MATLAB: Problem Implementing a sine wave with increasing frequency

sine

Hi,
I would implement a sine wave with frequency that increases from 0 to 50 and stay constant afterwards. The model i used is on the top left and frequency input on bottom left. However, the output results( firgure right) i obtained contains a frequency higher than 50Hz but I don't know why. What went wrong?
 matlab function code
function y = sin(f,t,ps)
%generates a sine wave of frequency f and phase shift of ps (in radians)
y = sin(2*pi*f*t+ps);
Here's my model

Best Answer

The problem with your model is dynamic freqency change faster than the generation of sine wave itself. Say for example, at a given instant the frequency input to the function call is 20HZ. Depending on the clock value at that instant, MATLAB refers to 20HZ sine wave and takes a sample out of it. For the very next sample, you are changing the frequency to 21HZ (say), and therefore matlab has to look for the 21HZ sine wave and depending on the clock, it gives the output. Therefore the output frequency can not be defined during the ramp period in your model.
In order to define the frequency effectively, you may have to reduce the sampling rate of your frequency alone such that matlab completes one cycle atleast for the frequency input. But in your case this seems to be not possible because for matlab to complete 1HZ sine wave, 1sec is requied.After 1sec, your ramp is already at 50HZ. Therefore you dont see the way you are looking for
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