Hi,
I know about the 1/f noise in oscillator.But this diagram shows the presence of 1/f4,1/f3 and 1/f2 apart from 1/f.
What is the reason of the presence of the 1/f4..1/f2 values in the phase noise diagram.How can it be avoided or reduced in our design work.

Hi Vivek,
Thanks a lot for the answer.I will try to come back after reading the papers.
This was a question I was asked,and i found it on the net.
Regards
V

You will find 1/f^4 (random walk FM noise or jitter) in ultra high precision clocks, such as quartz and cesium (atomic) clocks, which also exhibit 1/f^3 (flicker FM noise), and 1/f^2 (white FM noise). If you are really really curious and wish to learn more, check out this fascinating, introductory note: "The Science of Timekeeping," by David W. Allan, Neil Ashby, and Clifford C. Hodge, HP Application Note 1289, and classic technical references therein. For example, download at http://www.allanstime.com/Publications/DWA/Science_Timekeeping/

For an oscillator to exhibit 1/f^4 phase noise, the oscillator's natural (free-running) frequency needs to be a random walk process, which has increasing variance. Basically, the natural frequency is wandering significantly over time. In a quartz oscillator, the natural frequency is determined by a mechanical vibrating reference, that is known to be sensitive to long-term dimensional changes and mechanical stress caused by the oscillator's environment. Ref. 36 in "The Science of Timekeeping" and others often cite environmental factors such as mechanical shock, vibration and temperature as the cause for 1/f^4 noise. Let's suppose the oscillator's environment (such as temperature) is regulated by another oscillator over a longer time scale. This will cause the natural frequency to drift in a random walk fashion, thus giving rise to 1/f^4 noise. Quartz and atomic clocks are well-known to exhibit 1/f^4 noise, and so I won't be surprised if folks in physics know the various pathways to 1/f^4 noise. Having said all that, I don't think one should worry about 1/f^4 noise that is very close to the carrier, unless designing applications for GPS, satellite comm, .., where maintaining precise timing over a long time interval (long-term time/frequency stability) is needed.

Hi Ken,
Aging and environmental factors are commonly accepted explanation for crystal oscillator's natural frequency to drift signficantly from its nominal value. What phase noise spectrum would you expect due to this long-term frequency drift? Surely, this spectrum ought to fall faster than the usual white FM noise.

Hi Ken,
In "The Science of Timekeeping," Figure A1 on page 60 shows that for quartz oscillators, frequency stability curve starts to increase for time longer than 100 seconds. So, random walk FM noise becomes observable after 100 seconds. For the recent chip-level atomic clocks (http://tf.nist.gov/timefreq/ofm/smallclock/LongTermStability.htm), one can observe (flicker walk FM?) noise that falls -10 dB/decade faster than random walk FM, after 10 to 100 seconds. It is customary to remove systematic trends when frequency stability measurements are made and reported. So a linear frequency drift does not fully explain the observed random walk FM noise. While it is true that the oscillator's natural frequency is utimately bounded, I think it is sufficient that over a finite observation window, the variance is increasing with longer time interval in order to observe power law noise similar to random walk FM noise.