Notch filtr 50Hz

[Anonymous]

Hi

   

I use application AN2284 to create notch filter 50Hz. In this app is C code

   

IIR second-order notch filter:

   

diff1 = (x + xn_2) <<16;
y = ((diff1>>1)+(diff1>>2)+87301*(xn_1 - yn_1) -((yn_2<<16)>>1));
xn_2 = xn_1;
xn_1 = x;
yn_2 = yn_1;
yn_1 = y;

   

I know IIR filters but I don't understand where it came from value 87301 ?

   

I thought that the filter is formed from the coefficients. for example. b=-2*cos(2*PI*f)

   

I would be grateful someone explain how it works.

[ETRO_SSN583]

I think what you are seeing is scaling so the filter is done with

   

integers vs floating point which would eat up a lot of MIPS and

   

code space. Note the M8C core has a fast MAC in it.

       

       

Regards, Dana.