Daisy-Chain Timing Synchronization with PVT Compensation
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Solution Overview
Problem
Achieving sub-nanosecond precision in timing synchronization across nodes in digital networks is challenging due to propagation delays and variations caused by process, voltage, and temperature (PVT) conditions, which are difficult to predict and correct for, especially in large devices with complex on-chip routes and multiple buffers.
Innovation Solution
A daisy-chain network is used to distribute a timing signal, where the signal is looped back through each node, allowing each node to estimate latency and adjust its local time-of-day counter to synchronize with a common reference, thereby simplifying delay-balancing and tolerating PVT variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a timing pulse is transmitted from a timing master to nodes through network paths, then timing synchronization can be achieved, but propagation delay and PVT variations cause synchronization error exceeding sub-nanosecond precision
Solution Approach 1:
The patent implements a feedback mechanism where each node measures its own round-trip delay to the timing master and reports this measurement back. The timing master uses these feedback measurements to calculate and distribute timing offset corrections to each node, thereby achieving sub-nanosecond synchronization precision by compensating for propagation delays and PVT variations.
Solution Approach 2:
The patent replaces complex hardware-based delay correction mechanisms with a software/firmware-based measurement and calculation system. Instead of using hardware circuits to physically balance delays through careful routing and buffering, the system uses software to measure actual delays and compute correction values, simplifying the hardware design while achieving precise synchronization.
2Adaptability or versatility
If timing signal is distributed through long on-chip routes with numerous buffers, then all nodes can be connected, but latency varies by more than 5-10 ns exceeding required precision
Solution Approach 1:
Each node autonomously measures its own round-trip delay to the timing master and calculates its specific timing offset without requiring external calibration or manual adjustment. This self-service approach allows nodes connected through long on-chip routes to automatically compensate for their individual latency variations, enabling versatile node connectivity while maintaining sub-nanosecond precision.
3Measurement precision
If PVT variations are corrected using advance prediction, then timing accuracy can be improved, but prediction changes over time and is not consistent within or between nodes
Solution Approach 1:
The system performs preliminary measurement of round-trip delay at each node and stores this measurement for use in timing offset calculation. By measuring and storing the actual delay characteristics before normal operation, the system prepares accurate correction values that account for specific PVT conditions, improving timing accuracy while avoiding the reliability issues of predictive models that change over time.
Data Source
AI summary
System and method for synchronizing a plurality of nodes to a timing signal using a daisy-chain network having a forward transmission path and a reverse transmission path connected at a midpoint. Latency of the timing signal to the midpoint of the daisy-chain network is determined, a respective latency of the timing signal from the node to the midpoint of the daisy-chain network is determined, and a respective timing offset for each of the plurality of nodes is calculated. A local time-of-day counter at each of the plurality of nodes is adjusted based upon the respective timing offset of the node to synchronize the plurality of nodes to the timing signal.