Method and system for dynamically operating memory in a power-saving error correcting mode

• US 7,275,130 B2
• Filed: 07/06/2004
• Issued: 09/25/2007
• Est. Priority Date: 04/09/2002
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Klein, Dean A.
• Primary Examiner(s): Elmore; Reba I.
• Application Number:
  US10/886,063
• Publication Number:
  US 20040243886A1
• Time in Patent Office: 1,176 Days
• Field of Search: 711/105, 711/154, 711/166
• US Class Current: 711/105
• CPC Class Codes: G06F 1/3225 of memory devices
• CPC Class Codes: G06F 1/3275 Power saving in memory, e.g. RAM, cache
• CPC Class Codes: G06F 11/106 Correcting systematically all correctable errors, i.e. scrubbing
• CPC Class Codes: G11C 11/406 Management or control of the refreshing or charge-regeneration cycles
• CPC Class Codes: G11C 11/4076 Timing circuits for regeneration management G11C11/406
• CPC Class Codes: G11C 2207/2227 Standby or low power modes
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

A scrubbing controller used with a DRAM stores data in an error correcting code format. The system then uses a memory control state machine and associated timer to periodically cause the DRAM to read the error correcting codes. An ECC generator/checker in the scrubbing controller then detects any errors in the read error correcting codes, and generates corrected error correcting codes that are written to the DRAM. This scrubbing procedure, by reading error correcting codes from the DRAM, inherently refreshes memory cells in the DRAM. The error correcting codes are read at rate that may allow data errors to be generated, but these errors are corrected in the memory scrubbing procedure. However, the low rate at which the error correcting codes are read results in a substantial power saving compared to refreshing the memory cells at a higher rate needed to ensure that no data errors are generated.

Claims

1. A method of storing data in a dynamic random access memory (“

DRAM”

) device in either a normal operating mode when the DRAM device is active or a power-saving mode when the DRAM is inactive, the method comprising;

in the normal operating mode, refreshing memory cells in the DRAM device at a first rate, the memory cells being refreshed without being scrubbed in the normal operating mode; and

in the power-saving mode, scrubbing the memory cells in the DRAM device at a second rate that is substantially less than the first rate.

2. The method of claim 1 wherein the act of scrubbing the memory cells in the DRAM device at a second rate comprises scrubbing the memory cells in the DRAM device at a rate that is a function of the temperature of the DRAM device.

3. The method of claim 1 wherein the act of scrubbing the memory cells in the DRAM device at a second rate comprises scrubbing the memory cells in the DRAM device at a rate that is initially a function of the temperature of the DRAM device and is thereafter adjusted as a function of the number of memory errors that are found to exist in a prior memory scrubbing procedure.

4. The method of claim 1 wherein the act of scrubbing the memory cells in the DRAM at a second rate comprises:

sequentially scrubbing the memory cells from a first row to a last row of a memory array in the DRAM device; and

after scrubbing the last row of the memory array, waiting for a delay period corresponding to the second rate before repeating the sequential scrubbing of the memory cells from the first row to the last row of the memory array in the DRAM device.

5. The method of claim 1 wherein the act of scrubbing the memory cells in the DRAM at a second rate comprises:

sequentially scrubbing the memory cells from a first row to a last row of a memory array; and

after scrubbing each row of memory cells, waiting for a delay period corresponding to the second rate before scrubbing another row of memory cells.

6. The method of claim 1 wherein the act of scrubbing the memory cells results in correcting any memory errors that may exist in the DRAM device, and wherein the act of scrubbing the memory cells in the DRAM device at a second rate comprises scrubbing the memory cells in the DRAM device at a rate that is a function of the number of memory errors that are found to exist in a prior memory scrubbing procedure.

7. The method of claim 6 wherein the act of scrubbing the memory cells in the DRAM device at a rate that is a function of the number of memory errors that are found to exist comprises:

increasing the rate if the number of memory errors is greater than a predetermined value; and

decreasing the rate if the number of memory errors is less than a predetermined value.

8. The method of claim 1 wherein the act of scrubbing the memory cells in the DRAM device comprises:

reading data from the memory cells of the DRAM device;

reading check bits associated with the data from the DRAM device;

generating check bits from the read data;

generating a syndrome from the generated check bits and the read check bits; and

in the event the syndrome indicates there is an error in the read data and/or check bits, generating corrected data and/or check bits, and writing the corrected data and/or check bits to the memory cells of the DRAM device.

9. The method of claim 8 wherein the act of writing the corrected data and/or check bits to the memory cells of the DRAM device comprises:

combining the corrected data and the check bits to provide a corrected ECC; and

writing the corrected ECC to the DRAM device.

10. The method of claim 8 wherein the act of writing the corrected data and check bits to the memory cells of the DRAM device comprises:

writing the corrected data to a first location in the DRAM device; and

writing the corrected check bits to a second location in the DRAM device that is separate from the first location.

11. A dynamic random access memory (“

DRAM”

) device, comprising;

an array of memory cells arranged in rows and columns;

an addressing circuit receiving and decoding an external address;

a data path coupling data between a data bus and memory cells corresponding to the decoded memory address;

a command decoder receiving and decoding external memory commands, the command decoder generating control signals for controlling the operation of the DRAM device, the command decoder further causing the DRAM device to operate in either a normal mode or a power-saving mode;

a refresh controller operable to refresh the memory cells in the array at a first rate when the command decoder causes the DRAM device to operate in the normal mode; and

a scrubbing controller operable to scrub the memory cells in the array at a second rate that is substantially less than the first rate when the command decoder causes the DRAM device to operate in the power-saving mode, the scrubbing controller further being operable to inhibit scrubbing of the memory cells when the command decoder causes the DRAM device to operate in the normal mode.

12. The memory device of claim 11 wherein the second rate at which the scrubbing controller is operable to scrub the memory cells in the array is a function of the temperature of the DRAM device.

13. The memory device of claim 11 wherein the scrubbing controller is operable to read data from the memory cells, read check bits associated with the data from the DRAM device, generate check bits from the read data, generate a syndrome from the generated check bits and the read check bits, and, in the event the syndrome indicates there is an error in the read data and/or check bits, generate corrected data and/or check bits and write the corrected data and/or check bits to the memory cells.

14. The memory device of claim 11 wherein the second rate at which the scrubbing controller is operable to scrub the memory cells in the array is a function of the number of memory errors that are found to exist in a prior memory scrubbing procedure.

15. The memory device of claim 14 wherein the scrubbing controller is operable to increase the rate if the number of memory errors is greater than a predetermined value, and to decrease the rate if the number of memory errors is less than a predetermined value.