While the phase deviation of a noisy free-running oscillator will indeed grow without bound over time, the voltage deviation of course will not. This, however, is a nonlinear effect that is not taken into account when SpectreRF presents its results.

You can find the solution to your problem in equations (24) and (26) of Ken's paper "Predicting the phase noise and jitter of PLL-based frequency synthesizers" (http://www.designers-guide.com/Analysis/PLLnoise+jitter.pdf). SpectreRF presents the approximation according to equation (26), the real result, however, is given by equation (24).

By the way, the integral over equation (24) from -infinity to +infinity is always equal to 1. This means that the total power of the oscillator signal remains constant, it is only spread over a wider frequency range when there is more phase noise.

You can see the dimension of L in equation (22) where it is defined. S_v is in V²/Hz (see footnote 5), a₁ and b₁ are in V (see equation (23)). So you have (V²/Hz)/V² or 1/Hz.

I got the answer to my above question from "phase noise or L" thread.
http://www.designers-guide.com/Forum/?board=jitter;action=display;num=1036525104...


Spectre plots oscillator-phase-noise in dBc/Hz. To plot this curve in rad**2/Hz, I need to multiply the
10**(phasenoise(in_dbc/Hz) / 10.0) with the carrier power.(assuming that phase-nosie button in analog artist considers the Carrier power while plotting it in dBc/Hz)

PSS analysis gives the carrier power in V**2. If I multiply with this value with 10**(phasenoise(in_dbc/Hz) / 10.0), I will be left with the dimensions of Sphi as (rad*V)**2/Hz.

Or am I wrong somewhere?

Thanks
Tommy

Equation (27) equates L in (V²/Hz)/V² (or 1/Hz) with the phase noise in rad²/Hz (or 1/Hz), so the dimensions are ok. Remember that rad is a dimensionless quantity (arc length divided by radius).

Hello all,
              I am sorry for bringing up this thread again...I dug up into some of the old posts including http://www.designers-guide.org/Forum/YaBB.pl?num=1102124964/0

.....Now point is -- i understand that cadence uses the approximation of cfo²/Δf² as indicated in eq. 26 in Ken's paper -- http://www.designers-guide.com/Analysis/PLLnoise+jitter.pdf

Also i do understand that total power is constant, it's just that it's distributed over the spectrum....

BUT, Frank pointed out a way of obtaining correct plots by using eq. 24 instead of cadence's default eq 26....Can someone elaborate how exactly can i obtain a plot of eq. 24 from cadence ???

--expecting some help from big simulator gurus.....

-thanx in advance,
mayank

Hello Pancho & everyone,
  My Problem :-- I am getting +ve values of Phase Noise plot ( i.e. > 0 dBc )  that i obtain from pss/pnoise analysis using spectre(MMSIM7.0) in cadence Analog Design Environment. The ckt is a 10-stage single-ended Ring Oscilllator.                

My Question :--  How to get correct Phase Noise plot ??

My Analysis :--
  I went through the following threads :--
1. http://www.designers-guide.org/Forum/YaBB.pl?num=1102124964/0
2. http://www.designers-guide.org/Forum/YaBB.pl?num=1241894034
3. This thread itself.

In thread 1, Ken explains that > 0dBc plot is because spectre,like almost every other simulator, uses small-signal approximation.

In thread 3/this thread, Frank, in relation to Ken's paper   --  http://www.designers-guide.com/Analysis/PLLnoise+jitter.pdf   explains that --   Quote:


I want to know how to backcalculate the data required in eq. 24 from the standard outputs in cadence's spectreRF, and then apply equation 24 on that data,  & obtain actual and correct plot ??

& btw, i read the 2nd thread that you posted -- http://www.cadence.com/community/forums/T/12466.aspx ---says MMSIM7.1 has it fixed in HB/HBpnoise analysis of spectreRF.....dnt have the new updated version.....But it would be helpful if i could obtain it in this version of spectreRF through backcalculations...

seeking help,
mayank.

hello Pancho,
                   i was always a big fan of the very particular post u just pointed out to on the other thread....It was very clear & exhaustive....Coming back to this,

By +ve, as i already indicated in the statement, i meant  value of pnoise plot > 0 dBc at some offsets below linewidth frequency.

By backcalculations, i meant how to calculate Sv, fourier coeffs a1 & b1, or how to calculate c so that i can use eqns. 22 & 24

As from your post which you just pointed, you said   Quote:

What exactly did you mean by composed of ? Is it the equal to  (L_USB + L_LSB) / 2  or just the summation ??  

And you said,
Quote:


How do i obtain L_SSB plot from cadence which will follow eq. 24 not eq 26 ???

& Augmented HB-PSS/PNOISE with Oversampling factor=10 is giving me phase noise plot with a FLAT SPECTRUM uptil Linewidth frequency.... Is is CORRECT ??

--mayank