction between the elements with your circuit. This interaction did not provide the response that you would expect, ie somewhat imperfect.
