Method and apparatus for erasing an array of electrically erasable programmable read only memory cells
First Claim
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1. An apparatus for erasing memory cells while preventing overerasure of the cells comprising:
- a memory cell having a gate, a drain, a source, and a floating gate from which charge must be removed by placing a potential thereacross to erase said memory cell;
an erase node for applying said potential across said floating gate;
a stop transistor having a gate directly coupled to said drain of said memory cell, a source, and a drain directly coupled to said erase node, said stop transistor preventing overerasure of said memory cell when a threshold voltage is reached on said gate of said stop transistor; and
a resistive element having a first terminal coupled to said drain of said stop transistor and a second terminal.
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Abstract
An apparatus and method of erasing memory cells while preventing overerasure of the memory cells is disclosed. By applying a large voltage across the floating gate of the memory cells, charge is removed from the floating gate. Once sufficient charge is removed from the floating gates of the memory cells to render them erased, a stop transistor halts the erasure process, thus preventing the overerasure of memory cells.
15 Citations
19 Claims
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1. An apparatus for erasing memory cells while preventing overerasure of the cells comprising:
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a memory cell having a gate, a drain, a source, and a floating gate from which charge must be removed by placing a potential thereacross to erase said memory cell; an erase node for applying said potential across said floating gate; a stop transistor having a gate directly coupled to said drain of said memory cell, a source, and a drain directly coupled to said erase node, said stop transistor preventing overerasure of said memory cell when a threshold voltage is reached on said gate of said stop transistor; and a resistive element having a first terminal coupled to said drain of said stop transistor and a second terminal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for erasing memory cells while preventing overerasure comprising:
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memory cells, each having a gate, a drain, a source, and a floating gate from which charge must be removed by placing a potential thereacross to erase said cell, said cells connected in parallel columns and parallel rows which are orthogonal to said columns; an erase node associated with each memory cell for applying said potential across the floating gate of said memory cell; source lines, each coupled to the source of each cell in a column; drain lines, each coupled to the drain of each cell in a column; gate lines, each coupled to the gate of each cell in a row; erase lines, each directly coupled to said erase node of each cell in a column; stop transistors, each associated with one column and having a gate directly coupled to the drain line of said column, a source, and a drain coupled to the erase line associated with said column; and resistive elements, each associated with one stop transistor and having a first terminal coupled to the drain of said stop transistor and a second terminal. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A method for erasing a memory cell in a memory device while preventing overerasure, the memory device comprising the memory cell having a gate, a drain, a source, a floating gate from which charge must be removed by placing a potential thereacross to erase the cell, an erase node for applying the potential across the floating gate, a stop transistor having a gate directly coupled to the drain of the memory cell, a source and a drain directly coupled to the erase node, and a resistive element having a first terminal directly coupled to the drain of the stop transistor and a second terminal, the method comprising the steps of:
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applying a first voltage to the source of the memory cell; applying a second voltage to the source of the stop transistor; applying ground potential to the gate of the memory cell; applying a third voltage to the second terminal of the resistive element, said third voltage causing a voltage to be induced at the drain of the memory cell; activating the stop transistor with said induced voltage; and forcing a voltage drop across the resistive element, said voltage drop causing erasing of the memory cell to stop. - View Dependent Claims (16, 17, 18, 19)
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Specification