Sensing apparatus and method for fetching multi-level cell data

Static information storage and retrieval – Floating gate – Particular biasing

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3651852, 36518503, 365104, 365168, G11C 1626, G11C 1712

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06154390&

ABSTRACT:
A reading circuit for a multibit memory cell in a memory array, the memory cell having a threshold gate voltage within a range of one of a first, second, third and fourth predetermined threshold voltages corresponding respectively to one of four states of two bits stored in the memory cell. The reading circuit includes a circuit to provide a gate voltage to the multibit memory cell during a read cycle, the gate voltage having a first level between the second and third predetermined threshold voltages during a first time interval of the read cycle and a second level between the third and fourth predetermined threshold voltages during a second time interval of the read cycle, sensing circuit coupled to the multibit memory cell which compares current from the multibit memory cell to a first reference current and a second reference current, and produces a first output during the first time interval having a first logic state, if the current from the cell exceeds the first reference current and a second logic state if the current from the cell is less than the first reference current, and produces a second output during the second time interval having a first logic state if the current from the cell is less than the second reference current and greater than the first reference current, and a second logic state if the current from the cell is greater than the first reference current and greater than the second reference current.

REFERENCES:
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Calligaro et al., "Comparative Analysis of Sensing Schemes for Multilevel Non-Volatile Memories" 1996 Innovative Systems in Silicon Conference, pp. 266-273, May 1997.

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