Mayank, again see the followings.

http://www.designers-guide.org/Forum/YaBB.pl?num=1241894034/12#12http://www.designers-guide.org/Forum/YaBB.pl?num=1241894034/23#23Originally Lorentzian Spectrum Models were derived in the absence of flicker noise.

In the absence of 1/f noise, it is well known that phase noise should show a Lorentzian spectrum. We can easily apply this to evaluation of the phase noise characteristics.

But modeling as Lorentzian Spectrum does not yield meaningful results if 1/f noise is present.

There is an issue for the use of the Lorentzian spectrum in the presence of 1/f noise.

PM noise can become very large at low offset because of continued accumulation of phase close to the carrier, so it could go above 0dBc/Hz. Properly, units of PM noise should be "dBrad/Hz".

SideBand Noise, L

_{SSB}(f) is an approximation combining AM and PM noise, so L

_{SSB}(f) could also go above 0dBc/Hz at low offset especially in the presence of 1/f noise.

Your following HB-PSS/AUGMENTED-PNOISE results are all completely flat for small offset frequency region.

http://www.designers-guide.org/Forum/YaBB.pl?num=1050465395/15#15Even PM noise is also completely flat. These results are very suspicious.

Such completely flat phase noise reminds me phase noise of Agilent MDS or Agilent earlyday's ADS which underestimated phase noise for small offset frequency region.

See "Phase Noise Overview" of "Chapter 10: Oscillator Noise Simulation" in the following.

http://cp.literature.agilent.com/litweb/pdf/ads15/cktsim/index.htmlI think Cadence Spectre's HB-PSS/AUGMENTED-PNOISE is still very suspicious.

Apart from Spectre's HB-PSS/AUGMENTED-PNOISE, some analytical models have been proposed for phase noise with flicker noise.

These decompose the model into a Lorentzian for the white noise sources and Gaussian for the flicker noise source.

So these share the property of the Lorentzian spectrum so that it has an integrated area of one ; it conserves the overall power of the noiseless oscillator,

and has a finite value as the offset frequency approaches zero.

At small offsets the spectrum looks like a Gaussian when dominated by flicker noise ;

at larger offsets 1/f

^{3} behavior is seen, followed by 1/f

^{2} behavior.

[1] F. Herzel, "An Analytical Model for the Power Spectral Density of a Voltage-Controlled Oscillator and Its Analogy to the Laser Linewidth Theory", IEEE Transactions on Circuits and Systems . I: Fundamental Theory and Applications, vol. 45, pp. 904.908, Sept. 1998.

[2] G. V. Klimovitch, "Near-Carrier Oscillator Spectrum Due to Flicker and White Noise", Proc. of ISCAS 2000, IEEE International Symposium on Circuits and Systems, Geneva, pp. I-703.706, 2000.

[3] G. V. Klimovitch, "A Nonlinear Theory of Near-Carrier Phase Noise in Free-Running Oscillators", Proc. of Third IEEE International Conference on Circuits and Systems, Caracas, pp T80/1.6, 2000.

[4] A. Demir, "Phase Noise in Oscillators: DAEs and Colored Noise Sources", Proc. of ICCAD-98, pp. 170.177, 1998.