MT-023 Datasheet, PDF (2/11 Pages) Analog Devices – ADC Architectures IV: Sigma-Delta ADC Advanced Concepts and Applications

MT-023
into the passband. In audio, the idle tones can be heard just above the noise floor as the input
changes from negative to positive fullscale.
Figure 2: Repetitive Bit Pattern in Sigma-Delta Modulator Output
Figure 3 shows the correlated idling pattern behavior for a first order Σ-Δ modulator, and Figure
4 shows the relatively uncorrelated pattern for a second-order modulator. For this reason,
virtually all Σ-Δ ADCs contain at least a second-order modulator loop, and some use up to fifth-
order loops.
Figure 3: Idling Patterns for First-Order Sigma-Delta Modulator
(Integrator Output)
Page 2 of 11