The Designer's Guide Community Forum https://designers-guide.org/forum/YaBB.pl Measurements >> Phase Noise and Jitter Measurements >> Limits of Phase noise L(f) = Sphi(f)/2 https://designers-guide.org/forum/YaBB.pl?num=1490262214 Message started by deba on Mar 23rd, 2017, 2:43am

 Title: Limits of Phase noise L(f) = Sphi(f)/2 Post by deba on 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

 Title: Re: Limits of Phase noise L(f) = Sphi(f)/2 Post by Ken Kundert on 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

 Title: Re: Limits of Phase noise L(f) = Sphi(f)/2 Post by deba on Mar 24th, 2017, 4:11am Hi Ken,Thanks for the reference.