Method and apparatus for sensing the state of floating gate memo

Details Method and apparatus for sensing the state of floating gate memo Method and apparatus for sensing the state of floating gate memo

1994-09-29

1996-04-16

Nelms, David C.

Static information storage and retrieval

Floating gate

Particular biasing

365168, G11C 700

Patent

active

055089585

ABSTRACT:
A method and apparatus for sensing the state of floating gate memory cells in a memory array. Because of its stability and accuracy, the sensing apparatus may be used for sensing the state of multi-bit floating gate memory cells. The state of a memory cell is sensed by applying a variable gate voltage to the top gate of the floating gate memory cell and comparing the cell current to a fixed reference current. A circuit detects when the cell current is equal to the reference current. When the currents are equal, the value of the variable gate voltage indicates the state of the memory cell. For one embodiment, an analog-to-digital converter converts the variable gate voltage to a digital value that is latched when the currents are equal. The latched digital value indicates the state of the memory cell. For this embodiment, a ramp voltage or other suitable variable voltage may be used as the variable gate voltage. For another embodiment, a digital-to-analog converter is used to generate the variable gate voltage. A counter generates digital values to step the variable gate voltage. When the cell current equals the fixed reference current, the digital counter value is latched to indicate the state of the memory cell.

REFERENCES:
patent: 5043940 (1991-08-01), Harari
patent: 5163021 (1992-11-01), Mehrotra et al.
patent: 5270979 (1993-12-01), Harari et al.
patent: 5394359 (1995-02-01), Kowalski
patent: 5394362 (1995-02-01), Banks

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