How can I create a single square wave of varying duty cycle in MATLAB?

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

[dpb]

I've not messed with it enough to know for certain, but I think you could make this work with the pulstran function by setting the pulse time vector to the variable spacing to get the desired duty cycle while the pulse vector uses the same rectangular pulse generator function.

[Joel Kelly]

I have also had a play around with the pulstran function and this works also

Answer 1

[Gabriel Emile Hine]

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)

[Joel Kelly]

Yes, this is works exactly as intended!

Thank you!