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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.

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First Claim