CODING TECHNIQUES FOR IMPROVING THE SENSE MARGIN IN CONTENT ADDRESSABLE MEMORIES
First Claim
1. A method for operating content addressable memory, the method comprising:
- providing a plurality of memory cells in parallel circuit, the memory cells being electrically coupled to a match line, the match line configured to receive a collective current from the memory cells during a memory search operation;
receiving a data word of bit length L for storage in the memory cells;
transforming the data word into a code word of bit length greater than L such that at least one code word bit in the code word depends on at least two data word bits in the data word, the code word guaranteeing a mismatch of at least two code word bits of different binary values during the memory search operation when the data word does not match a search word; and
storing the code word in the memory cells.
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Abstract
A content addressable memory using encoded data words and search words, and techniques for operating such device. In one embodiment, the data word is transformed into a code word guaranteeing a mismatch of at least two code word bits of different binary values during the memory search operation when the data word does not match a search word. In another embodiment, the search word is transformed into a search code such that the Hamming distance between the code word and the search code is greater than a given threshold when there is a mismatch of at least one bit between the data word and the search word.
27 Citations
25 Claims
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1. A method for operating content addressable memory, the method comprising:
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providing a plurality of memory cells in parallel circuit, the memory cells being electrically coupled to a match line, the match line configured to receive a collective current from the memory cells during a memory search operation; receiving a data word of bit length L for storage in the memory cells; transforming the data word into a code word of bit length greater than L such that at least one code word bit in the code word depends on at least two data word bits in the data word, the code word guaranteeing a mismatch of at least two code word bits of different binary values during the memory search operation when the data word does not match a search word; and storing the code word in the memory cells. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for operating content addressable memory, the method comprising:
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providing a plurality of memory cells in parallel circuit, the memory cells being electrically coupled to a match line, the match line configured to receive a collective current from the memory cells during a memory search operation; receiving a data word of bit length L for storage in the memory cells; transforming the data word into a code word of bit length M, where M is greater than L, such that at least one code word bit depends on at least two data word bits; storing the code word in the memory cells; receiving a search word of bit length L for comparison against the data word during the memory search operation; transforming the search word into a search code of bit length M such that the Hamming distance between the code word and the search code is greater than a hamming threshold when there is a mismatch of at least one bit between the data word and the search word; and indicating a match if the collective current is above a bottom current threshold and below a top current threshold.
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12. A content addressable memory device comprising:
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a plurality of memory cells in parallel circuit, the memory cells being electrically coupled to a match line, the match line configured to receive a collective current from the memory cells during a memory search operation; a receiving unit configured to receive a data word of length L; and an encoding unit configured to transform the data word into a code word of length greater than L for storage in the memory cells, wherein at least one of the code word bits depends on at least two of the data word bits, the code word guaranteeing a mismatch of at least two code word bits of different binary values during the memory search operation when the data word does not match a search word. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A content addressable memory device comprising:
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a plurality of memory cells in parallel circuit, the memory cells being electrically coupled to a match line, the match line configured to receive a collective current from the memory cells during a memory search operation; a receiving unit configured to receive a data word of length L; and an encoding unit configured to transform the data word into a code word of length greater than L for storage in the memory cells, wherein at least one code word bit depends on at least two data word bits, the code word is configured to increase the current passing through the match line during the memory search operation when the data word does not match a search word.
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25. A computer program embodied in computer readable memory comprising:
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program codes coupled to the computer readable memory for operating computer memory, the computer memory including a plurality of memory cells in parallel circuit, the memory cells being electrically coupled to a match line, the match line configured to receive a collective current from the memory cells during a memory search operation, the computer codes configured to cause the computer program to; receive a data word of bit length L for storage in the memory cells; transform the data word into a code word of length greater than L, wherein at least one bit of the code word depends on at least two bits of the data word, the code word guaranteeing a mismatch of at least two code word bits of different binary values during the memory search operation when the data word does not match a search word; and store the code word in the memory cells.
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Specification