Method and circuitry for performing analog over-program and under-program detection for a multistate memory cell

A memory device comprising:

• an array of memory cells each adapted to store two bits of data;
• three sense amplifiers coupled to the array to sense the data stored on the memory cells;
• reference circuitry coupled to the three sense amplifiers to provide three reference voltages;
• and
• control circuitry coupled to the reference circuitry to control the reference circuitry to provide first reference voltages for a read operation, second reference voltages for an over program operation, and third reference voltages for an under program operation.

A method of storing data in a memory cell adapted to store multiple bits of data, the method comprising:

• programming the memory cell to a desired state;
• reading the memory cell to generate a first data signal;
• generating a first set of reference voltages;
• comparing the first data signal with the first set of reference voltages to determine if the memory cell is under programmed, and programming the memory cell again to the desired state if the memory cell is under programmed;
• generating a second set of reference voltages;
• reading the memory cell to generate a second data signal;
• and
• comparing the second data signal with the second set of reference voltages to determine if the memory cell is over programmed.

A non-volatile memory device comprising:

• an array of memory cells each adapted to store multiple bits of data;
• a plurality of sense amplifiers coupled to the array for sensing the data stored on the memory cells;
• and
• means for providing reference voltages to the plurality of sense amplifiers, such that first reference voltages are provided for a read operation, second reference voltages are provided for an over program operation, and third reference voltages are provided for an under program operation.

A memory device comprising:

• an array of multi-state memory cells, each cell being connected to a data line to provide a read signal on the data line;
• three sense amplifiers coupled to each data line to sense the read signal on the data line;
• and
• means for providing first reference voltages for a read operation, second reference voltages for an over program operation, and third reference voltages for an under program operation to the three sense amplifiers.

A method comprising:

• programming a multi-state flash memory cell to a desired one of a lowest threshold voltage defined below a lowest maximum threshold voltage, a highest threshold voltage defined above a highest minimum threshold voltage, and a plurality of intermediate threshold voltages, each intermediate threshold voltage being defined between a maximum threshold voltage and a minimum threshold voltage;
• performing an under-programming verification operation comprising:
• generating a plurality of first reference signals corresponding to, respectively, current in a multi-state flash memory cell having the highest minimum threshold voltage, and current in multi-state flash memory cells having, respectively, the minimum threshold voltages;
• reading the memory cell to generate a read signal corresponding to a threshold voltage of the memory cell;
• comparing the read signal with each of the first reference signals to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as under-programmed if the threshold voltage of the memory cell is lower than the desired threshold voltage;
• and
• performing an over-programming verification operation comprising:
• generating a plurality of second reference signals corresponding to, respectively, current in a multi-state flash memory cell having the lowest maximum threshold voltage, and current in multi-state flash memory cells having, respectively, the maximum threshold voltages;
• reading the memory cell to generate a read signal corresponding to the threshold voltage of the memory cell;
• comparing the read signal with each of the second reference signals to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as over-programmed if the threshold voltage of the memory cell is higher than the desired threshold voltage.

A method comprising:

• programming a multi-state flash memory cell to a desired one of a lowest threshold voltage defined below a lowest maximum threshold voltage, a highest threshold voltage defined above a highest minimum threshold voltage, and a plurality of intermediate threshold voltages, each intermediate threshold voltage being defined between a maximum threshold voltage and a minimum threshold voltage;
• performing an under-programming verification operation comprising:
• generating a plurality of reference signals corresponding to, respectively, current in a multi-state flash memory cell having the highest minimum threshold voltage, and current in multi-state flash memory cells having, respectively, the minimum threshold voltages;
• reading the memory cell to generate a read signal corresponding to a threshold voltage of the memory cell;
• comparing the read signal with each of the reference signals to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as under-programmed if the threshold voltage of the memory cell is lower than the desired threshold voltage.

A method comprising:

• programming a multi-state flash memory cell to a desired one of a lowest threshold voltage defined below a lowest maximum threshold voltage, a highest threshold voltage defined above a highest minimum threshold voltage, and a plurality of intermediate threshold voltages, each intermediate threshold voltage being defined between a maximum threshold voltage and a minimum threshold voltage;
• performing an over-programming verification operation comprising:
• generating a plurality of reference signals corresponding to, respectively, current in a multi-state flash memory cell having the lowest maximum threshold voltage, and current in multi-state flash memory cells having, respectively, the maximum threshold voltages;
• reading the memory cell to generate a read signal corresponding to a threshold voltage of the memory cell;
• comparing the read signal with each of the reference signals to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as over-programmed if the threshold voltage of the memory cell is higher than the desired threshold voltage.

A method comprising:

• programming a multi-state flash memory cell to a desired threshold voltage defined between a maximum threshold voltage and a minimum threshold voltage;
• performing an under-programming verification operation comprising:
• generating a first reference signal corresponding to current in a multi-state flash memory cell having the minimum threshold voltage;
• reading the memory cell to generate a read signal corresponding to a threshold voltage of the memory cell;
• comparing the read signal with the first reference signal to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as under-programmed if the threshold voltage of the memory cell is lower than the minimum threshold voltage;
• and
• performing an over-programming verification operation comprising:
• generating a second reference signal corresponding to current in a multi-state flash memory cell having the maximum threshold voltage;
• reading the memory cell to generate a read signal corresponding to the threshold voltage of the memory cell;
• comparing the read signal with the second reference signal to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as over-programmed if the threshold voltage of the memory cell is higher than the maximum threshold voltage.

