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Virtuoso Spectrum Warnings for ADC (ENOB, SINAD); gives NaN for spectrum toolbox


Mar 22, 2021
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Virtuoso Spectrum Warnings for ADC (ENOB, SINAD); gives NaN for spectrum toolbox
Yesterday at 5:16pm Hello Community,

I have a built a SAR ADC and was using the Spectrum Tool to calculate the simulation Parameters of FFT (ENOB, SINAD, SNR etc).

Using coherent sampling with Fin= (M/N * Fs), where M being prime number (and I was told its signal bins in the spectrum). N being the number of samples (I use 512). My Fsampling is 100 MHz. And I run the simulation for a little more than (Tsampling * sample Count= 5.12us) time (and I run it for 5.2us; is this ok, should I run more time; shouldn't the transient run remain the same regardless of Fin?)

When I use a smaller value of M=11 or 13, it gives me the expected results I need, but as soon as I move to higher values of M (a.k.a input signal frequnecies closer to Fs/2) which should be able to go upto half the sample count value "N", it gives me Nan (meaning not a number and the following set of warnings):

*WARNING* Sample point 1 is interpolated from raw data points.
*WARNING* Sample point 2 is interpolated from raw data points.
*WARNING* Sample point 3 is interpolated from raw data points.
*WARNING* The raw data points are non-uniform.
*WARNING* From/To are not aligned with the raw data points.
*WARNING* 466/512 sample points are interpolated, which could cause numerical errors. To remove these errors, use uniform raw data points, and align the sample points with raw data points.

In the above case I use M=211 (set signal bin to 210 meaning minus the DC component). Ive attached images for a clearer representation of the issue.
Ive gone throw the ViVa manuals and looked elsewhere what could be the reason, has anyone faced such a situation or can assist in aiding with a solution to these warnings. Somewhere on this forum it was mentioned using strobeperiod but how do I set it, can it be explained? @sutapanaki if you can see this post can you shed some light on it?

Also you write "Make sure your total FFT sample points span integer number of periods. The number of periods better be prime numbers." Newbie so would appreciate this to be explained more
Appreciate any help thanks


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