Driver circuitry with tuned output impedance

• US 6,522,083 B1
• Filed: 11/08/2001
• Issued: 02/18/2003
• Est. Priority Date: 11/08/2001
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Roach, Steven D.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Alemu, Ephrem
• Application Number:
  US09/986,256
• Time in Patent Office: 467 Days
• Field of Search: 315/224, 315/291, 315/248, 315/242, 315/244, 327/333, 327/382, 327/111, 333/32
• US Class Current: 315/224
• CPC Class Codes: H03K 19/0005 Modifications of input or output impedance
• CPC Class Codes: H04L 25/0266 Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching
• CPC Class Codes: H04L 25/028 Arrangements specific to the transmitter end

Abstract

Driver circuitry with a tuned output impedance is provided. Tuning is provided by an isolation circuit and matching network coupled to an output of the driver circuit. The isolation circuit isolates the capacitance associated portions of the driver circuit thereby reducing overall output capacitance. The matching network substantially compensates for reactive impedances associated with other portions of the driver circuit. These tuning circuits allow the driver circuit overcome intrinsic reactance and exhibit a substantially resistive output impedance characteristic.

Claims

1. A method for obtaining a substantially resistive output impedance characteristic from a driver circuit comprising:

isolating a reactive impedance associated with a sourcing circuit from a load; and

compensating for a reactive impedance associated with a sinking circuit to obtain a substantially resistive output characteristic from the sinking circuit.

2. The method of claim 1 wherein said isolating further comprises providing an isolation resistance.

3. The method of claim 1 wherein the reactive impedance associated with the sourcing circuit is derived at least in part from parasitic capacitance.

4. The method of claim 1 wherein the reactive impedance associated with the sinking circuit is derived at least in part from parasitic capacitance.

5. The method of claim 1 wherein the compensating further comprises providing a reactive network coupled to the sinking circuit to substantially cancel reactive effects associated with the sinking circuit.

6. The method of claim 5 wherein the providing a reactive network further comprises providing a broadband matching network.

7. The method of claim 5 wherein the providing a reactive network further comprises selecting the reactive network such that the output impedance of the driver circuit substantially matches a characteristic impedance of a transmission line.

8. The method of claim 5 wherein the providing a reactive network further comprises providing an inductance.

9. The method of claim 8 wherein the providing an inductance further comprises providing an adjustable inductor disposed on a semiconductor die.

10. The method of claim 8 wherein the inductance is at least partially derived from a lead of a semiconductor package.

11. The method of claim 8 wherein the inductance is at least partially derived from a bond wire of a semiconductor package.

12. A method for driving a load comprising:

providing a sourcing circuit that sources current to the load,

isolating a reactive impedance associated with the sourcing circuit from the load;

providing a sinking circuit that sinks current from the load; and

compensating for a reactive impedance associated with the sinking circuit to achieve a substantially resistive output characteristic from the sinking circuit.

13. The method of claim 12 wherein said isolating further comprises providing an isolation resistance.

14. The method of claim 12 wherein the compensating further comprises providing a reactive network coupled to the sinking circuit to substantially cancel reactive effects associated with the sinking circuit.

15. The method of claim 14 wherein the providing a reactive network further comprises providing a broadband matching network.

16. The method of claim 14 wherein the providing a reactive network further comprises selecting the reactive network such that the output impedance of the driver circuit substantially matches a characteristic impedance of a transmission line.

17. The method of claim 14 wherein the providing a reactive network further comprises providing an inductance.

18. The method of claim 17 wherein the providing an inductance further comprises providing an adjustable inductor disposed on a semiconductor die.

19. The method of claim 17 wherein the inductance is at least partially derived from a lead of a semiconductor package.

20. The method of claim 17 wherein the inductance is at least partially derived from a bond wire of a semiconductor package.

21. A method for driving a light emitting element coupled to a transmission line comprising:

providing a bias circuit that supplies a bias current to the light emitting element,

isolating reactive impedance associated with the bias circuit from the light emitting element;

providing a modulation circuit that supplies modulation current to the light emitting element; and

compensating for a reactive impedance associated with the modulation circuit to achieve a substantially resistive output characteristic so that an impedance of the modulation circuit and a characteristic impedance of the transmission line substantially match.

22. A circuit for tuning the output impedance of driver circuit to obtain a substantially resistive output impedance characteristic comprising:

an isolation resistor coupled to a sourcing circuit that isolates a reactive impedance associated with a sourcing circuit from a load; and

a reactive network configured to compensate for a reactive impedance associated with a sinking circuit to obtain a substantially resistive output characteristic from the sinking circuit.

23. The tuning circuit of claim 22 wherein the reactive network further comprises a broadband matching network.

24. The tuning circuit of claim 22 wherein the reactive network further comprises components for tuning the output impedance of the driver circuit such that the output impedance substantially matches a characteristic impedance of a transmission line.

25. The tuning circuit of claim 22 wherein the reactive network further comprises at least one inductor.

26. The tuning circuit of claim 25 wherein the at least one inductor is an adjustable inductor disposed on a semiconductor die.

27. The tuning circuit of claim 25 wherein the at least one inductor inductance is formed, at least partially, from a lead of a semiconductor package.

28. The tuning circuit of claim 25 wherein the at least one inductor inductance is formed, at least partially, from a lead of a bond wire of a semiconductor package.

29. A circuit for driving a load comprising:

a modulator circuit for providing a modulated signal to the load;

a reactive network coupled to the modulator circuit and to the load that substantially compensates for a reactive impedance associated with the modulation circuit to achieve a substantially resistive output characteristic from the modulator circuit;

a bias circuit for providing a bias signal to the load; and

an isolation circuit coupled to the bias circuit and to the modulator circuit for isolating a reactive impedance associated with the bias circuit from the load.

30. The circuit defined in claim 29 wherein the isolation circuit includes an isolation resistor.

31. The driver circuit of claim 29 wherein the reactive network further comprises components for turning the output impedance of the driver circuit such that the output impedance substantially matches a characteristic impedance of a transmission line.