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采用FPGA实现多级CIC滤波器的四倍抽取一

在实现多级CIC滤波器前我们先来懂得滑动匀称滤波器、微分器、积分器以及梳状滤波器道理。CIC滤波器在通信旌旗灯号处置惩罚中有侧紧张的利用。

1、滑动匀称滤波器

图1 8权值滑动匀称滤波器布局

滑动匀称滤波器(Moving Average Filter)的所有权值系数均为1,实现对旌旗灯号的平滑感化,具有低通特点。

Matlab

close all

clear all

clc

%set system parameter

fs = 1000; %The frequency of the local oscillator signal

Fs = 44100; %sampling frequency

N = 24; %QuantitaTIve bits

L = 8192;

%GeneraTIng an input signal

t =0:1/Fs:(1/Fs)*(L-1); %GeneraTIng the TIme series of sampling frequencies

sc =sin(2*pi*fs*t); %a sinusoidal input signal that produces a random starting phase

%滑动匀称滤波器

b =[1,1,1,1,1,1,1,1];

a =1;

sf=filter(b,a,sc).*(1/8);

图2 滑动匀称滤波器的幅频特性

2、微分器

图3 微分器布局

微分器有1和-1两个权值系数的滤波器,该滤波用具有简单的高通幅频相应特点。

y( k ) = x( k ) - x( k - 1 )

Matlab :

close all

clear all

clc

%set system parameter

fs = 1000; %The frequency of the local oscillator signal

Fs = 44100; %sampling frequency

N = 24; %Quantitative bits

L = 8192;

%Generating an input signal

t =0:1/Fs:(1/Fs)*(L-1); %Generating the time series of sampling frequencies

sc =sin(2*pi*fs*t); %a sinusoidal input signal that produces a random starting phase

%微分滤波器

b =[1,-1];

a =1;

sf=filter(b,a,sc);

图4 微分器幅频相应特性

3、积分器

图5 数字积分器布局

数字积分器是只有一个系数的IIR滤波器该滤波用具有低通的滤波器的幅频相应特点。

q( k ) = p (k) + q( k - 1)

Matlab :

close all

clear all

clc

%set system parameter

fs = 1000; %The frequency of the local oscillator signal

Fs = 44100; %sampling frequency

N = 24; %Quantitative bits

L = 8192;

%Generating an input signal

t =0:1/Fs:(1/Fs)*(L-1); %Generating the time series of sampling frequencies

sc =sin(2*pi*fs*t); %a sinusoidal input signal that produces a random starting phase

%积分滤波器

b =1;

a =[1,-1];

sf=filter(b,a,sc);

图6 积分器幅频相应特性

由图3,图4,和图5阐发,1khz基础未发生改变,44.1khz相对付352.8khz采样率1khz点变得松散。

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