Replica Delay Line for PVT-Stable Latch Setup Timing
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Solution Overview
Problem
High-speed I/O interfaces between processor devices and DDR SDRAM face reliability issues due to PVT variations, causing data-valid window distortions and potential memory access failures, especially since existing calibration methods increase power consumption and introduce memory latency.
Innovation Solution
Incorporating open-loop replicas of data and clock signal paths within the latching element to maintain constant setup time across PVT variations, ensuring that data and clock signal propagation delays remain synchronized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Calibrated Delay Circuit (CDC) is used to control delay time across PVT variations, then timing accuracy is improved, but power consumption increases and memory latency increases due to continuous calibration engine operation
Solution Approach 1:
The patent creates a replica of the data path portion within the latching element that mirrors the external data path delays. This replica circuit copies the timing characteristics of the external data path, allowing the latching element to automatically track setup time variations without requiring continuous external calibration, thereby reducing power consumption while maintaining timing accuracy.
Solution Approach 2:
The latching element performs self-calibration by using its internal replica circuit to automatically track and compensate for setup time variations caused by PVT changes. The replica circuit continuously monitors timing relationships and adjusts internal delays without external intervention, eliminating the need for continuous calibration engine operation and reducing both power consumption and memory latency.
2Measurement precision
If a Calibrated Delay Circuit (CDC) is used to control delay time across PVT variations, then timing accuracy is improved, but memory latency increases due to suspension of memory access operations during calibration code updates
Solution Approach 1:
The replica data path portion within the latching element continuously copies the timing characteristics of the external data path, enabling real-time tracking of setup time variations without requiring periodic calibration interruptions. This continuous copying mechanism eliminates memory access suspensions while maintaining timing accuracy.
Solution Approach 2:
The patent implements continuous timing tracking through the replica circuit that operates without interruption throughout PVT variations. Unlike discrete calibration updates that suspend memory access, the replica circuit provides continuous adaptation, ensuring uninterrupted memory operations and eliminating associated latency.
3Reliability
If delay time is adjusted to track setup time variations across PVT, then latching reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the replica data path portion directly into the latching element structure, combining the timing tracking function with the latching function in a single integrated unit. This integration eliminates the need for separate external calibration circuits and reduces overall device complexity while maintaining latching reliability across PVT variations.
Solution Approach 2:
The replica data path portion is nested within the latching element, with the timing tracking functionality embedded inside the latching structure. This nesting approach allows the complex timing tracking mechanism to be contained within the latching element without increasing external device complexity, while still providing reliable PVT compensation.
Data Source
AI summary
A latching element latches incoming data into an integrated circuit. The latching element (for example, a latch or flip-flop) can be considered to include a data path portion, a clock path portion, and an ideal latching element. In one embodiment, an open-loop replica of the data path portion is disposed in a clock signal path between a clock input terminal of the integrated circuit and a clock input lead of the latching element. In a second embodiment, an additional replica of the clock path portion is disposed in a data signal path between a data terminal of the integrated circuit and a data input lead of the latching element. The replica circuits help prevent changes in skew between a data path propagation time to the ideal latching element and clock path propagation time to the ideal latching element. Setup times remain substantially constant over PVT (process, supply voltage, temperature).