DDC.rar_chirp_ddc

%% Homework2.2-Down-conversion Simulation-chirp signal clc; clear all; close all; %% 参数设置 f0=60e6; %chirp信号中频 fs=80e6; %采样频率 B=8e6; ts=1/fs; tau=1e-3; %脉冲宽度 t=0:ts:tau-ts; k=B/tau; % chirp slope f_nco=20e6; %NCO频率 %% 信号 ut=cos(2*pi*f0.*t+pi*k.*t.^2); %Chirp信号 signal_in=ut; signal_nco_i=sin(2*pi*f_nco*t); %NCO signal_nco_q=cos(2*pi*f_nco*t); xi=signal_in.*signal_nco_i; xq=signal_in.*signal_nco_q; %% 低通滤波器 Hd=[-0.000509552317425067 0.000371832719073747 ... -2.44618142336023e-18 -0.000422345371283588 0.000653914483674189 ... -0.00051300840086792 3.97172054701057e-19 0.000648237670285558 ... -0.00103805305948637 0.000832713046447832 -1.44055249402109e-17 ... -0.00107147663368522 0.00171533438865906 -0.0013700728022455 ... 1.49748424538358e-17 0.00173474602821205 -0.00274933143849888 ... 0.00217272016206513 -1.00664883097235e-17 -0.00269259477337679 ... 0.00422346878396029 -0.00330491373545649 -5.06324472469145e-18 ... 0.0040229937639382 -0.00626058957283252 0.00486415663677792 ... -1.66404228224871e-17 -0.00585160870489404 0.00906475339859715 ... -0.00701739683384083 5.85437570436228e-17 0.00840723125601122 ... -0.0130193885689127 0.0100887097935733 -2.30053463735395e-17 ... -0.0121661147234315 0.018953868399222 -0.0148088567812163 ... 2.56041597453839e-17 0.0183109311931974 -0.0290491896372965 ... 0.0232296218816149 -2.75866619122871e-17 -0.0307619445738023 ... 0.051363785669012 -0.0440244907599678 2.88282849719697e-17 ... 0.0744525331295221 -0.158657515688882 0.224988028604281 ... 0.750377726738553 0.224988028604281 -0.158657515688882 ... 0.0744525331295221 2.88282849719697e-17 -0.0440244907599678 ... 0.051363785669012 -0.0307619445738023 -2.75866619122871e-17 ... 0.0232296218816149 -0.0290491896372965 0.0183109311931974 ... 2.56041597453839e-17 -0.0148088567812163 0.018953868399222 ... -0.0121661147234315 -2.30053463735395e-17 0.0100887097935733 ... -0.0130193885689127 0.00840723125601122 5.85437570436228e-17 ... -0.00701739683384083 0.00906475339859715 -0.00585160870489404 ... -1.66404228224871e-17 0.00486415663677792 -0.00626058957283252 ... 0.0040229937639382 -5.06324472469145e-18 -0.00330491373545649 ... 0.00422346878396029 -0.00269259477337679 -1.00664883097235e-17 ... 0.00217272016206513 -0.00274933143849888 0.00173474602821205 ... 1.49748424538358e-17 -0.0013700728022455 0.00171533438865906 ... -0.00107147663368522 -1.44055249402109e-17 0.000832713046447832 ... -0.00103805305948637 0.000648237670285558 3.97172054701057e-19 ... -0.00051300840086792 0.000653914483674189 -0.000422345371283588 ... -2.44618142336023e-18 0.000371832719073747 -0.000509552317425067]; %利用fdatool设计滤波器的系参数 %I=lowpassfilter1(xi); I=filter(Hd,1,xi); %经过低通滤波 Q=filter(Hd,1,xq); %% 基带信号生成 signal_baseband=I-1i.*Q; %基带信号 %% 画图 N=length(t); f=((0:N-1)/N-0.5)*fs/1e6; f1=(0:N-1)*fs/1e6; F_signal=fftshift(fft(signal_in)); figure(1) %输入信号时/频域图 subplot(211) plot(t,signal_in); xlabel('时间/s'); ylabel('幅度'); axis([0 5000/fs -1.1 1.1]); title('输入信号时域波形') subplot(212) plot(f,abs(F_signal)); xlabel('频率/MHz'); title('输入信号频谱') F_ncoi=fftshift(fft(signal_nco_i)); F_ncoq=fftshift(fft(signal_nco_q)); figure(2) %NCO信号时/频域图 subplot(221) plot(t,signal_nco_i); xlabel('时间/s'); ylabel('幅度'); axis([0 100/fs -1 1]); title('NCO-I信号') subplot(222) plot(f,abs(F_ncoi)); xlabel('频率/MHz'); title('NCO-I频谱') subplot(223) plot(t,signal_nco_q); xlabel('时间/s'); ylabel('幅度'); axis([0 100/fs -1 1]); title('NCO-Q信号') subplot(224) plot(f,abs(F_ncoq)); xlabel('频率/MHz'); title('NCO-Q频谱') figure(3) figure(3) %滤波器幅相特性 freqz(Hd); title('滤波器幅相特性'); F_I=fftshift(fft(I)); F_Q=fftshift(fft(Q)); figure(4) %DDC输出I/Q两路信号时/频域 subplot(221) plot(t,I); xlabel('时间/s'); ylabel('幅度'); axis([0 10000/fs -1 1]); title('DDC-I时域信号') subplot(222) plot(f,abs(F_I)); xlabel('频率/MHz'); title('I路信号频谱') subplot(223) plot(t,Q); xlabel('时间/s'); ylabel('幅度'); axis([0 10000/fs -1 1]); title('DDC-Q时域信号') subplot(224) plot(f,abs(F_Q)); xlabel('频率/MHz'); title('Q路信号频谱') F_baseband=fftshift(fft(signal_baseband)); figure(5) %基带信号时/频域 subplot(211) plot(t,real(signal_baseband)); title('基带信号时域波形') xlabel('时间/s'); ylabel('幅度'); %axis tight; subplot(212) plot(f,abs(F_baseband)); xlabel('频率/MHz'); title('基带信号频谱')