New suppression scheme of ΔΣ fractional-N spurs for PLL synthesizers using analog phase detectors

This paper presents a new suppression scheme of ΔΣ fractional-N spurs for PLL synthesizers using analog phase detectors. The proposed scheme optimizes a phase difference of two phase-detector input signals to suppress spurious emissions caused by the ΔΣ fractional modulation. The phase difference is controlled by a preset signal for phase lock acquisition. The developed VHF-band ΔΣ fractional-N PLL synthesizer with a 2nd order MASH modulator suppresses the largest spurious level by 15dB using the proposed scheme.