CAM circuit with radiation resistance

• US 20020159320A1
• Filed: 03/14/2002
• Published: 10/31/2002
• Est. Priority Date: 02/08/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Inventors: Lien, Chuen-Der, Miller, Michael J.
• Granted Patent: US 6,560,156 B2
• Time in Patent Office: Days
• US Class Current: 365/222
• CPC Class Codes: G11C 11/4125 Cells incorporating circuit means for protecting against loss of information
• CPC Class Codes: G11C 15/04 using semiconductor elements
• CPC Class Codes: G11C 15/043 using capacitive charge storage elements
• CPC Class Codes: G11C 15/046 using non-volatile storage elements

Abstract

A CAM circuit including a RAM array, a CAM array, and a control circuit that systematically writes data from the RAM array to the CAM array, thereby preventing soft errors by continually restoring data that has been corrupted by radiation. The RAM and CAM arrays can be formed on the same substrate, but are preferably fabricated on separate substrates and mounted in a single package or on a PCB. Both the CAM and RAM can be formed using any conventional memory type (e.g., SRAM, DRAM, NVRAM), and the CAM array can be a binary, ternary, or quad CAM array. The CAM and RAM arrays can be formed on different substrates, or the same substrate. A system including an SRAM ternary CAM array and a RAM array perform quad CAM functions by performing read functions utilizing only the RAM array, while performing lookup functions using the ternary CAM array.

Claims

1. A content addressable memory (CAM) circuit comprising:

a random access memory (RAM) array including a first memory cell;

a CAM array including a CAM cell, wherein the CAM cell includes a second memory cell; and

a control circuit connected to the RAM array and the CAM array for systematically refreshing the CAM array by reading a data value from the first memory cell, and then writing the data value to the second memory cell.

2. The CAM circuit according to claim 1, wherein the RAM array and the CAM array are fabricated on a single substrate.

3. The CAM circuit according to claim 1, wherein the RAM array and the CAM array are fabricated on separate substrates that are mounted in a single package.

4. The CAM circuit according to claim 1, wherein the RAM array and the CAM array are fabricated on separate substrates that are mounted on a printed circuit board.

5. The CAM circuit according to claim 1, wherein CAM cell is a binary CAM cell including the second memory cell and a logic circuit.

6. The CAM circuit according to claim 5,

wherein the logic circuit includes a first transistor, a second transistor, a third transistor and a fourth transistor, the first transistor being connected in series with the third transistor between a match line and a discharge line, and the second transistor being connected in series with the fourth transistor between the match line and the discharge line,

wherein the second memory cell comprises an SRAM cell including a first node connected to a gate terminal of the first transistor, and a second node connected to a gate terminal of the second transistor, and

wherein gate terminals of the third and fourth transistors are connected to complementary data lines.

7. The CAM circuit according to claim 5,

wherein the logic circuit includes a first transistor, a second transistor, and a third transistor, the first transistor being connected between a first data line and a gate terminal of the third transistor, the second transistor being connected between a second data line and the gate terminal of the third transistor, and the third transistor being connected between a match line and a discharge line,

wherein the second memory cell comprises an SRAM cell including a first node connected to a gate terminal of the first transistor, and a second node connected to a gate terminal of the second transistor, and

wherein first and second data lines are complementary data lines.

8. The CAM circuit according to claim 5, wherein the second memory cell of the CAM CELL comprises a DRAM cell.

9. The CAM circuit according to claim 5, wherein the first memory cell comprises a DRAM cell.

10. The CAM circuit according to claim 5, wherein the first memory cell comprises an SRAM cell.

11. The CAM circuit according to claim 5, wherein the first memory cell comprises a non-volatile RAM cell.

12. The CAM circuit according to claim 1, further comprising a second RAM array including a third memory cell, wherein the CAM cell is a ternary CAM cell including the second memory cell, a fourth memory cell, and a logic circuit.

13. The CAM circuit according to claim 12,

wherein the logic circuit includes a first transistor, a second transistor, a third transistor and a fourth transistor, the first transistor being connected in series with the third transistor between a match line and a discharge line, and the second transistor being connected in series with the fourth transistor between the match line and the discharge line,

wherein the second memory cell comprises an SRAM cell including a first node connected to a gate terminal of the first transistor,

wherein the fourth memory cell comprises an SRAM cell including a second node connected to a gate terminal of the second transistor, and

wherein gate terminals of the third and fourth transistors are connected to complementary data lines.

14. The CAM cell according to claim 12, wherein the second and fourth memory cells comprise one of an SRAM cell, a DRAM cell, and a non-volatile RAM cell.

15. The CAM cell according to claim 12, wherein the first and third memory cells comprise one of an SRAM cell, a DRAM cell, and a non-volatile RAM cell.

16. The CAM circuit according to claim 1, further comprising a second RAM array including a third memory cell,

wherein the CAM cell is a quad CAM cell including the second memory cell, a fourth memory cell, a logic circuit, and a translation circuit.

17. The CAM circuit according to claim 1, wherein the translation circuit includes a first logic gate having a first input terminal connected to receive a first data value from the first RAM cell, and a second data value from the second RAM cell, and a second logic gate having a first input terminal connected to receive the first data value from the first RAM cell, and the second data value from the second RAM cell,

wherein the second memory cell comprises a first SRAM cell connected to an output terminal of the first logic gate,

wherein the fourth memory cell comprises a second SRAM cell connected to an output terminal of the second logic gate.

18. The CAM circuit according to claim 17,

wherein the logic circuit includes a first transistor, a second transistor, a third transistor and a fourth transistor, the first transistor being connected in series with the third transistor between a match line and a discharge line, and the second transistor being connected in series with the fourth transistor between the match line and the discharge line,

wherein the first SRAM cell includes a first node connected to a gate terminal of the first transistor,

wherein the second SRAM cell includes a second node connected to a gate terminal of the second transistor, and

wherein gate terminals of the third and fourth transistors are connected to complementary data lines.

19. The CAM cell according to claim 12, wherein the second and fourth memory cells comprise one of an SRAM cell, a DRAM cell, and a non-volatile RAM cell.

20. The CAM cell according to claim 12, wherein the first and third memory cells comprise one of an SRAM cell, a DRAM cell, and a non-volatile RAM cell.

21. A content addressable memory (CAM) circuit comprising:

a random access memory (RAM) array including a first memory cell;

a CAM array including a CAM cell, wherein the CAM cell includes a second memory cell; and

means for systematically refreshing the CAM array by reading a data value from the first memory cell, and then writing the data value to the second memory cell.

22. A method for operating a content addressable memory (CAM) circuit including a random access memory (RAM) array having a first memory cell, and a CAM array having a second memory cell, the method comprising:

writing a data value to the first memory cell of the RAM array and to the second memory cell of the CAM array; and

systematically refreshing the CAM array by reading the data value from the first memory cell, and then writing the data value to the second memory cell.