Digital Electronics: Principles, Devices and Applications

Data Conversion Circuits – D/A and A/D Converters 511Kfs(Clock)V IN+S_Integrator+_comparator(1-bit ADC)To Digital filterand Decimator+V REF1-bit DAC1-bit Data stream-V REFFigure 12.39Block schematic representation of a delta modulator.Input signalfrom S/H+Max0-MaxQuantized output fromSigma-Delta ModulatorFigure 12.40Generation of a one-bit data stream.intervals of time, in which case the counter output would represent the digital equivalent of the analoguesignal over those time intervals. Practical sigma-delta A/D converters use a digital decimation filter atthe output of the delta modulator to process the one-bit data stream to produce an output in the desiredformat.Sigma-delta A/D converters are widely used for contemporary voice-band, audio and high-resolutionprecision industrial measurement applications. Their highly digital architecture is ideally suited forsuch applications as it allows easy addition of digital functionality without significantly increasingthe cost. AD 1871 from Analog Devices is one such high-performance A/D converter of sigma-deltaarchitecture intended for digital audio applications.