Looking for FFT of pulses train

[EngIntoHW]

Hi,

I tried to create FFT of 10% Duty-Cycle Pulses train, but failed to do so.

Do you know where one can be found?

Thanks!

 

[ikalogic]

What do you mean by create FFT?
Do you need to do FFT analysis on a signal?
Our SCANALOGIC-2 does exactly that. you can download ScanaStudio from our website, generate some 10% pwm signals, and build FFT graphs..

 

[EngIntoHW]

Hi ikalogic,

I'm familiar with your awesome software actually.
However, PWM isn't an impluse train, because an impluse train consists of impluses of the same width, which is 10% of the period, you see?

 

[ikalogic]

not really....
i don't see how a square signal with 10% duty cycle is not PWM....?

 

[panic mode]

here is some Matlab code and screenshots:

function FFT_test

%% ********************************************
%%      Basic example of FFT in MATLAB
%%          provided by panic mode
%% ********************************************

clc; clear all; close all; % always start fresh,
                           % reset and close anything that may be open

L = 2000;                  % length of signal (number of sample values)
f1  = 10000;               % set signal frequency
Duty = 10;                 % set duty of square wave             
Fs = 512000;               % recall Nyquist sampling frequency, it must be
                           % at least twice that of sampled signal
                           % but it is better if it is higher than that

for i=1:L                  % create pulse train with given duty cycle
    if mod(i,100)<Duty
        signal(i)=1;
    else
        signal(i)=0;
    end;
end;

    
T  = 1./Fs;                % sampling period
t  = [0:L-1]*T;            % time scale for time domain
f = Fs/2*linspace(-1,1,L); % frequency scale for freq. domain

FFTsignal = fft(signal)/L; % fft of signal (freq domain)

figure();                  % always create new figure for your plots

subplot(2,1,1),plot(t,signal); % top graph is time domain signal
axis([t(1) t(L) -0.25 1.25]);   % set convenient axis limits for plot
title('Signal in time domain'); % indicate what the plot represents

subplot(2,1,2),plot(f,abs(fftshift(FFTsignal))); % bottom is freq. domain 
title('Signal in frequency domain'); % indicate what the plot represents

 

[ikalogic]

Okay.. that looks nice..

so where is the problem exactly?

I recall your first post:

I tried to create FFT of 10% Duty-Cycle Pulses train, but failed to do so.

i still don't get what you mean by "create an FFT"? you seem to be doing just fine with matlab..

 

[panic mode]

?

you may be confusing EngIntoHW and me....

 

[ikalogic]

Absolutley

My mistake sorry!

Now it makes more sens

 

[panic mode]

forgot to mark screen captures but file names indicate the content (they are 10%, 25%, 50% and 97% duty cycle).