EP0500696A1 - Method of refreshing memory devices - Google Patents
Method of refreshing memory devicesInfo
- Publication number
- EP0500696A1 EP0500696A1 EP19900917039 EP90917039A EP0500696A1 EP 0500696 A1 EP0500696 A1 EP 0500696A1 EP 19900917039 EP19900917039 EP 19900917039 EP 90917039 A EP90917039 A EP 90917039A EP 0500696 A1 EP0500696 A1 EP 0500696A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- section
- refresh
- rate
- errors
- refresh rate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/406—Management or control of the refreshing or charge-regeneration cycles
- G11C11/40626—Temperature related aspects of refresh operations
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/406—Management or control of the refreshing or charge-regeneration cycles
Definitions
- This invention relates to a method of refreshing memory devices, in particular dynamic random access memories (DRAMs).
- DRAMs dynamic random access memories
- RAM Random access memory
- static RAM once the datum has been written to a storage cell no further action is required by the system to maintain the value in the cell. Static memory therefore needs no refreshing of its contents.
- DRAM dynamic RAM
- refreshing operation is carried out by performing a destructive read operation followed by a write operation which restores the charge in the cell to its proper level.
- DRAMs Digital Random Access Memory
- Manufacturers of DRAMs specify a rate at which the memory must be refreshed in order to guarantee that no information is lost.
- the major mechanism which causes the charge leakage is thermal and generally manufacturers specify a maximum refresh interval at the appropriate end of a device's operating temperature range, e.g. 8ms refresh period at 70 degrees Celsius.
- the thermal leakage rate is a function of temperature and a well known rule of thumb is that a reduction of 10 degrees Celsius halves the leakage rate and therefore doubles the maximum refresh period, i.e. to 16ms refresh period at 60 degrees Celsius.
- Noise effects are by their nature random and can include sources such as radiation and local electrical noise. If, as in the case of radiation, the noise destroys the charge in the cell, then this means that the level below which the charge can fall has to be raised so that a hit on the cell does not lead to loss of data. Electrical noise makes the sensing operation more difficult and in an electrically noisy environment the cell charge will have to be above a certain level for reliable sensing. The converse is also true; in an electrically quiet
- the cell charge can be smaller and still sensed reliably.
- RAS only refresh the system designer has to inform the RAM which row is to be refreshed and typically this involves setting up a 10 bit address to the chip and pulsing the RAS line.
- CAS before RAS refresh a counter internal to the RAM is used, but both RAS and CAS lines are pulsed.
- the chip will consume about 10% more power than in a RAS only refresh operation. In a complete system this will not translate to a 10% power saving, because power is required in the RAS only case to drive the address to the chip.
- an economical implementation would still be able to show power saving by using RAS only refresh.
- a method of refreshing DRAMs according to which a small section (S) of the DRAM is refreshed at a lower rate than the major section (M), data errors arising in section S are sensed, and the refresh rates of the two sections (S and M) are adjusted, whilst maintaining the M section refresh rate higher than the S section refresh rate, until data errors in section S are not significant.
- section S can reliably be employed as a sensor for the chip to determine the optimum refresh rate for existing environmental conditions.
- section S is subject to the same process variations as section M so that overall process variations are eliminated.
- section S will be subject to the same, or very similar, noise as section M, so that this effect can also be eliminated.
- the method provides a much more accurate temperature
- section M of the DRAM is refreshed at the manufacturer's specified rate.
- the refresh rate for Section S is then extended in suitable increments until a rate is attained at which errors are just significant, say a refresh rate E.
- the refresh rate for section M is then adjusted to the last error free rate of section S
- Section S continues to be refreshed at rate E and if the refresh rate for this section changes due to an increase or decrease in detected significant errors in the section, then the refresh rate for section M is changed appropriately through a simple control loop.
- a suitable safety factor for example of the order of 2.
- the technique is effectively setting the level at which the charge in a cell cannot be reliably sensed.
- the sense amplifiers in the memory are designed so that at this point they become very sensitive to a change in conditions.
- Figure 1 shows a DRAM organisation for use in the
- Figure 2 shows a typical DRAM cell and addressing
- Figure 3 is a simplified flow chart exemplifying the
- FIG. 4 is a more detailed flow chart which includes
- addressing is arranged such that the address of a word in the memory is given by:
- Row address A12 - A21, where An is the corresponding
- Refresh is then accomplished by pulsing RAS with an externally set up row address, which will refresh all cells within the row, i.e. cells normally addressed by A2 - A11.
- Section S is implemented as a row, or rows, of the memory and is refreshed at a lower rate than section M by not presenting its row address as often as that of Section M.
- This scheme has a number of advantages over a more straightforward technique which would refresh one chip less often than others. Firstly the sensing is effectively distributed across all devices, which will improve the error reporting/sensing and secondly, the errors will be confined to a contiguous block of memory because of the column addressing. The latter means that it is easier for the system to use the memory, both in conventional use and also when error detecting or
- FIG. 3 A flow chart for a basic refresh scheme is shown in Figure 3, and will be clear without further description.
- Figure 4 shows a more detailed scheme including refresh
- the scheme can be adapted to cope with such problems in a number of ways.
- One way is to augment the system with an external temperature sensor which is used to detect the rate of change of external temperature. Under high rates of change this would force an early re-evaluation of the system refresh rates.
- more areas of the chip may be used as sensors, enabling the refresh intervals for the sensors to be staggered so that the maximum interval between senses is always less than the thermal time constant of the system.
