An Algorithm for Implementing a Modulator Whose Output is Spur-Free after Nonlinear Distortion
Abstract
When the accumulated zero-mean output of a digital modulator encounters a nonlinear function, nonlinearity-induced spurs can arise in the spectrum of the resulting signal. These spurs occur with both periodic and aperiodic modulator outputs, and can appear in applications such as frequency synthesis at frequencies where filtering approaches are ineffective. The mechanism at the root of these spurs is the nonlinear transformation of the cyclostationary modulator-induced phase noise. An algorithm is presented which determines modulator parameters that guarantee a spur-free spectrum after the application of a memoryless nonlinearity to the accumulated modulator noise. The algorithm takes as its input a sampled representation of the in-loop nonlinearity function, and determines a matrix of probabilities to be applied by the modulator. The algorithm can handle arbitrary nonlinear functions and relies on straightforward, synthesizable operations. Simulations demonstrate the ability of the algorithm to program a modulator such that spur-free operation is obtained for an illustrative selection of nonlinearities.
Publication Title
IEEE Transactions on Circuits and Systems I: Regular Papers
Recommended Citation
Donnelly, Y., & Kennedy, M. (2021). An Algorithm for Implementing a Modulator Whose Output is Spur-Free after Nonlinear Distortion. IEEE Transactions on Circuits and Systems I: Regular Papers, 68 (10), 4259-4267. https://doi.org/10.1109/TCSI.2021.3098901
