Calibration methods and circuits to calibrate drive current and termination impedance

• US 7,564,258 B2
• Filed: 08/17/2007
• Issued: 07/21/2009
• Est. Priority Date: 09/08/2003
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Nguyen, Huy M., Gadde, Vijay, Lau, Benedict
• Primary Examiner(s): CHO, JAMES HYONCHOL
• Application Number:
  US11/893,804
• Publication Number:
  US 20070290714A1
• Time in Patent Office: 704 Days
• Field of Search: 326/30
• US Class Current: 326/30
• CPC Class Codes: H03K 19/0005 Modifications of input or output impedance
• CPC Class Codes: H03K 19/01 Modifications for accelerating switching
• CPC Class Codes: H03K 21/08 Output circuits
• CPC Class Codes: H03K 5/24 the characteristic being amplitude
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching
• CPC Class Codes: H04L 25/0298 Arrangement for terminating transmission lines

Abstract

Described are on-die termination (ODT) systems and methods that facilitate high-speed communication between a driver die and a receiver die interconnected via one or more signal transmission lines. An ODT control system in accordance with one embodiment calibrates and maintains termination resistances and drive currents to produce optimal output swing voltages. Comparison circuitry employed to calibrate the reference resistance is also used to calibrate the drive current. Termination elements in some embodiments are divided into two adjustable resistive portions, both of which are designed to minimize capacitive loading. One portion is optimized to produce a relatively high range of adjustment, while the other is optimized for fine-tuning and glitch-free switching.

Claims

1. An integrated circuit comprising:

a plurality of driver circuits to transmit data; and

a calibration circuit coupled to the plurality of driver circuits, the calibration circuit to calibrate a drive current and termination resistance of the plurality of driver circuits, the calibration circuit including;

a pad that couples to an external resistor;

a first adjustable impedance coupled to the pad, to develop a first voltage at a first node by drawing a first current through the external resistor, wherein the first impedance is controlled by a first control value, and wherein the first control value is based on a comparison between the first voltage and a reference voltage;

a second adjustable impedance that is controlled based on the first control value; and

a third adjustable impedance, coupled to the second adjustable impedance, to develop a second voltage at a second node by drawing a second current through the second adjustable impedance;

wherein the third adjustable impedance is controlled based on a second control value, wherein the second control value is based on a comparison between the first voltage at the first node and the second voltage at the second node.

2. The integrated circuit of claim 1, wherein, in operation:

the first adjustable impedance is controlled such that the first voltage matches the reference voltage; and

the third adjustable impedance is controlled such that the second voltage matches the first voltage.

3. The integrated circuit of claim 1, further comprising:

a multiplexer having a first input, a second input, and an output, the first input to receive the second voltage and the second input to receive the reference voltage; and

a comparator to compare the output of the multiplexer with the first voltage, wherein;

in response to a first state of a calibration signal, the multiplexer provides the reference voltage to the comparator and the comparator performs the comparison between the first voltage and the reference voltage; and

in response to a second state of the calibration signal, the multiplexer provides the second voltage to the comparator and the comparator performs the comparison between the second voltage and the first voltage.

4. The integrated circuit of claim 3, further comprising:

a first counter, coupled to an output of the comparator, to hold the first control value, wherein the first control value is adjusted in the first counter until the first voltage matches the reference voltage; and

a second counter, coupled to the output of the comparator, to hold the second control value, wherein the second control value is adjusted in the second counter until the second voltage matches the reference voltage.

5. The integrated circuit of claim 3, further comprising:

a digital filter coupled to the output of the comparator; and

a sampling latch coupled to an output of the digital filter, the sampling latch to sample a signal generated by the comparator.

6. The integrated circuit of claim 1, further comprising a digital-to-analog converter to receive the second control value and generate an analog control value, wherein:

the first adjustable impedance includes a first current source transistor that is controlled in response to the analog control value; and

the second adjustable impedance includes a second current source transistor that is controlled in response to the analog control value.

7. The integrated circuit of claim 6, wherein:

the first current source transistor is a pull-down device that sinks the first current; and

the second current source transistor is a pull-down device that sinks the second current.

