Sinewave Distortion vs Table Size

[danadak]

Update from original post, this update is 06/15/2021

Done using DAC fed by DMA Table of various size., No post filtering applied.

Spur at 12.4 Khz still trying to ID. But basic performance should still stand. Note Third Order
ignores the non harmonic components. I am still trying to ID the source on the test board
of this component as its roughly 20 db down, still high enough to investigate.

As you can see a table down to 16 entries still produces a decent sine for many applications.

64 samples -

8 Samples -

No additional filtering done out of DAC other than imposed by limited Slew Rate of OpAmp and its GBW.


Regards, Dana.

 

[rjenkinsgb]

The harmonic number is how many times the fundamental that frequency is.
1st Harmonic = fundamental frequency; 3rd harmonic = 3 x fundamental etc.

Harmonic - Wikipedia

en.wikipedia.org

Also your chart does not make sense in another way; it shows the fundamental frequency at around -18 for everything except 64 samples.

The 16 sample plot clearly shows it at the same level as the 64 sample one.

 

[danadak]

5'th is what is significant between 64 and 16 samples. But does not explain drop
in fundamental. I think I know what happened, 1X vs 10X on probe, I caught
it but forgot to change the table.

I have been for years thinking, as you point out, 1'st harmonic as 2X, but I see
the clear definition is fundamental is its own harmonic, which seems odd, but
I will self correct. I guess one can conclude a fundamental is in harmony with
itself, seems like a merry-go-round definition issue though )

I will check setup on the 10x change in fundamental going from 64 samples to
<= 32 samples. I remember when I did chart that stood out, meant to investigate,
got side tracked.. I will delete post if there is significant change, otherwise update.

Thanks for catching this....I am aged and need a minder as Mrs. points out, on a
regular basis.


Regards, Dana.

 

[danadak]

Original post has been updated with corrected table and graphs.

Regards, Dana.