- section S is 1024 bits long
- section M is 1048576 bits
- section S error rate is 1 in le6
- section M error rate 1 in le7 is 1048576 bits
- section S error rate is 1 in le6
- section M error rate 1 in le7 is 1048576 bits
- the error rate in section S will be dependent upon the pattern stored in the memory chip. For instance, if a cell with charge is surrounded on the chip by discharged cells then it will leak at a higher rate than one
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Computer Hardware Design (AREA)
- Dram (AREA)
Abstract
Procédé de rafraîchissement des RAM dynamiques selon lequel une petite section S de la puce est rafraîchie à un rythme plus lent que la section principale M, les erreurs de données apparaissant dans la section S sont détectées et les rythmes de rafraîchissement des deux sections sont ensuite réglés en maintenant un rythme de rafraîchissement de la section M plus élevé que celui de la section S par un facteur de sécurité, jusqu'à ce que les erreurs de données dans la section S soient insignifiantes.Dynamic RAM refresh method where a small section S of the chip is refreshed at a slower rate than the main section M, the data errors appearing in the section S are detected and the refresh rates of the two sections are then set maintaining a refresh rate of section M higher than that of section S by a safety factor, until the data errors in section S are insignificant.
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8926119A GB2239539B (en) | 1989-11-18 | 1989-11-18 | Method of refreshing memory devices |
GB8926119 | 1989-11-18 |
Publications (1)
Publication Number | Publication Date |
---|---|
EP0500696A1 true EP0500696A1 (en) | 1992-09-02 |
Family
ID=10666541
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19900917039 Withdrawn EP0500696A1 (en) | 1989-11-18 | 1990-11-14 | Method of refreshing memory devices |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0500696A1 (en) |
JP (1) | JPH05501628A (en) |
AU (1) | AU6741290A (en) |
GB (1) | GB2239539B (en) |
WO (1) | WO1991007756A1 (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5157634A (en) * | 1990-10-23 | 1992-10-20 | International Business Machines Corporation | Dram having extended refresh time |
US6021076A (en) | 1998-07-16 | 2000-02-01 | Rambus Inc | Apparatus and method for thermal regulation in memory subsystems |
DE602004018646D1 (en) * | 2003-01-29 | 2009-02-05 | St Microelectronics Sa | A method of refreshing a DRAM and associated DRAM device, in particular incorporated in a cellular mobile telephone |
JP4237109B2 (en) * | 2004-06-18 | 2009-03-11 | エルピーダメモリ株式会社 | Semiconductor memory device and refresh cycle control method |
EP2951832A4 (en) * | 2013-01-31 | 2017-03-01 | Hewlett-Packard Enterprise Development LP | Ram refresh rate |
US10978136B2 (en) * | 2019-07-18 | 2021-04-13 | Apple Inc. | Dynamic refresh rate control |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3796998A (en) * | 1971-09-07 | 1974-03-12 | Texas Instruments Inc | Mos dynamic memory |
US4218764A (en) * | 1978-10-03 | 1980-08-19 | Matsushita Electric Industrial Co., Ltd. | Non-volatile memory refresh control circuit |
US4344155A (en) * | 1979-12-31 | 1982-08-10 | Compagnie Internationale Pour L'informatique Cii-Honeywell Bull (Societe Anonyme) | Method of and apparatus for inscribing a control character in a memory |
US4380812A (en) * | 1980-04-25 | 1983-04-19 | Data General Corporation | Refresh and error detection and correction technique for a data processing system |
US4453237A (en) * | 1980-10-01 | 1984-06-05 | Intel Corporation | Multiple bit output dynamic random-access memory |
JPS6061992A (en) * | 1983-09-14 | 1985-04-09 | Nec Corp | Pseudo static memory |
JPS63121197A (en) * | 1986-11-07 | 1988-05-25 | Fujitsu Ltd | Semiconductor memory device |
JPS6432489A (en) * | 1987-07-27 | 1989-02-02 | Matsushita Electronics Corp | Memory device |
-
1989
- 1989-11-18 GB GB8926119A patent/GB2239539B/en not_active Expired - Fee Related
-
1990
- 1990-11-14 AU AU67412/90A patent/AU6741290A/en not_active Abandoned
- 1990-11-14 JP JP51580290A patent/JPH05501628A/en active Pending
- 1990-11-14 WO PCT/GB1990/001757 patent/WO1991007756A1/en not_active Application Discontinuation
- 1990-11-14 EP EP19900917039 patent/EP0500696A1/en not_active Withdrawn
Non-Patent Citations (1)
Title |
---|
See references of WO9107756A1 * |
Also Published As
Publication number | Publication date |
---|---|
GB2239539A (en) | 1991-07-03 |
JPH05501628A (en) | 1993-03-25 |
GB8926119D0 (en) | 1990-01-10 |
WO1991007756A1 (en) | 1991-05-30 |
AU6741290A (en) | 1991-06-13 |
GB2239539B (en) | 1994-05-18 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
17P | Request for examination filed |
Effective date: 19920504 |
|
AK | Designated contracting states |
Kind code of ref document: A1 Designated state(s): AT BE CH DE DK ES FR GB GR IT LI LU NL SE |
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RAP1 | Party data changed (applicant data changed or rights of an application transferred) |
Owner name: EO EUROPE LIMITED |
|
RBV | Designated contracting states (corrected) |
Designated state(s): DE FR GB IT |
|
17Q | First examination report despatched |
Effective date: 19940711 |
|
STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN |
|
18D | Application deemed to be withdrawn |
Effective date: 19941122 |