Page Buffer Match Accumulation for Fault-Tolerant In-Memory Search
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Solution Overview
Problem
In-memory searching systems, particularly in NAND flash memory, face inefficiencies when handling large data sets due to the likelihood of misjudged matches caused by defects in memory cells, leading to incorrect results when dividing input data into multiple search words across multiple memory cells.
Innovation Solution
The implementation of a scalable in-memory searching technology that uses a memory array with a page buffer and logic circuitry to accumulate match sense signals over a sequence of search words, employing storage elements like latches or flip-flops to apply a match sense signal and indicate a match or mismatch based on a threshold, thereby mitigating errors from faulty memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If input data is divided into multiple search words and distributed across multiple memory cells, then the system can handle larger data sets, but the likelihood of misjudged matches due to memory cell defects increases
Solution Approach 1:
The patent combines match results from multiple memory cells through accumulation logic that sums match signals across all search words. By merging individual match outcomes into a cumulative total and comparing against a threshold, the system achieves reliable match detection for large data sets while tolerating defects in individual memory cells.
Solution Approach 2:
The system implements feedback through threshold comparison of accumulated match signals. The accumulation logic continuously aggregates match results and feeds them back to a threshold comparison unit, which determines the final match outcome. This feedback mechanism allows the system to compensate for individual cell defects by considering the overall accumulation pattern across multiple search words.
2Quantity of substance
If multiple search words are applied in sequence across multiple NAND strings connected to a single global bit line, then the system can process large input data sets, but a single mismatch can result in a mismatch for the entire input data set
Solution Approach 1:
The patent segments the search process into discrete match signal generations for each search word, with each NAND string producing independent match outcomes. The accumulation logic then segments the counting process into incremental additions, allowing complex multi-word searching to be broken down into simple, repeatable units that can be processed sequentially across multiple NAND strings.
Solution Approach 2:
The patent introduces an intermediary accumulation logic unit that mediates between the individual match signals from multiple NAND strings and the final match determination. This intermediary component translates complex multi-word match patterns into a simplified threshold comparison, acting as a buffer that manages the complexity of sequential searching across multiple data partitions.
3Reliability
If storage elements are used to accumulate match sense signals over a sequence of search words, then errors from faulty memory cells can be mitigated, but the device complexity increases
Solution Approach 1:
The patent makes storage elements in the page buffer serve dual functions: traditional data storage and match signal accumulation. By programming the page buffer to perform both functions, the system achieves reliable error mitigation through accumulation without adding dedicated accumulation hardware, thereby reducing overall device complexity while maintaining improved reliability.
Solution Approach 2:
The page buffer serves itself by using its own storage elements for accumulation purposes. Rather than requiring external accumulation circuitry, the system repurposes the page buffer's inherent storage capability to accumulate match signals, allowing the component to serve multiple functions and reducing the need for additional dedicated structures.
Data Source
AI summary
A memory such as a 3D NAND array, having a page buffer having page buffer cells coupled to bit lines has a search word input such as a search word buffer coupled to word lines. A circuit, such as string select gates, is provided to connect a selected set of memory cells in the array to the page buffer. The page buffer includes sensing circuitry configured to apply a match sense signal to a latch in a plurality of storage elements for a stored data word and an input search word. Logic circuitry uses storage elements in the plurality of storage elements of the page buffer to accumulate the match sense signals output by the sensing circuitry over a sequence matching a plurality stored data words to one or more input search words. A match for a search is based on a threshold and the accumulated match sense signals.