Current source circuits with common mode noise rejection
AssigneeTellabs Oy
InventorCharles W. Chambers, Jr.
Life of this patent
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Abstract
An improved current source circuit is adapted for use with two-wire transmission systems of the type encountered in telephony, and has excellent common mode noise rejection. In its various embodiments, the current source provides an interface for coupling signals with a telephone pair, operates to cancel or negate the effect of unwanted impedances on the pair, generates a selected impedance across the pair, and functions as an electronic hybrid circuit for interfacing between a two and a four-wire telephone transmission facility, all while affording common mode rejection to noise on the line. In addition, the various embodiments of the current source are combined into an improved terminating set for a two to four-wire telephone transmission facility.
Claims26
A current source for interfacing between a source of voltage signals which vary in value and a two-wire transmission system on which longitudinal voltages are at least occasionally present, such as the tip and ring leads of a telephone pair, for generating a controlled current flow through the wires in accordance with the value and polarity of voltage signals from the source of voltage signals and for providing common mode rejection to longitudinal voltages on the wires, said current source having first and second outputs each for connection with a separate one of the wires and comprising first and second voltage amplifier means each having an input, an output and an output impedance connected between the amplifier means output and a separate one of said current source outputs, said first voltage amplifier means output being connected through its output impedance with said current source first output;
- means for connecting said first amplifier means output with said second amplifier means input so that voltage signals at said first amplifier means input control the voltages generated at each of said amplifier means outputs;
- feedback means coupled between said current source first output and said first amplifier means input;
- circuit means coupled between said current source outputs and said first amplifier means input, said feedback means and said circuit means coupling signals at said current source outputs from the wires of the transmission system to said first amplifier means input, said feedback means and said circuit means in response to equal longitudinal voltages on the wires coupling to said first voltage amplifier means input signals which cancel to zero at said first voltage amplifier means input so that said first and second voltage amplifier means do not generate voltages at their outputs in response to equal longitudinal voltages on the wires, whereby said current source has common mode rejection to equal longitudinal voltages on the wires;
- and means for coupling the source of voltage signals with said first voltage amplifier means input to generate at said current source outputs and through the wires current flows having values and directions in accordance with the value and polarity of voltage signals from the source of voltage signals.
A current source having first and second outputs each for connection with a separate one of the wires of a two-wire transmission system on which longitudinal voltages are at least occasionally present, such as with the tip and ring leads of a telephone pair, for generating a controlled current flow through the wires in accordance with the value and polarity of voltage signals from a source of voltage signals which vary in value and for providing common mode rejection to longitudinal voltages on the system, said current source comprising first and second current generators each having an input and an output, said first current generator output being coupled both with said current source first output and with said second current generator input and said second current generator output being coupled with said current source second output;
- means for coupling the source of voltage signals with said first current generator input, said current generators in response to voltage signals from the voltage signal source at said first current generator input providing at said current source outputs and therefore on the wires equal and opposite direction current flows having values and directions in accordance with the value and polarity of the voltage signals from the voltage signal source;
- and feedback means coupled between said current source outputs and said first current generator input for coupling signals at said outputs from the wires with said first current generator input, said feedback means in response to equal longitudinal voltages on the wires coupling to said first current generator input signals which cancel to zero at said first current generator input so that said first and second current generators do not generate current flows at their outputs in response to equal longitudinal voltages on the wires, whereby said current source exhibits common mode rejection to longitudinal voltages on the wires.
A current source for interfacing between a source of voltage signals which vary in value and a two-wire transmission system of a type which exhibits longitudinal voltages and a metallic impedance and voltage across the wires, said current source having first and second outputs each for connection with a separate one of the wires for generating through the wires and the metallic impedance a controlled current flow having a value and direction in accordance with the value and polarity of voltage signals from the source of voltage signals and for exhibiting common mode rejection to longitudinal voltages on the wires, said current source comprising a first operational amplifier (op amp) A1 connected at a noninverting input thereto with reference or ground potential;
- a resistor R1 connected at one end to an output from said op amp A1 and coupled at an opposite end with sai current source first output;
- a second op amp A2 connected at a noninverting input thereto with reference potential;
- a resistor R3 connected between the inverting input to and an output from said op amp A2;
- a resistor R4 connected between the output from said op amp A2 and an inverting input to said op amp A1;
- a resistor R5 connected between the inverting input to and the output from said op amp A1;
- a resistor R6 connected between said opposite end of said resistor R1 and the inverting input to said op amp A2;
- an op amp A3 connected at a noninverting input thereto with reference or ground potential;
- a resistor R8 connected between the output from said op amp A1 and an inverting input to said op amp A3;
- a resistor R9 connected between the inverting input to and an output from said op amp A3;
- a resistor R10 connected at one end with the output from said op amp A3 and coupled at an opposite end with said current source second output;
- a resistor R11;
- a resistor R12 connected in series with said resistor R11 between said opposite ends of said resistors R1 and R10 and at a juncture therebetween with the inverting input to said op amp A1;
- a resistor R13 connected betwenen said opposite end of said resistor R10 and ground;
- and means for coupling the source of voltage signals with the inverting input to said op amp A1.
Dependencies are inferred from the claim text.