ADC Effective Number of Bits

The Effective Number Of Bits (ENOB) value for an Analog-to-Digital Converter (ADC) is computed by substituting the measured Signal-to-Noise Ratio plus Distortion (SINAD) value into the equation that describes the Signal-to-Noise Ratio (SNR) for an ideal ADC and solving for N (number of bits). The equation below shows the calculation for ENOB.

(1)
\begin{equation} ENOB = (SINAD - 1.76dB)/6.02 \end{equation}

The ENOB is usually presented for a range of input frequencies and tells the designer how accurate the converter is as a function of input frequency and the chosen sampling rate. The figure below shows a graphical example of ENOB data taken from an ADC. Note that the sampling frequency and operating conditions have been specified.

adc-enob.PNG
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