Automatic hidden refresh in a dram and method therefor
View Patent ↗A memory ( 10 ) has a plurality of memory cells, a serial address port ( 47 ) for receiving a low voltage high frequency differential address signal, and a serial input/output data port ( 52, 54 ) for receiving a high frequency low voltage differential data signal. The memory ( 10 ) can operate in one of two different modes, a normal mode and a cache line mode. In cache line mode, the memory can access an entire cache line from a single address. A fully hidden refresh mode allows for timely refresh operations while operating in cache line mode. Data is stored in the memory array ( 14 ) by interleaving in multiple sub-arrays ( 15, 17 ). During a hidden refresh mode of operation, one sub-array ( 15 ) is accessed while another sub-array ( 17 ) is refreshed. Two or more of the memories ( 10 ) may be chained together to provide a high speed low power memory system.
1. An integrated circuit memory, comprising:
a memory array having a plurality of banks of refreshable memory cells;
a plurality of refresh counters, a refresh counter of the plurality of refresh counters for counting a number of refresh operations in a corresponding one of the plurality of banks; and
a clock counter coupled to the plurality of refresh counters, the clock counter for being initialized with a selectable predetermined value for determining a maximum time remaining for a refresh operation.
2. The integrated circuit memory of claim 1 , further comprising a bit field for selectively storing the maximum time remaining.
3. The integrated circuit memory of claim 1 , further comprising a control circuit for comparing a count value in each of the plurality of refresh counters to the maximum time, and in response to the count value in one of the plurality of refresh counters equaling the maximum time, stopping an access to the integrated circuit memory to allow a refresh operation to complete.
4. The integrated circuit memory of claim 3 , wherein the access is a cache line burst access.
5. The integrated circuit memory of claim 1 , wherein the maximum time remaining for a refresh operations is user selectable.
6. The integrated circuit memory of claim 1 , further comprising a bit field for selectively enabling an automatic hidden refresh mode of operation, wherein during the automatic hidden refresh mode of operation, access of one bank of the plurality of banks is automatically detected so that the other banks of the plurality of banks can be refreshed.
7. The integrated circuit memory of claim 1 , wherein the integrated circuit memory is a dynamic random access memory (DRAM).
8. The integrated circuit memory of claim 1 , wherein the selectable predetermined value for determining a maximum time remaining for a refresh operation is determined based on a temperature under which the intergrated circuit memory is expected to operate.
9. A method for refreshing a memory having a plurality of refreshable memory cells organized in a plurality of memory banks, comprising:
accessing the memory for a burst operation;
detecting an access to one of the plurality of memory banks during the burst operation;
refreshing memory cells of a bank of the plurality of memory banks that is not being accessed during the burst operation in response to the burst operation;
determining a maximum time remaining in a refresh period of a bank of the plurality of memory banks; and
storing the maximum time remaining in a register bit field.
10. The method of claim 9 , wherein the maximum time remaining in a refresh period is user programmable.
11. The method of claim 10 , wherein the maximum time remaining in a refresh period is determined based on a temperature under which the memory is expected to operate.
12. The method of claim 10 , wherein the maximum time remaining in a refresh period is determined based on a voltage under which the memory is expected to operate.
13. The method of claim 10 , further comprising
providing a refresh counter for each of the plurality of banks; and
comparing a count value in each of the plurality of refresh counters to the maximum time remaining, and in response to the count value in one of the plurality of refresh counters equaling the maximum time remaining, stopping an access to the integrated circuit memory to allow a refresh operation to complete.
14. The method or claim 9 , wherein the burst operation is a cache line burst.
15. The method of claim 9 , further comprising selectively enabling an automatic hidden refresh mode of operation, wherein during the automatic hidden refresh mode of operation, access of one bank of the plurality of banks is automatically detected so that the other banks of the plurality of banks can be refreshed.
16. The method of claim 9 , wherein memory is a dynamic random access memory (DRAM).
17. A method for refreshing a memory having a plurality of refreshable memory cells organized in a plurality of memory banks, comprising:
determining a maximum time remaining for refreshing a bank of the plurality of memory banks; and
storing the maximum time remaining in a user programmable register bit field.
18. The method of claim 17 , further comprising:
detecting an access to one of the plurality of memory banks during the burst operation; and
refreshing memory cells of a bank of the plurality of memory banks that is not being accessed during the burst operation in response to the burst operation within the maximum time remaining.
19. The method of claim 17 , further comprising
providing a refresh counter for each of the plurality of banks; and
comparing a count value in each of the plurality of refresh counters to the maximum time remaining, and in response to the count value in one of the plurality of refresh counters equaling the maximum time remaining, stopping an access to the integrated circuit memory to allow a refresh operation to complete.