Multibit-per-cell non-volatile memory with error detection and correction
US5909449A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 8, 1997 |
| Grant date | Jun 1, 1999 |
| Priority date | — |
| Expiry date | Sep 8, 2017 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11C2211/5634
- WIPO fieldMeasurement
- WIPO sectorInstruments
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.