How to read datasheets
A 16-bit A/D converter has a SINAD (signal-to-noise-and-distortion ratio) of 74 dB. Roughly what is its effective number of bits (ENOB)?
- AAbout 12 bits
- B16 bits
- CAbout 14 bits
Show answer and explanation
Answer: A. About 12 bits
The SNR of an ideal N-bit ADC is determined only by quantization noise and is 6.02N + 1.76 dB. Using this in reverse gives ENOB = (SINAD − 1.76)/6.02 = (74 − 1.76)/6.02 ≈ 12.0 bits. It means that, despite its 16-bit output, noise and distortion make its actual performance equivalent to an ideal 12-bit ADC. SINAD varies with input signal frequency and amplitude, so check the value or graph at a frequency close to your operating conditions. Resolution and actual accuracy are different things.