Measuring and correcting sense amplifier and memory mismatches using NBTI

• US 7,020,035 B1
• Filed: 10/10/2003
• Issued: 03/28/2006
• Est. Priority Date: 10/10/2003
• Status: Active Grant

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Levy, Howard L., Su, Jeffrey Y., Eleyan, Nadeem N.
• Primary Examiner(s): AUDUONG, GENE NGHIA
• Application Number:
  US10/683,633
• Time in Patent Office: 900 Days
• Field of Search: 365/205, 365/207, 365/201, 365/203, 365/233.5, 365/210, 365/189.01
• US Class Current: 365/207
• CPC Class Codes: G11C 11/41 forming static cells with positive feedback, i.e. cells not needing refreshing or charge regeneration, e.g. bistable multivibrator or Schmitt trigger
• CPC Class Codes: G11C 2207/2254 Calibration
• CPC Class Codes: G11C 29/02 Detection or location of defective auxiliary circuits, e.g. defective refresh counters
• CPC Class Codes: G11C 29/026 in sense amplifiers
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: G11C 7/02 with means for avoiding parasitic signals
• CPC Class Codes: G11C 7/06 Sense amplifiers; Associated circuits , e.g. timing or triggering circuits

Abstract

Post-manufacture compensation for a sensing offset can be provided, at least in part, by selectively exposing one of a pair of cross-coupled transistors in a sense amplifier to a bias voltage selected to cause a compensating shift in a characteristic of the exposed transistor. Such exposure may be advantageously provided in situ by causing the sense amplifier to sense values purposefully skewed toward a predominate value selected to cause the compensating shift. In some realizations, purposefully skewed values (e.g., value and value_1) are introduced directly into the sense amplifier. In some realizations, an on-chip test block is employed to identify and characterize sensing mismatch.

Claims

1. A memory circuit comprising:

a sensing circuit including a cross-coupled pair of transistors; and

a control block responsive to detection of a sensing offset of the sensing circuit, the control block at least partially compensating for the detected sensing offset by selectively exposing one of the transistors to a bias voltage selected to cause a compensating shift in a characteristic of the exposed transistor.

2. The memory circuit of claim 1,

wherein the selective exposure includes purposeful introduction, into the sensing circuit, of a data pattern having a predominate value selected to introduce data dependent creep in the characteristic of the exposed transistor.

3. The memory circuit of claim 2,

wherein the data pattern is sensed by the sensing circuit.

4. The memory circuit of claim 2,

wherein the data pattern consists of a sequence of the predominate value.

5. The memory circuit of claim 2,

wherein the data pattern is interspersed amongst memory cell data sensed by the sensing circuit.

6. The memory circuit of claim 2,

wherein the data pattern is introduced directly into the sensing circuit without writing to memory cells to which the sensing circuit is coupled.

7. The memory circuit of claim 2,

wherein the offsetting data dependent creep is associated with negative bias temperature instability.

8. The memory circuit of claim 1,

wherein the transistors are PMOS devices.

9. The memory circuit of claim 1,

wherein the shifted characteristic of the exposed transistor includes its threshold voltage (V_t).

10. The memory circuit of claim 1,

wherein the sensing offset results, at least in part, from an effect that disparately affects one of the pair of transistors as compared with the other, the disparate effect based on a skew in a history of values read out from associated memory elements.

11. The memory circuit of claim 10,

wherein the disparate effect is associated with negative bias temperature instability.

12. The memory circuit of claim 1,

wherein the sensing offset results, at least in part, from an accumulated data-dependent mismatch in characteristics of the cross-coupled transistors.

13. The memory circuit of claim 1,

wherein the sensing offset results, at least in part, from process variations in either the transistors or differential pair circuits to which the transistors are coupled.

14. The memory circuit of claim 10,

wherein the transistors are PMOS devices;

wherein the characteristic is threshold voltage (V_t); and

wherein the disparate effect involves a monotonic increase in V_t based on disparate voltage bias histories of the PMOS devices.

15. The memory circuit of claim 1, further comprising:

a test block configured to detect the sensing offset.

