| 摘要 |
A virtual ground array based flash memory device includes a virtual ground array containing individual memory elements with supporting input/output circuitry. Variations occur in the threshold voltage of memory elements contained in the virtual ground array caused by excessive usage of the memory elements. Characterization of the variation of threshold voltage as a function of usage as well as the distribution of the various threshold voltages is important for diagnostic purposes. External sources of voltage and means of determination are necessary to characterize the threshold voltages and the I-V characteristics, when the virtual ground array is in a diagnostic mode. In this mode, the drains, sources, and gates of selected memory elements in the virtual ground array may be under independent external control. The current from the source of the selected memory element is determined in response to the externally controlled voltages, thereby creating an I-V curve. Operational elements contained in input/output multiplexors to the virtual ground array pass externally controlled near ground voltages to the selected memory element. The present arrangement and method of characterizing selected memory elements in the virtual ground array using the source side of the memory elements saves time, conserves power, and is a useful diagnostic tool.
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