The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Measurements >> Phase Noise and Jitter Measurements >> SSB Phase noise in pnoise analysis
https://designers-guide.org/forum/YaBB.pl?num=1244213153

Message started by sanjay on Jun 5^th, 2009, 7:45am

Title: SSB Phase noise in pnoise analysis
Post by sanjay on Jun 5^th, 2009, 7:45am

Hi,
whether the direct plot artist plots SSB phase noise or DSB phase noise?
and how it internally(formula) calculates phase noise from pss & pnoise analysis?
Thank you.

Title: Re: SSB Phase noise in pnoise analysis
Post by Mayank on Jun 7^th, 2009, 8:43am

Hello Sanjay,
Cadence design artist plots SSB phase Noise....directly in dBc ... to get magnitude plots, you can use output noise option.

- mayank.

Title: Re: SSB Phase noise in pnoise analysis
Post by Forum Administrator on Jun 7^th, 2009, 2:38pm

I believe the term "SSB phase noise", which presumably means "Single-Side Band phase noise" is a non-sequitur. You need both sidebands to have phase noise. If you do not have both sidebands, it is just noise.

-Ken

Title: Re: SSB Phase noise in pnoise analysis
Post by Mayank on Jun 8^th, 2009, 10:06pm

Yes, you need both side bands for phase noise calculation. But both the side bands are equal in magnitude. So if you are using cadence, then the formula you use to calculate jitter must incorporate a factor of 2 to convert L(phi) to S(phi). If you are using eldo to calculate S(phi) , then you dont need to multiply by 2.

-mayank.

Title: Re: SSB Phase noise in pnoise analysis
Post by Mayank on Jun 9^th, 2009, 12:30am

Hello Pancho_hideboo,
I didnt understand the context of your reply properly. Is my assertion that both side bands are equal in magnitude, is not correct OR is the statement that cadence artist plot--> direct plot --> phase noise shows SSB phase noise i.e. L(phi), is wrong ?

According to me, the actual phase noise plot will be 3dB more degraded than L(phi) one. So we can compensate it while calculating jitter by adding a factor of 2..Tell me if i am right or wrong ???

-mayank.

Title: Re: SSB Phase noise in pnoise analysis
Post by Ken Kundert on Jun 9^th, 2009, 1:13am

It might be helpful to review http://www.designers-guide.org/Theory/cyclo-preso.pdf. This paper shows how modulation effects result in correlations in the upper and lower sidebands, and how those correlations result in AM and PM components in the noise. If you are looking at L_ssb, then you are only looking at one sideband, and so you cannot know from that alone if there is AM or PM modulation. With close-in noise in oscillators, the noise is almost always dominated by phase noise, so people often refer to L_ssb as phase noise, but formally L_ssb is not phase noise, it is normalized noise.

-Ken

Title: Re: SSB Phase noise in pnoise analysis
Post by pancho_hideboo on Jun 9^th, 2009, 4:32am

Mayank wrote on Jun 9^th, 2009, 12:30am:

Is my assertion that both side bands are equal in magnitude, is not correct ?
According to me, the actual phase noise plot will be 3dB more degraded than L(phi) one.
So we can compensate it while calculating jitter by adding a factor of 2.
Tell me if i am right or wrong ???

Not correct.

L_SSB(f) is small signal mixing noise, that is, sideband noise which include both AM and PM noises.
L_SSB(f) is composed of L_LSB(f) and L_USB(f).
They are not equal. But they are almost same.

S_Φ(f) is PM noise. This has no sideband.

S_Φ(f) is approximately twice of L_LSB(f) or L_USB(f).

But strictly speaking, L_SSB(f) is different from S_Φ(f) physically and conceptually.

Almost all current commercial RF simulators give PM and AM noises separately.

For example, Agilent GoldenGate give S_Φ(f) as "pnmx" directly.
Here we don't have to multiply "pnmx" by two to get S_Φ(f).
Note : "pnmx" of Agilent GoldenGate is twice of "pnmx" of Agilent ADSsim.
And GoldenGate also give L_LSB(f) and L_USB(f) as "side_band_left" and "side_band_right" respectively.

In Cadence Spectre Pnoise Analysis,

For noisetype="sources",
you can get Phase Noise in "pnoise of Direct Plot Form" as L_USB(f) if you use postive offset frequency value.

For noisetype="jitter" or "modulated",
you can get L_LSB(f), L_USB(f), AM noise, PM noise in "pnoise modulated of Direct Plot Form",
and also you can get Phase Noise in "pnoise jitter of Direct Plot Form" as true S_Φ(f).

Here this PM noise is 0.5*S_Φ(f) which is same as "pnmx" of Agilent ADSsim.
Phase Noise in "pnoise jitter of Direct Plot Form" is about 3dB larger value than L_USB(f).
But this is not 2*L_USB(f). This is true S_Φ(f).
Here we don't have to multiply Phase Noise in "pnoise jitter of Direct Plot Form" by two to get S_Φ(f) as same as in Agilent GoldenGate.

Title: Re: SSB Phase noise in pnoise analysis
Post by Andrew Beckett on Jul 10^th, 2009, 5:56am

Personally I think we should have the direct plot form change the prompt from "Phase Noise" to "Output noise in dBc" when using "sources" noiseType...

But it's not happened yet. In the meantime I always explain this to users when I am talking about the various noise outputs from SpectreRF.

Andrew.