FIR_LP Problem

Question

I have a problem of gain with a fir_lp (value < expected value )!!!

config :

filtre_type : low pass

sample rate :10khz

cutoff freq :500hz

coeff : 15

input number system : unsigned binary

ast_sink_data :INPUT data width 16 bits ( data signal 50hz ampl : 2.5V --> 65535 )

ast_source_data :OUTPUT width 27 bits full resolution

when i calculate RMS (value < expected value) :

{ data in for RMS : lp_out(lp_out'high downto lp_out'high-15) }

thinks for help

altera_forum · Answer

Cutoff freq is 1/20 of sample frequency, it's impossible to design a good FIR filter with 15 or 30 taps. A first or second order IIR filter will perform much better in this case.

altera_forum · Answer

Thanks for replying, Can i generate irr filter from megawizard or i should design it ?

altera_forum · Answer

There is no Altera IP for IIR filters as far as I know. MatLab or special filter tools can be used to calculate the difference equation coefficients.

altera_forum · Answer

ok thanks, So it's impossible to use altera FIR compiler with Cutoff freq 1/20 of sample frequency even if i change coeff?

altera_forum · Answer

fir attenuation image (http://img3.imageshack.us/img3/4210/firlp.jpg)

in this image

udat : input signal 16hz (16 bits)

fir_lp : width 37 bits

coeff : 100

(i have always an attenuation even with others coeff)

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FIR_LP Problem

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