MATLAB: How to create a single square wave of varying duty cycle in MATLAB

Question

Hello,

I am wanting to create a square wave in MATLAB that increases it's duty cycle with respect to time, however when I tried to implement this, I ran into the error of MATLAB only allowing scalar values for the duty cycle.

Is there any way around this?

Here is my current code, based off of this example: https://uk.mathworks.com/matlabcentral/answers/217746-implementing-a-sine-wave-with-linearly-changing-frequency

 Fs = 100000;
 t = 0:1/Fs:1;
 f_in_start = (100*1/3)/(100*0.1); %1-to-2 PFM

 f_in_end = 50/(100*0.1); %1-to-1 PFM

 f_in = linspace(f_in_start, f_in_end, length(t)); %Varying pulse frequency
 DC_start = 100*1/3; %1-to-2 PFM
 DC_end = 100*1/2; %1-to-1 PFM
 DC_in = linspace(DC_start, DC_end, length(t)); %Varying the duty cycle
 DC = cumsum(DC_in/Fs); %Duty cycle
 phase_in = cumsum(f_in/Fs); %frequency
 y = 0.5*square(2*pi*phase_in,DC) + 0.5;
 plot(t,y)

For context, the aim is to create a PFM waveform that increases in frequency with respect to time, increasing from a 1-to-2 mark space ratio to a 1-to-1 whilst keeping the 'on-time' of the signal constant.

Ideally, the waveform should look something like this at the start:

And end with something like this:

Thank you in advance

Answer 1

If I understood the problem, this code should work for you. If you have anu doubts, please ask me.

Duration = 10;
Fs = 100000;
t = 0:1/Fs:Duration;
pulse_width = 0.1;
duty_start = 1/3;
duty_end = 1/2;
N_pulses = Duration /((pulse_width/duty_start + pulse_width/duty_end) /2);
dutys = linspace(duty_start,duty_end,N_pulses);
cycle_periods = pulse_width./dutys;
cycle_starts = cumsum([0 cycle_periods]);
square_wave = double(sum(                                                   ...
                            bsxfun(@ge,t, cycle_starts(:)) &                ...
                            bsxfun(@le,t ,cycle_starts(:)+pulse_width(:))   ...
                         ,1)>0);
plot(square_wave)