Simulink spectrum analyzer problem

I have encountered a very strange problem. When I simulate a delta-sigma modulator, the spectrum analyzer reported the following error message "While setting the 'YData' property of Line: This is not a valid VectorData value. Complex inputs are not supported". I have selected the double-sided spectrum option, so I don't think it is because the input signal have complex spectrum. What's more weird is this problem occurred occasionally. When I first simulate, it's OK, no problem. But when I create a new design and encounter this problem, the previously OK design also report the same error message, seems this problems is "contagious". Does anyone have encountered similar problems?

Answer 1

[Davide Dias]

Yes! I am having the same problem in Simulink... Don't know why, already tryed to take out the complex input with abs and with separate the real part and the imaginary part and the same problem appears. Can someone help us?!