Phase Noise and Measurements

Abstract The phase of the electric signals or electromagnetic fields from the circuits and devices is often modulated or demodulated with important information in modern communication systems. However, there are always some random fluctuations in the phase of the signals. The termphase noiseis used to describe such short‐term random fluctuations of the signals. Those phase noise sources may come from the thermal noise (thermal motion of the carriers), shot noise (discrete properties of the electric current sources), or several other mechanisms inside the devices, circuits, or wired or wireless medium [1] The phase noise can affect the signal‐to‐noise ratio (SNR) and bit error rate (BER) of the received signals, and then the channel sensitivity, minimum detectable signal power, operating range, and selectivity in the communication systems. This article focuses on phase noise in the oscillators because most of the phase noise sources in the communication systems come from the oscillators. This article is divided into two main sections on phase noise theory and phase noise measurement techniques. In Section 1 (on phase noise theory), the author describes the simplified oscillator model and its phase dynamics. The oscillator phase noise can be derived by using small‐signal fluctuations around the operating (carrier) frequency, where the fluctuations are caused by the intrinsic noise sources. The Fourier transform and Wiener–Khintchine theorem are applied to the phase noise expressions [2–8]. The relationship between the noise resistance/admittance of the oscillator and Leeson's model is also derived. In Section 2 (on phase noise measurement) several popular measurement techniques [9–13] are explained, including the spectrum analyzer, frequency discrimination, and double‐balanced mixer methods. The author also explains the advantages and disadvantages of these measurement techniques. The article concludes with some references for the interested readers to 10 independently study phase noise theory and related measurement techniques in further detail [1,14–18].