Thank you Damian,
But I am confused as the SNR of ADC as described in the application report by texas instruments describes SNR as ratio between the power of signal to the average power of the noise floor which is due to the quantization noise and thermal noise of ADC.
http://www.ti.com/lit/an/slaa510/slaa510.pdf
By looking at the spectrum I can find the peak of individual frequencies but how to calculate average for a noise floor ?
Also you wrote ‘ the way it is set up right now it does not introduce any noise and therefore the SNR is unbounded ‘ so I have added noise also but it does not show up at the output.