Patent ID: 6842379

Claim:
In a digital memory system including a memory cell arranged to store charge corresponding to a first logical value when the quantity of stored charge lies within a first range of values and corresponding to a second logical value when the quantity of stored charges lies within a second range of values, the cell being arranged to store a predetermined one of the first and second logical values in response to a range of operating voltages received by the cell, apparatus for controlling the logical value and the integrity of the data represented by the charge comprising: a bit line coupled to the cell; a voltage generator arranged to generate a plurality of cell operating voltages varying from a first voltage to a second voltage in response to a voltage control signal, the first voltage being lower in value than the second voltage; and a controller arranged to generate the control signal and arranged to store a predetermined one of the logical values in the cell by generating a series of the operating voltages beginning with the first voltage and continuing with successively larger operating voltages greater than the first voltage, to transmit to the cell from the voltage generator the series of operating voltages, after each transmittal of one of the series of operating voltages to determine whether the predetermined one of the logical values has been stored in the cell in response to voltage on the bit line, and to terminate transmittal of the series of operating voltages to the cell in the event that the predetermined one of the logical states has been stored or in the event that one of the series of successively larger operating voltages equals the second voltage, the controller comprising a charge integrity estimating module operative during a first mode of operation to detect whether the quantity of the charge lies within the first range of values or the second range of values, operative during a second mode of operation to detect whether the quantity of the charge lies within a third range of values comprising a subset of the first range of values and operative during a third mode of operation to detect whether the quantity of the charge lies within a fourth range of values comprising a subset of the second range of values, wherein the controller determines whether the predetermined one of the logical values has been stored in the cell by initiating the operation of the charge integrity estimating module.