Effect of Phase Noise & Spurious Noise on a Signal

Hi.

Phase noise and spurious noise are impairments of PLL. The difference 
between phase noise and spurious noise is the latter is a pure tone while 
the former is a 'collection' of tones.

Phase noise, as the name implies, changes the phase of a signal while 
preserving the magnitude. I am unable to visualize how this is so. Can 
anyone point out useful links or explain the concept behind it?

So how about spurious noise? Does it only change the phase of a signal or 
the magnitude as well?

Thanks!

-- 
Regards,
kc 

ckiancho wrote:
> Hi.
>
> Phase noise and spurious noise are impairments of PLL. The difference

> between phase noise and spurious noise is the latter is a pure tone
while
> the former is a 'collection' of tones.
>
> Phase noise, as the name implies, changes the phase of a signal while

> preserving the magnitude. I am unable to visualize how this is so.
Can
> anyone point out useful links or explain the concept behind it?

You have to consider time and frequency domain separately. You can
(theoretically) change the phase and keep the magnitude in frequency
domain, but that's effectively a PM modulation in time domain.
Which means there will be some ripple introduced to the signal envelope

in time doamin.

I guess a more precise description would be that "Phase noise changes
the phase considerably while the effects on the signal envelope in
time domain are neglible".

> So how about spurious noise? Does it only change the phase of a
signal or
> the magnitude as well?

Well, I don't really know how to answer this...

The effects of spurious noise would be to mess up the signal in
time domain. Check out the "Additive White Gaussian Noise" (AWGN)
model.

The useful signal is modeled as a sinusoidal, which has a narrow-
band energy spectrum. The AWGN noise is broad-band in nature.
So the effects of AWGN noise is not so much that it messes with
the magnitude and phase of the useful signal (it does, to some
extent), as it is to introduce "amplitudes and phases" at frequency
components that have vanishing magnitudes in the noise-free signal.

Rune

"ckiancho" <northlandstarz-newsgroup@yahoo.com.sg> wrote in message 
news:d59lpu$1j5$1@nobel.pacific.net.sg...
> Hi.
>
> Phase noise and spurious noise are impairments of PLL. The difference 
> between phase noise and spurious noise is the latter is a pure tone while 
> the former is a 'collection' of tones.
>
> Phase noise, as the name implies, changes the phase of a signal while 
> preserving the magnitude. I am unable to visualize how this is so. Can 
> anyone point out useful links or explain the concept behind it?
>
> So how about spurious noise? Does it only change the phase of a signal or 
> the magnitude as well?
>
> Thanks!
>
> -- 
> Regards,
> kc
Hi kc :
http://rfdesign.com/mag/radio_managing_noise_spurious/   is not bad.

If you take just about any constant envelope signal , add unwanted 
'spurious' signals to it and then pass the whole thing through a 
hard-limiter you will have added spurious components which are , at least in 
theory, only modulating your signals phase. In practice, if you filter out 
some of your mixing products in a channel filter or some other narrow band 
processing after the hard limiter then you will find both phase and 
amplitude modulation of your wanted signal.

Best of Luck - Mike
http://www.es.oersted.dtu.dk/~pa/31636/pdf/plls.pdf#search='mixing%20products%20multiplier' 
might be useful.