Does ENOB tell the whole story?

摘要

Near the beginning and end of a total solar eclipse, the thin slice of the sun that's visible appears broken up into beads of light. These lights are called Baily's Beads, after the British astronomer Francis Baily, who first noted the phenomenon in 1836 (Reference 1). At the moment they occur, you can't see the full picture; much more is going on. For a short time, you cannot see the sun. In same way, the ENOB (effective-number-of-bits) spec describes only part of an ADC: noise and distortion-rather than providing a precise or accurate description of an ADC. Be aware of the ENOB pitfalls. It does not describe the converter's entire operation over the ranges of sampling frequencies and power supplies. Additionally, ENOB numbers exclude dc specifications, such as offset and gain error. Engineers use either an ac or a dc input signal to determine an ADC's ENOB.