Effective number of bits (ENOB) is a measure of the real dynamic range of an analog-to-digital converter (ADC), digital-to-analog converter (DAC), or associated circuitry.
Although the resolution of a converter may be specified by the number of bits used to represent the analog value, real circuits however are imperfect and introduce additional noise and distortion.
[1] ENOB is also used as a quality measure for other blocks such as sample-and-hold amplifiers.
An often used definition for ENOB is[2] where This definition compares the SINAD of an ideal converter of ENOB bits with the SINAD of the converter being tested.
The frequency band of a signal converter where ENOB is still guaranteed is called the effective resolution bandwidth and is limited by dynamic quantization problems.