Method for refreshing memory device where control circuit performs first refresh operation on first group and performs second refresh operation on victim row of second group without external command for victim row refresh

A method for refreshing a memory device, wherein the memory device comprises a plurality of memory banks, the method comprising:

• dividing the memory banks at least into a first group and a second group;
• performing a first refresh operation on one of the first group and the second group;
• and
• simultaneously performing a second refresh operation on a victim row of the other one of the first group and the second group,
• wherein after the first refresh operation is performed on one of the first group and the second group in response to an auto-refresh command, performing the second refresh operation on the victim row of the other one of the first group and the second group after a row precharge time,
• wherein dividing the memory banks at least into the first group and the second group further includes dividing the first group at least into a first sub-group and a second sub-group, and
• wherein after the first refresh operation is performed on one of the first sub-group and the second sub-group, performing the second refresh operation on the victim row of any one of the first sub-group and the second sub-group after the row precharge time.