Disciplined Clock Holdover Topology With Flywheel and Backup Oscillators
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Solution Overview
Problem
High-performance holdover oscillators in disciplined clocks are prone to failure and errors when external reference time signals are unavailable, leading to instability and potential clock failure, due to their complex and failure-prone design.
Innovation Solution
A disciplined clock system that incorporates a flywheel oscillator and a holdover oscillator, with a time comparator module to compare external reference and counter time signals, and a clock control module to adjust the flywheel oscillator frequency, reducing reliance on analog tuning and minimizing errors by using a digital-to-analog converter to control the flywheel oscillator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-performance holdover oscillator is used to maintain accuracy during external reference unavailability, then the clock accuracy is improved, but the device complexity and failure risk increase
Solution Approach 1:
The system divides the oscillator function into two separate components: a flywheel oscillator for normal operation and a holdover oscillator for backup during external reference unavailability. This segmentation allows each oscillator to be optimized for its specific function while reducing the overall complexity and failure risk of the system.
Solution Approach 2:
A digital-to-analog converter (DAC) is introduced as an intermediary component to control the flywheel oscillator frequency. The DAC receives digital control words from the microcontroller and converts them to analog voltage, providing precise frequency control while minimizing analog tuning errors and improving system reliability.
2Adaptability or versatility
If analog tuning is used to control the holdover oscillator frequency, then the frequency adjustment capability is improved, but the tuning linearity errors and stability degrade
Solution Approach 1:
The system replaces analog tuning mechanisms with digital frequency control using a DAC. The microcontroller generates digital control words that are converted to analog voltage by the DAC, providing frequency adjustment capability while eliminating analog tuning linearity errors and improving stability.
Solution Approach 2:
The system changes the control parameter from direct analog voltage tuning to digital control words. By using a DAC to convert digital values to analog voltage, the system maintains frequency adjustment capability while improving tuning linearity and reducing errors associated with analog potentiometers or voltage dividers.
3Reliability
If the holdover oscillator is heavily relied upon for external reference backup, then the clock reliability during holdover is improved, but the holdover oscillator becomes a critical failure point
Solution Approach 1:
The system implements a flywheel oscillator that runs continuously alongside the holdover oscillator. During normal operation, the flywheel oscillator provides the primary timekeeping, cushioning the system against holdover oscillator failures. The flywheel oscillator is periodically synchronized with external references, ensuring it remains accurate and can take over if the holdover oscillator fails.
Solution Approach 2:
The system creates a redundant timekeeping mechanism by implementing both a flywheel oscillator and a holdover oscillator. The flywheel oscillator serves as a copy or alternative timekeeping source that can replace the holdover oscillator in case of failure, reducing the criticality of any single oscillator component.
4Device complexity
If a simple quartz crystal oscillator is used for basic timekeeping, then the device complexity is reduced, but the accuracy deteriorates to approximately 10 ppm
Solution Approach 1:
The system merges a simple flywheel oscillator with a holdover oscillator to achieve high accuracy without the complexity of a single sophisticated oscillator. The flywheel oscillator provides basic timekeeping with minimal complexity, while the holdover oscillator adds accuracy during external reference unavailability. Together, they combine the benefits of simplicity and high precision.
Solution Approach 2:
The flywheel oscillator serves multiple functions: it provides primary timekeeping during normal operation, acts as a backup during holdover periods, and can be synchronized with external references. This multi-functionality allows a relatively simple oscillator to contribute significantly to overall system accuracy without requiring a complex design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances the stability and reliability of the clock system during holdover periods by reducing the impact of external reference signal unavailability and minimizing errors, while also reducing the risk of clock failure and increasing the longevity of the holdover oscillator.
Implementation Method 1
using a digital-to-analog converter to control the flywheel oscillator
Data Source
AI summary
System and methods for a clock system disciplined to an external reference. In one embodiment, the clock includes a flywheel oscillator controlled by the external reference and a free running holdover oscillator. The holdover oscillator provides increased accuracy during periods of holdover when the external reference is not available. In a further embodiment, the flywheel oscillator is additionally controlled by a phase-locked loop with the holdover oscillator frequency as input, and a control switch for switching the flywheel oscillator to analog control if the phase-locked loop exhibits a fault.