A method comprising:

• programming a multi-state flash memory cell to a desired threshold voltage defined between a maximum threshold voltage and a minimum threshold voltage;
• and
• performing an under-programming verification operation comprising:
• generating a reference signal corresponding to current in a multi-state flash memory cell having the minimum threshold voltage;
• reading the memory cell to generate a read signal corresponding to a threshold voltage of the memory cell;
• comparing the read signal with the reference signal to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as under-programmed if the threshold voltage of the memory cell is lower than the minimum threshold voltage.

A method comprising:

• programming a multi-state flash memory cell to a desired threshold voltage defined between a maximum threshold voltage and a minimum threshold voltage;
• and
• performing an over-programming verification operation comprising:
• generating a reference signal corresponding to current in a multi-state flash memory cell having the maximum threshold voltage;
• reading the memory cell to generate a read signal corresponding to a threshold voltage of the memory cell;
• comparing the read signal with the reference signal to determine the threshold voltage of the memory cell;
• and
• identifying the memory cell as over-programmed if the threshold voltage of the memory cell is higher than the maximum threshold voltage.

A method comprising:

• programming a multi-state memory cell to a desired state defined between a maximum and a minimum;
• performing an under-programming verification operation comprising:
• generating a first reference signal corresponding to the minimum;
• reading the memory cell to generate a read signal corresponding to a state of the memory cell;
• comparing the read signal with the first reference signal to determine the state of the memory cell;
• and
• identifying the memory cell as under-programmed if the state of the memory cell is lower than the minimum;
• and
• performing an over-programming verification operation comprising:
• generating a second reference signal corresponding to the maximum;
• reading the memory cell to generate a read signal corresponding to the state of the memory cell;
• comparing the read signal with the second reference signal to determine the state of the memory cell;
• and
• identifying the memory cell as over-programmed if the state of the memory cell is higher than the maximum.

A method comprising:

• programming a multi-state memory cell to a desired state defined between a maximum and a minimum;
• and
• performing an under-programming verification operation comprising:
• generating a reference signal corresponding to the minimum;
• reading the memory cell to generate a read signal corresponding to a state of the memory cell;
• comparing the read signal with the reference signal to determine the state of the memory cell;
• and
• identifying the memory cell as under-programmed if the state of the memory cell is lower than the minimum.

A method comprising:

• programming a multi-state memory cell to a desired state defined between a maximum and a minimum;
• and
• performing an over-programming verification operation comprising:
• generating a reference signal corresponding to the maximum;
• reading the memory cell to generate a read signal corresponding to a state of the memory cell;
• comparing the read signal with the reference signal to determine the state of the memory cell;
• and
• identifying the memory cell as over-programmed if the state of the memory cell is higher than the maximum.

A method comprising:

• programming a multi-state flash memory cell to hold a threshold voltage representing a unique data value and being located between an upper threshold voltage and a lower threshold voltage;
• performing an under-programming verification operation on the cell comprising:
• setting a first reference signal to correspond to the lower threshold voltage;
• reading the cell to generate a read signal corresponding to a data value stored in the cell;
• comparing the read signal with the first reference signal to determine the data value stored in the cell;
• and
• comparing the data value stored in the cell with the data value programmed to determine if the cell is under-programmed;
• and
• performing an over-programming verification operation on the cell comprising:
• setting a second reference signal to correspond to the upper threshold voltage;
• reading the cell to generate a read signal corresponding to the data value stored in the cell;
• comparing the read signal with the second reference signal to determine the data value stored in the cell;
• and
• comparing the data value stored in the cell with the data value programmed to determine if the cell is over-programmed.

A method comprising:

• programming a multi-state flash memory cell to hold a threshold voltage representing a unique data value and being located between an upper threshold voltage and a lower threshold voltage;
• and
• performing an under-programming verification operation on the cell comprising:
• setting a reference signal to correspond to the lower threshold voltage;
• reading the cell to generate a read signal corresponding to a data value stored in the cell;
• comparing the read signal with the reference signal to determine the data value stored in the cell;
• and
• comparing the data value stored in the cell with the data value programmed to determine if the cell is under-programmed.

A method comprising:

• programming a multi-state flash memory cell to hold a threshold voltage representing a unique data value and being located between an upper threshold voltage and a lower threshold voltage;
• and
• performing an over-programming verification operation on the cell comprising:
• setting a reference signal to correspond to the upper threshold voltage;
• reading the cell to generate a read signal corresponding to a data value stored in the cell;
• comparing the read signal with the reference signal to determine the data value stored in the cell;
• and
• comparing the data value stored in the cell with the data value programmed to determine if the cell is over-programmed.