Method of establishing reference levels for sensing multilevel memory cell states
US6618297B1 · kind B1 · utility
Assignee
Inventor
Key dates
| Filing date | Aug 2, 2002 |
| Grant date | Sep 9, 2003 |
| Priority date | — |
| Expiry date | Aug 2, 2022 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG11C2211/5645
- WIPO fieldComputer technology
- WIPO sectorElectrical engineering
Abstract
In order to establish boundary current levels for more than two memory states, a circuit is provided that uses reference currents defining the center of each state. The reference currents are defined by multiple pre-programmed reference memory cells or by a single reference memory cell together with a current mirror that sets the other reference currents at specified proportions of a first reference current. With these reference currents, an analog circuit block generates fractional currents at (1−m) and m of the reference currents, where m is a specified margin value equal to 50% for read operations and less than 50% for program verify operations, then combines fractional currents for adjacent states to produce the boundary current levels. The fractional currents may be obtained with pairs of current mirrors biased by sense amplifiers for the various reference currents.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.