Direct-digital time-domain oscillator stability measurement

Oscillators are the pacemaker of digital logic as well as communication systems. For the cooperation of systems equipped with different oscillators, the oscillator stability is of great interest, for instance to parametrize phase tracking loops, or to synchronize carrier frequencies for modulations using phase-shift keying. In most cases the Allan variance is used to describe the stability of oscillators which is measured using a heterodyne measurement system creating a low-frequency beat signal. This paper proposes a direct-digital time-domain oscillator stability measurement method. After capturing the oscillator´s signal using a sampling instrument, it is converted into its analytical representation using the Hilbert transform. The low-pass filtered analytical signal is then used to determine the phase of the signal and the exact instants of its zero crossings. Finally, measurements show the feasibility of the proposed approach and analyze its limitations.