Frequency Instability
Short-term frequency fluctuations in high-frequency oscillators degrade the signal integrity of communication and radar circuits. In high-speed circuit designs, phase noise represents the unwanted power occurring at frequencies close to the carrier signal. This variation originates from thermal noise and shot noise inside the active semiconductor devices and passive components of the clock circuit.
Signal Performance
Clock jitter and timing errors arise directly from these spectral fluctuations in the frequency generation system. When the clock signal driving an analog-to-digital converter has excessive noise, the sampling points become inconsistent, which reduces the effective number of bits of the converter. In high-speed serial links, this timing uncertainty limits the maximum achievable data rate by closing the horizontal dimension of the signal eye.
Selecting ultra-low-noise voltage regulators and optimizing the trace layout of the phase-locked loop prevents parasitic noise coupling from neighboring digital traces. Circuit boards must also incorporate dedicated ground planes to shield these sensitive analog nodes.
Measurement Technique
Evaluation of these spectral anomalies is performed using dedicated signal analyzers that measure the noise power in a one-hertz bandwidth at specified offset frequencies. The measurement is expressed in decibels relative to the carrier per hertz at a given distance from the center frequency. This quantitative characterization allows engineers to trace noise contributions back to specific circuit elements.
