Flash Memory Erasure Count Search Circuit
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Solution Overview
Problem
Existing semiconductor memory systems, such as NAND type flash memory, require significant time to search for a block with the minimum erasure count due to the need for repeated read and comparison operations by the CPU, which intervenes with instruction fetch cycles, leading to inefficient data management and reduced rewrite life.
Innovation Solution
A semiconductor device with a block management memory, a read address generation circuit, and a minimum erasure count search circuit that successively reads and compares erasure count data to identify and output the address of the block with the minimum erasure count, allowing for high-speed searching without interrupting instruction fetch cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the CPU repeatedly executes read control and comparison control to search for the block with minimum erasure count, then the erasure count search can be completed, but a large amount of time is consumed due to interventions of instruction fetch cycles
Solution Approach 1:
The patent extracts the erasure count search function from the CPU's general-purpose operation and implements it as a dedicated hardware search circuit. This circuit directly accesses the block management memory and compares erasure count data without requiring CPU instruction fetch cycles, thereby eliminating the time-consuming overhead while maintaining accurate search results.
Solution Approach 2:
The patent introduces a block management memory as an intermediary structure that stores erasure count data for all blocks. This intermediary allows the search circuit to efficiently access and compare erasure counts without requiring repeated CPU interventions, thus reducing search time while preserving measurement accuracy.
2Ease of operation
If the CPU sequentially executes read control and comparison control for each block, then the erasure count data can be processed, but the processing speed is reduced due to repeated instruction fetch cycles
Solution Approach 1:
The patent implements a self-service mechanism where the search circuit autonomously performs the erasure count search operation without requiring sequential CPU control instructions. The circuit automatically reads erasure count data from the block management memory, performs comparisons, and identifies the block with minimum erasure count, thereby maintaining operational simplicity while dramatically improving processing speed.
Solution Approach 2:
The patent replaces the mechanical sequential control system (CPU executing instruction cycles) with a parallel hardware comparison system. The search circuit uses dedicated comparison units that can simultaneously compare multiple erasure count values, eliminating the sequential bottleneck while keeping the control interface simple through automatic operation.
3Measurement precision
If the CPU performs control of reading erasure count data and comparing erasure count data repeatedly, then the block with minimum erasure count can be identified, but the rewrite life of flash memory is reduced due to frequent interventions
Solution Approach 1:
The patent extracts the erasure count search operation from CPU-controlled sequences and implements it as an autonomous hardware search circuit. This eliminates repeated CPU interventions that would require multiple read cycles from the flash memory, thereby reducing wear on the flash memory cells while maintaining accurate identification of the block with minimum erasure count through dedicated comparison logic.
Solution Approach 2:
The patent implements preliminary action by maintaining a block management memory that continuously stores and updates erasure count data for all blocks. This pre-organized data structure allows the search circuit to perform comparisons without requiring repeated reads from the flash memory itself, thus preserving flash memory rewrite life while ensuring accurate minimum erasure count identification is always available.
Data Source
AI summary
A semiconductor device and search circuit for and method of searching for a count of erasures in a semiconductor memory. The semiconductor device includes a semiconductor memory in which data erasure is performed in units of blocks. A block management memory stores, corresponding to each of the blocks, a piece of erasure count data representing a count of erasures of data performed in the block. An erasure count search circuit successively reads the pieces of erasure count data from the block management memory so as to search for a block corresponding to a piece of erasure count data representing an intended erasure count from among the pieces of erasure count data read from the block management memory. The circuit also outputs an address of the searched block as an erasure count address.