Telephone subscriber line circuit
AssigneeBell Telephone Laboratories, Incorporated
InventorsLaimons Freimanis, Harry Edward Mussman, DeWitt Paul Smith
Life of this patent
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Abstract
A communication line interface circuit including a floating current source supplying a constant current substantially independent of loop length is disclosed. The line interface circuit is provided with circuitry for line supervision and the detection of dial pulse signaling.
Claims12
A line interface circuit for detecting both off-hook and dial pulse signaling on a line comprising:
- a constant current power supply having an output transformer;
- a sense winding magnetically coupled to said transformer;
- a source of reference potential;
- a comparator circuit having one input connected to said sense winding and another input connected to said source of reference potential;
- circuit means connected between said sense winding and said source of reference potential and responsive to the potential induced in said sense winding;
- and
- signal generating means alternatively responsive to said comparator circuit and said circuit means to generate an output signal.
A line interface circuit comprising:
- a transformer;
- a sense winding magnetically coupled to said transformer;
- a source of reference potential;
- circuit means including a diode connected between said sense winding and said source of reference potential;
- and
- signaling generating means including a transistor responsive to current flow through said circuit means for generating an output signal, said diode being responsive to a potential at said sense winding exceeding said reference potential source for conducting current, whereby further increase in output voltage from said transformer is prevented.
A line interface circuit connectable to a telephone line and adapted to detect both off-hook conditions on the line and dial pulse signaling on the line represented by open and closed circuit conditions comprising:
- a constant current power supply having an output transformer including a secondary winding;
- means for applying clock pulse signals to the interface circuit;
- first and second control flip-flops each having a set and a reset state;
- means connected to said first and second control flip-flops for activating said power supply only in the presence of one of said clock pulse signals when said first flip-flop is in said set state and for activating said power supply circuit independent of said clock pulse signals when said second flip-flop is in said set state;
- a sense winding magnetically coupled to said transformer secondary winding whereby a potential is induced across said sense winding from said secondary winding;
- reference potential source means;
- a comparator circuit having one input terminal connected to said sense winding and another input terminal connected to said reference potential source means for generating a comparator output signal when the potential induced in said sense winding exceeds a predetermined potential of said reference potential source means;
- circuit means connected between said sense winding and said reference potential source means said responsive to the potential induced in said sense winding exceeding a predetermined potential of said reference potential source means to generate a circuit means signal;
- and
- output signal generating means responsive alternatively to said comparator output signal and said circuit means signal for generating output signals representing off-hook conditions and dial pulse signaling on said line.
Dependencies are inferred from the claim text.