Method and apparatus for non-disruptive telecommunication loop condition determination

A circuit for detecting whether a telecommunication line is in use, said telecommunication line comprising first and second signal lines, said circuit comprising:

• a voltage divider for coupling between said first and second lines and having first and second nodes across which appears a scaled version of a voltage across said first and second lines;
• a differential analog-to-digital converter having first and second analog input terminals and a digital output terminal;
• a signal line for selectively enabling said circuit when said signal is in a first state and disabling said circuit when said signal is in a second state;
• a first transistor having a control terminal coupled to said signal line and first and second current flow terminals coupled between said first node and said first input terminal of said analog-to-digital converter;
• a second transistor having a control terminal coupled to said signal line and first and second current flow terminals coupled between said second node and said second input terminal of said analog-to-digital converter, wherein:
• when said signal line is in said first state, said analog-to-digital converter receives a scaled version of the voltage across said first and second lines, and, when said signal line is in said second state, said analog-to-digital converter receives no signal from said voltage divider.

A telecommunication apparatus for coupling to a telecommunication link, said telecommunication link comprising first and second lines that are biased to a first voltage when said link is on-hook and a second voltage when said link is in use, said apparatus comprising:

• a processor;
• a first circuit for taking said apparatus in use so that said apparatus may receive or transmit information via said telecommunication link;
• a voltage divider for coupling between said first and second lines and having first and second nodes across which appears a scaled version of a voltage across said first and second lines;
• a differential analog-to-digital converter having first and second analog input terminals and a digital output terminal;
• a signal line for selectively enabling said circuit when said signal is in a first state and disabling said circuit when said signal is in a second state;
• a first transistor having a control terminal coupled to said signal line and first and second current flow terminals coupled between said first node and said first input terminal of said analog-to-digital converter;
• a second transistor having a control terminal coupled to said signal line and first and second current flow terminals coupled between said second node and said second input terminal of said analog-to-digital converter, wherein:
• when said signal line is in said first state, said analog-to-digital converter receives a scaled version of the voltage across said first and second lines, and, when said signal line is in said second state, said analog-to-digital converter receives no signal from said voltage divider;
• and
• said processor is adapted to disable said first circuit responsive to said analog-to-digital converter receiving said second voltage and enable said first circuit responsive to said analog-to-digital converter receiving said first voltage.

A method for detecting whether a telecommunication line is in use without affecting the line impedance, said telecommunication line comprising first and second signal lines, said method comprising the steps of:

• modulating a DC voltage that appears across said first and second lines;
• passing said modulated DC voltage through an electrical high voltage interface circuit;
• and
• determining whether said telecommunication line is in use as a function of said modulated DC voltage.

A method for detecting whether a telecommunication line is in use, said telecommunication line comprising first and second signal lines, said method comprising:

• a voltage divider coupling between said first and second lines without an intervening transistor and presenting, at a node, a scaled version of a voltage across said voltage divider;
• and
• a transistor producing an output signal at an output terminal, wherein:
• the transistor comprises a control terminal coupled to said node, a first current flow terminal coupled to a voltage source, and a second current flow terminal coupled to said output terminal, and
• said output terminal bears a value that is indicative of a voltage across said first and second lines and thus whether said telecommunication line is in use.