Non-volatile semiconductor memory device and method for reading the same

A circuit for reading data from a non-volatile semiconductor memory device comprising a plurality of memory cells, the circuit comprising:

• a first current generation circuit of generating a first verification reference current used for erase verification of the memory cell;
• a second current generation circuit of generating a second verification reference current used for write verification of the memory cell;
• a first current supply circuit of supplying a read current as a first current to the memory cell to be read;
• a second current supply circuit of supplying a second current based on the first verification reference current and the second verification reference current;
• and
• a comparison section of calculating data stored in the memory cell to be read, depending on whether the first current is larger than, smaller than, or equal to the second current.

A method for reading data, in a non-volatile semiconductor memory device comprising a plurality of memory cells and a plurality of reference cells, from the memory cell set in one of at least two states, wherein

• a first reference cell is set so that a read current thereof coincides with a maximum or minimum value of a read current of the memory cell set in a first state, and
• a second reference cell is set so that a read current thereof coincides with a maximum or minimum value of a read current of the memory cell set in a second state,
• the method comprising the steps of:
• obtaining a read current of the memory cell to be read as a first current;
• obtaining a second current based on the read current of the first reference cell and the read current of the second reference cell;
• and
• calculating data stored in the memory cell to be read, depending on whether the first current is larger than, smaller than, or equal to the second current.

A method for reading data, in a non-volatile semiconductor memory device comprising a plurality of memory cells and a plurality of reference cells, from the memory cell set in one of at least three states, wherein

• a first one of the reference cells is set so that a read current thereof coincides with a maximum or minimum value of a read current of the memory cell set in a first state,
• a second one of the reference cells is set so that a read current thereof coincides with a maximum or minimum value of a read current of the memory cell set in a second state, and
• the remaining reference cell or cells are set so that a read current thereof coincides with a predetermined value,
• the method comprising the steps of:
• obtaining a read current of the memory cell to be read as a first current;
• obtaining a second current based on the read current of the first reference cell and the read current of the second reference cell;
• obtaining a third current based on read currents of two of the reference cells other than the first reference cell;
• calculating a first comparison result, depending on whether the first current is larger than, smaller than, or equal to the second current;
• calculating a second comparison result, depending on whether the first current is larger than, smaller than, or equal to the third current;
• and
• calculating data stored in the memory cell to be read based on the first comparison result and the second comparison result.

A circuit for reading data from a non-volatile semiconductor memory device comprising a plurality of memory cells, the circuit comprising:

• a first reference cell set so that a read current thereof coincides with a maximum or minimum value of a read current of the memory cell set in a first state;
• a second reference cell set so that a read current thereof coincides with a maximum or minimum value of a read current of the memory cell set in a second state;
• a first current supply circuit of supplying a read current as a first current to the memory cell to be read;
• a second current supply circuit of supplying a second current based on the read current of the first reference cell and the read current of the second reference cell;
• and
• a comparison section of calculating data stored in the memory cell to be read, depending on whether the first current is larger than, smaller than, or equal to the second current.

A method for reading data, in a non-volatile semiconductor memory device comprising a plurality of memory cells and a plurality of reference cells, from the memory cell, wherein

• the memory cells are divided into a first type such that the memory cell is set to be one of at least four states on a block-by-block basis, and a second type such that the memory cell is set to be one of at least two states,
• each memory cell block is associated with at least four reference cells,
• the first to fourth reference cells of the first type memory cell are set so that respective read currents coincide with a maximum or minimum value of a read current of a memory cell set in one of the four states,
• the first and third reference cells of the second type memory cell are set so that respective read currents coincide with a maximum or minimum value of a read current of a memory cell set in one of the two states, and
• the second and fourth reference cells of the second type memory cell are set so that respective read currents coincide with a maximum or minimum value of a read current of a memory cell set in the other of the two states,
• the method comprising the steps of:
• obtaining a read current of the memory cell to be read as a first current;
• obtaining a second current based on the read current of the first reference cell and the read current of the second reference cell;
• obtaining a third current based on the read current of the second reference cell and the read current of the third reference cell;
• obtaining a fourth current based on the read current of the third reference cell and the read current of the fourth reference cell;
• and
• calculating data stored in the memory cell to be read, depending on whether the first current is larger than, smaller than, or equal to the second to fourth currents.