Leeson's equation
Leeson's equation is an empirical expression that describes an oscillator's phase noise spectrum. Leeson's expression for single-sideband (SSB) phase noise in dBc/Hz (decibels relative to output level per hertz) and augmented for flicker noise: L ( f m ) = 10 log 10 [ 2 F k T P s ( ( f 0 2 Q l f m ) 2 + 1 ) ( f c f m + 1 ) ] {\displaystyle L(f_{\text{m}})=10\log _{10}{\bigg [}{\frac {2FkT}{P_{s}}}{\bigg (}{\bigg (}{\frac {f_{0}}{2Q_{\text{l}}f_{\text{m}}}}{\bigg )}^{2}+1{\bigg )}{\bigg (}{\frac {f_{\text{c}}}{f_{\text{m}}}}+1{\bigg )}{\bigg ]}} where f0 is the output frequency, Ql is the loaded quality factor, fm is the offset from the output frequency (Hz), fc is the 1/f corner frequency, F is the noise factor of the amplifier, k is the Boltzmann constant, T is absolute temperature, and Ps is the available power at the sustaining amplifier input.