Tones frequencies that match conditions

[yefj]

Hello,i have an analog to digital converter with input tone of 120Mhz which is sampled at 800Mhz
SFDR=15dB(ration between the largest noise and input tone) and THD=-11.15dB (total harmonic distortion)
SNQR=1.76+6.02*3
assuming amplitute of signal is 1v then power rms=1/2
the output has 4 tones.

one tone we can get from SFDR=15dB=3db-Largest spur
We have two other spurs we need to calculate from THD
What combination of tone power could meat the THD
We have one degree of freedom and gues one tone.
i need to guess one tone power so i will get the other and meat the THD SFDR conditions.
Thanks

 

[KlausST]

Hi,

assuming amplitute of signal is 1v then power rms=1/2

A sinewave with 1V amplitude has an RMS voltage of sqrt(2)V. (wrong)
corrected after post#4:
A sinewave with 1V amplitude has an RMS voltage of 1/sqrt(2)V.


Klaus

 

[yefj]

Hello. Yes i ment the power of the signal is 1/2.Ho to do the combition of the tones to fit the demands?
Thanks.

 

[stenzer]

A sinewave with 1V amplitude has an RMS voltage of sqrt(2)V.

It should be 1 V / sqrt(2) = 0.707 V

BR

--- Updated Sep 11, 2020 ---

Hi,

I do not really get your point. Why are you “guessing a tone“? As you have sampled the signal you should be able to generate a frequency spectrum of your sampled signal. This should provide you with all the information you need to perform your calculations.

BR

 

[yefj]

you mean to perform FFT.
Thanks

 

[stenzer]

Yes exactly.

 

[KlausST]

Hi,

It should be 1 V / sqrt(2) = 0.707 V

Thanks, you are correct..

Initally i wanted to write 1/sqrt(2) ... in either case 0.707 V is correct.
(Now corrected post #2)

Klaus