PLL Frequency Synthesizer Phase Noise Measurement Without Loop Perturbation
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Solution Overview
Problem
Frequency synthesizers in automotive radar systems face challenges in continuously monitoring and managing phase noise, which can lead to unreliable radar measurements and potential failure in detecting obstacles, due to the generation of phase spurs and noise that exceed acceptable levels during operation.
Innovation Solution
The implementation of a phase noise measurement circuitry with a replica error detector and charge pump, configured to match the frequency synthesizer's components, allows for dynamic estimation of phase noise across frequencies, avoiding perturbation of the synthesizer and providing built-in-self-testing capabilities, enabling accurate measurement of phase noise and spurs without disrupting the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional external measurement methods are used to monitor phase noise, then measurement capability is provided, but the synthesizer is perturbed and normal operation is disrupted
Solution Approach 1:
The patent implements a replica error detector that copies the structure and functionality of the original PLL error detector. This replica detector measures phase noise by processing a copy of the reference signal and synthesized signal through identical processing paths, enabling measurement without injecting external test signals that would perturb the synthesizer's normal operation.
Solution Approach 2:
The replica error detector acts as an intermediary measurement device that sits parallel to the main synthesizer path. It receives signals from the same sources (reference oscillator and synthesized output) but processes them independently through its own error detection circuitry, providing measurement data without interfering with the main feedback loop.
2Reliability
If continuous monitoring of phase noise is implemented, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the measurement function with the existing PLL error detector structure. By replicating the error detector circuitry rather than adding completely separate measurement equipment, the design leverages existing components and signal paths, reducing the incremental complexity compared to implementing entirely independent measurement systems.
Solution Approach 2:
The replica error detector is self-contained and autonomously performs phase noise measurements using its own internal processing. It independently receives reference and synthesized signals, performs error detection, and generates measurement outputs without requiring external measurement equipment or complex external test setups.
3Measurement precision
If phase noise measurement circuitry is added to the frequency synthesizer, then measurement precision is improved, but the frequency synthesizer structure becomes more complex
Solution Approach 1:
The patent segments the measurement function into a separate replica error detector module that operates parallel to the main synthesizer. This modular approach isolates the measurement complexity from the core synthesizer functionality, allowing the measurement circuitry to be added as a distinct segment rather than integrating it throughout the entire synthesizer structure.
Data Source
AI summary
A method of measuring phase noise (PN). A PLL frequency synthesizer is provided including a first phase frequency detector (PFD) receiving a reference frequency signal coupled to a first charge pump (CP) coupled to a VCO having an output fedback to the first PFD through a feedback divider that provides a divided frequency signal to the first PFD which outputs an error signal, and PN measurement circuitry including a replica CP coupled to an output of a second PFD or the first PFD. The error signal is received at the replica CP or the divided and reference frequency signal are received at the second PFD, wherein the replica CP outputs a scaled phase error current which is current-to-voltage converted and amplified to provide an amplified phase error voltage, and digitized to provide a digital phase error signal. The digital phase error signal is frequency analyzed to generate a PN measurement.