Synchronous Network Time System for CT Scanner Clock Drift
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Solution Overview
Problem
Clock drift and jitter among networked components in CT scanners, such as those used in medical imaging, can degrade image quality due to variations in oscillator frequencies and network transit times, affecting the accuracy of position readings and correlation data.
Innovation Solution
A synchronous network time system that frequency-locks component clocks to a master clock, using a clock encoder to modulate master clock pulses onto a serial data stream and a clock decoder to recover and synchronize component clocks, eliminating the need for repeated discrete time signals and dedicated channels, thereby achieving zero overhead synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If periodic master clock time signals are transmitted over the network to synchronize component clocks, then clock synchronization is achieved with low network overhead, but clock drift and jitter occur due to variations in network transit times and oscillator frequencies
Solution Approach 1:
The system pre-determines and stores transit time values for multiple different transit times in a lookup table. When synchronizing clocks, the system queries this pre-computed table rather than calculating transit times in real-time, allowing for rapid compensation of network delays without adding computational overhead during operation.
Solution Approach 2:
The patent introduces an intermediary mechanism that measures actual network transit times and uses these measurements to select appropriate pre-determined transit time values from the lookup table. This intermediary layer decouples the time signal transmission from the synchronization calculation, allowing the system to adapt to varying network conditions without changing the core synchronization protocol.
2Measurement precision
If dedicated physical layer channels are used for continuous time signal transmission, then clock synchronization precision is improved, but network overhead increases and data transmission capability is reduced
Solution Approach 1:
The patent merges the time synchronization function with the existing data communication infrastructure by transmitting time signals through the same network switches and communication channels used for data transmission. The system achieves this by encoding time information in a manner that can be extracted from the data stream without requiring separate dedicated channels, thereby combining multiple functions into a single communication pathway.
Solution Approach 2:
The network infrastructure is designed to serve multiple functions simultaneously: it transmits both data packets and time synchronization signals through the same physical layer channels. The universal communication protocol can carry either data or time information depending on the transmission mode, allowing the network to be highly efficient for data transmission while still providing accurate time synchronization when needed.
3Duration of action of moving object
If component clocks independently increment based on their own oscillators between time signals, then continuous timekeeping is maintained, but clock drift accumulates due to frequency variations in different oscillators
Solution Approach 1:
The system implements feedback by continuously monitoring the actual network transit time and using this information to adjust the selection of pre-determined transit time values from the lookup table. This feedback loop allows the synchronization system to adapt to changing network conditions and compensate for drift that would otherwise accumulate between periodic time signals.
Solution Approach 2:
The patent changes the parameter being compensated for from fixed oscillator frequency differences to variable network transit times. By storing multiple pre-determined transit time values and selecting the appropriate one based on actual network conditions, the system addresses the source of clock drift (network delay variations) rather than trying to correct oscillator frequency differences after they have caused drift to accumulate.
Data Source
AI summary
A method for synchronizing a plurality of components that are networked via a plurality of high speed switches, the method includes frequency-locking to a master clock component clocks of the plurality of components, and synchronizing to a master counter, driven by the master clock, component counters of the plurality of components, so that the frequency-locked component clocks drive the component counters in synchrony with the master counter.