MEMORY SYSTEM WITH DELAY LOCKED LOOP (DLL) BYPASS CONTROL

• US 20120020171A1
• Filed: 07/21/2010
• Published: 01/26/2012
• Est. Priority Date: 07/21/2010
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gower, Kevin C., Gower, Lisa C., Kim, Kyu-Hyoun, Maule, Warren E.
• Granted Patent: US 8,379,459 B2
• Time in Patent Office: Days
• US Class Current: 365/193
• CPC Class Codes: G11C 2207/2227 Standby or low power modes
• CPC Class Codes: G11C 7/22 Read-write [R-W] timing or clocking circuits; Read-write [R-W] control signal generators or management
• CPC Class Codes: G11C 7/222 Clock generating, synchronizing or distributing circuits within memory device

Abstract

A memory system with delay locked loop (DLL) bypass control including a method for accessing memory that includes receiving a memory read command at a memory device. The memory device is configured to operate in a DLL off-mode to bypass a DLL clock as input to generating a read clock. A DLL power-on command is received at the memory device and in response to receiving the DLL power-on command a DLL initialization process is performed at the memory device. The memory read command is serviced at the memory device operating in the DLL off-mode, the servicing overlapping in time with performing the DLL initialization process. The memory device is configured to operate in a DLL on-mode to utilize the DLL clock as input to generating the read clock in response to a specified period of time elapsing. The specified period of time is relative to receiving the DLL power-on command.

Claims

1. A method for accessing memory, the method comprising:

receiving a memory read command at a memory device, the memory device comprising a delay locked loop (DLL) for generating a DLL clock, and the memory device configured to operate in a DLL off-mode to bypass the DLL clock as input to generating a read clock;

receiving a DLL power-on command at the memory device;

performing a DLL initialization process at the memory device in response to receiving the DLL power-on command;

servicing the memory read command at the memory device, the servicing overlapping in time with performing the DLL initialization process and the servicing performed by the memory device operating in the DLL off-mode, the servicing comprising utilizing the read clock for capturing read data; and

configuring the memory device to operate in a DLL on-mode to utilize the DLL clock as input to generating the read clock, the configuring the memory device to operate in a DLL on-mode performed in response to a specified period of time elapsing, the specified period of time relative to receiving the DLL power-on command.

2. The method of claim 1, further comprising:

receiving a second memory read command after configuring the memory device to operate in the DLL on-mode; and

servicing the second memory read command after the initialization process has completed.

3. The method of claim 1, wherein the DLL initialization process comprises locking in the DLL clock to produce a stable DLL clock.

4. The method of claim 3, wherein the DLL initialization process further comprises aligning a reference clock with a data strobe signal to generate the DLL clock.

5. The method of claim 1, wherein the DLL off-mode is characterized by the DLL clock not being stable.

6. The method of claim 1, wherein a memory read has a first latency when the memory device is configured to operate in the DLL off-mode and a second latency when the memory device is configured to operate in the DLL on-mode, the first latency longer than the second latency.

7. The method of claim 1, wherein the specified period of time is specified as a number of clock cycles.

8. The method of claim 1, wherein the specified period of time is selected to elapse prior to the DLL initialization process completing.

9. A memory system comprising:

a memory device configured to operate in a DLL off-mode to bypass a DLL clock as input to generating a read clock, the memory device comprising;

a delay locked loop (DLL) in a power-off state for outputting the DLL clock in an unlocked state;

a command interface for receiving a DLL power-on command, the DLL power-on command including instructions for performing a DLL initialization process to generate a DLL clock in a locked state and for configuring the memory device in a DLL on-mode to utilize the DLL clock as input to generating the read clock; and

latency circuitry for delaying the configuring the memory device in a DLL on-mode until after a specified period of time has elapsed, the specified period of time relative to receiving the DLL power-on command, thereby allowing the memory device to service memory read commands in the DLL off-mode while the DLL initialization process is being performed.

10. The memory system of claim 9, wherein a second memory command received after the specified period of time has elapsed is serviced after the initialization process has completed.

11. The memory system of claim 9, wherein the DLL off-mode is characterized by the DLL clock not being locked.

12. The memory system of claim 9, wherein a memory read has a first latency when the memory device is configured to operate in the DLL off-mode and a second latency when the memory device is configured to operate in the DLL on-mode, the first latency longer than the second latency.

13. The memory system of claim 9, wherein the specified period of time is specified as a number of clock cycles.

14. The memory system of claim 9, wherein the specified period of time is selected to elapse prior to the DLL initialization process completing.

15. A method for accessing memory, the method comprising:

receiving a memory read request at a memory controller, the memory read request corresponding to a memory device that is configured in a DLL off-mode;

transmitting a memory read command to the memory device in response to receiving the memory read request;

calculating an expected data return time for the memory read command responsive to the memory device being configured in the DLL off-mode;

transmitting a DLL power-on command to the memory device, the DLL power-on command specifying a period of time to wait between receiving the DLL power-on command and configuring the memory device to operate in a DLL power-on mode; and

calculating an expected DLL power-on command completion time, the calculating responsive to a DLL initialization processing performed in response to the DLL power-on command overlapping in time with servicing the memory read request at the memory device.

16. The method of claim 15, further comprising:

transmitting receiving a second memory read command to the memory device after the specified period of time has elapsed; and

calculating an expected data return time for the second memory read command responsive to the memory device waiting to service the second memory read command until after the DLL initialization processing has completed and to the memory device being configured in a DLL power-on mode.

17. The method of claim 15, wherein the DLL initialization processing comprises locking in a DLL clock for use as a read clock.

18. The method of claim 15, wherein memory read commands have a first expected latency when the memory device is configured to operate in the DLL off-mode and a second expected latency when the memory device is configured to operate in the DLL on-mode, the first expected latency longer than the second expected latency.

19. The method of claim 15, wherein the specified period of time is specified as a number of clock cycles.

20. The method of claim 15, wherein the specified period of time is selected to elapse prior to the DLL initialization processing being completed.