Atomic Clock Holdover Calibration for Reference Signal Loss
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Solution Overview
Problem
Current atomic clock systems face challenges in maintaining phase and frequency continuity during disruptions in the primary timing reference, such as loss of GPS signals, leading to inaccuracies in downstream systems.
Innovation Solution
The atomic clock system incorporates a tunable local oscillator, follower circuit, atom referenced circuit, switch, controller, and memory to selectively apply digital pumping signals, allowing it to maintain the output frequency and phase by using stored operating settings when an external reference signal is removed, ensuring continuity with the last detected reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the atomic clock output is locked to a primary timing reference using conventional techniques, then the timing accuracy is improved during normal operation, but the phase and frequency continuity is lost when the reference signal is disrupted
Solution Approach 1:
The system performs preliminary calibration by storing calibration data that represents the atomic clock's operating parameters when synchronized with the primary reference. This pre-stored data enables the clock to rapidly restore continuity after disruption without recalibration, resolving the contradiction between maintaining accuracy and ensuring continuity during reference loss
Solution Approach 2:
The system continuously monitors the correlation between the local oscillator and external reference signal, using this feedback to detect disruptions and trigger the appropriate mode switching. This feedback mechanism ensures seamless transition between locked and holdover modes, maintaining both accuracy during normal operation and continuity during disruptions
2Adaptability or versatility
If the atomic clock reverts to free running frequency after reference disruption, then operational independence is improved, but timing accuracy deteriorates due to phase and frequency deviation
Solution Approach 1:
The system dynamically switches between two operational modes: locked mode for normal operation and holdover mode for reference disruption. This dynamic adaptation allows the clock to maintain high accuracy when reference is available while ensuring continuity when reference is lost, resolving the contradiction between independence and accuracy
Solution Approach 2:
By pre-calibrating and storing the relationship between the local oscillator and reference signal, the system prepares the holdover mode in advance. When disruption occurs, the clock immediately applies stored calibration data to maintain accurate timing without reverting to free-running mode, thus preserving both independence and accuracy
3Measurement precision
If continuous calibration to external reference is implemented, then timing accuracy is improved, but system complexity increases due to additional calibration mechanisms
Solution Approach 1:
The system extracts only the essential calibration data (operating parameters representing the relationship between local oscillator and reference) and stores it for later use. This extraction approach maintains high timing accuracy while avoiding the complexity of continuous calibration mechanisms, as the critical calibration information is captured and preserved for rapid restoration
Data Source
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AI summary
An atomic clock is provided. An output of a tunable LO is coupled to a user output of the atomic clock. A charge pump adjusts the tunable LO with a LO tuning voltage. A follower circuit sets an output frequency of the atomic clock to a frequency of an external reference signal coupled to an external reference input. An atom referenced circuit sets the output frequency of the atomic clock to a frequency based on stored operating settings. A controller stores then current operating settings generated based on a then current external reference signal coupled to the external reference input. The controller is further configured to apply the stored then current operating settings to the atom referenced circuit when the then current external reference signal is removed from the external reference input to maintain the output frequency of the atomic clock at the output frequency set by the follower circuit.