Spectral Purity
Signal integrity loss in oscillators manifests as short-term frequency fluctuations that broaden the spectral power of the carrier wave. Phase noise degradation occurs when random noise sources inside the circuit or the environment interfere with the timing of the periodic signal. This effect creates unwanted sidebands that can interfere with neighboring channels in a communication system.
It is measured as the ratio of noise power in a one hertz bandwidth to the total carrier power. High performance clocks must maintain extremely low noise levels to support high speed data rates.
Jitter Contribution
Timing uncertainty in the time domain is the direct result of frequency instability. As phase noise degradation increases, the uncertainty of the zero-crossing point grows. This leads to bit errors in digital systems and reduced resolution in imaging radar.
Measurement Bandwidth
Evaluation of the signal requires a specialized spectrum analyzer with a low internal noise floor. The technician measures the phase noise degradation at various offset frequencies from the carrier. This data is plotted on a logarithmic scale to show the noise distribution.
Thermal Floor
Limits on the achievable signal quality are set by the random movement of electrons. Even in a perfectly designed circuit, phase noise degradation cannot drop below the thermal noise limit. Cryogenic cooling is sometimes used in laboratory settings to reach the absolute minimum.
