Method and apparatus for generating multi-level reference voltage in systems using equalization or crosstalk cancellation

• US 20060233278A1
• Filed: 06/15/2006
• Published: 10/19/2006
• Est. Priority Date: 10/19/1999
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Zerbe, Jared, Werner, Carl
• Granted Patent: US 8,320,494 B2
• Time in Patent Office: Days
• US Class Current: 375/286
• CPC Class Codes: G11C 7/1051 Data output circuits, e.g. read-out amplifiers, data output buffers, data output registers, data output level conversion circuits
• CPC Class Codes: G11C 7/1057 Data output buffers, e.g. comprising level conversion circuits, circuits for adapting load
• CPC Class Codes: G11C 7/106 Data output latches
• CPC Class Codes: G11C 7/1078 Data input circuits, e.g. write amplifiers, data input buffers, data input registers, data input level conversion circuits
• CPC Class Codes: G11C 7/1084 Data input buffers, e.g. comprising level conversion circuits, circuits for adapting load
• CPC Class Codes: G11C 7/1087 Data input latches
• CPC Class Codes: H04L 25/0272 Arrangements for coupling to multiple lines, e.g. for differential transmission
• CPC Class Codes: H04L 25/0282 Provision for current-mode coupling
• CPC Class Codes: H04L 25/03019 adaptive, i.e. capable of adjustment during data reception
• CPC Class Codes: H04L 25/03878 Line equalisers; line build-out devices
• CPC Class Codes: H04L 25/08 Modifications for reducing interference; Modifications for reducing effects due to line faults ; Receiver end arrangements for detecting or overcoming line faults
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation
• CPC Class Codes: H04L 7/0332 with an integrator-detector

Abstract

A system and method are shown for generation of at least one reference voltage level in a bus system. A reference voltage generator on a current driver includes at least one reference voltage level, at least one control signal, and an active device. The active device is coupled to the at least one control signal, such as a current control signal, and a selected reference voltage of the at least one reference voltage level. The active device is arranged to shift the at least one reference voltage level based on the at least one current control signal such as an equalization signal, a crosstalk signal, or the combination thereof, employed on the current driver.

Claims

1. A reference voltage generator, comprising:

a voltage divider coupled between first and second voltage pins, the first voltage pin to supply a first voltage and the second voltage pin to supply a second voltage, the voltage divider to output a plurality of distinct reference voltages between the first and second voltages, the plurality of distinct reference voltages serving as threshold voltages from which a respective bit in a multilevel signal is determined to correspond to one of a plurality of data symbols; and

at least one active device coupled to the voltage divider to level-shift the plurality of reference voltages according to at least one coefficient associated with the multilevel signal.

2. The reference voltage generator of claim 1, wherein the at least one coefficient is selected from a group consisting of equalization and crosstalk coefficients associated with the multilevel signal.

3. The reference voltage generator of claim 2, wherein the at least one active device includes an active current source controlled by at least one control signal that is dependent on the set of equalization and crosstalk coefficients, the active current source generating an offset current according to the control signal.

4. The reference voltage generator of claim 3, wherein the voltage divider includes a plurality of resistors serially coupled with each other between the first and second voltage pins, and wherein the offset current is scaled by a scaling factor from a current used to generate a logic state in the multilevel signal, the scaling factor being dependent on at least one of the plurality of resistors.

5. The reference voltage generator of claim 1, wherein the multilevel signal includes transitions among at least three logic states that are shifted respectively to allow currents selected from a group consisting of equalization and crosstalk currents to overdrive the transitions, and wherein the at least one coefficient reflects shifts in the logic states.

6. The reference voltage generator of claim 1, wherein the plurality of reference voltages includes first, second, and third reference voltages, the at least one active device pulling a predetermined amount of current from a line outputting the first reference voltage.

7. The reference voltage generator of claim 1, wherein the at least one active device is coupled to the voltage divider through a channel.

