[经验]

我写的fir滤波器

2013-5-12 22:56:05

2187 fir滤波器

我写了一个滤波器的程序，但是仿真的结果不符合，我找不到错误，希望你能抽空帮我看一下。滤波器的系数为-12    9 -12 -22 -3 -1 -38 -32 61 124 61 -32 -38 -1 -3 -22 -12 9 -12

程序如下，其中constant为滤波器的系数
library ieee;
use ieee.std_logic_arith.all;
use ieee.std_logic_1164.all;

entity filter is  port(
clk,reset  :in std_logic;
sample_in  :in signed (8 downto 0);
result_out :out signed(21 downto 0));
end filter;

architecture behave of filter is
type coef_arr is array(0 to 18) of signed (7 downto 0);
  constant coefs : coef_arr:=("10001100","00001001","10001100","10010110","10000011",
  "10000001","10100110","10100000","00111101","01111110","00111101","10010000","10100110",
  "10000001","10000011","10010110","10001100","00001001","10001100");
begin
process(clk,reset)
      type  shift_register is array (18 downto 0) of signed (8 downto 0);
      variable shift  : shift_register;
      variable temp : signed(8 downto 0);
      variable mul_value :signed(16 downto 0);
      variable acc_value : signed (21 downto 0);

begin

      if(reset='0')then
         for i  in 0 to 17 loop
            shift(i):="000000000";
         end loop;
   result_out<="0000000000000000000000";
   elsif (clk'event and clk='1')then
            temp:=sample_in;
            mul_value:=temp*coefs(0);
            acc_value:=conv_signed(mul_value,22);
            for i in 17 downto 0 loop
                              mul_value:=shift(i)*coefs(i+1);
                              acc_value:=acc_value+conv_signed(mul_value,22);
                              shift(i+1):=shift(i);
            end loop;
            shift(0):=temp;
      end if;
      result_out<=acc_value;
end process;
end behave;

我输入一个从1到10的序列用matlab进行卷积的结果为
din=[1:1:10];
>> h=[-12,9,-12,-22,-3,-1,-38,-32,61,124,61,-32,-38,-1,-3,-22,-12,9,-12];
>> conv(h,din)
ans =
  Columns 1 through 8
      -12       -15       -30       -67       -107       -148       -227       -338
  Columns 9 through 16
      -388       -314       -47       -31       169       490       621       711
  Columns 17 through 24
      1197       1664       1128       -162       -883       -642       -303       -333
  Columns 25 through 28
      -340       -135       -18       -120
仿真结果如下为什么两个不一样啊

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