Read circuit which uses a coarse-to-fine search when reading the

Details Read circuit which uses a coarse-to-fine search when reading the Read circuit which uses a coarse-to-fine search when reading the

1996-03-26

1998-05-05

Nelms, David C.

Static information storage and retrieval

Floating gate

Particular biasing

36518503, 36518523, 36523006, G11C 1134

Patent

active

057485330

ABSTRACT:
A read circuit includes a driver which changes a gate voltage of a memory cell and a sense circuit which identifies when the memory cell trips. The driver searches for the threshold voltage of the memory cell using stages which ramp up gate voltage and stages which ramp down the gate voltage. Each stage ends when the sense circuit senses that the memory cell trips, i.e. begins or stops conducting. Initial stages of the search have high ramp rates so that the gate voltage reaches the threshold voltage. These initial stages can give inaccurate threshold voltage readings because high ramp rates change the gate voltage during the period between the transistor tripping and sensing the trip. Later stages ramp the gate voltage slowly to provide an accurate threshold voltage reading. The low ramp rate of the last stage provides accuracy, and the high ramp rate of the initial stages reduces read time. To further reduce read time, the search process can begin at a median voltage for possible threshold voltages.

REFERENCES:
patent: 5128895 (1992-07-01), Park
patent: 5487033 (1996-01-01), Keeney et al.

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