8. The integrated circuit of claim 7, wherein the second control value is a digital control value that includes a first set of bits and a second set of bits, wherein, during operation, the first set of bits are held steady and the second set of bits are modified to compensate for changes in environmental fluctuations, wherein the environmental fluctuations include any of supply voltage and temperature fluctuations.

9. The integrated circuit of claim 8, wherein the third adjustable impedance is a digitally adjustable resistor that includes a plurality of transistors coupled to a common node, wherein transistors in the plurality of transistors are selectively activated in response to specific bits of the second control value.

10. The integrated circuit of claim 1, wherein the reference voltage is developed on the integrated circuit device.

11. The integrated circuit of claim 1, wherein the reference voltage is developed external to the integrated circuit device.

12. The integrated circuit of claim 1, wherein the first control value calibrates the drive current and the second control value calibrates the termination resistance of the plurality of driver circuits, and wherein each driver circuit of the plurality of driver circuits comprises a termination resistor that operates in accordance with the termination resistance.

13. An integrated circuit comprising;

a pad that couples to an external resistor;

a first adjustable impedance, coupled to the pad, to develop a first voltage by drawing a first current through the external resistor;

a first circuit, coupled to the first adjustable impedance, to provide a first value that calibrates an impedance setting of the first adjustable impedance, wherein the first value is based on a first comparison between the first voltage and a second voltage;

a second adjustable impedance that is controlled based on the first value;

a third adjustable impedance, coupled to the second adjustable impedance, to develop a third voltage by drawing a second current through the second adjustable impedance;

a second circuit, coupled to the second adjustable impedance, to provide a second value that calibrates an impedance setting of the third adjustable impedance, wherein the second value is based on a second comparison between the second voltage and the third voltage; and

a plurality of circuits to transmit data, wherein, for each circuit of the plurality of circuits, both a drive current and a termination resistance are set based on the first value and the second value.

14. The integrated circuit of claim 13, wherein:

during the first comparison, the second voltage is equal to a reference voltage and the first value adjusts both the first adjustable impedance and the second adjustable impedance such that the first voltage equals the second voltage; and

during the second comparison, the second voltage is equal to the first voltage and the second value adjusts the third adjustable impedance such that the third voltage equals the second voltage.

15. The integrated circuit of claim 14, wherein the reference voltage is developed on the integrated circuit device.

16. The integrated circuit of claim 14, wherein the reference voltage is developed external to the integrated circuit device.

17. The integrated circuit of claim 13, further comprising:

a multiplexer having a first input, a second input, and an output, the first input to receive the third voltage and the second input to receive the second voltage; and

a comparator to compare the output of the multiplexer with the first voltage, wherein;

in response to a first state of a calibration signal, the multiplexer provides the second voltage to the comparator and the comparator performs the comparison between the first voltage and the second voltage; and

in response to a second state of the calibration signal, the multiplexer provides the third voltage to the comparator and the comparator performs the comparison between the third voltage and the first voltage.

18. The integrated circuit of claim 17, further comprising:

a first counter, coupled to an output of the comparator, to hold the first value, wherein the first value is adjusted in the first counter until the first voltage matches the reference voltage; and

a second counter, coupled to the output of the comparator, to hold the second value, wherein the second value is adjusted in the second counter until the second voltage matches the reference voltage.

19. The integrated circuit of claim 17, further comprising:

a digital filter coupled to the output of the comparator; and

a sampling latch coupled to an output of the digital filter, the sampling latch to sample a signal generated by the comparator.

20. The integrated circuit of claim 13, further comprising a digital-to-analog converter to receive the second value and generate an analog value, wherein the first adjustable impedance includes a first current source transistor that is controlled in response to the analog value;

and the second adjustable impedance includes a second current source transistor that is controlled in response to the analog value.

21. The integrated circuit of claim 20, wherein the first current source transistor is a pull-down device that sinks the first current, and the second current source transistor is a pull-down device that sinks the second current.

