| 摘要 |
Innovative self-adaptive and self-calibrated methods and structures for Multi-Level Cell (MLC) Non-Volatile Memory (NVM) are disclosed. In the MLC NVM, NVM cells are self-adaptively programmed into a fixed response tolerance window centered at the reference current or voltage corresponding to a selected level gate voltage applied to the controlled gates of NVM cells. The fixed response tolerance window is related to the threshold voltage tolerance window through the sense circuit gain. Properly choosing the sense circuit gain and the response window can control the threshold voltage tolerance window to a desired value. An incremental gate voltage larger than the threshold voltage tolerance window of each NVM cell will guarantee that each NVM cell will produce the correct output current (voltage) in response to applying to the control gate of the NVM cell the stepped voltage corresponding to the level of information stored in the NVM cell. As the stepped voltage applied to the gate of an NVM cell transitions from a voltage just below the threshold voltage of the NVM cell to a voltage corresponding to the threshold voltage of the NVM cell, the output current (voltage) from the NVM cell will pass the current (voltage) transition in comparison with the reference current (voltage). The current (voltage) transition can be detected and converted into the bit-word information representing the voltage level stored in the NVM cell. When the response of an NVM cell falls outside the response tolerance window into the guard-band regions, the NVM cell can be re-calibrated and the bit-word information can be saved from fading away.
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