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why the oscillator phase noise flat out when it is far away from the center freq (Read 579 times)
liletian
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why the oscillator phase noise flat out when it is far away from the center freq
Mar 29th, 2018, 7:04pm
 
why the oscillator phase noise flat out when it is far away from the center frequency instead of 1/f^2?

Does anyone has a good explanation?

Thanks,
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Andrew Beckett
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Re: why the oscillator phase noise flat out when it is far away from the center freq
Reply #1 - Mar 29th, 2018, 10:46pm
 
Numerous discussions of this including at http://www.signalpro.biz/phasenoise.pdf - the second page shows a common shape of the phase noise. I assume you're talking about the flat bit to the right of the curve on that page? If so, this is due to the thermal noise floor (see explanations further on in that document). I'm sure there are better descriptions out there - this was from a quick google search.

Regards,

Andrew.
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R.kumar
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Re: why the oscillator phase noise flat out when it is far away from the center freq
Reply #2 - Apr 23rd, 2018, 5:12am
 
liletian wrote on Mar 29th, 2018, 7:04pm:
why the oscillator phase noise flat out when it is far away from the center frequency instead of 1/f^2?

Does anyone has a good explanation?

Thanks,


If you were to measure the VCO output directly you would only see a -20dBc/dec clope with no thermal noise floor. However in reality the output can only be measured after going through some buffers/IO circuittry and its thermal noise dominates at large frequency offsets.
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