A Proposal on Reduction Method of Phase Noise based on PLL Systems for Reference Frequency Signal

Abstract

Measuring the phase noise using a PLL is known as a highly precise method. But the method can't be used when the stability of a test oscillator is higher than the stability of a reference frequency source in the PLL.
So we propose a new method that reduces the phase noise in the reference frequency source. This method adds outputs of m PLLs locked by the standard oscillator which is the reference frequency source. In this paper, we clarify theoretically that L(f) can be improved by 10 logm dB in Fourier frequency range which is higher than the PLL's natural frequency and substantiate this experimentally.