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在振荡器的许多应用中,频率稳定度是十分重要的。然而对几种基本噪声(尤其是近载频噪声)的起因和起源还不太了解。在用体声波(BAW)和表面声波(SAW)石英声频谐振器或介质谐振器作高Q稳频元件的稳定振荡器中,存在着频率起伏。本文评述有关频率起伏源及其特性的新认识。简要讨论了定量表示随机频率起伏特性的各种参数,并比较开环和闭环相位噪声测量的优缺点。稳定振荡器的相位噪声一般源于加性电压起伏和直接参数调制。加性噪声(如Johnson噪声)是大家清楚的,故只作简单讨论。另一方面,对调制噪声,如闪烁噪声和随机游动频率噪声,则了解甚少,我们将较详细地予以阐述。我们还将讨论放大器和谐振器中的闪烁噪声测量值,以及闪烁噪声大小和谐振器频率、有载与无载Q值和振荡回路功率电平的关系。还介绍了降低振荡器闪烁频率噪声的措施。最后,简单说明振荡器中随机游动频率噪声的已知特性。
In many applications of oscillators, frequency stability is very important. However, the causes and origins of several basic noises (especially near-carrier frequency noise) are not well understood. In a stable oscillator using a bulk acoustic wave (BAW) and a surface acoustic wave (SAW) quartz acoustic resonator or a dielectric resonator as a high-Q frequency stabilization element, there is a frequency fluctuation. This article reviews new understandings of sources of frequency fluctuations and their characteristics. The various parameters that quantitatively represent random frequency fluctuations are briefly discussed, and the advantages and disadvantages of open-loop and closed-loop phase noise measurements are compared. Stable oscillator phase noise is generally derived from additive voltage fluctuations and direct parametric modulation. Additive noise (such as Johnson noise) is clear, so only a brief discussion. On the other hand, little is known about modulation noise, such as flicker noise and random walk frequency noise, which we will describe in more detail. We will also discuss the flicker noise measurements in amplifiers and resonators, as well as the flicker noise magnitude and resonator frequency, the relationship between the on-load and unloaded Q values, and the power level of the tank. Also introduced to reduce the oscillator flicker frequency noise measures. Finally, a brief description of the known characteristics of random walk frequency noise in an oscillator is given.