DDR5 Command Shifter Circuit for Odd-Latency Timing
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Solution Overview
Problem
The issue with handling odd-numbered latency counts in DDR5 DRAMs arises when latency counting of commands is performed using a divided clock signal, leading to challenges in managing clock cycles.
Innovation Solution
A command shifter circuit is implemented in the DDR5 DRAM, utilizing non-swap and swap paths with latch circuits and multiplexers to achieve even and odd clock cycle delays for internal commands, ensuring sufficient operation margins by generating internal commands with precise timing adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If latency counting of commands is performed using a divided clock signal, then operation margin is secured, but handling of odd-numbered latency counts becomes problematic
Solution Approach 1:
The command shifter circuit is divided into multiple independent shift units (first shift unit, second shift unit, third shift unit, fourth shift unit) that can be selectively activated. Each shift unit handles specific latency count scenarios (even or odd numbers), allowing the system to maintain operation margins while adapting to different latency requirements through selective activation of appropriate segments.
Solution Approach 2:
The circuit employs dynamic selection mechanisms where shift units are selectively activated or deactivated based on the specific latency count requirement. Control signals dynamically enable the appropriate shift unit configuration, allowing the system to transition between handling even-numbered and odd-numbered latency counts while maintaining sufficient operation margins in both modes.
2Speed
If clock signal frequency is increased, then processing speed improves, but operation margin decreases
Solution Approach 1:
The command shifter circuit performs preliminary shifting operations on command signals before they reach subsequent processing stages. By pre-adjusting command timing through the shift units, the circuit ensures that even at higher clock frequencies, commands are properly synchronized and timed, thereby maintaining adequate operation margins despite increased processing speeds.
3Reliability
If latency counting pitch is set to two clock cycles, then operation margin is improved, but handling of odd-numbered counts becomes difficult
Solution Approach 1:
The command shifter circuit acts as an intermediary between the divided clock signal (with two-clock cycle latency counting pitch) and the command processing logic. It introduces intermediate shifting stages that can add or adjust clock cycle delays, enabling the system to maintain the stable two-clock-cycle counting pitch while still achieving precise odd-numbered latency counts through the combined operation of multiple shift units.
Data Source
AI summary
An example apparatus includes a command shifter configured to shift a first command responsive to a first clock signal to generate a second command, a first additional path coupled to the first command shifter and configured to generate a third command responsive to the first clock signal, a second additional path coupled to the first command shifter and configured to generate a fourth command responsive to a second clock signal having different phase from the first clock signal, and a first gate circuit coupled to the first and second additional paths and configured to generate a fifth command based on the third command and the fourth command.