Driver circuit and a method for matching the output impedance of a driver circuit with a load impedance

• US 20060006912A1
• Filed: 07/06/2004
• Published: 01/12/2006
• Est. Priority Date: 07/06/2004
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Leonowich, Robert H., Quan, Xiaohong
• Granted Patent: US 7,609,097 B2
• Time in Patent Office: Days
• US Class Current: 327/112
• CPC Class Codes: H03K 19/0005 Modifications of input or output impedance
• CPC Class Codes: H04L 25/0278 Arrangements for impedance matching
• CPC Class Codes: H04L 25/028 Arrangements specific to the transmitter end

Abstract

A line driver circuit with an output impedance that is set to a value which is based at least in part on the impedance of one or more current sources of the driver circuit. The current source impedance varies depending on the desired output amplitude of the driver circuit. Once the current source impedance is determined, a resistor is selected to be placed in parallel connection with the current source so that the combination of the resistor and the current source impedance will produce a desired output impedance for the driver circuit. Preferably, the driver circuit includes a second current source and second resistor in parallel with each other and a source termination resistor, such that the combination of the current source impedance values and the resistor values produces a desired output impedance for the driver circuit.

Claims

1. A line driver circuit of an integrated circuit (IC) comprising:

a first current source having a first impedance value; and

a first resistor connected in parallel with the first current source, the first resistor having a first resistor value that is selected based at least in part on the first impedance value to provide the line driver circuit with a desired output impedance.

2. The line driver circuit of claim 1, further comprising:

a second current source having a second impedance value; and

a second resistor connected in parallel with the second current source, the second resistor having a second resistor value that is selected based at least in part on the second impedance value to provide the line driver circuit with a desired output impedance.

3. The line driver circuit of claim 2, further comprising:

a source termination resistor connected across output terminals of the driver circuit, wherein the first and second resistor values and the source termination resistor value are set such that a combination of the first and second impedances, the first and second resistors and the source termination resistor provides the driver circuit with a desired output impedance.

4. The line driver circuit of claim 3, wherein the source termination resistor value is infinity.

5. The line driver circuit of claim 1, wherein the current sources are transistors.

6. A line driver circuit of an integrated circuit (IC) comprising:

a first current source having a first impedance value;

a first resistor connected in parallel with the first current source, the first resistor having a first resistor value;

a second current source having a second impedance value;

a second resistor connected in parallel with the second current source, the second resistor having a second resistor value; and

a source termination resistor connected across output terminals of the driver circuit, wherein the first and second resistor values and the source termination resistor value are set such that a combination of the first and second impedances, the first and second resistors and the source termination resistor provides the driver circuit with a desired output impedance.

7. The line driver circuit of claim 6, wherein the source termination resistor value is infinity.

8. The line driver circuit of claim 6, wherein the current sources are transistors.

9. A method for providing a line driver circuit of an integrated circuit (IC) with a desired output impedance, the method comprising:

selecting a value of a first resistor; and

placing the first resistor in parallel with a first current source of the driver circuit, the first current source having a first impedance value, and wherein the value of the first resistor is selected such that a combination of the first resistor value and the first impedance value provides the driver circuit with a desired output impedance.

10. The method of claim 9, further comprising:

selecting a value of a second resistor; and

placing the second resistor in parallel with a second current source of the driver circuit, the second current source having a second impedance value, and wherein the value of the second resistor is selected such that a combination of the first resistor value, the second resistor value, the first impedance value and the second impedance value provides the driver circuit with a desired output impedance.

11. The method of claim 10, further comprising:

selecting a value for a source termination resistor; and

placing a source termination resistor across output terminals of the driver circuit, and wherein the combination of the first and second impedance values, the first and second resistor values and the source termination resistor value produces a desired output impedance for the driver circuit.

12. The method of claim 11, wherein the value of the source termination resistor is infinity.

13. A method for providing a line driver circuit of an integrated circuit (IC) with a desired output impedance, the method comprising:

selecting a value of a first resistor;

placing the first resistor in parallel with a first current source of the driver circuit, the first current source having a first impedance value;

selecting a value of a second resistor;

placing the second resistor in parallel with a second current source of the driver circuit, the second current source having a second impedance value;

selecting a value for a source termination resistor; and

placing a source termination resistor across output terminals of the driver circuit, and wherein the combination of the first and second impedance values, the first and second resistor values and the source termination resistor value produces a desired output impedance for the driver circuit.

14. The method of claim 13, wherein the value of the source termination resistor is infinity.