What type of spectral impurity components might be generated by a phase-locked-loop synthesizer?

A phase-locked-loop (PLL) synthesizer is designed to generate accurate frequency signals, but it can also introduce various types of spectral impurities. Broadband noise is a common component that might be generated by a PLL synthesizer.

Broadband noise arises from the various processes within the PLL, including the phase detector, loop filter, and voltage-controlled oscillator (VCO). As the PLL attempts to maintain a locked frequency, the inherent noise within these components can manifest as random fluctuations in the synthesized signal. This leads to a noise floor that contributes to spectral impurity, impacting the overall signal quality.

In contrast, harmonic distortion refers to signal components that are integer multiples of a fundamental frequency and could be present in any nonlinear system, while intermodulation distortion involves the generation of additional frequencies that are the sum or difference of the original signals. These are different phenomena compared to the noise created in a PLL. Phase jitter, which is a measure of the short-term variations in the timing of a signal relative to a reference, relates more to timing accuracy rather than the noise spectrum of the output signal itself. While all these components can be important in various contexts, broadband noise specifically relates to the spectrum of signals generated by PLL synthesizers.