On-Die Termination Impedance Selection Using Signal Eye Sampling
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Solution Overview
Problem
As high-speed data communication interfaces increase in speed, traditional methods of compensating for poor data eye margins become increasingly difficult due to variations in DIMM, DRAM, and CPU package impedances, leading to unacceptable data eye margins.
Innovation Solution
An on-die termination (ODT) network with adjustable resistors and a signal eye sampler dynamically optimizes impedance settings by iteratively adjusting resistance values during the power-on initialization phase to maximize signal eye margins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional fixed impedance termination methods are used, then device complexity is reduced, but data eye margin deteriorates due to impedance variations in DIMM, DRAM, and CPU package
Solution Approach 1:
The patent implements dynamic impedance adjustment by providing multiple ODT impedance levels (first, second, third levels) that can be selectively activated based on detected impedance conditions. The receiver dynamically switches between different termination impedance values to match varying source impedance conditions, thereby optimizing data eye margin while maintaining manageable device complexity through structured impedance selection.
Solution Approach 2:
The patent changes the termination impedance parameter from a fixed value to multiple selectable values. By detecting actual impedance conditions and selecting appropriate ODT impedance levels, the system adapts termination parameters to match source impedance variations, resolving the contradiction between maintaining simple fixed termination and achieving reliable signal transmission under varying conditions.
2Reliability
If impedance optimization is performed during power-on initialization, then data communication reliability improves, but power-on time increases
Solution Approach 1:
The patent performs impedance detection and ODT impedance selection during the power-on initialization phase before normal data communication begins. By completing the impedance optimization process in advance, the system ensures reliable data transmission from the start of operation, accepting the time cost only during initialization rather than during ongoing communication.
Solution Approach 2:
The patent accelerates the impedance optimization process by performing rapid impedance detection and selection during power-on initialization, then skipping further optimization steps and proceeding directly to normal data communication. This approach minimizes the time spent on optimization while ensuring reliability is established before operational phase.
Data Source
AI summary
A receiver includes an ODT network and a signal eye sampler. The ODT network terminates a data communication interface at a selectable impedance including a nominal impedance, at least one higher impedance, and at least one lower impedance. The signal eye sampler determines an eye margin for data received on the data communication interface. The receiver selects the nominal impedance, determines a nominal eye margin associated with the nominal impedance, selects a delta impedance from one of the higher impedance and the lower impedance, determines a delta eye margin associated with the delta impedance, determines whether the delta eye margin is greater than the nominal eye margin, and sets a run time impedance value for the data communication interface to the delta impedance when the delta eye margin is greater than the nominal eye margin.