TABLE OF CONTENTS The theoretical phase noise performance of an RF oscillator is governed by Leesons equation [1]. This appendix provides further details of this model and its implications for oscillator circuit design.
The form of the phase noise characteristic exhibited by a typical RF oscillator (without external interference and hence spurs) is given in Figure B.1. This figure shows the three main regions in the characteristic:
Flicker noise: At low offsets from the oscillation frequency, flicker noise in the active device dominates the phase noise characteristic. This is characterised by a 1/ f frequency response and leads to a slope of 9 dB per octave [2].
Leesons equation: At larger offsets, such that the 1/ f noise component has decayed to an appropriate degree, Leesons equation applies, and the phase noise characteristic decays at 6 dB per octave.
Intrinsic noise floor: At still larger offsets, the intrinsic noise floor of the system dominates and this is flat with frequency. This may be set by the thermal noise of the active device itself, that of subsequent amplification or other similar mechanisms.
The level of SSB phase noise present in an oscillator output, as a function of frequency, in the region between f f and f l in Figure B.1, is given by Leesons equation:
