The inventive concept relates to semiconductor memory devices, and more particularly, to a device that refreshes data of a volatile semiconductor memory device, such as a dynamic random access memory.
A volatile semiconductor memory device, such as a dynamic random access memory (DRAM), periodically performs a refresh operation to not lose data stored in memory cells of the DRAM. Typically there are two refresh operation modes for a DRAM—an auto-refresh operation mode and a self-refresh operation mode.
In an auto-refresh operation mode, a DRAM refreshes memory cells in response to an externally applied refresh command In a self-refresh operation mode, a DRAM internally and autonomously refreshes memory cells based on an operation of a refresh counter.
In the case in which a DRAM is used in a cellular phone, an application processor AP for a digital TV or a chip for a FRC (frame rate control), the DRAM may be used to provide a memory area for a frame buffer processing image data. Since image data is temporarily stored in the frame buffer memory area and a frame rate is faster than a refresh rate of the DRAM, image data stored in the frame buffer memory area does not need to become a target of a refresh operation.
A refresh operation of a memory area of a DRAM that is not used or in which data is not stored may also be skipped to reduce power consumption and/or increase performance.