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High Performance Static Content Addressable Memory Cell

IP.com Disclosure Number: IPCOM000035870D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Lipa, RA: AUTHOR [+3]

Abstract

Content addressable memory (CAM) cell performance is limited by discharge of match lines in near-miss comparisons. By using a new static cell design, match line load for a given word length is significantly lower and drive cabability is much higher than that of cell designs currently in use which require equivalent semiconductor area.

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High Performance Static Content Addressable Memory Cell

Content addressable memory (CAM) cell performance is limited by discharge of match lines in near-miss comparisons. By using a new static cell design, match line load for a given word length is significantly lower and drive cabability is much higher than that of cell designs currently in use which require equivalent semiconductor area.

Referring to the figure, a portion of the circuit comprised of transistors T1, T2, T3, T4, T5, and T6 is a standard random-access memory (RAM) cell. The new CAM cell design has a word line 2, a bit line pair 4 and 6, and match line 8. In typical operation, true and complement data is presented to a cell on bit line pair 4 and 6. Stored data controls pass-gate devices T7 and T8 and either allows a positive bit line to activate transistor T11 (no-match) or blocks the positive signal (match) effecting a comparison. Don't care conditions are handled by holding both bit lines 4 and 6 to a logical 0 state. Word line 2 is used to write bit line contents into the cell. Match lines are precharged before each comparison.

Comparisons are made at a speed determined by discharge of match line 8. An essential design aspect of this cell is the configuration of match line pull down device T11, a first pass-gate comprised of devices T7 and T8 and a second pass gate comprised of devices T9 and T10. This configuration provides low match line load by using one pull down device T11 and increases dr...