Phase Noise

The sources of phase noise of a frequency are thermal noise, shot effect, and flicker noise of active and passive components. The spectrum of the phase noise is displayed over the offset frequency from the carrier. The phase noise of a carrier signal is interpreted as phase modulation with small modulation index by a noise source. There are various mathematical terms for quantifying phase noise. All of them relate to the measurable quantity of the spectral power density. The Allan variance is a measure of the frequency stability in the range of a few seconds or more. The short‐term stability is described with the phase noise. Frequency multiplication and frequency division have a direct effect on the phase noise of the multiplied or divided frequency. Signal sources fluctuate not only in frequency but also in amplitude.