What is the Difference between S/N and SINAD?

[MVK]

Hey,

can any one give me the answer for the following question.

What is the difference between S/N and SINAD?

[GovBob]

For the short answer: S/N is probably actually refering to signal to noise ratio (SNR) which is actually (S+N/N) signal plus noise to noise ratio. SINAD is Signal + Noise + Distortion to Noise + Distortion (S+N+D/N+D). SINAD (dB) = 20 log [Vsignal +Vnoise+Vdistortion/Vnoise+Vdistortion].

Hope this helps.

[Andy_Hinde]

S/N measures the difference typically between the signal (or full scale input range) and the thermal noise floor, usually in dB.

SINAD is similar except for the fact that it also takes into account spurs in the frequency domain. So SINAD should always be <= S/N. SINAD is similar to Spurious-Free Dynamic Range (SFDR).

Dynamic range is a term sometimes used for these concepts, but dynamic range is vague in that it doesn't make clear whether spurs should be taken into account. SFDR eliminates that ambiguity, as well as S/N or SNR.

Regards,
Andy Hinde
National Instruments

[William1225]

I wonder if the following derivation is correct?

Could someone give me some suggestion or feedback?

Thanks a lot!

THD = Sum(P_Harmonic) / Sum( P_Total)

THD+N = Sum(P_Harmonic) + Sum(P_Noise) / Sum(P_Total)

THD+N - THD = Sum(P_Noise) / Sum(P_Total)

if Signal is dominent, THD+N - THD = Sum(P_Noise) / Sum(P_Signal) = 1 / SNR

SNR = 1 / (THD+N - THD)