Optical coupling circuit for a data access arrangement (DAA)
AssigneeTexas Instruments Incorporated
InventorsJohn Norsworthy, Darin Kincaid
Life of this patent
Estimating the term…
Abstract
There is disclosed a system and method of providing electrical isolation between a telephone line and a connected device, such as a computer. In one embodiment the telephone line is 2-wire and the connected device is 4-wire and includes a feedback elimination circuit. A pair of controlled CTR opto diodes are used in the communication path to effect electrical isolation. The opto diodes are used in conjunction with an electronic inductor constructed using a pair of cascoded darlington transistors to control the telephone line voltage and current and the circuit is designed to maintain the optocouplers within their linear operating range.
Claims45
A telephone line interface for interfacing between a telephone line and a device, said interface comprising:
- an input connectable to said telephone line;
- an output connectable to said device;
- a circuit having first and second connections connected across said input for terminating the telephone line voltage and current;
- first and second optocouplers each connected across said circuit;
- said first optocoupler having one side of its input connected to said first connection of said circuit to control the impedance presented by said line circuit to said telephone line via said connected input and the other side of its input connected to said second connection of said circuit, said second optocoupler having one side of its output connected to said first connection of said circuit and the other side of its output connected to said second connection of said circuit;
- wherein an output of said first optocoupler is connected to a receive portion of said output and wherein the input of said second optocoupler is connected to a transmit portion of said output.
The method of interfacing between a telephone line and a device, said method comprising the steps of:
- receiving a communication signal over said telephone line and presenting said received signal to a circuit having first and second connections connected across said telephone line, said circuit including first and second optocouplers each connected across said circuit;
- said first optocoupler having one side of its input connected to said connection of said circuit to control the impedance presented by said circuit to said telephone line via said connected input and the other side of its input connected to said second connection of said circuit, said second optocoupler having one side of its output connected to said first connection of said circuit and the other side of its output connected to said second connection of said circuit;
- wherein an output of said first optocoupler is connected to a receive portion of said output and wherein the input of said second optocoupler is connected to a transmit portion of said output;
- and
- bidirectionally presenting telephone line signals to and from said device through said optocouplers to achieve electrical isolation between said telephone line and said device.
The method of interfacing communication signals between a telephone line and a communication device, said method including the steps of:
- terminating said telephone line across an electronic inductor which presents a low impedance to DC voltage and a high impedance to AC signals, said electronic inductor providing a regulated biasing voltage to both transmit and receive optocoupler circuits;
- presenting signals received from said telephone line to the LED portion of said receive optocoupler;
- and
- presenting signals from said communication device to the LED portion of said transmit optocoupler.
An interface circuit for connection between a telephone line and a communication device, said circuit comprising:
- an electronic inductor for terminating said telephone line, said electronic inductor operable for presenting a low impedance to DC voltage and a high impedance to AC signals, said electronic inductor providing a regulated biasing voltage to both transmit and receive optocoupler circuits;
- means for presenting signals received from said telephone line to the LED portion of said receive optocoupler;
- and
- means for presenting signals received from said communication device to the LED portion of said transmit optocoupler.
Dependencies are inferred from the claim text.