# US 6,721,224 B2 · Memory refresh methods and circuits

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- Number: US 6,721,224 B2
- Document ID: US6721224B2
- Status: Granted
- Kind: B2
- Application number: 10/228,530
- Filed: 2002-08-26
- Published: 2004-02-26
- Granted: 2004-04-13
- Earliest claimed: 2002-08-26
- Assignees: Mosel Vitelic, Inc.
- Inventors: Steve S. Eaton; Michael Murray; Li-Chun Li
- Web page: https://patentgrep.com/patent/US6721224B2

## CPC

- G11C 11/40603: {Arbitration, priority and concurrent access to memory cells for read/write or refresh operations}
- G11C 11/406: Management or control of the refreshing or charge-regeneration cycles
- G11C 2211/4061: Calibration or ate or cycle tuning
- G11C: STATIC STORES (semiconductor memory devices H10B)

## Abstract

A memory performs a hidden refresh only at the end of a read operation or when the memory is disabled but is supposed to retain data in the disabled state. When the memory is in the enabled state, the refresh is not performed at the end of any operation other than read. This is done to ensure that execution of any memory access command will not be delayed by a refresh as long as the user follows certain timing rules. Other embodiments arc also provided.

## Claims

### Claim 1

A memory circuit comprising:
a plurality of memory cells that need to be refreshed from time to time; circuitry for:
receiving commands to perform memory access operations;
for at least each command of a first type:
performing a memory access operation specified by the command;
at a predetermined time defined by the memory access operation, if a refresh is pending, then:
(A) if the memory circuit has received an indication of a new command following the command of the first type, then not performing the refresh to leave the memory circuit available for executing the new command;
(B) if the memory circuit has not received an indication of a new command following the command of the first type, then performing the refresh.

### Claim 2 (depends on 1)

The memory circuit of claim 1 wherein an indication of a new command is received when the memory circuit detects command signals identifying the new command regardless of whether or not the command signals remain stable after being detected.

### Claim 3 (depends on 1)

The memory circuit of claim 1 wherein:
an indication of a new command is received when the memory circuit detects that command signals identifying the new command have arrived and remained stable for a predetermined interval of time; and
in the case (A) recited in claim 1, the circuitry is to execute the new command.

### Claim 4 (depends on 1)

The memory circuit of claim 1 wherein said predetermined time defined by the memory access operation is either at the end of the memory access operation or a predetermined time after initiation of the memory access operation.

### Claim 5 (depends on 1)

The memory circuit of claim 1 wherein the operation (B) is operable to be performed only for the commands of the first type.

### Claim 6 (depends on 5)

The memory circuit of claim 5 wherein the commands of the first type are read commands.

### Claim 7 (depends on 5)

The memory circuit of claim 5 wherein the commands of the first type include read commands issued by changing one or more of address input signals and also include read commands issued by enabling the memory circuit after the memory circuit was disabled but was to retain data while being disabled, but the commands of the first type do not include read commands issued by changing the memory circuit's write enable input.

### Claim 8 (depends on 5)

The memory circuit of claim 5 wherein as long as the memory circuit is enabled to execute the commands of the first type, the refresh is operable to be performed only in operations (B).

### Claim 9

A method comprising:
receiving commands to access a memory comprising a plurality of memory cells that need to be refreshed from time to time;
for at least each command of a first type:
performing a memory access operation specified by the command;
at a predetermined time defined by the memory access operation, if a refresh is pending, then:
(A) if the memory circuit has received an indication of a new command following the command of the first type, then not performing the refresh to leave the memory circuit available for executing the new command;
(B) if the memory circuit has not received an indication of a new command following the command of the first type, then performing the refresh.

### Claim 10 (depends on 9)

The method of claim 9 wherein an indication of a new command is received when the memory circuit detects command signals identifying the new command regardless of whether or not the command signals remain stable after being detected.

