For Analog-to-Digital Converter (ADC) applications where the signal is steady-state or has an extremely low frequency compared to the ADC sampling frequency, DC specifications have the most significance. When the signal frequency is increased, however, other measures must be used to determine the performance of the ADC. In this case, the performance of the ADC in the frequency domain becomes significant to the designer. Imperfections of the ADC introduce noise and distortion into the sampled output. In fact, even the ideal ADC introduces errors into the sampled AC signal in the form of noise. The AC specifications of an ADC tell the designer how much noise and distortion has been introduced into the sampled signal and the accuracy of the converter for a given input frequency and sampling rate.
ADC AC Specifications