SEMICONDUCTOR MEMORY DEVICE WHICH STORES MULTIVALUED DATA
First Claim
1. A semiconductor memory device comprising:
- a memory which includes a plurality of memory cells, each of which stores data when one of an n number of threshold voltages (n being a natural number not less than two) is set; and
a controller which reads data from the memory and whichreads data from the memory cells at each of the threshold voltages in a read operation that checks a distribution of threshold voltages of the memory cells,calculates difference data on data read at each of the threshold voltages,calculates a minimum value of the distribution of the threshold voltages from the difference data,calculates a range of threshold voltages lower than the minimum value based on the minimum value, andsets a central voltage in the calculated range of threshold voltages as a read voltage.
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Abstract
According to one embodiment, a semiconductor memory device includes a memory and a controller. The memory includes a plurality of memory cells each of which stores data when one of an n number of threshold voltages (n being a natural number not less than two) is set. The controller reads data from the memory. The controller reads data from the memory cells at each of the threshold voltages in a read operation that checks a distribution of threshold voltages of the memory cells, calculates difference data on data read at each of the threshold voltages, calculates a minimum value of the distribution of the threshold voltages from the difference data, calculates a range of threshold voltages lower than the minimum value based on the minimum value, and sets a central voltage in the calculated range of threshold voltages as a read voltage.
51 Citations
20 Claims
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1. A semiconductor memory device comprising:
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a memory which includes a plurality of memory cells, each of which stores data when one of an n number of threshold voltages (n being a natural number not less than two) is set; and a controller which reads data from the memory and which reads data from the memory cells at each of the threshold voltages in a read operation that checks a distribution of threshold voltages of the memory cells, calculates difference data on data read at each of the threshold voltages, calculates a minimum value of the distribution of the threshold voltages from the difference data, calculates a range of threshold voltages lower than the minimum value based on the minimum value, and sets a central voltage in the calculated range of threshold voltages as a read voltage. - View Dependent Claims (2, 3, 4, 5)
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6. A semiconductor memory device comprising:
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a memory which includes a plurality of memory cells each of which stores data when one of an n number of threshold voltages (n being a natural number not less than two) is set; and a controller which reads data from the memory and which reads data from the memory cells at each of the threshold voltages in a read operation that checks a distribution of threshold voltages of the memory cells, calculates difference data on data read at each of the threshold voltages, calculates a maximum value of the distribution of the threshold voltages from the difference data, calculates a range of threshold voltages higher than the maximum value based on the minimum value, and sets a central voltage in the calculated range of threshold voltages as a read voltage. - View Dependent Claims (7, 8, 9)
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10. A semiconductor memory device comprising:
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a memory which includes a plurality of memory cells each of which stores data when one of an n number of threshold voltages (n being a natural number not less than two) is set; and a controller which reads data from the memory and which reads data from the memory cells at each of the threshold voltages in a read operation that checks a distribution of threshold voltages of the memory cells, calculates difference data on data read at each of the threshold voltages, performs a first search operation of detecting a threshold voltage corresponding to a maximum value higher than a first threshold value based on the difference data and further detecting threshold voltages which are lower than a second threshold value and correspond to a first and a second minimum value lying on both sides of the maximum value, sets a first and a second bottom region including the first and second minimum values based on the threshold values corresponding to the first and second minimum values detected in the first search operation and performing a second search operation, and detects threshold voltages corresponding to minimum values of a first and a second threshold voltage from the central positions of the first and second bottom regions. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification