Solid state telephone line circuit

Details Solid state telephone line circuit Solid state telephone line circuit

H - Electricity

04

M

379/63

H04M 19/00 (2006.01)

Patent

CA 2031180

A SOLID STATE TELEPHONE LINE CIRCUIT ABSTRACT A solid state telephone line circuit is disclosed which is connected via a subscriber loop to a subscriber station and via a PCM bus to a central office switching system. The solid state telephone line circuit of the present invention includes an interface circuit, having a voltage to current converter connected to the subscriber loop. The voltage to current converter converts feed voltage from a central office battery to loop feed current on the subscriber loop. A differential amplifier circuit connected to a sensing network, develops an output voltage that is proportional to the voltage dropped across the subscriber loop and sensed by the sensing network. A control circuit having a loop current shaping circuit is connected to the differential amplifier circuit. The loop current shaping circuit receives the differential amplifier circuit voltage and applies to the current converter a control voltage which operates the voltage to current converter to apply feed current to the subscriber loop, that is proportional to loop resistance. A PCM conversion circuit is also included that is connected to the PCM bus. The PCM conversion circuit converts PCM encoded speech signals received on the PCM bus, into analog speech signals for transmission to the subscriber station and alternatively, converts analog speech signals received from the subscriber station to PCM encoded speech signal for transmission on the PCM bus. A receive voice path includes a receive coupling network connecting the PCM conversion circuit to a summing amplifier on the interface circuit. The output of the summing amplifier is fed to the voltage to current converter were the receive analog voice signals are superimposed on the feed current of the subscriber loop. In the transmit voice path, analog speech signals from the subscriber station, appear as differential speech signals on the subscriber loop. The analog speech signals are picked up by the sensing network and fed to the differential amplifier circuit were the differential amplifier circuit converts the differential speech signals into single ended analog speech signals. The analog speech signals are coupled to an amplifier circuit on the control circuit. The amplified analog speech signals are then routed to the PCM conversion circuit, converted to PCM encoded speech signals and transmitted to the PCM bus.

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