DDR Memory Read Data Path Calibration Circuit
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Solution Overview
Problem
DDR memory controllers face challenges in efficiently capturing and processing memory data due to high clock rates and timing skews, leading to increased silicon real estate requirements and latency, while existing solutions rely heavily on asynchronous FIFOs and multiple delay elements that consume significant resources and introduce latency.
Innovation Solution
A DDR memory controller design that eliminates delay elements on data inputs and uses a core clock domain for synchronization, incorporating a self-configuring logic circuit to dynamically calibrate timing and compensate for system-level variations, reducing silicon usage and latency by transferring data quickly and adaptively managing timing irregularities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If asynchronous FIFOs and multiple delay elements are used to handle timing skews, then timing adaptation capability is improved, but silicon real estate consumption increases
Solution Approach 1:
The patent extracts and removes delay elements from the data path, eliminating the need for multiple delay stages while maintaining timing skew compensation through a simplified synchronization mechanism using a single delay element and asynchronous FIFO
Solution Approach 2:
The patent merges the timing adaptation function into the clock domain synchronization mechanism, combining what were previously separate functions (delay adjustment and data synchronization) into a unified approach that reduces overall circuit complexity and silicon area
2Adaptability or versatility
If asynchronous FIFOs and multiple delay elements are used to handle timing skews, then timing skew compensation is improved, but device complexity increases
Solution Approach 1:
The patent removes multiple delay elements from the circuit, extracting only the essential timing adjustment function and implementing it with a single delay element, thereby reducing circuit complexity while maintaining timing skew compensation capability
Solution Approach 2:
Instead of adding delay elements to compensate for timing skews, the patent inverts the approach by using early sampling with a single delay element and relying on the asynchronous FIFO to handle the timing alignment, simplifying the overall circuit architecture
3Loss of time
If early sampling of read data is implemented, then latency is reduced, but timing margin decreases
Solution Approach 1:
The patent introduces an asynchronous FIFO as an intermediary buffer between the early-sampled data and the core logic, allowing data to be captured early with reduced latency while the FIFO provides the necessary timing margin and synchronization without affecting the critical path speed
Data Source
AI summary
A method for calibrating a read data path for a DDR memory interface circuit from time to time in conjunction with functional operation of a memory circuit is described. The method uses the steps of issuing a sequence of read commands so that a delayed dqs signal toggles continuously. Next, delaying a core clock signal originating within the DDR memory interface circuit to produce a capture clock signal. The capture clock signal is delayed from the core clock by a capture clock delay value. Next, determining an optimum capture clock delay value. The output of the read data path is clocked by the core clock. The timing for the read data path with respect to data propagation is responsive to at least the capture clock.