Pulse width modulation

Table of Contents

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details <https://www.gnu.org/licenses/>.

This code was developed by Miodrag Bolic for the book PERVASIVE CARDIAC AND RESPIRATORY MONITORING DEVICES: https://github.com/Health-Devices/CARDIAC-RESPIRATORY-MONITORING. We acknowledge that we used the code developed by Sourangsu Banerji, 2013 at https://www.mathworks.com/matlabcentral/fileexchange/42168-pulse-width-modulation.

% Changing the path from main_folder to a particular chapter
main_path=fileparts(which('Main_Content.mlx'));
if ~isempty(main_path)
    %addpath(append(main_path,'/Chapter2'))
    cd (append(main_path,'/Chapter3/Generating Signals'))
    addpath(append(main_path,'/Service'))
end
SAVE_FLAG=0; % saving the figures in a file

PWM Signal generation

The code below shows a 10 Hz modulation waveform. The input signal is the sine wave with a frequency of 1 Hz. The code then generates the the output PWM signal.

% This code has been modified from Sourangsu Banerji, 2013 at

% https://www.mathworks.com/matlabcentral/fileexchange/42168-pulse-width-modulation

clc;

clear all;

t = 0:0.001:1;

fc = 10; % the Frequency of Carrier Signal

fm = 1; % Frequency of the input signal

a = 1 ; %Amplitude of Modulation signal

b = 1; % Amplitude of the input signal

vc = a.*sawtooth(2*pi*fc*t);

vm = b.*sin(2*pi*fm*t);

n = length(vc);

for i = 1:n

if (vm(i)>=vc(i))

pwm1(i) = 1;

else

pwm1(i) = 0;

end

% Representation of the Message Signal

subplot(2,1,1);

plot(t,vm,'black');

xlabel('Time (s)');

ylabel('Amplitude (V)');

ylim([-1, 1.5])

%title('Input Signal');

grid on;

% Representation of the Carrier Signal

hold on

plot(t,vc);

legend('Input signal', 'Modulation Signal');

grid on;

% Representation of the PWM Signal

subplot(2,1,2);

plot(t,pwm1,'red');

xlabel('Time (s)');

ylabel('Amplitude (V)');

%title('PWM Signal');

legend('PWM Signal');

ylim([0, 1.2])

%axis([0 1 0 2]);

grid on;

% Add title to the Overall Plot

ha = axes ('Position',[0 0 1 1],'Xlim',[0 1],'Ylim',[0 1],'Box','off','Visible','off','Units','normalized', 'clipping' , 'off');

text (0.5, 1,'\bf Pulse Width Modulation ','HorizontalAlignment','center','VerticalAlignment', 'top')

exportgraphics(gcf,"Fig3.29.jpg", 'Resolution',600)