Frequency-agile strobe window generation

• US 8,824,224 B2
• Filed: 07/10/2012
• Issued: 09/02/2014
• Est. Priority Date: 08/05/2011
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Ware, Frederick A., Leibowitz, Brian S., Tsern, Ely
• Primary Examiner(s): Dinh, Son
• Assistant Examiner(s): NGUYEN, NAM THANH
• Application Number:
  US13/545,255
• Publication Number:
  US 20130033946A1
• Time in Patent Office: 784 Days
• Field of Search: 365/193, 365/194, 365/233.1
• US Class Current: 365/193
• CPC Class Codes: G06F 13/1689 Synchronisation and timing concerns synchronisation on a memory bus G06F13/4234
• CPC Class Codes: G11C 29/022 in I/O circuitry
• CPC Class Codes: G11C 29/023 in clock generator or timing circuitry
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: G11C 7/1066 Output synchronization
• CPC Class Codes: H03K 5/135 by the use of time reference signals, e.g. clock signals

Abstract

The disclosed embodiments relate to components of a memory system that support frequency-agile strobe enable window generation during read accesses. In specific embodiments, this memory system contains a memory controller which includes a timing circuit to synchronize a timing-enable signal with a timing signal returned from a read path, wherein the timing signal includes a delay from the read path. In some embodiments, the timing circuit further comprises two calibration loops. The first calibration loop tracks the timing-enable signal with respect to a cycle-dependent delay in the delay, wherein the cycle-dependent delay depends on a frequency of the strobe signal. The second calibration loop tracks the timing-enable signal with respect to a cycle-independent delay in the delay, wherein the cycle-independent delay does not depend on the frequency of the strobe signal. In some embodiments, the first calibration loop and the second calibration loop are cascaded.

Claims

1. An integrated circuit, comprising:

a timing circuit to synchronize a timing-enable signal with a timing signal returned from a read path on a memory device, wherein the timing signal includes a delay caused by the read path,

wherein the timing circuit comprises;

a first programmable adjustment circuit to track the timing-enable signal with respect to a first delay in the delay, wherein the first delay depends on a frequency of the timing signal; and

a second calibration circuit to track the timing-enable signal with respect to a second delay in the delay; and

wherein the timing-enable signal provides an enable window for the timing signal to receive read data returned through the read path.

2. The integrated circuit of claim 1,

wherein the first delay is a cycle-dependent delay;

and

wherein the second delay is a cycle-independent delay.

3. The integrated circuit of claim 2, wherein the cycle-dependent delay is associated with a cycle-dependent portion of the read path.

4. The integrated circuit of claim 3, wherein the cycle-dependent delay includes a delay associated with a serializer for serializing the read data or control/command/address (CA) information associated with the read access.

5. The integrated circuit of claim 3, wherein the cycle-dependent delay includes a value representing a number of cycles in the delay caused by the cycle-dependent portion of the read path.

6. The integrated circuit of claim 5, wherein the value representing the number of cycles does not change with the period of the timing signal.

7. The integrated circuit of claim 5, wherein the value representing the number of cycles changes with the period of the timing signal.

8. The integrated circuit of claim 5, wherein the first programmable adjustment circuit includes a first calibration loop to determine the number of cycles in the cycle-dependent delay.

9. The integrated circuit of claim 8, wherein the first calibration loop operates to determine the number of cycles in the cycle-dependent delay by using a value of the clock reference cycle time from the allowable cycle time range such that the cycle-independent delay is less than one cycle time of the clock reference.

10. The integrated circuit of claim 9, wherein the maximum value of the clock reference cycle time is used from the allowable cycle time range.

11. The integrated circuit of claim 9, wherein the first calibration loop includes circuitry for sampling a series of delayed versions of the timing-enable signal with respect to the timing signal, wherein the series of delayed versions of the timing-enable signal are separated by one cycle time of the clock reference.

12. The integrated circuit of claim 8, wherein the first calibration loop initially determines the number of cycles in the cycle-dependent delay prior to performing a series of read accesses.

13. The integrated circuit of claim 1, wherein the period of the timing signal is variable.

14. The integrated circuit of claim 2, wherein the cycle-independent delay is associated with a cycle-independent portion of the read path.

15. The integrated circuit of claim 1, wherein the timing signal is a strobe signal.

16. The integrated circuit of claim 1, wherein the timing signal is a clock signal.

17. The integrated circuit of claim 2, wherein the second programmable adjustment circuit is to track the cycle-independent delay which includes:

a clock-to-output delay of a register element in the read path;

an output multiplexer delay of a transmitter element in the read path; and

a driver delay of a transmitter element in the read path.

18. The integrated circuit of claim 2, wherein the second programmable adjustment circuit includes a second calibration loop to calibrate the cycle-independent delay.

19. The integrated circuit of claim 18, wherein the second calibration loop calibrates the cycle-independent delay at a clock reference such that the cycle-independent delay is substantially equal to one cycle time of the clock reference.

20. The integrated circuit of claim 17, wherein the second calibration loop calibrates the cycle-independent delay by matching the cycle-independent delay in the timing signal with an adjustable delay associated with an adjustable delay element using a phase-alignment circuitry.

21. The integrated circuit of claim 20, wherein the second calibration loop receives a previously generated calibrated cycle-dependent delay, and generates the timing-enable signal which is delayed by the calibrated cycle-dependent delay and the calibrated cycle-independent delay.

22. The integrated circuit of claim 20, wherein the second calibration loop adjusts the cycle-independent delay using a minimum cycle time value of the cycle time range when a value for the cycle time ranges becomes comparable to or greater than the cycle time.

23. The integrated circuit of claim 22, wherein the second calibration loop adjusts the cycle-independent delay by using a value of the clock reference cycle time from the allowable cycle time range such that the cycle-independent delay is greater than one cycle time of the clock reference.