16. The memory circuit of claim 1, further comprising:

a test block that selectively introduces balanced discharge paths into respective halves of a differential circuit sensed by the sensing circuit, the balanced discharge paths allowing the test block to characterize a direction of the sensing offset.

17. The memory circuit of claim 16,

wherein the test block further selectively introduces imbalanced discharge paths into respective halves of the differential circuit to further characterize a magnitude of the sensing offset.

18. The memory circuit of claim 1, further comprising:

a test block that selectively introduces a calibrated imbalance into a differential circuit sensed by the sensing circuit, the calibrated imbalance allowing the test block to characterize the sensing offset.

19. The memory circuit of claim 1,

wherein the control block is responsive to an in situ test operation that characterizes the sensing offset.

20. The memory circuit of claim 19,

wherein the in situ test operation is executed periodically.

21. The memory circuit of claim 19,

wherein the in situ test operation introduces and successively increases an imbalance in a differential circuit sensed by the sensing circuit.

22. The memory circuit of claim 1,

embodied in computer readable descriptive form suitable for use in design test or fabrication of an integrated circuit.

23. The memory circuit of claim 1,

embodied in a cache of a processor integrated circuit.

24. The memory circuit of claim 1,

embodied in a computer system as memory addressable by a processor thereof.

25. The memory circuit of claim 24,

wherein the addressable memory includes cache memory integrated with the processor as a processor integrated circuit.

26. A method of operating a semiconductor memory, the method comprising:

detecting a sensing offset in a sensing circuit that includes a cross-coupled pair of transistors; and

at least partially compensating for the detected sensing offset by selectively exposing one of the transistors to a bias voltage selected to cause a compensating shift in a characteristic of the exposed transistor.

27. The method of claim 26, further comprising:

introducing into the sensing circuit a data pattern having a predominate value selected to cause data dependent creep in the characteristic of the exposed transistor.

28. The method of claim 27,

wherein the data pattern is sensed by the sensing circuit.

29. The method of claim 27,

wherein the data pattern is interspersed amongst memory cell data sensed by the sensing circuit.

30. The method of claim 27,

wherein the compensating shift includes a negative bias temperature instability induced shift in threshold voltage (V_t) of the exposed transistor based on voltage bias history thereof.

31. The method of claim 27, further comprising:

directly introducing the data pattern into the sensing circuit without writing to memory cells to which the sensing circuit is coupled.

32. The method of claim 27,

wherein the data dependent creep is associated with negative bias temperature instability (NBTI).

33. The method of claim 26,

wherein the transistors are PMOS devices.

34. The method of claim 26,

wherein the characteristic of the exposed transistor includes its threshold voltage (V_t).

35. The method of claim 26,

wherein the sensing offset results, at least in part, from an accumulated data-dependent mismatch in characteristics of the cross-coupled transistors.

36. The method of claim 26,

wherein the sensing offset results, at least in part, from a disparate, negative bias temperature instability induced shift in threshold voltage (V_t) of at least one of the cross-coupled transistors based on disparate voltage bias histories thereof.

37. The method of claim 26,

wherein the sensing offset results, at least in part, from process variations in either the transistors or differential pair circuits to which the transistors are coupled.

38. The method of claim 26,

wherein the transistors are PMOS devices;

wherein the characteristic is threshold voltage (V_t); and

wherein the sensing offset involves a monotonic increase in V_t based on disparate voltage bias histories of the PMOS devices.

39. The method of claim 26, further comprising:

introducing a balanced pair of discharge paths into respective halves of a differential circuit sensed by the sensing circuit; and

characterizing a direction of the sensing offset based on a value sensed in presence of the introduced discharge paths.

40. The method of claim 39, further comprising:

introducing imbalanced discharge paths into respective halves of the differential circuit to further characterize a magnitude of the sensing offset.

41. The method of claim 26, further comprising:

introducing a calibrated imbalance into a differential circuit sensed by the sensing circuit; and

sensing the differential circuit to characterize the sensing offset.

42. The method of claim 26,

performing an in situ test operation to characterize the sensing offset.

43. The method of claim 42,

wherein the in situ test operation is executed periodically.

