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phase noise of ring oscillator using spectre (Read 57195 times)
Mayank
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Re: phase noise of ring oscillator using spectre
Reply #15 - Nov 23rd, 2009, 5:04am
 
Hello pancho,
   Gotcha,  So summing up our discussions so far,
    1.  For +ve Offset Frequencies, Lssb = Lusb,
    2.  For -ve Offset Frequencies, Lssb = Llsb...
    3.  Cadence plots Lssb, which is Lusb or Llsb depending on whether the offset specified as +1 or -1. defualt being +1, it is Lusb.
    4.  pnoise modulated gives all components separately
    5.  pnoise jitter plots true Sphi which should be equal to PM noise from pnoise modulated  .

Am i correct so far ??


I simulated with HB-PSS/augmented-PNOISE and i am attaching the waveforms obtained for LSB, USB, AM & PM noise plots....

In HB-PSS/AUGMENTED-PNOISE, To my surprise, AM plot is coming too close to the PM plot....Also LLSB is totally wierd and nothin similar to LUSB...Totally confused by the results.....

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pnoise1.png
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pancho_hideboo
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Re: phase noise of ring oscillator using spectre
Reply #16 - Nov 23rd, 2009, 5:19am
 
Mayank wrote on Nov 23rd, 2009, 5:04am:
    1.  For +ve Offset Frequencies, Lssb = Lusb,
    2.  For -ve Offset Frequencies, Lssb = Llsb...
    3.  Cadence plots Lssb, which is Lusb or Llsb depending on whether the offset specified as +1 or -1. defualt being +1, it is Lusb.
Am i correct so far ??
I can't understand your expressions.

Mayank wrote on Nov 23rd, 2009, 5:04am:
In HB-PSS/AUGMENTED-PNOISE, To my surprise, AM plot is coming too close to the PM plot....Also LLSB is totally wierd and nothin similar to LUSB...Totally confused by the results.....
I think you treat LLSB and AM noises wrongly.
Maybe your AM noise is LLSB and your LLSB is AM noise.
Confirm your AM noise and LLSB.

Do you have Agilent GoldenGate(4.3.6 or 4.3.7) or Agilent RFDE(ADSsim 2008U2 or 2009) ?

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Mayank
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Re: phase noise of ring oscillator using spectre
Reply #17 - Nov 23rd, 2009, 6:33am
 
Hello Pancho,
         
            At first i also thought so.....But i rechecked it twice....The image i attached previously is correct...I plotted USB,LSB, AM & PM from pnoise_modulated of Direct plot Form.....It is showing LLSB wierdly.....& it shows PM Noise = AM Noise ....Totally wierd !!!

However, the plots without augmented pnoise analysis are the ones i am attaching now....

Is this a bug in spectreRF that it exchanges AM & LLSB plots OR is it a bug in augmented pnoise analysis OR is it really possible ?   i have no clue....

And i dont have access to any tools from Agilent...  :(

mayank
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pancho_hideboo
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Re: phase noise of ring oscillator using spectre
Reply #18 - Nov 23rd, 2009, 6:39am
 
Mayank wrote on Nov 23rd, 2009, 6:33am:
Is this a bug in spectreRF that it exchanges AM & LLSB plots OR is it a bug in augmented pnoise analysis OR is it really possible ?   i have no clue....
Post your questions in http://www.cadence.com/Community/forums/33.aspx

I think these are bugs and augmented pnoise is still unreliable and suspicious..
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Mayank
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Re: phase noise of ring oscillator using spectre
Reply #19 - Nov 23rd, 2009, 9:02pm
 
Hello Pancho,
                   Thanx for all the help and your quick replies....They helped a lot....One of my best discussions on the forum....

mayank
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pancho_hideboo
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Re: phase noise of ring oscillator using spectre
Reply #20 - Nov 24th, 2009, 3:21am
 
Mayank, again see the followings.
http://www.designers-guide.org/Forum/YaBB.pl?num=1241894034/12#12
http://www.designers-guide.org/Forum/YaBB.pl?num=1241894034/23#23

Originally 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, LSSB(f) is an approximation combining AM and PM noise, so LSSB(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#15

Even 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.html

I 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/f3 behavior is seen, followed by 1/f2 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.
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« Last Edit: Nov 25th, 2009, 12:41am by pancho_hideboo »  
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Mayank
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Re: phase noise of ring oscillator using spectre
Reply #21 - Nov 25th, 2009, 12:14am
 
Hello Pancho,
                   I want to reserarch more on this so that i can resolve the issue....Could you provide me the 3rd paper you mentioned -- Quote:
[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.


It would be very helpful....
  Also i wanted to ask Can AM noise become equal to PM noise at such low offsets as 10kHz ??
  Have you verified any silicon vs. CAD results so that i can know what matches silicon results better ?? -- the flattened Pnoise plot  OR  the actual > 0dB plot  ??

mayank
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Re: phase noise of ring oscillator using spectre
Reply #22 - Nov 25th, 2009, 1:45am
 
Mayank wrote on Nov 25th, 2009, 12:14am:
Also i wanted to ask Can AM noise become equal to PM noise at such low offsets as 10kHz ??
I don't think so.

