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Simulators >> Circuit Simulators >> About IMD simulation
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Message started by urian on Dec 15^th, 2012, 10:43pm

Title: About IMD simulation
Post by urian on Dec 15^th, 2012, 10:43pm

Hi,there
As we know that when we designing an ADC, we can perform trans analysis and apply FFT on the result of an ideal DAC to get the spectrum. Then we can measure dynamic parameters as SNR, SFDR. But, how could we simulate the IMD of the ADC? All I can image is two ways:

a) using a Vsin source and set two close spaced frequencies and perform the normal FFT analysis.
b)using two Vsin sources with two close spaced frequencies respectively and apply them to the ADC input simultaneously.

I have only tried the first method and find that the IMD is very low in my 8b ADC case, about 20dBc. But the SFDR is as high as 64dBc. So I think this method may be wrong.
Now I heard that the only way in spectre to simulate the IMD is perform pss analysis, but as the ADC scale is large, I doubt the pss is no use for the large circuit. What's your option?

Regards
urian

Title: Re: About IMD simulation
Post by sheldon on Dec 22^nd, 2012, 9:24pm

Urian,

You should probably provide more information about your setup.
There is a process for defining the input frequency for single tone tests.
Have you applied the same approach to selecting the tones for the IMD
measurement? Spectral leakage could explain the results you are
reporting. One other option is to try using a window function, Cosine^2,
to reduce spectral leakage. However, this requires that the tones are
relatively far apart, that is, you may need to add extra points to the
FFT.

Best Regards,

Sheldon