在完成多级CIC滤波器前咱们先来了解滑动均匀滤波器、微分器、积分器以及梳状滤波器原理。CIC滤波器在通讯信号处理中有着重要的使用。
1、滑动均匀滤波器
图1 8权值滑动均匀滤波器结构
滑动均匀滤波器(Moving Average Filter)的所有权值系数均为1,完成对信号的滑润效果,具有低通特性。
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
%滑动均匀滤波器
b =[1,1,1,1,1,1,1,1];
a =1;
sf=filter(b,a,sc).*(1/8);
图2 滑动均匀滤波器的幅频特征
2、微分器
图3 微分器结构
微分器有1和-1两个权值系数的滤波器,该滤波器具有简略的高通幅频呼应特性。
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 微分器幅频呼应特征
3、积分器
图5 数字积分器结构
数字积分器是只要一个系数的IIR滤波器该滤波器具有低通的滤波器的幅频呼应特性。
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 积分器幅频呼应特征
由图3,图4,和图5剖析,1khz根本未产生改动,44.1khz相对于352.8khz采样率1khz点变得疏松。