Low-Noise Signal Source With PLL Feedback Phase Noise Control

The patent introduces a phase-locked loop (PLL) as an intermediary system between the signal source and the measurement apparatus. The PLL includes a voltage-controlled oscillator (VCO) that locks to the input signal, and a phase detector that generates an error signal proportional to phase deviations. This intermediary PLL structure enables sensitive phase noise measurements while automating the measurement process, thereby resolving the contradiction between measurement precision and device complexity.

The patent implements feedback control through the PLL mechanism where the phase detector continuously compares the VCO output phase with the input signal phase and generates a feedback error signal. This feedback automatically adjusts the VCO to maintain lock and enables automated measurement of phase noise without manual intervention, resolving the contradiction between measurement precision and ease of operation.

The patent converts the inherent phase noise of ordinary, low-cost signal sources into a useful measurement signal. By using the PLL to lock onto the input signal and measuring the error signal required to maintain lock, the system measures and characterizes the phase noise of inexpensive sources. This allows ordinary sources to achieve effective ultra-low noise performance in the measurement context, resolving the contradiction between noise floor reduction and cost.

The patent enables ordinary signal sources to serve their own noise measurement needs through the automated PLL-based measurement system. The system automatically acquires the input signal, locks the VCO, measures phase deviations, and generates phase noise spectra without requiring expensive external reference sources or manual measurement procedures. This self-service capability allows cost-effective achievement of low noise floor measurements.