FFT analysis of ADC, how to explain the HD

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urian

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Hi, there!

Recently I am testing an 8b ADC and get the FFT results. Then I can find the SNR and SFDR as usual. But I find the HD2 of some chips is higher than HD3, the left is not. And sometimes the HD2 is larger more than 15dB than HD3, but part of them are close to HD3. So I want to know what does it mean?
Are there materials about the detail FFT analysis of ADC, such as how to determine the source of HD2, HD3 or higher HD?


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urian
 

Hi,shahbaz. The HD1 means the number of harmonic. e.g. HD3 stands for the 3rd harmonic.

Regards
 

I think it will help in analyzing it if you tell us what type of ADC we are talking about.
 

Hi,alifalif.
It's an 8b 100M pipeline ADC with 5 pipeline stages which are all 1.5bit, followed by a 3b flash stage.
 

urian said:
Are there materials about the detail FFT analysis of ADC, such as how to determine the source of HD2, HD3 or higher HD?
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May be this treatise can be helpful?
 

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    urian

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Thx,erikl
The treatise is useful, but it is more about the concept and setup of FFT, not the explanation of HD or spur, maybe the references can give me a hint:wink:
 

Hi urian,
Mismatch or non linearity in each parts of the stages will give you either odd HD or even one.
My suggestion is to do a matlab or C model simulation and see which unidealities creates your HD.
 

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