The role of charge pump mismatch in the generation of integer boundary spurs in fractional-N frequency synthesizers: Why worse can be better
Abstract
Fractional-N frequency synthesizers exhibit spurious tones (spurs). Spurs outside the loop bandwidth can be attenuated by the loop filter. By contrast, in-band spurs cannot be removed by filtering and are therefore a major cause for concern. The frequency-to-phase conversion of the output of a digital sigma-delta modulator followed by charge-pump mismatch is known to cause in-band spurs; larger mismatch is thought to make the problem worse. By considering a simplified nonlinear model of the mechanism, we show how larger mismatch can paradoxically make the spur problem disappear. We illustrate our predictions using a simplified MATLAB model and confirm them by simulation using the CppSim behavioral simulator. © 2004-2012 IEEE.
Publication Title
IEEE Transactions on Circuits and Systems II: Express Briefs
Recommended Citation
Sadeghi, V., Miar Naimi, H., & Kennedy, M. (2013). The role of charge pump mismatch in the generation of integer boundary spurs in fractional-N frequency synthesizers: Why worse can be better. IEEE Transactions on Circuits and Systems II: Express Briefs, 60 (12), 862-866. https://doi.org/10.1109/TCSII.2013.2285968
