A Fundamental Consideration for Phase Noise Measurement of Extremely Low Phase Noise Oscillator

Since the phase noise of an oscillator is determined by the ratio of signal power to noise power, it should technically be possible to design an ultralow-phase-noise oscillator with an extremely high output power level. When the phase noise of an oscillator is evaluated, therefore, adjustment of the output power level is needed to match the dynamic range of the measurement system. However, the target—how the phase noise is to be measured while influenced by this level adjustment—has not been elucidated.We make clear in this report that several patterns can be expected for observed phase-noise distributions that depend on the relative magnitude of phase noise and thermal agitation noise and methods for level setting. The perspective was also obtained that phase-noise measurement of an extremely low phase noise oscillator can be made by utilizing the above.