Direct digitalized phase comparison between signals with different nominal frequencies

In this paper, the direct digitalized phase comparison which has phase continuous and high resolution is proposed to measure the phase variation of the high-precision frequency standard with different nominal frequencies. During the least common multiple period, the phase difference between the two comparison signals is regular, therefore the phase comparison between arbitrary frequency signals is achieved directly through using a high-speed analog-to-digital converter as the counter and the equivalent phase-detecter. By experiments and analysis, it was shown that no-interval frequency measurement can be converted into the phase difference measurement and the frequency stability evaluated as the Allan deviation accords with the change law of 1/tau.