PLL Frequency Synthesizer Spur Measurement Using a Replica Charge Pump
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Solution Overview
Problem
Existing frequency synthesizers in automotive radar systems face challenges in continuously monitoring phase noise, which can lead to unreliable radar performance due to high phase noise or spurs, potentially causing false obstacle detection and system failure.
Innovation Solution
A phase noise measurement circuitry with a replica error detector is integrated on the same semiconductor substrate as the frequency synthesizer, allowing for dynamic estimation of phase noise and spurs without perturbing the synthesizer operation, using a replica phase frequency detector and charge pump to measure phase noise and spurs, and providing built-in-self-testing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a frequency synthesizer is used in automotive radar systems, then flexible and cost-effective implementation is achieved, but phase noise and spurs can cause false detection and unreliable radar measurements
Solution Approach 1:
The patent implements a replica charge pump that copies the structure and function of the original charge pump in the phase-locked loop. This replica pump measures the phase noise and spurs generated by the frequency synthesizer without disrupting the main radar signal generation. By creating an identical copy dedicated to measurement purposes, the system can continuously monitor synthesizer performance and detect phase noise degradation that would otherwise cause unreliable radar measurements.
2Reliability
If phase noise monitoring is implemented to ensure radar reliability, then detection accuracy improves, but system complexity increases
Solution Approach 1:
The patent merges the measurement function with the existing charge pump structure by implementing a replica charge pump that shares the same basic architecture and components as the original. The replica pump is integrated into the same phase-locked loop system and uses similar circuit elements, thereby reducing overall system complexity compared to implementing a completely separate measurement system. This merging approach allows reliability monitoring without proportionally increasing device complexity.
3Measurement precision
If continuous phase noise measurement is performed, then timely detection of performance degradation is achieved, but measurement precision is compromised by perturbation of synthesizer operation
Solution Approach 1:
The patent segments the charge pump function into two separate entities: the original charge pump that generates radar signals and the replica charge pump that measures phase noise. This segmentation allows the measurement function to operate independently without interfering with the signal generation function. The replica pump measures phase noise by processing a copy of the reference signal and feedback signal, thereby maintaining synthesizer operation stability while achieving continuous measurement capability.
4Stability of the object's composition
If a replica charge pump is used for measurement, then synthesizer operation is not perturbed, but the system requires additional components
Solution Approach 1:
The patent uses a replica charge pump that is a simplified copy of the original charge pump, requiring additional components but maintaining operational stability. The replica pump includes essential charge pump elements (current sources, switches, and output nodes) that mirror the original structure sufficiently to measure phase noise accurately without needing to be a complete duplicate of all surrounding circuitry.
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.