Mayank wrote on Nov 25th, 2009, 12:14am:
Have you verified any silicon vs. CAD results so that i can know what matches silicon results better ?? -- the flattened Pnoise plot  OR  the actual > 0dB plot  ??
In actual Measurement using Actual Instruments, LSSB(f) never go above 0dBc,
while PM(f) can be go above 0dBrad/Hz.
Using Vector Signal Analyzer, we can evaluate AM and PM noises.

https://forums.tm.agilent.com/community/viewtopic.php?f=33&t=2504
https://forums.tm.agilent.com/community/download/file.php?id=570

I have Agilent 4352B VCO/PLL Signal Analyzer and 89400 & 89600 Vector Signal Analyzer.
I don't have E5052B which is new replacement of 4352B.

Agilent E5052B Signal Source Analyzer can measure AM noise directly.
http://cp.literature.agilent.com/litweb/pdf/5989-7273EN.pdf
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« Last Edit: Nov 25th, 2009, 4:10am by pancho_hideboo »  
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Mayank
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Re: phase noise of ring oscillator using spectre
Reply #23 - Nov 25th, 2009, 9:08pm
 
Heloo Pancho,
                      The Document on Choosing Phase Noise Techniques by Agilent was quite helpful.....
     
     But i didnt exactly understand this concept....PM Noise refers to Phase Modulation due to noise.....& Phase Noise is a cumulative effect of both AM & PM.....Then shouldn't Phase Noise also go higher than 0 dBrad/Hz if one of it's components are going above 0dBrad/Hz .....
 
     If LSSB doesnt go above 0dBc , then is it the correct representation of Phase Noise ??

--mayank.
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Re: phase noise of ring oscillator using spectre
Reply #24 - Nov 25th, 2009, 10:36pm
 
Mayank wrote on Nov 25th, 2009, 9:08pm:
Then shouldn't Phase Noise also go higher than 0 dBrad/HzdBc/Hz
if one of it's components are going above 0 dBrad/Hz .....
SideBand Noise, LSSB(f) is an approximation combining AM and PM noise,
so in simulation using current EDA Tool, LSSB(f) could also go above 0 dBc/Hz at low offset especially in the presence of 1/f noise.

Mayank wrote on Nov 25th, 2009, 9:08pm:
If LSSB doesnt go above 0dBc, then is it the correct representation of Phase Noise ??
What I can say surely is
"Cadence Spectre's HB-PSS/AUGMENTED-PNOISE is very suspicious".
That's all.

Modeling as Lorentzian Spectrum does not yield meaningful results if 1/f noise is present.
Again see the followings.
http://www.designers-guide.org/Forum/YaBB.pl?num=1241894034/12#12
http://www.designers-guide.org/Forum/YaBB.pl?num=1241894034/23#23

Also see last append by "RFMEMS" in http://www.cadence.com/community/forums/T/12466.aspx
Even RFMEMS has a doubt now.

I think results of HB-PSS/Pnoise without Augmented is rather proper.

But even using Agilent GoldenGate Simulator, LSSB for small offset frequency can not be matched to actual measurement well.


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Mayank
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Re: phase noise of ring oscillator using spectre
Reply #25 - Dec 10th, 2009, 10:17pm
 
Hi Pancho,
               I am too confised at this stage Sad
                Just confirming Once Again :----

1. According to the doc you poited out on Choosing PhaseNoise Techniques by Agilent, I should trust SΦ/2 values instead of LUSB.

So does the true SΦ plot (given by pnoise jitter option in Direct Plot Main Form of cadence as pointed out by you in your post  http://www.designers-guide.org/Forum/YaBB.pl?num=1244213153/6#6) never go above 0 dBc/Hz ??

2.  If you have compared Silicon vs CAD results, which is  a better approximation to actual measurements out of these  ----->  
1. Augmented Pnoise  ??
2. SΦ/2 below linewidth & LΦ after Linewidth  ??
3.  Only LUSB plot of vanilla Pnoise  ??


--  mayank.
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pancho_hideboo
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Re: phase noise of ring oscillator using spectre
Reply #26 - Dec 11th, 2009, 12:55am
 
Mayank wrote on Dec 10th, 2009, 10:17pm:
1. According to the doc you poited out on Choosing PhaseNoise Techniques by Agilent, I should trust SΦ/2 values instead of LUSB.
Strictly speaking,  SΦ/2 is diffefrent from LUSB physically and conceptually.

Mayank wrote on Dec 10th, 2009, 10:17pm:
So does the true SΦ plot (given by pnoise jitter option in Direct Plot Main Form of cadence as pointed out by you in your post  http://www.designers-guide.org/Forum/YaBB.pl?num=1244213153/6#6) never go above 0 dBc/Hz ??
SΦ(f) could go above 0 dBrad/Hz.

