Abstract:

In this paper,the effect of noise on oscillators is taken into account,the internal noise of the active device of oscillators can be considered as an external input signal of the oscillator, no matter what kinds of operating states are,the oscillator may be considered as a noise amplifier with deep positive feed back and the sine wave signal of the oscillator output is taken as a narrow band Gaussian noise signal .According to above-metioned ideas,oscillators are analyzed and studied. The main spectrum of the sine wave signals of oscillators outputs,its equivalent bandwidth and the relation between spectrum and operation parameters of the active device are presented. Meanwhile,some new concepts,such as,the formation mechanism of the random walk noise in oscillators,the limit of the lowest frequency of the signal being able to cause modulation phenomenons and the variance of fractional frequency fluctuation which is convergent are put forward.Finally,the experimental circuit and the measured phase noise spectrum of a 200MHz crystal oscillator are given. Results of the experiment are in agreement with the practice of oscillators.

Key words: phase noise, power spectral density, noise amplifier, equivalent bandwidth, narrow band, Gaussian noise