The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 01, 1999
Filed:
Sep. 08, 1997
Hock C So, Redwood City, CA (US);
Sau C Wong, Hillsborough, CA (US);
Invox Technology, Campbell, CA (US);
Abstract
A multilevel non-volatile memory divides the suitable threshold voltages of memory cells into ranges corresponding to allowed states for storage of data and ranges corresponding to forbidden zones indicating a data error. A read process in accordance automatically checks whether a threshold voltage is in a forbidden zone. In alternative embodiment, a refresh process includes reprogramming the threshold voltage into an allowed state or in the case of a flash memory, reading a sector of the memory, saving data from the sector in a buffer, erasing the sector, and rewriting the data from the buffer back in the sector. Refresh process for the non-volatile memory can be perform in response to detecting a threshold voltage in a forbidden zone, as part of a power-up procedure for the memory, or periodically with a period on the order of days, weeks, or months.