Enhanced high voltage line interface circuit

An enhanced high voltage line interface circuit connected to a subscriber instrument via the tip lead and a ring lead of a subscriber loop, said enhanced high voltage line interface circuit comprising:

• tip drive means connected to said tip lead arranged to convert feed voltage from a central office battery to tip feed current on said subscriber loop;
• ring drive means connected to said ring lead arranged to convert feed voltage from a central office battery to ring feed current on said subscriber loop;
• common-mode sensing means connected to said tip and said ring leads and to said tip drive and said ring drive means, said common-mode sensing means arranged to sense the voltage dropped across said subscriber loop and output a control voltage to said tip drive means and said ring drive means, for controlling the tip feed current and the ring feed current produced by said tip drive means and said ring drive means, respectively;
• tip current sensing means connected to said tip lead, said tip current sensing means arranged to sense and develop an output signal when current is flowing in the subscriber loop responsive to said subscriber instrument going off-hook;
• ring current sensing means connected to said ring lead, said ring current sensing means arranged to sense and develop an output signal when current is flowing in the subscriber loop responsive to said ring lead at said subscriber instrument connected to earth ground;
• tip lead protection means connected to said tip lead, said tip lead protection means arranged to detect overcurrent conditions in said tip lead of said subscriber loop and to provide an output voltage that is proportional to the current flowing in said subscriber loop;
• ring lead protection means connected to said ring lead, said ring lead protection means arranged to detect overcurrent conditions in said ring lead of said subscriber loop and to provide an output voltage that is proportional to the current flowing in said subscriber loop;
• differential amplifier means connected to said tip lead and said ring lead for detecting the voltage difference between said tip lead and said ring lead associated with the transmission of voice signals from said subscriber instrument, said differential amplifier means further arranged to develop signal ended output signals responsive to said voice signal transmissions;
• transmit amplifier means connected to said differential amplifier means and arranged to receive and convert said differential amplifier means single ended output into a fully differential voltage representation of said voice signal transmissions;
• line sensing means connected to said tip current sensing means and said ring current sensing means, and operated in response to said tip current sensing means output signal, to generate a logic signal indicating that a current is flowing in the tip lead of said subscriber loop, and further operated in response to said ring current sensing means output signal to generate a ring sense amplifier output signal, and said line sensing means further connected to said tip lead protection means and said ring lead protection means, and operated in response to said tip lead protection means output voltage or, alternatively, said ring lead protection means output voltage, exceeding a preset threshold, to generate a logic signal which signals an overcurrent condition in said subscriber loop;
• ring trip amplifier means connected to said subscriber loop arranged to sense and develop a ring trip output signal responsive to a dc current flowing in said subscriber loop when said subscriber instrument goes off-hook during a ringing cycle;
• selection means connected to said ring trip amplifier means and said line sensing means, said selection means arranged to receive said ring trip output signal and said ring sense amplifier output signal, said selection means developing a logic signal indicating either a ring trip or a ground sense condition, respectively, in said subscriber loop;
• battery feed circuit means connected to the output signal of said differential amplifier means and to a source of precision reference current, said battery feed circuit means summing said differential amplifier means output signal with said precision reference current and developing and applying to said tip drive means and said ring drive means in said subscriber loop;
• and
• receive amplifier means connected to a source of differential voltage audio voice signals intended to be transmitted to said subscriber instrument, said receive amplifier means converting said differential voltage voice signals to single ended voice signals and transmitting said single ended voice signals to said tip drive means and said ring drive means for transmission to said subscriber instrument.