Telecommunication line driver having synthesized output impedance derived from output current sensing circuit

• US 7,130,412 B2
• Filed: 11/29/2001
• Issued: 10/31/2006
• Est. Priority Date: 11/29/2001
• Status: Active Grant

• Current Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Original Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Inventors: Foran, Christopher J., Gewin, Robert E., Joffe, Daniel M.
• Primary Examiner(s): Tran, Sinh
• Assistant Examiner(s): Briney, III, Walter F
• Application Number:
  US09/997,228
• Publication Number:
  US 20030099346A1
• Time in Patent Office: 1,797 Days
• Field of Search: 379/394, 379/398, 330/253, 330/255, 330/260, 330/264, 330/265
• US Class Current: 379/387.01
• CPC Class Codes: H04M 1/76 Compensating for differences in line impedance
• CPC Class Codes: H04M 19/005 Feeding arrangements without the use of line transformers
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A synthetic impedance telecommunication line driver has no electrical energy-dissipating elements in series with its output, and synthesizes its output impedance in accordance with current fed back from an output current (mirror) sensing circuit. This allows the driver to realize substantially reduced power requirements for driving a telecommunication line, such as, but not limited to a DSX-1 line. The driver includes an operational amplifier having a first polarity input coupled through an input resistor to an input port, to which a signal voltage to applied to an output port is coupled. A second polarity input of the amplifier is coupled to a reference voltage. A feedback resistor is coupled between the amplifier output and its inverting input. An output current-dependent current source, such as a current mirror coupled in circuit with the output node, generates a current as a small fraction k of the output current. This mirrored fraction of the output current is fed back to an input of the amplifier, and enables the output impedance Zout of the driver to be defined in terms of the mirror current ratio k and the value of the driver amplifier'"'"'s feedback resistor.

Claims

1. An amplifier driver for driving a load, comprising:

a first operational amplifier having first and second differential polarity inputs and an output;

an inverting level shifter connected to said output of said first operational amplifier and producing first and second level-shifted outputs;

complementary first and second output transistor circuits and first and second current mirror circuits operatively connected to respective first and second level-shifted outputs and operative with each other, wherein said first and second current mirror circuits form a current mirror node and said first and second output transistor circuits form an output node, wherein at a no-load condition, the voltage at the current mirror node and voltage at the output node are substantially the same;

a current feedback circuit extending from the current mirror node to an input of the first operational amplifier, and including a feedback operational amplifier positioned within the current feedback circuit and having an output, and a first input operatively connected to said output node and a second input operatively connected to said current mirror node, and first and second auxiliary bias current source circuits and first and second current mirror circuits operatively connected to said output of said feedback operational amplifier such that the current mirror node substantially tracks the output voltage at the output current node and substantially removes current mirror distortion for different values of load resistance.

2. The amplifier driver according to claim 1, wherein said current feedback circuit is connected to an inverting input of the first operational amplifier.

3. The amplifier driver according to claim 1, and further comprising a resistor circuit within said current feedback circuit.

4. The amplifier driver according to claim 1, wherein said first input of said feedback operational amplifier comprises a non-inverting input and said current feedback circuit is connected thereto.

5. The amplifier driver according to claim 1, and further comprising a feedback transistor operatively connected to said output of said feedback operational amplifier.

6. The amplifier driver according to claim 5, wherein said feedback transistor comprises a MOSFET, and said feedback operational amplifier is operative as a gate driver for said MOSFET.

7. The amplifier driver according to claim 6, wherein said MOSFET has a source-drain path coupled to voltage rails through the first auxiliary bias current source circuit.

8. An amplifier driver for driving a load, comprising:

a first operational amplifier having first and second differential polarity inputs and an output;

an inverting level shifter connected to said operational output of said first amplifier and producing first and second level-shifted outputs;

complementary first and second output transistor circuits and first and second current mirror circuits operatively connected to respective first and second level-shifted outputs and operative with each other, wherein said first and second current mirror circuits form a current mirror node and said first and second output transistor circuits form an output node, wherein at a no-load condition, the voltage at the current mirror node and voltage at the output node are substantially the same;

a current feedback circuit extending from the current mirror node to an input of the first operational amplifier, and including a feedback operational amplifier positioned within the current feedback circuit and having an output and a first input operatively connected to said output node and a second input operatively connected to said current mirror node, and first and second auxiliary bias current source circuits and first and second current mirror circuits operatively connected to said output of said feedback operational amplifier such that the current mirror node substantially tracks the output voltage at the output current node and substantially removes current mirror distortion for different values of load resistance, wherein said second current mirror circuit and second auxiliary bias current source are operatively connected to an input of said operational amplifier.

9. The amplifier driver according to claim 8, wherein said second auxiliary bias current source is operatively connected to an inverting input of the first operational amplifier.

10. The amplifier driver according to claim 9, wherein said auxiliary bias current source circuit is referenced to ground.

11. The amplifier driver according to claim 8, wherein said current feedback circuit is connected to an inverting input of the first operational amplifier.

12. The amplifier driver according to claim 8, and further comprising a resistor circuit within said current feedback circuit.

13. The amplifier driver according to claim 8, wherein said first input of said feedback operational amplifier comprises a non-inverting input and said current feedback circuit is connected thereto.

14. The amplifier driver according to claim 8, and further comprising a feedback transistor operatively connected to said output of said feedback operational amplifier.

15. The amplifier driver according to claim 14, wherein said feedback transistor comprises a MOSFET, and said feedback operational amplifier is operative as a gate driver for said MOSFET.

16. The amplifier driver according to claim 15, wherein said MOSFET has a source-drain path coupled to voltage rails through the first auxiliary bias current source circuit.