《微波测量基础》第2章7相位噪声.pptx

2.7 相位噪声Noise in Oscillators? A cos?ωot ?φ ?Vo,idealv?n? A?t ?? f ?ωot ?φ?t ??Vo,practical14243periodic functionperiod ?2πwithPMAMωo ?ωmωoωo ?ωmωo ?ωmFMωoPMω ?ωomAMTotal noise power equally split into phase noise power and amplitude noise powerRandom walk FM (random walk of frequency), Sf plot goes down as 1/f4.Flicker FM (flicker of frequency), Sf plot goes down as 1/f3.White FM (white of frequency), Sf plot goes down as 1/f2.Flicker PM (flicker of phase), Sf plot goes down as 1/f.White PM (white of phase), Sf plot is flat.Random walk FM (1/f4) noise is difficult to measure since it is usually very close to the carrier.Random walk FM usually relates to the OSCILLATORS PHYSICAL ENVIRONMENT. If random walk FM is a predominant feature of the spectral density plot then MECHANICAL SHOCK, VIBRATION, TEMPERATURE, or other environmental effects may be causing random shifts in the carrier frequency.Flicker FM (1/f3) is a noise whose physical cause is usually not fully understood but may typically be related to the PHYSICAL RESONANCE MECHANISM OF AN ACTIVE OSCILLATOR or the DESIGN OR CHOICE OF PARTS USED FOR THE ELECTRONICS, or ENVIRONMENTALPROPERTIES. Flicker FM is common in high-quality oscillators, but may be masked by white FM (1/f2) or flicker PM (1/f) in lower-quality oscillators.White FM (1/f2) noise is a common type found in PASSIVE-RESONATOR FREQUENCY STANDARDS. These contain a slave oscillator, often quartz, which is locked to a resonance feature of another device which behaves much like a high-Q filter. Cesium and rubidium standards have white FM noise characteristics.Flicker PM (1/f) noise may relate to a physical resonance mechanism in an oscillator, but it usually is added by NOISY ELECTRONICS. This type of noise is common, even in the highest qualityoscillators, because in order to bring the signal amplitude up to a usable level, amplifiers are used after the signal source. Flicker PM noise may be introduced in these stages. It may also be introduced in a f