### Claim 11 (depends on 9)

The method of claim 9 wherein:
an indication of a new command is received when the memory detects that command signals identifying the new command have arrived and remained stable for a predetermined interval of time; and
the method further comprises, in the case (A), executing the new command.

### Claim 12 (depends on 9)

The method of claim 9 wherein said predetermined time defined by the memory access operation is either at the end of the memory access operation or a predetermined time after initiation of the memory access operation.

### Claim 13 (depends on 9)

The method of claim 9 wherein the operation (B) is performed only for the commands of the first type.

### Claim 14 (depends on 13)

The method of claim 13 wherein the commands of the first type are read commands.

### Claim 15 (depends on 13)

The method of claim 13 wherein the commands of the first type include read commands issued by changing one or more of address input signals and also include read commands issued by enabling the memory after the memory was disabled but was to retain data while being disabled, but the commands of the first type do not include read commands issued by changing the memory's write enable input.

### Claim 16 (depends on 13)

The method of claim 13 wherein as long as the memory is enabled to execute the commands of the first type, the refresh is performed only in operations (B).

### Claim 17

A method for operating a memory that comprises a plurality of memory cells that need to be refreshed from time to time, the method comprising issuing commands to access the memory, wherein at least each command C1 of a first type is issued in either:
a long memory cycle, the long cycle being a cycle in which no indication of a new command is delivered to the memory for a while to allow the memory sufficient time to perform both a memory access operation specified by the command C1 and also to perform a refresh operation; or
a short memory cycle, the short cycle being a cycle in which an indication of a new command is delivered to the memory early enough to block the memory from performing a refresh operation immediately after the command C1.

### Claim 18 (depends on 17)

The method of claim 17 wherein an indication of a new command is delivered to the memory when command signals identifying the new command are delivered to the memory regardless of whether or not the command signals remain stable after being delivered.

### Claim 19 (depends on 17)

The method of claim 17 wherein an indication of a new command is delivered to the memory when command signals identifying the new command are delivered to the memory and held stable for a predetermined interval of time.

### Claim 20 (depends on 17)

The method of claim 17 further comprising issuing the commands of the first type to perform a long cycle at least once in each predetermined interval of time to allow each of said memory cells to be refreshed sufficiently frequently to prevent data loss.

### Claim 21 (depends on 17)

The method of claim 17 further comprising, at least once in each predetermined interval of time, either issuing the commands of the first type to perform a long cycle or disabling the memory to allow each of said memory cells to be refreshed sufficiently frequently to prevent data loss, wherein the memory retains data while being disabled.

### Claim 22

A system comprising:
a memory comprising a plurality of memory cells that need to be refreshed from time to time;
circuitry for issuing commands to access the memory, wherein at least each command C1 of a first type is issued so as to perform either:
a long memory cycle, the long cycle being a cycle in which no indication of a new command is delivered to the memory for a while to allow the memory sufficient time to perform both a memory access operation specified by the command C1 and also to perform a refresh operation; or
a short memory cycle, the short cycle being a cycle in which an indication of a new command is delivered to the memory early enough to block the memory from performing a refresh operation immediately after the command C1.

### Claim 23 (depends on 22)

The system of claim 22 wherein an indication of a new command is delivered to the memory when command signals identifying the new command are delivered to the memory regardless of whether or not the command signals remain stable after being delivered.

### Claim 24 (depends on 22)

The method of claim 22 wherein an indication of a new command is delivered to the memory when command signals identifying the new command are delivered to the memory and held stable for a predetermined interval of time.

### Claim 25 (depends on 22)

The system of claim 22 wherein the circuitry is to issue the commands of the first type to perform a long cycle at least once in each predetermined interval of time to allow each of said memory cells to be refreshed sufficiently frequently to prevent data loss.

### Claim 26 (depends on 22)

The system of claim 22 wherein, at least once in each predetermined interval of time, the circuitry is to either issue the commands of the first type to perform a long cycle or disable the memory to allow each of said memory cells to be refreshed sufficiently frequently to prevent data loss, wherein the memory is to retain data while being disabled.