RESONANCE MITIGATION FOR HIGH-SPEED SIGNALING

• US 20110228864A1
• Filed: 12/03/2009
• Published: 09/22/2011
• Est. Priority Date: 12/03/2008
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Abbasfar, Aliazam, Amirkhany, Amir, Aryanfar, Farshid
• Granted Patent: US 8,917,783 B2
• Time in Patent Office: Days
• US Class Current: 375/259
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission
• CPC Class Codes: H04L 25/03878 Line equalisers; line build-out devices

Abstract

The frequency response of a first component signal path of a differential signaling link is adjusted to off-set a notch in the frequency response from a corresponding notch in the frequency response of a second component signal path of the differential signaling link.

Claims

1. A method of conveying information over a differential signaling link formed by first and second component signal paths, the method comprising:

offsetting a notch in the frequency response of the first component signal path from a notch in the frequency response of the second component signal path; and

transmitting a signal over the differential signaling link at a signaling rate that exceeds the center frequencies of the notches in the first and second component signal paths.

2. The method of claim 1 wherein offsetting the notch in the frequency response of the first component signal path from the notch in the frequency response of the second component signal path comprises adjusting an electrical characteristic of the first component signal path to offset the center frequency of the notch in the frequency response of the first component signal path relative to the center frequency of the notch in the frequency response of the second component signal path.

3. The method of claim 2 wherein adjusting an electrical characteristic of the first component signal path to offset the center frequency of the notch in the frequency response of the first component signal path relative to the center frequency of the notch in the frequency response of the second component signal path comprises shifting the center frequency of the notch in the frequency response of the first component signal path to a lower frequency by a frequency-offset sufficient to avoid spectral overlap between the notches in the frequency responses of the first and second component signal paths.

4. The method of claim 3 wherein shifting the center frequency of the notch in the frequency response of the first component signaling path by a frequency-offset sufficient to avoid spectral overlap comprises shifting by a frequency-offset at least large enough to avoid overlap between a first frequency interval, defined by the frequency range between upper and lower cutoff frequencies of the notch in the frequency response of the first component signal path, and a second frequency interval, defined by the frequency range between upper and lower cutoff frequencies of the notch in the frequency response of the second component signal path.

5. The method of claim 1 wherein the first and second component signal paths include first and second signal-path segments, respectively, that extend from respective signaling circuits of an integrated circuit (IC) device to an external interface of the IC device.

6. The method of claim 5 wherein the IC device comprises an IC die disposed within an IC package, wherein the signaling circuits are disposed on the IC die and the external interface comprises interconnect structures of the IC package.

7. The method of claim 5 wherein the IC device comprises an IC die, and wherein the signaling circuits and the external interface are disposed on the IC die.

8. The method of claim 5 wherein the respective signaling circuits comprise first and second receiver circuits coupled to the first and second-signal path segments, respectively

9. The method of claim 5 wherein the respective signaling circuits comprise first and second transmitter circuits coupled to the first and second signal-path segments, respectively.

10. The method of claim 5 wherein the IC device comprises a first frequency-response adjustment element and a first switching element coupled between the first frequency-response adjustment element and the first signal-path segment, and wherein offsetting a notch comprises switchably coupling the first frequency-response adjustment element to the first signal-path segment via the first switching element.

11. The method of claim 10 wherein the IC device comprises a programmable register coupled to the first switching element and wherein switchably coupling the first frequency-response adjustment element to the first component signal path via the first switching element comprises storing within the programmable register a control value that sets the first switching element to a conducting state.

12. The method of claim 10 wherein the first frequency-response adjustment element comprises a stub that is switchably coupled to the first component signal path via the first switching element.

13. The method of claim 10 wherein the first frequency-response adjustment element comprises a reactive element that is switchably coupled to the first component signal path via the first switching element.

14. The method of claim 10 wherein the IC device further comprises a plurality of additional frequency-response adjustment elements, a plurality of additional switching elements and a programmable register to store a control value having constituent bits that control respective ones of the switching elements, including the first switching element, to enable each of the frequency-response adjustment elements, including the first frequency-response adjustment element, to be switchably coupled, via a respective one of the switching elements, to the first component signal path according to the state of the corresponding bit of the control value.

