Explanation: Phase-locked-loop (PLL) synthesizers inherently generate broadband noise. All active electronic components within the PLL, such as the Voltage-Controlled Oscillator (VCO), phase detector, and loop filter amplifiers, contribute thermal noise. This noise, particularly phase noise from the VCO and noise injected from the reference, phase detector, and dividers, is processed and amplified by the loop. It manifests as a general increase in the noise floor across a range of frequencies surrounding the desired carrier, which is characterized as broadband noise. Spurs (A) are discrete, unwanted frequency components, typically resulting from harmonic leakage, mixer products, or digital clocking signals, rather than the inherent random noise floor. Randomly drifting spurs (B) are not a characteristic impurity. Digital conversion noise (D) is a term more applicable to ADCs/DACs and doesn't accurately describe the spectral impurity of a PLL synthesizer.