Precision measurement of ADC effective number of bits using multi tones

A pure sine wave is the conventional test signal used for measuring the effective number of bits (ENOB) of an analogue to digital converter (ADC) integrated circuit. Although an important figure for many applications of ADCs, ENOB has not traditionally been used to indicate the performance of audio systems. Sine wave testing of ADCs weights the result so that peak level distortion is highlighted and this is known to be less appropriate for audio. This paper demonstrates how a multi-tone test signal can be used to measure ENOB. As this test signal has a normal distribution it gives more weighting to the central region of the ADC code range and more weighting to higher order distortion. It may therefore produce an ENOB more relevant to audio