全数字FM接收机2---仿真
在MATLAB下仿真程序
1 %Simple PLL m-file demonstration 2 3 %This m-file demonstrates a PLL which tracks and demodulates an FM carrier. 4 clear all; 5 close all; 6 f=1000;%Carrier frequency 7 fs=100000;%Sample frequency 8 N=5000;%Number of samples 9 Ts=1/fs; 10 t=(0:Ts:(N*Ts)- Ts); 11 %Create the message signal 12 f1=100;%Modulating frequency 13 msg=sin(2*pi*f1*t); 14 kf=.0628;%Modulation index 15 %Create the real and imaginary parts of a CW modulated carrier to be tracked. 16 Signal=exp(j*(2*pi*f*t+2*pi*kf*cumsum(msg)));%Modulated carrier 17 Signal1=exp(j*(2*pi*f*t));%Unmodulated carrier 18 %Initilize PLL Loop 19 phi_hat(1)=30; 20 e(1)=0; 21 phd_output(1)=0; 22 vco(1)=0; 23 %Define Loop Filter parameters(Sets damping) 24 kp=0.15; %Proportional constant 25 ki=0.1; %Integrator constant 26 %PLL implementation 27 for n=2:length(Signal) 28 vco(n)=conj(exp(j*(2*pi*n*f/fs+phi_hat(n-1))));%Compute VCO 29 phd_output(n)=imag(Signal(n)*vco(n));%Complex multiply VCO x Signal input 30 e(n)=e(n-1)+(kp+ki)*phd_output(n)-ki*phd_output(n-1);%Filter integrator 31 phi_hat(n)=phi_hat(n-1)+e(n);%Update VCO 32 end; 33 %Plot waveforms 34 startplot = 1; 35 endplot = 1000; 36 37 figure(1); 38 subplot(3,2,1); 39 plot(t(startplot:endplot), msg(startplot:endplot)); 40 title('100 Hz message signal'); 41 %xlabel('Time (seconds)'); 42 ylabel('Amplitude'); 43 grid; 44 45 figure(1); 46 subplot(3,2,2); 47 plot(t(startplot:endplot), real(Signal(startplot:endplot))); 48 title('FM (1KHz carrier modulated with a 100 Hz message signal)'); 49 %xlabel('Time (seconds)'); 50 ylabel('Amplitude'); 51 grid; 52 53 figure(1) 54 subplot(3,2,3); 55 plot(t(startplot:endplot), e(startplot:endplot)); 56 title('PLL Loop Filter/Integrator Output'); 57 %xlabel('Time (seconds)'); 58 ylabel('Amplitude'); 59 grid; 60 61 subplot(3,2,4); 62 plot(t(startplot:endplot), real(vco(startplot:endplot))); 63 title('VCO Output (PLL tracking the input signal)'); 64 %xlabel('Time (seconds)'); 65 ylabel('Amplitude'); 66 grid; 67 68 subplot(3,2,5); 69 plot(t(startplot:endplot), phd_output(startplot:endplot)); 70 title('Phase Detecter Output'); 71 xlabel('Time (seconds)'); 72 ylabel('Amplitude'); 73 grid; 74 75 subplot(3,2,6); 76 plot(t(startplot:endplot), real(Signal1(startplot:endplot))); 77 title('Unmodulated Carrier'); 78 xlabel('Time (seconds)'); 79 ylabel('Amplitude'); 80 grid;
仿真结果
OPTIMISM, PASSION & HARDWORK