15. The method of claim 1 wherein offsetting the notch in the frequency response of the first component signal path from the notch in the frequency response of the second component signal path comprises selectively coupling frequency-response adjustment elements to the first component signal path via respective switching elements.

16. The method of claim 15 wherein the frequency-response adjustment elements comprise at least one of a stub or a reactive element.

17. The method of claim 15 wherein the switching elements comprise transistor switches and wherein selectively coupling frequency-response adjustment elements to the first component signal path via respective switching elements comprises selectively switching the transistor switches to a conductive state.

18. The method of claim 15 wherein the switching elements comprise selectively formed hardwired interconnections.

19. An integrated circuit (IC) device comprising:

first and second interconnection structures to couple to first and second external signaling lines, respectively; and

first and second internal signaling lines coupled respectively to the first and second interconnection structures and to form, together with the first and second external signaling lines, at least a portion of a differential signaling link having first and second component signal paths, the first component signal path being formed at least in part by the first internal signaling line and the first external signal line, and the second component signal path being formed at least in part by the second internal signaling line and the second external signaling line; and

a frequency-response adjustment element switchably coupled to the first internal signaling line to enable a notch in the frequency response of the first component signal path to be offset from a notch in the frequency response of the second component signal path.

20. The IC device of claim 19 further comprising:

a switching element coupled between the first internal signaling line and the frequency- response adjustment element; and

a register coupled to the switching element to set the switching element to either a conducting state or a non-conducting state according to a value stored within the register.

21. The IC device of claim 19 further comprising a transmitting circuit coupled to the first and second internal signaling lines to output a differential signal onto the differential signaling link.

22. The IC device of claim 21 wherein the frequency-response adjustment element is a component of the transmitting circuit.

23. The IC device of claim 19 further comprising a receiving circuit coupled to the first and second internal signaling lines to receive a differential signal via the differential signaling link.

24. The IC device of claim 19 further comprising an IC package and an IC die disposed within the IC package, wherein the first and second interconnection structures are disposed at a periphery of the IC package and the first and second internal signal paths extend from the IC die to the first and second interconnection structures.

25. The IC device of claim 24 wherein the frequency-response adjustment element is disposed on the IC die.

26. The IC device of claim 19 further comprising an IC die on which and second interconnection structures, the first and second internal signal paths and the frequency-response adjustment element are formed.

27. A signaling system comprising:

a differential transmitter;

a differential receiver;

a differential signaling link coupled between the differential transmitter and differential receiver and formed by first and second signaling paths; and

a frequency-response adjustment element coupled to the first signaling path of the differential signaling link to offset a notch in the frequency response of the first signaling path from a notch in the frequency response of the second signaling path.

28. The signaling system of claim 27 further comprising:

a first integrated circuit die having the differential transmitter formed thereon; and

a second integrated-circuit die having the differential receiver disposed thereon.

29. The signaling system of claim 28 wherein at least one of the first integrated circuit die and the second integrated circuit die comprises a register to store one of a plurality of possible control values that correspond to respective offsets between the notches in the frequency responses of the first and second signaling paths, the register to output a control signal to the frequency-response adjustment element in accordance with the one of the plurality of possible control values.

30. In a differential signaling system, in which a signal is transmitted as two or more signal components of opposite polarity, a method comprising:

creating at least two paths that connect a transmitter with a receiver, the two paths having substantially identical path length and routing, such that the two or more signal components are transmitted and received in unison on respective ones of the paths; and

creating a path reflection mismatch in one of the paths, to create a reflection-type intersymbol interference pattern that is different for the one component relative to the other components;

wherein the mismatch is selected relative to a frequency null associated with the substantially identical path length and routing, such that a corresponding frequency null of the one component is offset relative to a corresponding null of at least one of the other components, notwithstanding the substantially identical path length and routing.

31. An apparatus for conveying information over a differential signaling link formed by first and second component signal paths, the apparatus comprising comprising:

means for offsetting a notch in the frequency response of the first component signal path from a notch in the frequency response of the second component signal path; and

means for transmitting a signal over the differential signaling link at a signaling rate that exceeds the center frequencies of the notches in the first and second component signal paths.

