NAND Flash Memory Valley Voltage Scanning for Read Accuracy

The patent applies preliminary action by performing a scanning operation before the actual read operation to determine the valley voltage. The controller scans the memory cells to obtain threshold voltage distribution information, identifies the valley voltage, and then uses this pre-determined voltage for the subsequent read operation. This preliminary scanning and voltage determination step ensures that the read operation uses the most accurate reference voltage, thereby improving reading accuracy while managing the added complexity through automation.

The patent implements self-service by enabling the memory system to automatically adapt to threshold voltage changes without external intervention. The controller autonomously performs scanning operations to detect threshold voltage distribution, automatically determines the valley voltage, and adjusts the read reference voltage accordingly. This self-adjusting mechanism ensures high reading reliability under varying conditions (read disturbance, temperature changes, baking) while minimizing time loss by eliminating the need for manual calibration or external voltage adjustment.

The patent applies partial action by performing scanning operations selectively rather than continuously. The controller scans memory cells to determine valley voltage primarily when threshold voltage changes are detected or suspected (e.g., after write operations, temperature changes, or baking processes). For routine read operations where threshold voltage stability is confirmed, the system uses previously determined valley voltages without performing new scanning. This selective scanning approach maintains high reference voltage accuracy while significantly reducing the time penalty associated with continuous scanning.