Unified erase method in flash EEPROM
First Claim
1. A unified erase method used in an array of flash EEPROM memory cells arranged in a plurality of sectors for performing either a single-sector, multiple-sector, or all-sector erasing operation with a reduced amount of total erase time, said erase method comprising the steps of:
- turning an erase-signal ON in only certain ones of said plurality of sectors which are required to be erased;
programming initially all bytes in said certain ones of said plurality of sectors which are required to be erased;
setting current address in said certain ones of said plurality of sectors which are required to be erased to a first address;
(a) determining whether a first sector of said plurality of sectors has its erase-on signal turned OFF;
(b) bypassing said first sector if said erase-on signal is turned OFF and proceeding to a second sector of said plurality of sectors;
(c) determining whether the current address has been erased if said erase-on signal is not turned OFF;
(d) proceeding to the second sector of said plurality of sectors if the current address has not been erased and storing in an address register the current address;
(e) determining whether the current address is the last address of said first sector if the current address has been erased;
(f) increasing the current address by one if the current address is not the last address and repeating steps (c)-(e);
(g) turning OFF said erase-on signal if the current address is the last address and proceeding to the second sector of said plurality of sectors;
repeating steps (a) through (g) for the remaining sectors of said plurality of sectors except for a last sector;
determining whether the last sector of said plurality of sectors has its erase-on signal turned OFF;
determining whether the erase-on signal for all sectors of said plurality of sectors are turned OFF if the last sector has its erase-on signal turned OFF;
(i) determining whether the current address of the last sector has been turned OFF if said erase-on signal is not turned OFF;
(j) storing current address in an address register if the current address is not erased;
(k) determining whether the current address is a last address of said last sector if the current address has been erased;
increasing the current address by one if the current address is not the last address and repeating steps (i) through (k);
turning OFF said erase-on signal if the current address is the last address;
applying an erase pulse to all bytes in all sectors simultaneously in which the erase-on signals have not been turned OFF if the current address of the last sector has not been erased or if the erase-on signal for all sectors have not been turned OFF and repeating steps (a) through (k); and
terminating the erasing operation when the erase-on signal has been turned OFF in all sectors of said plurality of sectors.
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Accused Products
Abstract
A unified erase method used in an array of flash EEPROM memory cells arranged in a plurality of sectors for performing either a single-sector, multiple-sector, or all-sector erasing operation with a reduced amount of total erase time and a uniform VT distribution as good as that of a single-sector erase operation is provided. An erase-verify operation is performed sequentially on the plurality of sectors from a first sector to a last sector beginning with a first address of each sector if its corresponding erase-on signal is not turned OFF. The current address of each sector is stored at a point where the erase-verify operation failed. An erase pulse is applied only to all sectors simultaneously that have not passed the erase-verify operation. The erase-verify operation is then repeated beginning at the current address stored. The erasing operation is terminated when the erase-on signal has been turned OFF in all sectors in the plurality of sectors.
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Citations
12 Claims
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1. A unified erase method used in an array of flash EEPROM memory cells arranged in a plurality of sectors for performing either a single-sector, multiple-sector, or all-sector erasing operation with a reduced amount of total erase time, said erase method comprising the steps of:
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turning an erase-signal ON in only certain ones of said plurality of sectors which are required to be erased;
programming initially all bytes in said certain ones of said plurality of sectors which are required to be erased;
setting current address in said certain ones of said plurality of sectors which are required to be erased to a first address;
(a) determining whether a first sector of said plurality of sectors has its erase-on signal turned OFF;
(b) bypassing said first sector if said erase-on signal is turned OFF and proceeding to a second sector of said plurality of sectors;
(c) determining whether the current address has been erased if said erase-on signal is not turned OFF;
(d) proceeding to the second sector of said plurality of sectors if the current address has not been erased and storing in an address register the current address;
(e) determining whether the current address is the last address of said first sector if the current address has been erased;
(f) increasing the current address by one if the current address is not the last address and repeating steps (c)-(e);
(g) turning OFF said erase-on signal if the current address is the last address and proceeding to the second sector of said plurality of sectors;
repeating steps (a) through (g) for the remaining sectors of said plurality of sectors except for a last sector;
determining whether the last sector of said plurality of sectors has its erase-on signal turned OFF;
determining whether the erase-on signal for all sectors of said plurality of sectors are turned OFF if the last sector has its erase-on signal turned OFF;
(i) determining whether the current address of the last sector has been turned OFF if said erase-on signal is not turned OFF;
(j) storing current address in an address register if the current address is not erased;
(k) determining whether the current address is a last address of said last sector if the current address has been erased;
increasing the current address by one if the current address is not the last address and repeating steps (i) through (k);
turning OFF said erase-on signal if the current address is the last address;
applying an erase pulse to all bytes in all sectors simultaneously in which the erase-on signals have not been turned OFF if the current address of the last sector has not been erased or if the erase-on signal for all sectors have not been turned OFF and repeating steps (a) through (k); and
terminating the erasing operation when the erase-on signal has been turned OFF in all sectors of said plurality of sectors. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A unified erase method used in an array of flash EEPROM memory cells arranged in a plurality of sectors for performing either a single-sector, multiple-sector, or all-sector erasing operation with a reduced amount of total erase time, said erase method comprising the steps of:
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selectively turning ON an erase-on signal in only certain ones of said plurality of sectors which are required to be erased;
programming initially all bytes in said certain ones of said plurality of sectors which are required to be erased;
setting current address in said certain ones of said plurality of sectors which are required to be erased to a first address;
determining whether each sector of said plurality of sectors has its corresponding erase-on signal turned OFF;
sequentially performing an erase-verify operation on said plurality of sectors from a first sector to a last sector beginning with the first address of said sector if its said corresponding erase-on signal is not turned OFF;
turning OFF said corresponding erase-on signal for each sector that has passed the erase-verify operation;
storing current address of each sector at a point where the erase-verify operation failed;
applying an erase pulse simultaneously to all sector that has not passed the erase-verify operation and repeating the erase-verify operation beginning at the current address stored; and
terminating the erasing operation when the erase-on signal has been turned OFF in all sectors of said plurality of sectors. - View Dependent Claims (9, 10, 11, 12)
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Specification