Systems and methods are provided for determining optimal read reference voltages used for reading data in non-volatile storage devices. A method may include reading data stored in a non-volatile storage device using a group of soft read reference voltages, decoding the data and obtaining the number of ones and number of zeros for each of a plurality of zones delineated by the soft read reference voltages, determining that one of the soft read reference voltages is a boundary of a zone in which a comparison result of the number of ones compared to the number of zeros is greater than zero and a boundary of another zone in which a comparison result is less than zero and setting the soft read reference voltage adjusted by an adjustment as an optimal read reference voltage. The adjustment may be obtained based on the two comparison results.

A memory system includes: a semiconductor memory device; and a controller. When receiving the first read instruction, the semiconductor memory device issues a strobe signal at a first timing to read data from the first memory cell and the second memory cell. When receiving the second read instruction, the semiconductor memory device sets the first memory cell to a non-read target and reads data from the second memory cell based on a strobe result of the data at the first timing.

During a phase of programming the cell, a first voltage is applied to the source region and a second voltage, higher than the first voltage, is applied to the drain region until the cell is put into conduction. The numerical value of the item of data to be written is controlled by the level of the control voltage applied to the control gate and the item of data is de facto written with the numerical value during the putting into conduction of the cell. The programming is then stopped.

During a phase of programming the cell, a first voltage is applied to the source region and a second voltage, higher than the first voltage, is applied to the drain region until the cell is put into conduction. The numerical value of the item of data to be written is controlled by the level of the control voltage applied to the control gate and the item of data is de facto written with the numerical value during the putting into conduction of the cell. The programming is then stopped.

During a phase of programming the cell, a first voltage is applied to the source region and a second voltage, higher than the first voltage, is applied to the drain region until the cell is put into conduction. The numerical value of the item of data to be written is controlled by the level of the control voltage applied to the control gate and the item of data is de facto written with the numerical value during the putting into conduction of the cell. The programming is then stopped.

Methods and apparatus are provided for adaptive read threshold voltage tracking with gap estimation between default read threshold voltages. A read threshold voltage for a memory is adjusted by estimating a gap between two adjacent default read threshold voltages; determining statistical characteristics of two adjacent memory levels based at least in part on a type of statistical distribution of the memory levels, a distribution of data values read from one or more cells using a plurality of read threshold voltages and the gap; computing an adjusted read threshold voltage associated with the two adjacent memory levels by using the statistical characteristics of the two adjacent memory levels; and updating the read threshold voltage with the adjusted read threshold voltage. The adjustment is optionally performed responsive to one or more read errors.