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1、设计低通FIR滤波器。通带边缘频率10KHz，阻带边缘频率22KHz，阻带衰减75dB，采样频率50KHz窗函数选定：阻带衰减75dB，选择blackman窗截止频率：2pi*（10+（22-10）/2）/50=0.64pi窗函数长度：blackman窗的过渡带宽为5.98，单位为2pi/N，而要设计的低通滤波器的过渡带宽为2pi*12/50=0.48pi，二者相等，得N=24.9，取25。理想低通滤波器脉冲响应：h1[n]=sin(nΩ1)/n/pi=sin(0.64pi*n)/n/pi窗函数为：w[n]=0.42-0.5cos(2pi*n/24)+0.8cos
2、(4pi*n/24)则滤波器脉冲响应为：h[n]=h1*w[n]
3、n
4、<=12h[n]=0
5、n
6、>12#include"DSP281x_Device.h"DSP281xHeaderfileIncludeFile#include"DSP281x_Examples.h" DSP281xExamplesIncludeFile#include"f2812a.h"#include"math.h"#defineFIRNUMBER25#defineSIGNAL1F1000#defineSIGNAL2F4500#defineSAMPLEF 1000
7、0#definePI3. floatInputWave();floatFIR(); floatfHn[FIRNUMBER]={0.0,0.0,0.001,-0.002,-0.002,0.01,-0.009, -0.018,0.049,-0.02,0.11,0.28,0.64,0.28, -0.11,-0.02,0.049,-0.018,-0.009,0.01, -0.002,-0.002,0.001,0.0,0.0
8、 };floatfXn[FIRNUMBER]={0.0};floatfInput,fOutput;floatfSignal1,fSignal2;floatfStepSignal1,fStepSignal2;floatf2PI;inti;floatfIn[256],fOut[256];intnIn,nOut; main(void){ nIn=0;nOut=0; f2PI=2*PI; fSignal1=0.0; fSignal2=PI*0.1; fStepSignal1=2*PI/30; fStepSignal2=2*PI*1.4; while(1
9、) { fInput=InputWave(); fIn[nIn]=fInput; nIn++;nIn%=256; fOutput=FIR(); fOut[nOut]=fOutput; nOut++; if(nOut>=256) { nOut=0; /*请在此句上设置软件断点*/ } }} floatInputWave(){ for(i=FIRNUMBER-1;i>0;i--) fXn[i]=fXn[i-1]; fXn[0]=sin(fSignal1)+cos(fSignal2)/6.0; fSignal1+=fStepSignal1;
10、 if(fSignal1>=f2PI) fSignal1-=f2PI; fSignal2+=fStepSignal2; if(fSignal2>=f2PI) fSignal2-=f2PI; return(fXn[0]);} floatFIR(){ floatfSum; fSum=0; for(i=0;i
