2012 Volume 3 Issue 3 Pages 258-286
Digital Delta-Sigma Modulators (DDSMs) are almost univerally used in integrated circuits for wireless communications and digital audio, particularly in fractional-N frequency synthesizers and oversampled digital-to-analog converters (DACs). A DDSM is a nonlinear dynamical system which reduces the wordlength of an oversampled digital signal without significantly degrading the SNR in the signal band. DDSMs can exhibit a number of behaviors that are characteristic of nonlinear dynamical systems such as oscillation, coexisting steady-state solutions, sensitivity to initial conditions, and sensitivity to the input. This paper explains the root cause of deterministic spurious and idle tones in DDSMs—short periodic cycles—and describes strategies to eliminate them. The use of a DDSM simplifies the design of analog circuitry in a mixed-signal system. By reducing the bus width in a prescribed way, a DDSM can also permit more efficient downstream digital signal processing—in terms of power and speed—with negligible degradation in performance.
