Memory device and its operating method, memory system and operating method thereof

A memory system, comprising:

• one or more memory device, comprising:
• an array of memory cells, including a plurality of memory cells, wherein a preset number of the plurality memory cells form a code word;
• a peripheral circuit coupled to the array of memory cells and configured to:
• obtain a first result corresponding to at least one of the code words at a target read voltage, wherein the first result includes the number of bits which represents the number of bits in at least one of the code words which are flipped in two results of reading at a first read voltage and a second read voltage, and wherein a difference between the first read voltage and the second read voltage is less than a preset voltage;
• adjust the target read voltage in accordance with the first result corresponding to at least one of the code words at the target read voltage;
• obtain a first result corresponding to at least one of the code words at the adjusted read voltage;
• and
• determine a valley voltage in accordance with a plurality of the first results, wherein the valley voltage is a read voltage for performing a read operation on at least one of the code words;
• and
• a memory controller coupled to the memory device and controlling the memory device.

A method for operating a memory device, comprising:

• obtaining a first result corresponding to at least one of code words at a target read voltage, wherein the first result includes a number of bits which represents the number of bits in at least one of the code words which are flipped in two results of reading at a first read voltage and a second read voltage, wherein a difference between the first read voltage and the second read voltage is less than a preset voltage, and wherein the memory device includes an array of memory cells, the array of memory cells includes a plurality of memory cells, and a preset number of the plurality memory cells form a code word;
• adjusting the target read voltage in accordance with the first result corresponding to at least one of the code words at the target read voltage;
• obtaining a first result corresponding to at least one of the code words at the adjusted read voltage;
• and
• determining a valley voltage in accordance with a plurality of the first results, wherein the valley voltage is a read voltage for performing a read operation on at least one of the code words.