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How to read SNDR from this graph?

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kickbeer

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Hi everyone,

Please see my attachment. To read the value of SFDR is not a problem. But how the author got the value on SNDR=36.10dB?

Thanx in advanced
 

JoannesPaulus

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you cannot "read" the SNDR from a picture. You need to integrate the power of the noise (including harmonics, for SNDR) over the band (Nyquist, in this case). Then you divide the integrated signal power by the integrated noise plus distortion.
 

    kickbeer

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kickbeer

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JoannesPaulus said:
you cannot "read" the SNDR from a picture. You need to integrate the power of the noise (including harmonics, for SNDR) over the band (Nyquist, in this case). Then you divide the integrated signal power by the integrated noise plus distortion.

hi joannes,

i still did not understand what did you mean. So, how to read or get the value of the noise from the graph?
 

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I do not think you really can... of course you could estimate the power in a small set of bins but it would just be a guess.
A graph like the one you show is mostly used to show the level of harmonics and SFDR but you cannot really "calculate" anything else.
 

    kickbeer

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kickbeer

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JoannesPaulus said:
I do not think you really can... of course you could estimate the power in a small set of bins but it would just be a guess.
A graph like the one you show is mostly used to show the level of harmonics and SFDR but you cannot really "calculate" anything else.

Thanks for that another reply. What i did to calculate the SFDR was, connect The ADC under test with an ideal DAC and did a FFT test to the output of the DAC. But i'm wondering there might be modification of the testbench to calculate SNR and SNDR. Do you have any idea?
 

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