# Designing a lowpass Butterworth filter

1. Nov 3, 2011

### rusty009

Hi all,

I am trying to design a lowpass filter using the following conditions

Passband edge f = 10 Khz (Ωp)
passband stop f = 30 Khz (Ωs)
Minimum stopband attenuation = 50db (1/A)
Maximum passband attenuation = 0.4db( 1/$\sqrt{1+ε2}$ )

and am having quite a lot of trouble with it. I have tried to determine the order but it comes out as a complex number, the formula I am using is,

n= log( ε/$\sqrt{(A2-1)}$)/log(Ω[/B]ps)

can anyone help me out? Thanks

Last edited: Nov 3, 2011
2. Nov 27, 2011