RF Phase Noise Analyzer Based on Phase Estimation Algorithm With Undersampling Samples

A radio frequency (RF) phase noise analyzer (PNA) based on a phase estimation algorithm with undersampling samples is proposed and investigated. The signal under test (SUT) is digitally sampled by an analog-to-digital converter (ADC) that has a sampling rate lower than the frequency of the SUT. The undersampling samples are processed by the phase estimation algorithm, which divides the samples into groups and establishes a system of linear equations in terms of the in-phase and quadrature (I/Q) components of the SUT for each group. The I/Q components are estimated as the least-squares solution of the linear equations, and the phase is obtained with the estimated I/Q components. The experimental results verify the feasibility of the phase estimation algorithm and the PNA. Ultrahigh measurement accuracy is achieved at low offset frequencies, while the accuracy at high offset frequencies is a little degraded due to the low-pass filtering effect on phase fluctuation. The sensitivity of the PNA is theoretically and experimentally investigated, which shows that the sensitivity is mainly limited by the sampling jitter and the quantizing noise of the ADC. A dual-channel PNA with a cross-correlation technique is established to enhance the sensitivity. With 1000-times average, the sensitivity of the dual-channel PNA is better than -130 dBc/Hz at 10 kHz for a 1-GHz carrier frequency.