| 摘要 |
PURPOSE: A circuit for preventing over-erase is provided to detect the level variation of a threshold voltage of a flash cell during erase operation to prevent over-erase when the threshold voltage falls below a predetermined level. CONSTITUTION: The circuit includes a reference voltage selector(1), a comparator(2) and a source controller(3). The reference voltage selector selects the reference voltage of a predetermined level and outputs the reference voltage. The comparator compares the reference voltage selected at the reference voltage selector with a drain voltage of the flash cell. The source controller controls the voltage applied on a source node of the flash cell based on a source control signal and the output of the comparator and prevents the over-erase of the flash cell based on the output of the comparator. The source control further includes the first inverter, a NAND gate and the second inverter. The NAND gate controls the voltage applied on the source node of the flash cell based on the output of the comparator and the source control signal which is inverted at the first inverter.
|
