Soft errors handling EEPROM devices
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Accused Products
Abstract
Soft errors occur during normal use of a solid-state memory such as EEPROM or Flash EEPROM. A soft error results from the programmed threshold voltage of a memory cell being drifted from its originally intended level. The error is initially not readily detected during normal read until the cumulative drift becomes so severe that it develops into a hard error. Data could be lost if enough of these hard errors swamps available error correction codes in the memory. A memory device and techniques therefor are capable of detecting these drifts and substantially maintaining the threshold voltage of each memory cell to its intended level throughout the use of the memory device, thereby resisting the development of soft errors into hard errors.
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Citations
42 Claims
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1-34. -34. (canceled)
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35. A method for determining the necessity for refreshing memory cells of a flash memory, comprising:
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providing a first reference current;
providing a second reference current;
measuring a cell current of at least one of the memory cells of the flash memory;
comparing the measured cell current to the first reference current;
comparing the measured cell current to the second reference current; and
refreshing the memory cell when the measured cell current is greater than the first reference current but less than the second reference current, wherein the first reference current represents a low memory cell logic value, and the second reference current represents a high memory cell logic value. - View Dependent Claims (36, 37)
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38. A method for determining the necessity for refreshing memory cells of a flash memory, comprising:
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providing a first reference memory cell;
measuring a current of the first reference memory cell;
providing a second reference memory cell;
measuring a current of the second reference memory cell;
measuring a cell current of one of the memory cells of the flash memory;
comparing the measured cell current to the current of the first reference memory cell;
comparing the measured cell current to the current of the second reference memory cell; and
refreshing the memory cell when the measured cell current is greater than the current of the first reference memory cell but less than the current of the second reference memory cell. - View Dependent Claims (39, 40, 41, 42)
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Specification