Non-terminated Active DRAM Termination for Multi-Rank Memory Bus
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Solution Overview
Problem
In multi-rank memory bus architectures, maintaining a sufficient data eye at the active DRAM becomes increasingly difficult as data rates rise, due to undesirable reflections caused by mismatched input impedance in non-terminated DRAMs, leading to power consumption issues and interference.
Innovation Solution
The active DRAM is non-terminated, while inactive DRAMs are terminated, presenting a non-uniform interface to the communication channel, which increases the signal edge rate and improves the data eye at the active DRAM, and additional inactive DRAMs in higher-order architectures remain non-terminated to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the active DRAM is terminated to match impedance and reduce reflections, then signal integrity improves, but the data eye width deteriorates at high data rates
Solution Approach 1:
The patent inverts the conventional termination approach by making the active DRAM non-terminated and the inactive DRAM terminated. This reversal resolves the contradiction by allowing the active DRAM to benefit from reflection-induced edge rate enhancement (improving data eye) while the inactive DRAM absorbs reflections (maintaining signal integrity).
Solution Approach 2:
The patent applies different termination states to different DRAMs based on their operational status. The active DRAM is non-terminated to enhance its data eye, while inactive DRAMs are terminated to absorb reflections. This localized differentiation resolves the contradiction by optimizing each DRAM's termination state for its specific function.
2Manufacturing precision
If the active DRAM is non-terminated to improve data eye, then data eye width improves, but reflections increase causing signal interference
Solution Approach 1:
The patent extracts the reflection absorption function from the active DRAM and assigns it to the inactive DRAM. By terminating the inactive DRAM, the harmful reflections generated by the non-terminated active DRAM are captured and dissipated, resolving the contradiction between data eye improvement and reflection suppression.
Solution Approach 2:
The patent converts the harmful reflections into a beneficial effect by allowing them to occur at the active DRAM (improving edge rate) while using the terminated inactive DRAM to absorb them. The reflection that would normally be harmful is instead utilized to enhance the data eye before being absorbed elsewhere in the system.
3Reliability
If inactive DRAMs are terminated to absorb reflections, then signal integrity improves, but power consumption increases
Solution Approach 1:
The patent applies termination only to inactive DRAMs rather than all DRAMs simultaneously. This partial application of termination provides sufficient reflection absorption during mode transitions while allowing active DRAMs to remain non-terminated and power-efficient, resolving the contradiction between signal integrity and power consumption.
Solution Approach 2:
The patent implements dynamic termination switching where inactive DRAMs are terminated only during mode transitions when reflections are most problematic. During steady-state operation, termination can be deactivated to save power. This periodic application of termination resolves the contradiction by providing it only when necessary.
Data Source
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AI summary
A multi-rank memory bus architecture is provided in which an active DRAM is unterminated and an inactive DRAM terminates to increase the data eye width at the active DRAM.