DRAM Gear Down Clocking for Stable Command Timing Margins
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Solution Overview
Problem
Synchronous dynamic random access memories (DRAMs) face challenges with insufficient setup margins and hold margins for external command signals when operating with high-frequency external clock signals, particularly due to timing differences between gear down mode ON and OFF, which complicates design and increases chip area requirements.
Innovation Solution
A semiconductor device with a frequency division circuit that generates a second clock signal, a logic circuit to synthesize chip select signals, and a command generation circuit activated based on the second chip select signal, allowing the command signal to be enabled every n active edges of the clock signal, eliminating timing differences between gear down modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency division is used to increase setup and hold margins, then setup margin and hold margin are improved, but timing difference occurs between gear down mode ON and OFF
Solution Approach 1:
The patent applies dynamics by making the clock signal path adaptive - when gear down mode is ON, the external clock signal passes through the frequency division circuit to generate a frequency-divided clock signal; when gear down mode is OFF, the frequency division circuit is bypassed. This dynamic switching allows the system to adapt its timing characteristics to operational requirements, resolving the timing difference issue between modes.
Solution Approach 2:
The patent changes the frequency parameter of the clock signal dynamically - using frequency division (reducing frequency) when gear down mode is enabled to increase setup and hold margins, and bypassing frequency division when gear down mode is disabled to maintain original timing. This parameter change approach allows flexible adjustment of timing margins without permanent structural modification.
2Reliability
If delay elements are added to cancel timing difference, then timing consistency is improved, but chip area increases
Solution Approach 1:
The patent extracts and removes the frequency division operation from the critical timing path when gear down mode is OFF by providing a bypass path. Instead of adding delay elements to compensate for timing, the solution removes the source of timing difference by allowing the clock signal to skip the frequency division circuit entirely when not needed, thereby eliminating the timing inconsistency without adding extra components.
Solution Approach 2:
The patent implements a dynamic switching mechanism that connects or disconnects the frequency division circuit from the clock signal path based on the gear down mode status. This dynamic reconfiguration eliminates the need for static delay elements, achieving timing consistency through adaptive signal routing rather than fixed timing compensation structures.
3Reliability
If frequency division circuit is always used, then setup and hold margins are improved, but productivity decreases due to reduced clock frequency
Solution Approach 1:
The patent dynamically switches between frequency-divided clock signal and original clock signal based on operational mode. When gear down mode is ON, frequency division is applied to improve setup and hold margins; when gear down mode is OFF, the frequency division circuit is bypassed to maintain higher operation speed. This dynamic approach allows the system to optimize between reliability and productivity based on real-time requirements.
Solution Approach 2:
The patent changes the clock frequency parameter adaptively - using a lower frequency (frequency-divided) when setup and hold margin requirements demand it, and switching to the original higher frequency when maximum productivity is needed. This parameter switching enables the system to achieve both high reliability and high productivity at different operational phases.
Data Source
AI summary
Disclosed herein is a device that includes: a frequency division circuit that divides a frequency of a first clock signal to generate a second clock signal; a first logic circuit that receives a first chip select signal and the second clock signal to generate a second chip select signal; and a command generation circuit that is activated based on the second chip select signal, and generates a second command signal based on a first command signal.