Fast quaternary content addressable memory cell
First Claim
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1. A quaternary content addressable memory (CAM) cell for storing a data value having one of four possible states represented by first and second data bits, the CAM cell comprising:
- first and second memory cells for storing the first and second data bits, respectively;
a first match line; and
a first compare circuit coupled to the first and second memory cells and the match line, and configured to discharge the first match line through one of two parallel paths between the first match line and ground potential if there is a mismatch condition between a first comparand bit and the data value, wherein each of the two parallel paths between the first match line and ground potential in the CAM cell consists of a single transistor.
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Abstract
Quaternary CAM cells are provided that include one or more compare circuits that each has a minimal number of pull-down transistors coupled between the match line and ground potential. For some embodiments, the compare circuit includes two parallel paths between the match line and ground potential, with each parallel path consisting of a single pull-down transistor having a gate selectively coupled to the stored data value in response to a comparand value.
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Citations
17 Claims
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1. A quaternary content addressable memory (CAM) cell for storing a data value having one of four possible states represented by first and second data bits, the CAM cell comprising:
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first and second memory cells for storing the first and second data bits, respectively; a first match line; and a first compare circuit coupled to the first and second memory cells and the match line, and configured to discharge the first match line through one of two parallel paths between the first match line and ground potential if there is a mismatch condition between a first comparand bit and the data value, wherein each of the two parallel paths between the first match line and ground potential in the CAM cell consists of a single transistor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A quaternary content addressable memory (CAM) cell for storing a data value having one of four possible states represented by first and second data bits, the CAM cell comprising:
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first and second memory cells for storing the first and second data bits, respectively; a match line; and a compare circuit for comparing a comparand bit with the data value, the compare circuit comprising; a first pull-down transistor connected between the match line and ground potential, and having a gate; a first pass transistor connected between the first memory cell and the gate of the first pull-down transistor, and having a gate to receive the comparand bit; and a first gating transistor coupled between the gate of the first pull-down transistor and ground potential, and having a gate to receive the comparand bit. - View Dependent Claims (11, 12, 13, 14)
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15. A quaternary content addressable memory (CAM) cell for storing a data value having one of four possible states represented by first and second data bits, the CAM cell comprising:
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first and second memory cells for storing the first and second data bits, respectively; a match line to indicate a match condition in response to compare operations between the data value and a comparand bit; and a compare circuit coupled to the first and second memory cells and the match line, and comprising; a first pull-down transistor connected between the match line and ground potential, and having a gate that selectively receives the first data bit in response to the comparand bit; and a second pull-down transistor connected between the match line and ground potential, and having a gate that selectively receives the second data bit in response to a complemented comparand bit, wherein the first and second pull-down transistors are in parallel with each other. - View Dependent Claims (16, 17)
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Specification