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Oscillator question about noise

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svensl

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I am not certain what upconversion means in an oscillator. Maybe someone can help me understand the following:
Flicker noise falls at 10 dB per decade in a typical spectral density plot. When the noise is up-converted by the oscillation frequency in a VCO, it is characterized by the spectral density of the oscillator falling at 30 dB per decade.

I do not understand the process of up-conversion and see how the noise changes from 10db per decade to 30db per decade.

Thanks
 

pi331133

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Flick Noise locates at low frequency, e.g. 1/f so in the spectral density plot it is 10db, but due to the upconversion process, the low frequency flicker noise is up convertered to 1/f3, so the slope is 30 db. The 30 db means the slope of close-in phase noise within 1/f3 part
 

mazelk

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Upconverted flicker noise is made with the noise contributions from each harmonic, which are modulated by central fequency. According with phase noise theory (Hajimiri et. al), the accumulative noise near to central frequency depends to 1/(2*pi*f)^3. Base-band flicker noise gives a great amount of this skirt-looked power spectral density.
 

qslazio

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I think you should check out the ali's or T.H.Lee's paper on oscillator's phase noise, in which they developed the LTV theory for phase noise.
Because of the inherent integral of noise charge injection and the phase modulation, there will exist the 1/f^(x+2) noise in which the 1/f^x is the psd of original noise.
 

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