24. The integrated circuit of claim 21, wherein the minimum value of the clock reference cycle time is used from the allowable cycle time range.

25. The integrated circuit of claim 23, wherein the one or more phase-shift delays include a quadrature delay which is equal to one-half of a bit interval.

26. The integrated circuit of claim 23, wherein the second calibration loop uses the phase-alignment circuitry to phase-align the third timing-enable signal with respect to the timing signal by calibrating the adjustable delay.

27. The integrated circuit of claim 18, wherein the second calibration loop periodically recalibrates the cycle-independent delay.

28. The integrated circuit of claim 2, wherein the first programmable adjustment circuit and the second programmable adjustment circuit are coupled serially such that the second programmable adjustment circuit receives a calibrated value of the cycle-dependent delay as an input, which is subsequently combined with a calibrated value of the cycle-independent delay to produce the timing-enable signal.

29. A method for operating a memory controller, comprising:

receiving a timing signal returned from a read path on a memory device, wherein the timing signal includes a delay caused by the read path;

calibrating a timing-enable signal based on the timing signal by;

synchronizing the timing-enable signal with respect to a first delay in the delay, wherein the first delay depends on a frequency of the timing signal; and

synchronizing the timing-enable signal with respect to a second delay in the delay;

using the calibrated timing-enable signal to enable the timing signal; and

receiving read data returned through the read path using the enabled timing signal.

30. The method of claim 29,

wherein the first delay is a cycle-dependent delay;

and

wherein the second delay is a cycle-independent delay.

31. The method of claim 30, wherein the cycle-dependent delay is associated with a cycle-dependent portion of the read path.

32. The method of claim 31, wherein the cycle-dependent delay includes:

a delay associated with a serializer for serializing the read data or control/command/address (CA) information associated with the read access;

a delay associated with a deserializer for deserializing the read data or the CA information; and

a delay associated with a read operation for retrieving the read data from a memory component.

33. The method of claim 31, wherein the cycle-dependent delay includes a value representing a number of cycles in the delay caused by the cycle-dependent portion of the read path.

34. The method of claim 33, wherein the value representing the number of cycles does not change with the period of the timing signal.

35. The method of claim 33, wherein the value representing the number of cycles changes with the period of the timing signal.

36. The method of claim 33, wherein synchronizing the timing-enable signal with respect to the cycle-dependent delay involves determining the number of cycles in the cycle-dependent delay.

37. The method of claim 33, wherein the method further comprises determining the number of cycles in the cycle-dependent delay at a clock reference such that a maximum cycle time range for the cycle-independent delay is less than one cycle time of the clock reference.

38. The method of claim 37, wherein determining the number of cycles involves sampling a series of delayed versions of the timing-enable signal with respect to the timing signal, wherein the series of delayed versions of the timing-enable signal are separated by one cycle time of the clock reference.

39. The method of claim 36, wherein the method further comprises initially determining the number of cycles in the cycle-dependent delay prior to performing a series of read accesses.

40. The method of claim 29, wherein the period of the timing signal can change on a cycle-to-cycle basis.

41. The method of claim 29, wherein the cycle-independent delay is associated with a cycle-independent portion of the read path.

42. The method of claim 41, wherein tracking the cycle-independent delay includes tracking one or more of the following components:

a clock-to-output delay of a register element in the read path;

a propagation delay of a signal within a device in the read path;

an output multiplexer delay of a transmitter element in the read path;

a driver delay of a transmitter element in the read path;

a propagation delay of a signal between a transmitter element on one device in the read path and a receiver element on another device in the read path;

a level conversion delay and amplification delay in a receiver element in the read path; and

a data-to-clock-setup delay of a register element in the read path.

43. The method of claim 30, wherein synchronizing the timing-enable signal with respect to the cycle-independent delay involves calibrating the cycle-independent delay in a unit of time.

44. The method of claim 43, wherein the method further comprises calibrating the cycle-independent delay at a clock reference such that the cycle-independent delay is substantially equal to one cycle time of the clock reference.

45. The method of claim 43, wherein calibrating the cycle-independent delay involves matching the cycle-independent delay in the timing signal with an adjustable delay using a phase detection circuit.

46. The method of claim 45, wherein the method further comprises:

receiving a previously generated calibrated cycle-dependent delay; and

generating the calibrated timing-enable signal which is delayed by the calibrated cycle-dependent delay and the calibrated cycle-independent delay.

47. The method of claim 45, wherein calibrating the cycle-independent delay involves using a minimum cycle time value of the cycle time range when a value for the cycle time ranges becomes comparable to or greater than the cycle time.

48. The method of claim 43, wherein the method further comprises periodically recalibrating the cycle-independent delay.

49. A memory controller, comprising:

a timing circuit to synchronize a timing-enable signal with a timing signal associated with a read access, wherein the timing signal includes a delay,

wherein the timing circuit further comprises;

a first programmable adjustment circuit to track the timing-enable signal with respect to a first delay in the delay, wherein the first delay depends on a frequency of the timing signal; and

a second programmable adjustment circuit to track the timing-enable signal with respect to a second delay in the delay; and

wherein the timing-enable signal provides an enable window for the timing signal to retime read data associated with the read access.

50. A method for operating a memory controller, comprising:

receiving a timing signal associated with a read access, wherein the timing signal includes a delay;

calibrating a timing-enable signal based on the timing signal by;

synchronizing the timing-enable signal with respect to a first delay in the delay, wherein the first delay depends on a frequency of the timing signal; and

synchronizing the timing-enable signal with respect to a second delay in the delay;

using the calibrated timing-enable signal to enable the timing signal; and

receiving read data associated with the read access using the enabled timing signal.