An Efficient Cross-Correlation Method for a Digital Phase Noise Measurement System

In this paper, we propose a digital phase noise measurement using a 10-bit digital oscilloscope MXR608A from Keysight Technologies. The digital oscilloscope’s four channel data are used for digital phase noise measurement: two channels are assigned for the equally divided SUT (source under test), while the other two are assigned for the equally divided reference signals. First, we propose a cross correlation method to identify the phase noises added by the ADCs in the digital oscilloscope from the measured phase noises. Then, we propose a novel cross correlation method to extract the SUT phase noise. The cross-correlation output of the proposed method yields only the SUT phase noise and does not contain the reference signal phase noise unlike the traditional method. The proposed method was applied to measure the phase noises of the two SUTs, Keysight’s synthesized signal generator E8257D and function generator 33600A. The measured phase noises of the two SUTs were compared and found to show remarkable agreements with those measured using Keysight’s signal source analyzer E5052B. The phase noise floor of our digital phase noise measurement system is about -160 dBc/Hz.