Mayank wrote on Dec 10th, 2009, 10:17pm:
2.  If you have compared Silicon vs CAD results, which is  a better approximation to actual measurements out of these  ----->
It depends on whether you measure LSSB(f) or SΦ(f)/2.
Simple measurements using Spectrum Analyzer give  LSSB(f) not SΦ(f)/2.

Mayank wrote on Dec 10th, 2009, 10:17pm:
1. Augmented Pnoise  ??
I don't use Cadence Spectre as RF Reference Simulator.
Due to lack of Agilent licenses, I often have to use Cadence Spectre reluctantly
http://www.designers-guide.org/Forum/YaBB.pl?num=1227668750/8#8

Of course, I don't trust Augmented Pnoise at all.

Mayank wrote on Dec 10th, 2009, 10:17pm:
2. SΦ/2 below linewidth & LΦ after Linewidth  ??
How do you define "linewidth" in your results of http://www.designers-guide.org/Forum/YaBB.pl?num=1050465395/17#17 ?
From very suspicious results of Augmented Pnoise ?

Modeling as Lorentzian Spectrum is not proper if 1/f noise is present.
http://www.designers-guide.org/Forum/YaBB.pl?num=1050465395/20#20

Mayank wrote on Dec 10th, 2009, 10:17pm:
3.  Only LUSB plot of vanilla Pnoise  ??
In Cadence Spectre, LSSB(f) is completely same as SΦ(f)/2 although they are physically and conceptually different.

You may trust "3" less than -10dBc/Hz region where assumption of small signal noise seems to be valid.

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Mayank
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Re: phase noise of ring oscillator using spectre
Reply #27 - Dec 11th, 2009, 1:22am
 
Pancho,
          Also pls have a look & reply to my recent post...It's a related one :---
http://www.designers-guide.org/Forum/YaBB.pl?num=1260521995

There i had a query regarding obtaining true Sphi plots in cadence....

regards & thanx,
mayank.
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Re: phase noise of ring oscillator using spectre
Reply #28 - Jan 4th, 2010, 3:58am
 
Finally had the time to read through this thread properly.

First of all, some comments (in no particular order):

  • I believe in most simulators, the phase noise at low offsets is problematic, because it breaks the small-signal limitations of the noise analysis. In spectre, we tell you this frequency (the "line width") where the results become non-physical.
  • The "augmented" mode in pnoise was originally introduced to add an improved algorithm for cases where there is a long time constant in the circuit - in such cases, the previous algorithm could sometimes incorrectly include the noise contributions from the long-time-constant parts of the circuit (things like the bias circuitry in an oscillator). This is not a universal problem, and most customers have seen simulation results that match with measure data.
  • The "augmented" mode in shooting pnoise in particular had some problems initially, but as far as I'm aware, there aren't outstanding problems.
  • The "augmented" mode in hb pnoise is in fact now used all the time (for the algorithm).
  • Augmented is not enabled by default for shooting, because it's actually more costly to compute, and isn't always needed.
  • The traditional "sources" mode in pnoise doesn't really compute phase noise (although the the direct plot form calls it that) but instead plots the output noise in dBc (so it's just the output noise divided by the magnitude of the carrier) - which is often close to the phase noise for many oscillators. The "modulated" mode does the separation of AM and PM noise by simulating both sidebands around the carrier, and computing correlations between the two sidebands.
  • Augmented (with HB) flattens the phase noise curve below the line width frequency. Strictly this is not really anything to do with the augmented algorithm, but because we had a request that the phase noise over 0dBc should not be displayed. You can argue too that the flattened phase noise is also not physical - so perhaps this is where Pancho Hideboo's "suspicion" comes from? I've certainly discussed with R&D that we need to be very careful about displaying results which are not physical however we choose to do it.
  • Augmented (with shooting) doesn't do this flattening - but I don't think that means that the low-frequency results are really better or worse - they're just displayed differently.
  • I believe other simulators use some sort of heuristics to shape the phase noise at low offsets. I'd like to hear if others are really "accurate" at such low offsets.


Please note that none of the above is any kind of official "Cadence" statement. This is just my personal take, and I am stating these things in the interest of trying to clarify what is going on, as well as trying to understand what is missing or wrong with SpectreRF's pnoise (bearing in mind that it is seen as accurate for the majority of our customer base, despite what some posters would say ;-> )

Kind Regards,

Andrew.
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Re: phase noise of ring oscillator using spectre
Reply #29 - Jan 4th, 2010, 6:40am
 
Andrew Beckett wrote on Jan 4th, 2010, 3:58am:
  • Augmented (with HB) flattens the phase noise curve below the line width frequency.
    Strictly this is not really anything to do with the augmented algorithm,
    but because we had a request that the phase noise over 0dBc should not be displayed.
    You can argue too that the flattened phase noise is also not physical
    - so perhaps this is where Pancho Hideboo's "suspicion" comes from?
  • No.
    Again compare the followings.
    http://www.designers-guide.org/Forum/YaBB.pl?num=1050465395/15#15
    http://www.designers-guide.org/Forum/YaBB.pl?num=1050465395/17#17
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