Backplane Timing Distribution via Programmable Delay Lines
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Solution Overview
Problem
Packet-based timing methods, such as Precision Timing Protocol (PTP), face timing impairments due to packet delay variation and asymmetry in transmission paths within packet-switched networks, necessitating the intra-network distribution of precise phase and frequency alignment between network elements.
Innovation Solution
A backplane phase and frequency alignment system that broadcasts a downstream signal from a master module to slave modules using a backplane trace down and transmits an upstream signal back to the master module using a backplane trace up, employing Manchester encoding and phase-locked-loop techniques to synchronize clock and phase references, with programmable delay lines for precise timing alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If packet-based timing methods (PTP) are used to deliver timing over network, then timing information can be transmitted from master to slave clocks, but packet delay variation and transmission path asymmetry introduce timing impairments
Solution Approach 1:
The patent implements a feedback mechanism where slave clocks transmit upstream signals to the master clock, enabling the master to measure round-trip delay and compensate for packet delay variation. This feedback loop allows continuous adjustment and compensation of timing impairments introduced by the packet-switched network.
Solution Approach 2:
The patent introduces boundary clocks as intermediary elements between the master and slave clocks. These boundary clocks perform local timing adjustments and compensate for network-induced delays, acting as mediators that reduce the impact of packet delay variation and transmission path asymmetry on the overall timing accuracy.
2Reliability
If boundary clocks are used to mitigate packet delay variation, then timing alignment can be improved, but system complexity increases
Solution Approach 1:
The patent makes the master clock perform multiple functions: it not only distributes timing information downstream to slave clocks but also receives upstream signals from slaves to measure delay and generate compensation data. This multi-functionality reduces the need for separate boundary clock devices, thereby managing system complexity while maintaining timing alignment.
3Reliability
If intra-network-element timing distribution is implemented, then timing alignment between master and slave is achieved, but electromagnetic interference may increase
Solution Approach 1:
The patent replaces direct electrical timing distribution with packet-based communication over the network. Instead of transmitting timing signals through physical electrical connections that generate electromagnetic interference, the system uses digital packets carrying timing information, thereby eliminating the source of electromagnetic interference while maintaining timing alignment capability.
Data Source
AI summary
A master and slave module are described that facilitate the distribution of timing, both frequency and phase over a backplane. The method is applicable over any pair of shared transmission medium. The signal transmitted from the master to the slave is suitable for delivering a frequency reference and an approximate phase. The precise phase at the slave is obtained by delaying the 1PPS by a programmable amount estimated by measuring the round-trip delay between the master and slave.