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Notch filtr 50Hz | Cypress Semiconductor

Notch filtr 50Hz

Summary: 1 Reply, Latest post by danaaknight on 07 Jan 2015 04:00 PM PST
Verified Answers: 0
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Waldas's picture
10 posts


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.

user_14586677's picture
7646 posts

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.



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