Dear Technical Support Team,
I want to measure ENOB for AD7124-8 ADC, by using EVAL-AD7124-8 evaluation board.
I used a 16-bit precision sine wave as input. Via python (numpy.fft), I processed the conversion results and got the signal spectrum.
ENOB = (SINAD[db] - 1.76)/6.02.
SINAD = 20 * log10(V_rms/RSS) , V_rms - fundamental tone amplitude, RSS = sqrt((A1^2 + A2^2 + ... + An^2)/(n - 1)) - average of the sum of squares all frequencies in the
Nyquist band (Fs/2) excluding DC and fundamental tone.
I get values of ENOB for different input frequencies, but all of these are less than indicated in datasheet.
I use full power mode, sync4, filter word 384, gain 8. (page 28 in datasheet). According to datasheet ENOB = 21,9bit , but I got only 12.9 (for 1Hz input)
By the way, this value of ENOB (21,9) indicated for the entire frequency range or it should decrease with increasing input frequency?
ENOB very important for me.
What am I doing wrong?