US Patent 7385867 Memory device and operating method thereof

A method of operating a memory device adapted for determining a program/erase state of a memory cell in the memory device. The method includes applying a drain operation voltage to a drain of the memory cell so that the memory cell generates a working voltage. The working voltage is a function of the drain operation voltage. Then, the working voltage to the drain operation voltage is differentiated to obtain a slope of the working voltage to the drain operation voltage. The program/erase state of the memory cell is determined according to the slope.