Hi,
I got into a strange doubt while doing signal conditioning at the input of ADC. The Signal to Noise ratio is defined as the ratio of average signal power to the average noise power.
SNR = Psignal/Pnoise ; Where P is average power
(or)
SNR = (Asignal/Anoise)^2 ; Where A is rms value
Let us take the second equation for our analysis. Consider the signal as DC. The signal line has some high frequency noise which is not filtered out(it means that there is no LPF ) before reaching the ADC. According to the definition of SNR,
Signal RMS value = Adc (It is a DC value)
Noise RMS value = An (say, the noise is a sine wave with some higher frequency)
SNR = (Adc/An)^2 --> (eqn1)
case 1. Consider the sampling frequency which is lower than the noise frequency. - Will that calculated SNR affect the ENOB of ADC
case 2. Consider the sampling frequency which is higher than the noise frequency. - Will that calculated SNR affect the ENOB of ADC
My argument: In both the cases there is a probability of sampling the noise along with signal. In case 2, the noise aliases back to the signal frequency. Even in case 1 the probability of noise getting sampled along with signal is not zero.
So, in the scenario like case1 what kind of analysis to be carried out in order to estimate the SNR at the input of ADC.
Thanks,
Jebas.