PWM of a signal

Pulse Width Modulation can be used to convert an analog signal to digital or mimic an analog signal with digital (e.g. Arduino's analogWrite()). PWM basically converts the signal sample values into pulse width values (amplitude of pulses is constant). Below is a Matlab script that demonstrates PWM of a sine wave.

	%Matlab script to demonstrate PWM of sine signal
	clc; clear all; close all;
	nSample = 36;
	dAngle_rad = deg2rad(20);
	sinp1 = zeros(nSample,1);
	dutyCyle = zeros(nSample,1);
	angle_rad = zeros(nSample,1);
	pwmX = zeros(nSample,1);
	for i = 1:nSample
	angle_rad(i) = dAngle_rad * (i-1);
	sinp1(i) = 1 + sin(angle_rad(i)); %signal is between [0, 2]
	dutyCyle(i) = sinp1(i) / 2; %PWM duty cycle
	pwmX(i) = (dutyCyle(i)*dAngle_rad);
	end
	subplot(2,1,1);
	plot(angle_rad, sinp1, 'o-')
	title('PWM of sine'); grid on; set(gca, 'xgrid', 'off');
	ylim([-0.1, 2.1]); xlim([min(angle_rad), max(angle_rad)+0.2])
	for i=1:nSample
	line(angle_rad(i)*[1, 1], [0 sinp1(i)], 'color', 'k');
	end
	subplot(2,1,2);
	plot(angle_rad, sinp1, 'o-');
	grid on; hold on; set(gca, 'xgrid', 'off'); ylim([-0.1, 2.1]);
	xlim([min(angle_rad), max(angle_rad)+0.2]); xlabel('angle [rad]')
	pwmMag = max(sinp1);
	for i=1:nSample-1
	%ON
	line([angle_rad(i), angle_rad(i)+pwmX(i)], [pwmMag pwmMag], 'color', 'r');
	line(angle_rad(i)*[1 1], [0 pwmMag], 'color', 'r');
	line(angle_rad(i)+pwmX(i)*[1 1], [0 pwmMag], 'color', 'r');
	%OFF
	line([angle_rad(i)+pwmX(i), angle_rad(i)+pwmX(i) + dAngle_rad-pwmX(i)], [0 0], 'color', 'r');
	end

view raw sinePWM.m hosted with ❤ by GitHub