Wandering spur suppression in a 4.9-GHz fractional-N frequency synthesizer

Fractional-N frequency synthesizers that use a digital Δ-Σ modulator (DDSM) to control the feedback divider can exhibit spurious tones that move about in the frequency domain; these are known colloquially as ``walking'' or wandering spurs. Building upon a theoretical explanation of the origin of wandering spurs, this article presents two methods to suppress them. It describes a 4.9-GHz 180-nm SiGe BiCMOS charge-pump phase-locked loop (CP-PLL) fractional-N frequency synthesizer platform with a divider controller that can function as: 1) a standard MASH 1-1-1; 2) a MASH 1-1-1 with high-amplitude dither; and 3) a MASH 1-1-1 with a modified third stage. Measurements confirm the effectiveness of the wandering spur suppression strategies

Performance improvement of fractional N-PLL synthesizers for digital communication applications

Loop filter with two order was designed to improve the performance of the fractional N-phase locked loop (PLL) circuit (reference spurs noise and switching time), decreasing these two factors give good characteristic to fractional N-PLL circuit, the second order and third order loop filters are widely used in frequency synthesizer because they give good stability tolerance and for their simple architecture. They are designed at bandwidth B=125 KHz and its multipoles, at two values of the phase margin (pm)= 35°, 57°. MATLAB program was used to find the lock time, the component values for each element in the loop filter, also the filter impedance T(s), the bode plot of frequency response for close loop (CL) and open loop gain (OL). It is found by comparing the result of the frequency response for the 2nd order loop filter and 3rd order loop filter, that increasing the order of the filter will reduce the spurs noise that destroy the received signal at receiving side

Wandering Spurs in MASH 1-1 Delta-Sigma Modulators

Wandering spurs are a little-studied phenomenon seen in MASH and SQ-digital delta-sigma modulators. They take the form of frequency-modulated spurs which periodically appear in-band. Since modulators are often employed as divide ratio controllers in fractional-N phase lock loops, these spurs can feed into the output phase noise spectrum. In this paper, we explain the mechanism which creates the wandering spurs and offer a prediction for the behavior of these spurs in the MASH 1-1 modulator. Simulation results are presented which confirm our theoretical predictions.Enterprise IrelandIrish Research CouncilScience Foundation Irelan