Specifying Local Oscillator Phase Noise Performance: How Good is Good Enough?

Definitive criteria are provided for specifying local oscillator phase noise performance for use in communication systems. In the absence of such criteria, many oscillators tend to be either under or over-specified. The emphasis is on digital modulation and demodulation, but analog communications are also considered. LO phase noise is analyzed for loss in demodulator performance, and also for impact on the modulation process. The results may be used to select an appropriate oscillator, or to tailor the noise characteristics of a frequency synthesizer design.