22. The integrated circuit of claim 13, wherein the second value is a digital control value that includes a first set of bits and a second set of bits, wherein, during operation, the first set of bits are held steady and the second set of bits are modified to compensate for changes in environmental fluctuations, and wherein the environmental fluctuations include any of supply voltage and temperature fluctuations.

23. The integrated circuit of claim 13, wherein the third adjustable impedance is a digitally adjustable resistor that includes a plurality of transistors coupled to a common node, and wherein the transistors in the plurality of transistors are selectively activated in response to specific bits of the second control value.

24. A method of generating control values used to calibrate termination impedances for a drive current and termination resistance of a plurality of communication circuits disposed on an integrated circuit device, the method comprising:

developing a first voltage by drawing a first current through a first adjustable impedance and an external resistor;

comparing the first voltage to a reference voltage to provide a first control value to calibrate an impedance setting of the first adjustable impedance;

developing a second voltage by drawing a second current through a second adjustable impedance and a third adjustable impedance, wherein the second adjustable impedance is controlled based on the first value that represents the first impedance setting; and

comparing the second voltage to the reference voltage to provide a second control value that represents a second impedance setting of at least one of the second and third adjustable impedances.

25. The method of claim 24, the method further comprising comparing the second voltage with the reference voltage to provide a second control value and calibrating, with the second control value, the third adjustable impedance.

26. The method of claim 24, wherein calibrating the impedance settings comprises adjusting the first control value to set the first voltage to the reference voltage.

27. The method of claim 24, further comprising generating the reference voltage in the integrated circuit device.

28. The method of claim 24, further comprising inputting the second voltage from a source that is external to the integrated circuit device.

29. The method of claim 24, wherein at least one of the first and second control values is a digital value.

30. The method of claim 24, wherein the second adjustable impedance mirrors the first adjustable impedance.

31. An integrated circuit comprising:

a plurality of communication circuits to transmit and receive data; and

a calibration circuit coupled to the plurality of communication circuits, the calibration circuit to establish control values that calibrate a drive current and termination resistance of the plurality of communication circuits, the calibration circuit including;

a pad that couples to an external resistor;

a first current source coupled to the pad, the first current source to draw a first current through the external resistor and develop a first voltage at a first node, wherein the first current source is controlled by a first control value, and wherein the first control value holds the first voltage equal to a reference voltage;

a second current source that is controlled based on the first control value; and

an adjustable resistor, connected in series with the second current source, to develop a second voltage at a second node by passing a second current through the second current source, wherein the adjustable resistor is controlled based on a second control value to hold the second voltage equal to the reference voltage.

32. The integrated circuit of claim 31, wherein the first current and the second current are equal.

33. The integrated circuit of claim 31, wherein each of the communication circuits includes a driver.

34. The integrated circuit of claim 31, wherein each of the communication circuits includes a receiver.

35. An integrated circuit comprising:

a pad that couples to an external resistor;

a first current source, coupled to the pad, to develop a first voltage by drawing a first current through the external resistor;

a first plurality of register bits, coupled to the first current source, to store a first value that calibrates the first current of the first current source, wherein the first value is based on a first comparison between the first voltage and a reference voltage;

a second current source that is controlled based on the first value;

a digitally adjustable resistor, coupled to the second current source, wherein a second voltage is developed by drawing a second current through the digitally adjustable resistor and the second current source;

a second plurality of register bits, coupled to the second adjustable impedance, to store a second value that calibrates an impedance setting of the third adjustable impedance, wherein the second value is based on a second comparison between the second voltage and the reference voltage; and

a plurality of drivers to transmit data, wherein, for each driver of the plurality of drivers, at least one of a drive current and a termination resistance is set based on the first value and the second value.

36. The integrated circuit of claim 35, further comprising a comparator having a first input coupled to the pad, a second input, and an output coupled to the first plurality of register bits.

37. The integrated circuit of claim 36, further comprising a multiplexer having a first multiplexer input coupled to the reference voltage, a second multiplexer input coupled to the third adjustable impedance to receive the second voltage, and a multiplexer output coupled to the second input of the comparator.

38. The integrated circuit of claim 35, further comprising a second pad to receive the reference voltage.