32. A method of conveying information over a differential signaling link formed by first and second component signal paths, the method comprising:

transmitting a first signal component over the first component signal path, the first signal path having a first frequency response exhibiting a first notch with a first center frequency;

transmitting a second signal component over the second component signal path, the second signal path having a second frequency response exhibiting a second notch with a second center frequency;

wherein the first and second signal components cooperate to form a differential signal, and the first and second center frequencies are offset in frequency by a predetermined value.

33. The method according to claim 32 wherein the first signal component frequency response includes a local peak value and the second signal component frequency response includes a local minimum value, and wherein the predetermined value is based at least in part on aligning the respective frequency responses of the first and second signal component paths such that the local peak value substantially aligns with the local minimum value.

34. The method according to claim 32 wherein the frequency response of one of the first and second signal component paths includes a notch minimum value and the frequency response of the other of the first and second signal components includes a cutoff frequency attenuation value, wherein the predetermined value is based at least in part on aligning the respective frequency responses of the first and second signal component paths such that the notch minimum value is less than the cutoff frequency attenuation value.

35. The method according to claim 32 wherein each of the first and second notches include a low-frequency cutoff attenuation value and a high-frequency cutoff attenuation value, and wherein the predetermined value is based at least in part on aligning the respective frequency responses of the first and second signal component paths such that the low-frequency cutoff attenuation value of one of the first and second notches substantially aligns with the high-frequency cutoff attenuation value of the other of the first and second notches.

36. The method according to claim 32 wherein each of the frequency responses of the first and second signal component paths exhibit primary and secondary notches, the primary and secondary notches being displaced in frequency by a displacement range, and wherein the predetermined value is based at least in part on aligning the respective frequency responses of the first and second signal component paths such that the first notch is offset from the second notch by no more than the displacement range.

37. The method according to claim 36 wherein the predetermined value is based at least in part on aligning the respective frequency responses of the first and second signal component paths such that the first notch is offset from the second notch by no more than half the displacement range.

38. The method according to claim 32 wherein the frequency response of one of the first and second signal component paths includes a notch minimum attenuation value and the frequency response of the other of the first and second signal components includes a receiver sensitivity value, wherein the predetermined value is based at least in part on aligning the respective frequency responses of the first and second signal component paths such that the notch minimum attenuation value has a lower value than the receiver sensitivity value.

39. The method according to claim 32 wherein each of the first and second notches include a low-frequency receiver sensitivity value and a high-frequency receiver sensitivity value, and wherein the predetermined value is based at least in part on aligning the respective frequency responses of the first and second signal component paths such that the low-frequency receiver sensitivity value of one of the first and second notches substantially aligns with the high-frequency receiver sensitivity value of the other of the first and second notches.

40. A method of conveying information over a signaling link formed by first and second component signal paths, the first and second component signal paths having respective frequency response characteristics, the method comprising:

transmitting a first signal component over the first component signal path, and a second signal component over the second component signal path;

asymmetrically offsetting the frequency response characteristics associated with the first and second signal component paths by a predetermined value through use of passive circuitry to mitigate a resonance condition associated with the first and second signal components.

41. The method according to claim 40 wherein the first and second signal component paths cooperate to form a differential link, and asymmetrically offsetting the frequency response characteristics includes:

offsetting a first frequency response characteristic of the first signal path with respect to a second frequency response characteristic of the second signal path such that respective first and second notches associated with the first and second frequency response characteristics are offset in frequency by the predetermined value.

42. The method according to claim 40 wherein the first and second signal component paths cooperate to form a single-ended multi-drop signaling link, and asymmetrically offsetting the frequency response characteristics includes:

attenuating the second signal component by coupling at least one frequency-selective attenuator to one or both of the first and second signal component paths.

43. Computer-readable media having information embodied therein that includes a description of an integrated-circuit (IC) memory device, the information including descriptions of:

first and second interconnection structures to couple to first and second external signaling lines, respectively; and

first and second internal signaling lines coupled respectively to the first and second interconnection structures and to form, together with the first and second external signaling lines, at least a portion of a differential signaling link having first and second component signal paths, the first component signal path being formed at least in part by the first internal signaling line and the first external signal line, and the second component signal path being formed at least in part by the second internal signaling line and the second external signaling line; and

a frequency-response adjustment element switchably coupled to the first internal signaling line to enable a notch in the frequency response of the first component signal path to be offset from a notch in the frequency response of the second component signal path.