Command Generating Circuit Latch Setup Time Margin
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Solution Overview
Problem
The increasing clock frequency in semiconductor memory devices reduces the timing margin gained by the prefetch system, making it challenging to ensure a sufficient setup time for command generation in command generating circuits, particularly in high-speed data transfer operations.
Innovation Solution
A command generating circuit that latches operation mode and bank select signals in synchronization with complementary internal clocks, using a latch circuit with a transfer gate and inverter circuit, and performing logical operations with one of the internal clocks as an enable signal, while delaying signal latching by at least three stages of logic gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If clock frequency is increased to improve data transfer speed, then productivity is improved, but setup time margin is reduced
Solution Approach 1:
The patent applies preliminary action by decoding the command and address signals during the setup time period before the active clock edge. The command decoding circuit and address decoding circuit perform their decoding operations in advance during the setup time, so that the internal command is ready when needed. This allows the system to maintain high clock frequencies while still having sufficient time margin for reliable operation.
2Productivity
If prefetch system is used to speed up command generation, then productivity is improved, but timing margin is reduced as clock frequency increases
Solution Approach 1:
The patent segments the command generation process into distinct decoding stages. The command signal is separated into command decoding (producing operation mode signal) and address decoding (producing bank select signal) that occur independently during setup time. This segmentation allows each decoding operation to be optimized and completed within the available setup time, improving reliability while maintaining high-speed operation.
3Reliability
If setup time specification is made strict to ensure reliable operation, then reliability is improved, but productivity is reduced
Solution Approach 1:
By performing command and address decoding during the setup time period before the active clock edge, the patent ensures that all decoding operations are completed in advance. This preliminary action during setup time allows the system to meet strict setup time specifications while maintaining high clock frequencies for reliable high-speed operation.
Data Source
AI summary
In a command generating circuit, operation mode signals (signals determining internal operations, such as ACTIVE, READ, WRITE, and PRECHARGE) are determined by decoding command signals /CS, /RAS, /CAS, and /WE. The operation mode signals and bank select signals (BS0, BS1, BS2, and BS3) are latched by internal clocks. Thereafter, a logical product (AND) of each of the latched operation mode signals and each of the latched bank select signals is calculated.