But it gave me some negative values in the spectrum: 
So why there are negative values? Is there anything wrong in the dft function setting? Thanks. Edit The time domain signal is as follows 
I had the following setting for the dft function in Cadence Virtuoso Calculator: But it gave me some negative values in the spectrum: So why there are negative values? Is there anything wrong in the dft function setting? Thanks. Edit The time domain signal is as follows
\$\begingroup\$ 1) What is the time domain signal? 2) Are you sure that there are negative values in the output, try setting the Y-axis to logarithmic in stead of linear. 3) The "number of samples" is always rounded down to a multiple of 2^n so here that would be 8192 (instead of 10000) 4) make sure you have more than 8192 datapoints in your time signal. I suggest experimenting with the dft function on a known signal (like a sinewave) to learn how it works. \$\endgroup\$
Commented Mar 22, 2021 at 18:30\$\begingroup\$ @Bimpelrekkie Thanks. I have posted the time domain signal. It has no negative value. I have tried setting the number of samples to 2^n and make sure there are 2^n points in the time signal. But there are still negative values. \$\endgroup\$
Commented Mar 22, 2021 at 18:45\$\begingroup\$ the time domain signal.. negative value I suggest that you learn more about how the Fourier transformation works (dft is a Fourier transformation function). A negative value in the time domain signal has no relation to the frequency spectrum. What might be an issue is that your signal is very random so you get a lot of noise in the frequency domain as a result. \$\endgroup\$
