著者

Howard Andy Poore Rick 明石 芳雄

出版者

一般社団法人電子情報通信学会

雑誌

電子情報通信学会ソサイエティ大会講演論文集

巻号頁・発行日

vol.1997, no.1, pp.331-332, 1997-08-13

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Oscillator phase noise can be analyzed from two different viewpoints : FM noise and mixing noise. FM noise may be viewed as noise generated within the oscillator modulating the oscillation frequency. Conceptually, this could be thought of as applying a noise signal to the control input of a noiseless VCO, with the tuning characteristic differing for each noise source. Mixing noise comes from the nonlinear behavior of the oscillator, where noise mixes with the oscillator signal and harmonics to either sideband of the oscillator signal. These two viewpoints are different ways of looking at the same problem. There should be a region of offset frequencies where mixing noise and FM noise produce the same phase noise results. FM noise is obtained from the large-signal(harmonic balance) oscillator solution. The sensitivity of the oscillation frequency, ω_0, is obtained with respect to any noise source in the circuit. After summing over all of the noise sources, the total spectral density of frequency fluctuations is obtained and converted to phase noise. This noise has a characteristic shape of 1/f^2(or 1/f^3 if 1/f noise sources are present.) this description is valid at small offset frequencies, but is no good at large offsets as it goes to zero; it will not exhibit a noise floor. To model oscillator phase noise via mixing, the noise at the sidebands on either side of the carrier (ω_0 ± ω, where ω is the noise offset frequency) are obtained from a small signal mixer analysis where noise sources (ω ± kω_0) mix with the oscillator large signals (kω_0) to produce these noise sidebands. The noise at these two sideband frequencies and their correlation is then manipulated to produce the phase noise. Mixing noise tends to be valid at large offset frequencies and will show a finite noise floor. HP MDS releases up to and including 7.0 computed phase noise by adding the FM and mixing phase noise together. However, these are not independent (being different views of the same process) and thus should not be added to produce the overall phase noise. To correct this, HP MDS Release 7.1 outputs the phase noise contributions (directly in dBc) due to FM noise and mixing noise, separately. Figure 1 is an example phase noise simulation that shows the two different components, as a function of offset frequency. The higher phase noise at a particular offset frequency should be used. For more details, refer to the HP MDS Release Notes 7.1.