Patent ID: 7286414
Filing Date: 2007-10-23
Classification: G11C

Abstract:
1. A non-volatile semiconductor memory device comprising: a plurality of non-volatile memory cells each of which has a threshold voltage representing data of at least two bits, wherein threshold voltages of the plurality of non-volatile memory cells are shiftable among at least three threshold levels which indicate mutually different programming states and which also differ from a threshold level indicating an erase state; parameter generating circuitry generating a first programming reference parameter, a first read reference parameter, a second programming reference parameter, a second read reference parameter, a third programming reference parameter and a third read reference parameter; and sensing/program-verifying circuitry receiving a parameter which represents threshold voltage of one non-volatile memory cell, the first programming reference parameter, the first read reference parameter, the second programming reference parameter, the second read reference parameter, the third programming reference parameter and the third read reference parameter; wherein the first read reference parameter is allocated between a value corresponding to the threshold level indicating the erase state and the first programming reference parameter, the second read reference parameter is allocated between the first programming reference parameter and the second programming reference parameter, and the third read reference parameter is allocated between the second programming reference parameter and the third programming reference parameter, wherein, in a normal read operation, the sensing/program-verifying circuitry generates data of at least two bits represented by the one non-volatile memory cell threshold voltage, and in a verify operation, the sensing/program-verifying circuitry verifies whether the one non-volatile memory cell threshold voltage is shifted to the threshold level indicating a programmed state, and programs the one non-volatile memory cell until it is verified that the one non-volatile memory cell threshold voltage has been shifted to that threshold level, said sensing/program-verifying circuitry time-sharing common circuit components between a normal read operation and a verify operation.