Static information storage and retrieval – Associative memories – Ferroelectric cell
Reexamination Certificate
2000-05-01
2001-05-29
Nelms, David (Department: 2818)
Static information storage and retrieval
Associative memories
Ferroelectric cell
C365S189040
Reexamination Certificate
active
06240003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of semiconductor memory devices and, more particularly to a content addressable memory (CAM) device utilizing part of the search content as an address.
2. Description of the Related Art
Content addressable memory (CAM) devices are becoming more important in today's highly technical society. CAM devices are frequently employed in network equipment, particularly routers and switches, computer systems and other devices that require content searching. CAM devices are sometimes referred to as associative memories.
A CAM device does not operate like a random access memory (RAM) device. In a RAM device, an address is provided by a controller, the address is used to access a particular memory location within the RAM memory array and then the content stored in the addressed memory location is retrieved from the memory array. A CAM device, on the other hand, is interrogated by a desired content. That is, in a CAM device, “key data” corresponding to the desired content is generated and used to search the memory locations of the entire CAM memory array. When the content stored in the CAM memory array does not match the key data, the CAM device returns a no match indication. When the content stored in the CAM memory array matches the key data, the CAM device outputs information associated with the content.
In network router or switch, for example, CAM devices are used to store Internet Protocol (IP) addresses and routing instructions associated with each address. When an IP packet is received and the IP address obtained, the router must retrieve the routing information for the packet in order to send it on the most direct route to the desired IP address. By using a CAM memory device, the router can search the CAM for the desired IP address (i.e., the desired content). If there is a match, the CAM returns the associated routing information.
Traditional CAM devices have been implemented using SRAM memory cells. However, with this structure, each CAM cell uses a large number of transistors so that all of the cells in the array may be read at once. Alternative CAM devices are being made from other RAM memory cells. Unfortunately, these devices require the rows of the CAM device to be read sequentially one row at a time and is prohibitively slow.
Accordingly, there is a desire and need for a CAM device with minimized cell structure and high speed searching capabilities.
SUMMARY OF THE INVENTION
The present invention provides a content addressable memory (CAM) device with minimized cell structure and high speed searching capabilities.
The above and other features and advantages of the invention are achieved by providing a CAM device that utilizes a portion of a desired content as a row address. A row in a CAM memory array is accessed using the row address portion of the desired content. The remaining portion of the desired content is used as a key data tag for comparison with content stored within memory locations of the addressed row. This way, the CAM device does not have to sequentially access each row in the memory array to locate memory cells having the desired content. The CAM can comprise a standard DRAM memory array, sense amplifiers and compare logic located in the sense amplifiers. Alternatively, the CAM device can comprise a standard SRAM memory array and associated compare logic. By accessing the CAM device using a portion of the desired content as a row address, the CAM device can perform a high speed search while also reducing the complexity of the CAM circuitry.
REFERENCES:
patent: 4622653 (1986-11-01), McElroy
patent: 4791606 (1988-12-01), Threewitt et al.
patent: 5042011 (1991-08-01), Casper et al.
patent: 5226009 (1993-07-01), Arimoto
patent: 5280205 (1994-01-01), Green et al.
patent: 5450351 (1995-09-01), Heddes
patent: 5568415 (1996-10-01), McLellan et al.
patent: 5627785 (1997-05-01), Gilliam et al.
patent: 5642322 (1997-06-01), Yoneda
patent: 5949696 (1999-09-01), Threewitt
patent: 5978246 (1999-11-01), Shindo
patent: 5995401 (1999-11-01), Schultz et al.
patent: 5999434 (1999-12-01), Yoneda et al.
patent: 5999435 (1999-12-01), Henderson et al.
patent: 6009504 (1999-12-01), Krick
Loring Wirbel, “MOSAID Preps Family of DRAM-Based CAMs,” Semiconductors, Electronic Engineering Times, Sep. 27, 1999, pp. 49 and 58.
Dickstein , Shapiro, Morin & Oshinsky, LLP
Micro)n Technology, Inc.
Nelms David
Tran M.
LandOfFree
DRAM content addressable memory using part of the content as... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with DRAM content addressable memory using part of the content as..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and DRAM content addressable memory using part of the content as... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2563943