Multi-Rank Memory Module Clock Delay Alignment for Signal Integrity
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Solution Overview
Problem
In multi-rank memory systems, achieving signal integrity for command/address signals is challenging due to variations in signal distribution between ranks, leading to performance degradation and increased burden on memory controllers.
Innovation Solution
A memory module with a first and second rank, where both ranks share command/address and clock signals, and include variable adjustment circuits to match the timing of these signals, using delay control logic and flip-flops to adjust the clock signal based on external control, with training methods to optimize timing alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If individual clock timing control is implemented for each rank in the memory controller, then signal integrity is improved, but device complexity and controller burden increase
Solution Approach 1:
The clock skew compensation function is extracted from the memory controller and relocated to the memory devices themselves. Each memory device includes a variable delay circuit that independently adjusts its clock signal timing, removing the burden of centralized timing control from the controller while maintaining signal integrity across multiple ranks.
Solution Approach 2:
Each memory device performs self-adjustment of its clock timing through built-in variable delay circuits. The memory devices autonomously compensate for skew by adjusting their own clock signals based on training results, eliminating the need for complex external control while ensuring reliable operation.
2Device complexity
If multiple ranks share common CA and clock signals, then device complexity is reduced, but signal integrity deteriorates due to distribution variations between ranks
Solution Approach 1:
While maintaining a common signal distribution architecture for simplicity, each rank is equipped with local variable delay circuits that provide rank-specific timing adjustment. This allows the system to benefit from simplified signal distribution while compensating for local variations in signal arrival times at each rank.
Solution Approach 2:
The clock signal timing is made dynamically adjustable through variable delay circuits in each memory device. The delay characteristics can be changed based on training results to optimize timing alignment, transforming the static signal distribution into a dynamically adaptable system that maintains signal integrity across varying conditions.
Data Source
AI summary
There is provided a memory module including a first memory device constituting a first rank, and a second memory device constituting a second rank sharing a command/address signal and a clock signal with the first memory device. The first memory device and the second memory device receive the command/address signal and the clock signal in a matched type, and the first memory device includes a variable delay line for adjusting a delay of the received clock signal.