Dual-Port SRAM Memory Using Single-Port Memory Cell

• US 20080005492A1
• Filed: 06/29/2006
• Published: 01/03/2008
• Est. Priority Date: 06/29/2006
• Status: Active Grant

• Current Assignee: Mosys Incorporated (Peraso, Inc.)
• Original Assignee: Monolithic System Technology
• Inventors: Leung, Wingyu
• Granted Patent: US 7,533,222 B2
• Time in Patent Office: Days
• US Class Current: 711/149
• CPC Class Codes: G11C 11/406 Management or control of the refreshing or charge-regeneration cycles
• CPC Class Codes: G11C 11/40603 Arbitration, priority and concurrent access to memory cells for read/write or refresh operations
• CPC Class Codes: G11C 7/1075 for multiport memories each having random access ports and serial ports, e.g. video RAM

Abstract

A dual-port memory system is implemented using single-port memory cells. An access arbiter having a synchronization circuit is used to prioritize and synchronize the access requests associated with the two ports. The access arbiter can also prioritize and synchronize refresh requests, in the case where the single-port memory cells require refresh. Access requests on the two ports and the refresh requests can be asynchronous. The access arbiter synchronizes the various requests by latching the requests into first-stage registers when a row access signal (RAS) is activated, and subsequently latching the contents of the first-stage registers into second-stage registers after a selected delay.

Claims

1. A semiconductor memory system comprising:

a memory array comprising a plurality of single-port memory cells;

two access ports, including a first port and a second port; and

an access arbiter configured to arbitrate synchronous or asynchronous access requests on the first and second ports by synchronizing and prioritizing these access requests.

2. The semiconductor memory system of claim 1, wherein the access arbiter comprises a synchronizer circuit having a first stage clocked by a memory access control signal used to initiate an access of the memory array, and a second stage clocked by a delayed version of the memory access control signal.

3. The semiconductor memory system of claim 2, further comprising a delay circuit configured to introduce a delay to the memory access control signal, thereby creating the delayed version of the memory access control signal.

4. The semiconductor memory system of claim 2, further comprising a multiplexer coupled to the first port and the second port, wherein the multiplexer is configured to selectively route signals from the first port or the second port to the memory array in response to signals provided by the second stage of the synchronizer circuit.

5. The semiconductor memory system of claim 1, further comprising a multiplexer coupled to the first port and the second port, wherein the multiplexer is configured to selectively route signals from the first port or the second port to the memory array in response select signals generated by the access arbiter.

6. The semiconductor memory system of claim 1, further comprising a memory sequencer configured to sequentially activate and deactivate a plurality of control signals for accessing the memory array in response to a memory request signal provided by the access arbiter.

7. The semiconductor memory system of claim 1, wherein the single-port memory cells require refreshing, the semiconductor memory system further comprising a refresh controller configured to activate a refresh request signal, which is provided to the access arbiter.

8. The semiconductor memory system of claim 7, wherein the second port is a read-only port enabled in response to a clock signal, and wherein the refresh controller is configured to activate the refresh request signal in response to the clock signal.

9. The semiconductor memory system of claim 8, wherein the first port is an asynchronous read-write port.

10. The semiconductor memory system of claim 7, wherein the access arbiter is further configured to arbitrate refresh requests indicated by the activated refresh request signal.

11. The semiconductor memory system of claim 7, wherein the access requests on the first and second ports and the refresh request signal are asynchronous with respect to one another.

12. The semiconductor memory system of claim 1, wherein the first and second ports are asynchronous read-write ports.

13. A method of operating a memory system comprising:

storing data in single-port memory cells of a memory array;

accessing the memory array in response to access requests on a first port;

accessing the memory array in response to access requests on a second port; and

arbitrating asynchronous access requests on the first and second ports by synchronizing and prioritizing these access requests.

14. The method of claim 13, wherein the access requests on the first and second ports are synchronized by:

storing the access requests on the first and second ports in first stage registers in response to a memory access control signal used to initiate an access of the memory array; and

storing the access requests in the first stage registers in second stage registers in response to a delayed version of the memory access control signal.

15. The method of claim 14, further comprising introducing a delay to the memory access control signal, thereby creating the delayed version of the memory access control signal.

16. The method of claim 14, further comprising selectively routing access control signals from the first port or the second port to the memory array in response to signals provided by the second stage of the synchronizer circuit.

17. The method of claim 13, wherein the step of arbitrating comprises activating a memory request signal to indicate a granted access request, the method further comprising sequentially activating and deactivating a plurality of control signals for accessing the memory array in response to the activated memory request signal.

18. The method of claim 13, further comprising periodically refreshing the single-port memory cells.

19. The method of claim 18, further comprising:

performing only read accesses to the second port, wherein the access requests on the second port are provided by a clock signal; and

generating refresh requests for the single-port memory cells in response to the clock signal.

20. The method of claim 19, further comprising performing read and write accesses on the first port in an asynchronous manner with respect to the clock signal.

21. The method of claim 19, further comprising arbitrating the refresh requests with the access requests on the first and second ports.