Oscillator Phase Noise: Theory Vs. Practicality
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By Greenray Industries, Inc.
Modern electronics use time bases for a wide variety of applications. Communications systems rely on time bases for modulation and demodulation of data, GPS systems rely on them for accurate positioning, and a host of other applications rely on time bases to manage the flow of data within their system.
As the range of applications grows and the frequency increases, designers need time bases that are tighter in stability and lower in noise. As a result, oscillator designers need to continually push the limit of tight stability, low noise oscillator design.
One of the major issues facing oscillator designers is the phase noise phenomenon. Phase noise is an undesirable entity that is present in all real world oscillators and signal generators. It can cause distortion or complete loss of incoming information in traditional receivers, and high bit error rates in phase modulated applications. It is, therefore, necessary to understand and to quantify phase noise so that its effects on the higher level product are minimized.
Time is a concept all humans innately grasp as a function of life. It defines our world into days, months and years. When we look at a clock we know what time it is. However, do we really understand time and how it is defined? Like all measurements, time is measured with a degree of uncertainty. In engineering applications we use time bases that are imperfect by nature and add uncertainties to the applications that are driven by them. One byproduct of this uncertainty is phase noise. The inherent instability present in every oscillator manifests itself as a spectrum of noise around the frequency of the oscillator. This noise band is generally measured from the carrier to 1MHz away from the carrier. It is depicted as a graph of dBc/Hz vs. f(Hz), which shows how far down from the carrier power the noise power at a given frequency is.
© 2008 Greenray Industries. First appeared in the April 2008 issue of Microwave Journal.
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•White Paper: Oscillator Phase Noise: Theory Vs. Practicality