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Phase Noise or L? (Read 245 times)
Eugene
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Re: Phase Noise or L?
Reply #15 - Apr 03rd, 2003, 7:24pm
 
I looked over the new papers. It looks like we agree now. Thanks.
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M.S. McCorquodale
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Re: Phase Noise or L?
Reply #16 - Jul 10th, 2003, 2:51pm
 
Speaking of conversions, I have a simple observation. In the paper, "Predicting the Phase Noise and Jitter of
PLL-Based Frequency Synthesizers," page 30, section 10.1, I am confused by the relationship between the PSD and the autocorrelation function. Specifically, they do not appear to be related correctly, unless I am overlooking something.

The PSD and the autocorrelation function should be Fourier transform pairs. Thus, by integrating the autocorrelation function in tau (i.e. t1 - t2), one should obtain the DSB PSD. Thus, integrating equation (64) in tau would yield "c." However, the SSB PSD given in equation (63) is "2c." Considering that this is an SSB PSD, I would assume it should be c/2, thus giving a DSB PSD of "c" as is obtained by integration.

Or, similarly, the equations would be as follows:

(63) Sn(f) = c

(64) Rn(t1 - t2) = 2c delta(t1 - t2)

Where (63) is an SSB PSD. I find this to be of significace because it changes the phase noise to period jitter conversion expressions using (73) and (77) by a factor of 2. I also have a copy of an earlier version of this article where these particular expressions are different by a factor of 2.

Any help is appreciated.

Thanks,

Michael
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YDJ
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Re: Phase Noise or L?
Reply #17 - Jul 20th, 2003, 11:55pm
 
Hi Ken,

Following the post about "Phase Noise or L?" , I am using Cadence 4.4.6 version to perform PSS/pnoise simulation on the PFD/CP with reference frequency 2.5MHz and 20 max sideband. When I press  the "phase noise " button in the direc-plot function, is it showing the curve of a normalized current noise, or L?
Is it normalized with respect to  the charge pump current?  How come I get the result with unit is dBc/Hz not dBc?

As you said that the current noise at output of the CP is change with the current switch turn on time. How come  this "phase noise" is not change with CP current pulse time  ( I have simulated) ?

    Is this normalized current noise (dBc/Hz) or the total current noise (A/sqrt Hz) of CP  affect the PLL output phase noise more? and How to reduce the normailed current noise (dBc/Hz) in the design stage?

I've read thru some articles, they are talking about the 1HZ noise floor in PFD/CP. Is that any relationship between the normalized phase noise with this 1Hz noise floor?

Thanks for your help.
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August West
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Re: Phase Noise or L?
Reply #18 - Jul 21st, 2003, 10:21am
 
YDJ,
The normalized current noise and L are the same thing. L is the noise density normalized to the total noise, that is why the units are dBc/Hz rather than dBc. In other words, L(f) is the noise power in a 1 Hz bandwidth centered at f relative to the total power in the signal. Before converting to decibels, the units are (W/Hz)/(W), after converting to decibels the units become dBc/Hz.

I'm afraid I do not understand the rest of your questions. Could you rephrase them?

-August
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Jitter Man
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Re: Phase Noise or L?
Reply #19 - Dec 21st, 2003, 11:03am
 
[quote author=McCorquodale  link=1036525104/15#16 date=1057873899]Speaking of conversions, I have a simple observation. In the paper, "Predicting the Phase Noise and Jitter of
PLL-Based Frequency Synthesizers," page 30, section 10.1, I am confused by the relationship between the PSD and the autocorrelation function. Specifically, they do not appear to be related correctly, unless I am overlooking something.

The PSD and the autocorrelation function should be Fourier transform pairs. Thus, by integrating the autocorrelation function in tau (i.e. t1 - t2), one should obtain the DSB PSD. Thus, integrating equation (64) in tau would yield "c." However, the SSB PSD given in equation (63) is "2c." Considering that this is an SSB PSD, I would assume it should be c/2, thus giving a DSB PSD of "c" as is obtained by integration.

Or, similarly, the equations would be as follows:

(63) Sn(f) = c

(64) Rn(t1 - t2) = 2c delta(t1 - t2)

Where (63) is an SSB PSD. I find this to be of significace because it changes the phase noise to period jitter conversion expressions using (73) and (77) by a factor of 2. I also have a copy of an earlier version of this article where these particular expressions are different by a factor of 2.

Any help is appreciated.

Thanks,

Michael [/quote]

The single- and double-sided PSDs are related as follows (found in a footnote on page 13),
   SDS(0) = SSS(0)
   SDS(f) = SSS(f)/2 for f != 0
As such, the double-sided equivalent to (63) is
   Sn(f) = c,
which is the transform of (64). Thus, the equations given in the paper appear to be correct (or at least consistent).

Jitter Man
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Eugene
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Re: Phase Noise or L?
Reply #20 - Feb 28th, 2004, 2:51pm
 
Egan's book gives a pretty clear explanation of the relationship between L and S with a simple FM example.

William Egan,  "Phase-Lock Basics". John Wiley and Sons.
pages 304-310
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