| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To cope with a fact that the threshold voltage distribution can change in a memory element group. <P>SOLUTION: A threshold voltage distribution of a set of storage elements in a memory device is measured by sweeping a control gate voltage while measuring a characteristic of the set of storage elements as a whole. The characteristic indicates how many of the storage elements meet a given condition, such as being in a conductive state. For example, the characteristic may be a combined current, voltage or capacitance of the set which is measured at a common source of the set. The control gate voltage can be generated internally within a memory die. Similarly, the threshold voltage distribution can be determined internally within the memory die. Optionally, storage elements which become conductive can be locked out, such as by changing a bit line voltage, so they no longer contribute to the characteristic. New read reference voltages are determined based on the threshold voltage distribution to reduce errors in future read operations. <P>COPYRIGHT: (C)2009,JPO&INPIT</p> |
