Calibration methods and circuits for optimized on-die termination

• US 20060071683A1
• Filed: 11/23/2005
• Published: 04/06/2006
• Est. Priority Date: 12/19/2003
• Status: Active Grant

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Best, Scott C., Leung, David, Wong, Anthony Koon
• Granted Patent: US 7,408,378 B2
• Time in Patent Office: Days
• US Class Current: 326/30
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching

Abstract

Described are on-die termination (ODT) systems and methods that facilitate high-speed communication between a transmitter 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 the termination resistances for the signal transmission lines. The ODT control system derives a number of calibration currents from precision voltage and resistance references and distributes the reference currents to a number of transmitters. Each transmitter then derives an ODT calibration signal using the respective reference current and another precision resistor, and then employs the calibration signal to calibrate local termination elements. Distributing calibrated currents provides excellent noise immunity, while limiting the requisite number of external voltage references reduces cost.

Claims

1. An integrated circuit die comprising:

a. a current source having a plurality of calibration-current output nodes providing a corresponding plurality of calibration currents;

b. a plurality of communication circuits, each communication circuit including;

i. a first calibration-circuit input node coupled to a respective one of the calibration-current output nodes and receiving one of the calibration currents;

ii. a second calibration-circuit input node coupled to a reference resistor;

iii. a calibration-circuit output port providing a termination-control signal; and

iv. a termination element exhibiting a termination characteristic and including a termination control port coupled to the calibration-circuit output port and receiving the termination-control signal.

2. The integrated circuit die of claim 1, wherein the termination characteristic comprises termination resistance.

3. The integrated circuit die of claim 1, further comprising a control system deriving a reference current from a reference voltage and a reference resistance, wherein the current source derives the calibration currents from the reference current.

4. The integrated circuit die of claim 1, further comprising a plurality of differential signal-line pairs, each signal-line pair including a first signal line coupled to the termination element.

5. The integrated circuit die of claim 1, further comprising a plurality of pads, each pad coupled to a corresponding one of the termination elements and adapted to convey signals between the die and a communication channel.

6. The integrated circuit die of claim 5, wherein the communication channel comprises a signal-line pair.

7. The integrated circuit die of claim 1, wherein the communication circuit comprises a multi-channel transmitter.

8. The integrated circuit die of claim 1, wherein the communication circuit comprises a multi-channel receiver.

9-27. -27. (canceled)

28. An integrated circuit comprising:

a. a current source having a plurality of calibration-current output nodes;

b. a plurality of reference pads to couple to external reference impedances;

c. a plurality of calibration circuits, each calibration circuit coupled to one of the calibration-current output nodes and one of the external reference impedances and adapted to derive a termination control signal from the one calibration-current output node and the one external reference impedance; and

d. a plurality of termination elements, each termination element including a termination control port coupled to one of the calibration circuits to receive the respective termination control signal.

29. The integrated circuit of claim 28, wherein the current source includes a reference node to connect to an external reference voltage.

30. The integrated circuit of claim 28, wherein the current source includes a reference node to connect to a second external reference impedance.

31. An integrated circuit comprising:

a. a plurality of communication circuits, each communication circuit including a termination-calibration circuit;

b. a plurality of pads to connect each of the termination-calibration circuits to respective external reference resistors; and

c. a current source having a plurality of calibration-current output nodes, each output node coupled to a respective one of the termination-calibration circuits.

32. The integrated circuit of claim 31, further comprising an additional pad to connect to an additional external resistor to the current source, wherein each of the calibration-current output nodes provides a calibration current proportional to a resistance of the additional external resistor.

33. The integrated circuit of claim 32, wherein each of the calibration current is proportional to an external reference voltage.

34. The integrated circuit of claim 31, wherein each communication circuit is a transmitter.

35. The integrated circuit of claim 31, wherein each communication circuit is a multi-channel communication circuit having multiple termination elements coupled to the termination-calibration circuit.

36. A method of calibrating a plurality of termination elements on an integrated-circuit die, the method comprising:

a. providing a first calibration current to each of the plurality of communication circuits;

b. for each of the plurality of communication circuits;

i. producing a second calibration current proportional to the first calibration current;

ii. producing a third calibration current proportional to the first calibration current;

iii. drawing the second calibration current through a reference resistor external to the die to develop a first reference voltage;

iv. drawing the third calibration current through an adjustable reference on-die-termination (ODT) resistor on the die to develop an ODT voltage;

v. comparing the first reference voltage to the ODT voltage; and

vi. adjusting at least one of the plurality of termination elements in response to the comparing.

37. The method of claim 36, further comprising connecting an external voltage reference to the die, connecting an external reference resistor to the die, and deriving the first calibration currents using the voltage reference and the external reference resistor.

38. The method of claim 36, further comprising adjusting the adjustable reference ODT resistor in response to the comparing.

39. The method of claim 38, wherein adjusting the reference ODT resistor comprises conveying a termination control signal to the reference ODT resistor and termination elements.

40. A signal communication system comprising:

a. a plurality of communication circuits, each communication circuit including at least one termination element and a local reference element;

b. a termination calibration system including;

i. means for distributing each of a plurality of calibration currents to respective ones of the communication circuits; and

ii. means for calibrating the at least one termination element in each of the plurality of communication circuits using the respective calibration current.

41. The signal communication system of claim 40, wherein the means for calibrating the at least one termination element in each of the plurality of communication circuits includes a current mirror receiving the respective calibration current.

42. The signal communication system of claim 40, wherein the current mirror includes a reference termination resistor, and wherein the current mirror derives from the respective calibration current a third calibration current through the reference termination resistor.

43. A method of controlling a desired termination impedance disposed on an integrated-circuit die, the method comprising:

a. establishing the desired termination impedance; and

b. maintaining the desired termination by;

i. detecting an actual termination impedance;

ii. sensing a first parameter based on an external reference impedance;

iii. generating a calibration current external to the die;

iv. sensing a second parameter based on the calibration current;

v. comparing the first parameter to the second parameter;

vi. generating a control signal based upon the comparison; and

vii. modifying the detected actual termination resistance based on the control signal.

44. The method of claim 43, wherein the control signal is a control current.

45. The method of claim 44, further comprising distributing the control current to a plurality of termination elements.