44. A method of compensating for accumulated data-dependent post-manufacture creep in a characteristic of one or more devices of a sensing circuit of a semiconductor memory, the method comprising:

performing an in situ test operation that characterizes a sensing offset of the sensing circuit; and

selectively exposing one of the devices to a bias voltage selected to cause a compensating shift in a characteristic thereof and thereby at least partially correct the sensing offset.

45. A method as in claim 44,

wherein the devices include PMOS devices configured in opposition;

and

wherein the characteristic is a threshold voltage (V_t) of the PMOS devices.

46. A method as in claim 44,

wherein the post-manufacture creep results from disparate voltage bias histories experienced by the devices.

47. A method as in claim 44,

wherein the post-manufacture creep results from negative bias temperature instability induced shifts in a threshold voltage (V_t) of the devices.

48. A method as in claim 44,

wherein compensating shift results from negative bias temperature instability induced shift in a threshold voltage (V_t) of the exposed device.

49. A method as in claim 44,

wherein the devices are configured in opposition;

and

wherein the post-manufacture creep disparately affects one of the opposing devices as compared with the other, the disparate effect based on a skew in a history of values read out from memory elements associated with the sensing circuit.

50. A method as in claim 44,

wherein the compensating shift results from post-manufacture creep that disparately affects one of the opposing devices as compared with the other, the disparate effect based on a purposefully introduced skew in a history of values sensed by the sensing circuit.

51. An integrated circuit comprising:

a differential circuit susceptible to an accumulated data-dependent post-manufacture creep in a characteristic of a first device thereof, the characteristic creep affecting a sensing offset of the differential circuit; and

a biasing circuit introducible into the differential circuit to cause an accumulated compensating shift in the characteristic of a second device thereof and thereby at least partially reducing the sensing offset.

52. The integrated circuit of claim 51, further comprising:

a test circuit, the biasing circuit responsive to the test circuit.

53. The integrated circuit of claim 51, further comprising:

a test circuit that at least characterizes a direction of the sensing offset.

54. The integrated circuit of claim 51,

wherein the integrated circuit includes a differential bit-line pair and the differential circuit includes a sense amplifier coupled thereto.

55. The integrated circuit of claim 51,

wherein the data-dependent post-manufacture creep is associated, at least in part, with a negative bias temperature instability (NBTI) effect.

56. The integrated circuit of claim 51,

wherein the compensating shift is associated, at least in part, with a negative bias temperature instability (NBTI) effect.

57. The integrated circuit of claim 51,

wherein the device is a PMOS device and the characteristic includes threshold voltage thereof.

58. The integrated circuit of claim 51,

embodied in computer readable descriptive form suitable for use in design, test, or fabrication of the integrated circuit.

59. The integrated circuit of claim 51,

embodied in a cache of a processor integrated circuit.

60. The integrated circuit of claim 51,

embodied in a computer system as memory addressable by a processor thereof.

61. An integrated circuit chip that compensates, in situ, for a sensing offset at least in part by selectively exposing one of a pair of cross-coupled transistors to a bias voltage selected to cause a compensating shift in a characteristic of the exposed transistor.

62. The integrated circuit chip of claim 61,

wherein the cross-coupled devices are PMOS devices;

and

wherein the characteristic is a threshold voltage (V_t) of the PMOS devices.

63. The integrated circuit chip of claim 61,

wherein the sensing offset is associated, at least in part, with a negative bias temperature instability (NBTI) effect.

64. The integrated circuit chip of claim 61,

wherein the compensating shift is associated, at least in part, with a negative bias temperature instability (NBTI) effect.

65. The integrated circuit chip of claim 61, further comprising:

a test block that at least characterizes a direction of the sensing offset.

66. The integrated circuit chip of claim 61,

embodied as a semiconductor memory.

67. The integrated circuit chip of claim 61,

embodied as a processor integrated circuit including memory or cache.

68. An apparatus comprising:

means for sensing a differential pair in a semiconductor memory;

means for at least partially compensating for a sensing offset exhibited by the sensing means, the compensating means causing an accumulated data-dependent effect on a characteristic of at least one device of the sensing means, wherein the compensating means, when employed, at least partially compensates for the sensing offset.