US Patent 7450427 Non-volatile semiconductor memory device

A non-volatile semiconductor memory device includes a memory cell, and a reference cell including a same structure as the memory cell. A detecting circuit detects a timing when a voltage of a reference bit line connected with the reference cell becomes lower than or equal to a setting voltage, and generates a control signal in response to the detection of the timing. A sense amplifier senses and amplifies a difference between a voltage of a bit line connected with the memory cell and a reference voltage in response to the control signal.