(duc/ddc) digital up mixing / quadrature down mixing principle and MATLAB simulation

Digital up mixing 、 Down-Convertor matlab Simulation , If readers are interested, please update later FPGA Implementation code .

In the code lowpass For low pass filter matlab Inside APP Filter Designer Generate , The specific configuration is as follows ：

Simulation results ：

 

 

 

 

 

 

 

 

Simulation code ：

%%   Digital up conversion 、 Digital quadrature down conversion simulation 
clc;
clear;
close all;

%%   Parameter setting 
T = 20e-6;      % Pulse width 20us
B = 50e6;      % bandwidth 50M
f0 = 120e6;    % 120M Intermediate frequency 
Fs = 960e6;    %1G sampling 
N = T*Fs;
K = B/T;
t = linspace(-T/2, T/2, N);
F = ((1:N)-1)*Fs/N - Fs/2;

%% DUC  Digital up conversion 
%LFM
sig = exp (-1j*pi*K*(t).^2);

figure;
plot(real(sig)) ;
hold on;
plot(imag(sig)) ;
title(' Original signal time domain ( Real component )');

% Pulse pressure 
coe = exp(1j*pi*K*(t).^2);
len = length (coe);
coe = coe.*hamming(len).';
pc = conv(sig, coe);
figure;
plot(abs(pc));
title(' Original signal pulse compression result ');

figure;
plot(20*log10(abs(pc)/max(abs(pc))));
title(' Original signal pulse compression result (dB)');

figure;
plot(F/1e6, abs(fftshift(fft(sig))));
xlabel(' frequency /Mz');
title(' Baseband signal spectrum ');

% Intermediate frequency 
mid_f =exp(1j*2*pi*f0*t);

figure;
plot (F/1e6, abs(fftshift(fft(mid_f))));
xlabel(' frequency /MHz');
title(' If signal spectrum ');

% Up mixing 
f_up = sig.*mid_f;
figure;
plot(F/1e6,abs(fftshift(fft(f_up))));
xlabel(' frequency /MEz');
title(' Up mixing signal spectrum ');

%% DDC  Digital down conversion 
% Digital quadrature down mixing 
mid_f_in = cos(2*pi*f0*t + pi*K*(t).^2);

figure,
plot(F/1e6, abs(fftshift(fft(mid_f_in))));
xlabel(' frequency /MHz');
title(' Down mixing input signal spectrum ');

mif_f_sin = sin(2*pi*f0*t);
mif_f_cos = cos(2*pi*f0*t);

f_down_real = mid_f_in.*-mif_f_sin;
f_down_imag = mid_f_in.*mif_f_cos;
f_down = f_down_real + 1j*f_down_imag;

figure;
plot(F/1e6, abs(fftshift(fft(f_down))));
xlabel(' frequency /MHz');
title(' Digital quadrature down mixing signal spectrum ');

% IQ The two channels are respectively low-pass filtered 
f_down_new_real = zeros(1,50000);
f_down_new_real(1:length(f_down_real)) = f_down_real;
f_down_new_imag = zeros(1,50000);
f_down_new_imag(1:length(f_down_imag)) = f_down_imag;

%5OM low pass filter 
load lowpass
f_down_lowpass_real = filter(lowpass, 1, f_down_new_real);
f_down_lowpass_imag = filter(lowpass, 1, f_down_new_imag);
f_down_lowpass = f_down_lowpass_real + 1j*f_down_lowpass_imag;

figure;
plot(abs(fftshift(fft(f_down_lowpass))));
% xlabel(' frequency /MHz');
title(' Low pass filtered signal spectrum ');

figure;
plot(imag(f_down_lowpass)) ;
hold on;
plot(real(f_down_lowpass));
title(' Time domain of low-pass filtered signal （ Real component )');

pc = conv(f_down_lowpass, coe);
figure;
plot(abs(pc));
title(' Low pass filtered signal pulse compression results ');
figure;
plot (20*log10(abs(pc)/max(abs(pc))));
title(' Low pass filtered signal pulse compression results (dB)');