8. The reference voltage generator of claim 1, wherein the plurality of reference voltages are output via respective ones of a plurality of op-amps.

9. A method for generating a plurality of reference voltages, comprising:

dividing a difference between first and second voltages to generate a plurality of distinct voltage levels between the first and second voltages; and

level-shifting the plurality of voltage levels to generate the plurality of reference voltages according to at least one coefficient associated with a multilevel signal, the plurality of reference voltages serving as threshold voltages from which a respective bit in the multilevel signal is determined to correspond to one of a plurality of data symbols.

10. The method of claim 9, wherein the multilevel signal includes transitions among at least three logic states that are shifted respectively to allow currents selected from a group consisting of equalization and crosstalk currents to overdrive the transitions, and wherein the at least one coefficient is related to at least some of the equalization and crosstalk currents.

11. The method of claim 9, wherein the level-shifting includes generating an offset current and controlling the offset current using at least one control signal that is dependent on the at least one coefficient.

12. The method of claim 10, wherein the offset current is derived from equalization and crosstalk cancellation currents used to generate at least one of a plurality of logic states in the multilevel signal.

13. The method of claim 9, wherein the level-shifting includes pulling a predetermined amount of current from a line outputting one of the plurality of reference voltages.

14. The method of claim 9, wherein the level-shifting includes receiving an offset current via a communication channel, the offset current being controlled by a control signal dependent on the at least one coefficient.

15. The method of claim 9, wherein the multilevel signal includes transitions among at least three logic states that are shifted respectively to allow the respective transitions be overdriven for equalization, and wherein the at least one coefficient reflects shifts in the logic states.

16. A reference voltage generator, comprising:

a voltage divider coupled between first and second voltage pins, the first voltage pin to supply a first voltage and the second voltage pin to supply a second voltage, the voltage divider to output a plurality of distinct reference voltages between the first and second voltages, the plurality of distinct reference voltages serving as threshold voltages from which a respective bit in a multilevel signal is determined to correspond to one of a plurality of data symbols; and

at least one active device coupled to the voltage divider to level-shift the plurality of reference voltages based on at least one of a set currents used to generate the multilevel signal.

17. The reference voltage generator of claim 16, wherein the at least one active device is to level-shift the plurality of reference voltages based on a combined current derived from the set of currents.

18. The reference voltage generator of claim 17, wherein the at least one active device includes an active current source to generate an offset current scaled by a scaling factor from one of the combined current and a first current in the set of currents.

19. The reference voltage generator of claim 18, wherein the voltage divider includes a plurality of resistors serially coupled with each other between the first and second voltage pins, and wherein the scaling factor is dependent on at least one of the resistors.

20. The reference voltage generator of claim 16, wherein the set of currents is selected from a group consisting of equalization currents and crosstalk cancellation currents that compensate for signal errors associated with transmitting the multilevel signal through a communication channel.

21. The reference voltage generator of claim 16, wherein the plurality of reference voltages includes first, second, and third reference voltages, the at least one active device pulling a predetermined amount of current from a line outputting the first reference voltage.

22. The reference voltage generator of claim 16, wherein the at least one active device is coupled to the voltage divider through a communication channel.

23. The reference voltage generator of claim 16, wherein the multilevel signal includes transitions among at least three logic states and the set of currents includes equalization currents that overdrive the respective transitions.

24. A reference voltage generator, comprising:

means for dividing a difference between first and second voltages to output a plurality of distinct reference voltages between the first and second voltages, the plurality of distinct reference voltages serving as threshold voltages from which a respective bit in a multilevel signal is determined to correspond to one of a plurality of data symbols; and

means to level-shift the plurality of reference voltages according to at least one coefficient associated with the multilevel signal.

25. The reference voltage generator of claim 24, wherein the multilevel signal includes transitions among at least three logic states that are shifted respectively to allow currents selected from a group consisting of equalization and crosstalk currents to overdrive the transitions, and wherein the at least one coefficient is related to at least some of the equalization and crosstalk currents.