Phase noise in the regenerative frequency dividers

The authors report on a theoretical analysis of the phase noise in regenerative dividers, and provide design rules for the best spectral unity. The spectral purity is, in fact, the reason why regenerative dividers may be preferred to simpler schemes whenever that characteristic is a fundamental requirement. This class of dividers is suitable for high frequencies, out of reach to other techniques. The nucleus of the theory is the description of the mixer, driven by coherent signals, in terms of differential phase gain, so as to relate noise at the divider output to the noise generated inside the divider itself. After introducing a model of the mixer and some related measurement techniques, it is shown that the most favorable noise condition for the divider is reached by tuning it off the maximum output amplitude. Methods for approximating this condition are then outlined. The experiments prove the feasibility of the proposed approach, and reported results show a phase noise reduction of 10 dB with respect to the maximum amplitude condition