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Limits of Phase noise L(f) = Sphi(f)/2 (Read 2566 times)
deba
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Limits of Phase noise L(f) = Sphi(f)/2
Mar 23rd, 2017, 2:43am
 
Hi,

The phase noise L(f) is defined as
L(f) = Power in 1 Hz at offset (Fo+f)/Power of fundamental(Fo). This equation is in Voltage domain. If one consider small angle approximation for phase than, L(f) = Sphi(f)/2, where Sphi(f) is the single sided PSD of phase. Under what conditions, L(f) is not equal to Sphi(f)/2. In other words, if a voltage spectrum of clock is given, in which region does one can apply L(f)=Sphi(f)/2?

Thanks
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Ken Kundert
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Re: Limits of Phase noise L(f) = Sphi(f)/2
Reply #1 - Mar 23rd, 2017, 6:48pm
 
This is discussed in Introduction to RF Simulation and its Application, in the section on oscillator (3.2). Basically, the approximation breaks down at very low frequencies (at frequencies less than the linewidth if flicker noise is neglected). Generally these frequencies are so low as to be uninteresting to designers.

-Ken
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deba
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Re: Limits of Phase noise L(f) = Sphi(f)/2
Reply #2 - Mar 24th, 2017, 4:11am
 
Hi Ken,

Thanks for the reference.
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