Patent ID: 7362618

Claim:
A method of operating a memory system having data memory cells for storing multi-level data values, said method comprising the steps of: causing a charge representative of one of said data values to be stored in each of a plurality of said data memory cells, each having first and second terminals and a charge storage element for storing said charge, said stored charge determining a conductivity value measured between said first and second terminals, including: applying appropriate voltage conditions in parallel to the plurality of said data memory cells, thereby to alter the charge stored on said plurality of data memory cells, determining the conductivity value ranges in which individual ones of said plurality of data memory cells lies, and terminating said application of appropriate voltage conditions to individual ones of said plurality of data memory cells upon their being determined to have reached desired conductivity value ranges while continuing to apply said appropriate voltage conditions to others of said plurality of data cells until all of the plurality of data cells are determined to have reached their desired conductivity value ranges; and causing each of a plurality of predetermined charges to be stored in a corresponding one of a plurality of reference memory cells, each reference memory cell having first and second terminals, and a charge storage element for storing said charge, said stored charge determining a conductivity value measured between said first and second terminals of that reference memory cell, wherein said data memory cells are read using said reference memory cells.