Telephonic communications – Subscriber line or transmission line interface – Power supply
Reexamination Certificate
1998-10-07
2001-06-26
Woo, Stella (Department: 2643)
Telephonic communications
Subscriber line or transmission line interface
Power supply
C379S158000, C379S156000
Reexamination Certificate
active
06252957
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to telephones having two or more lines, and more particularly to a circuit that automatically connects a line to a voice circuit in a telephone that does not have an external power source.
2. Background Information
Telephone sets having more than one line for use in a private branch exchange (PBX) system are well-known in the art. A problem with these phones is that mechanical switches are required to select which line is active. The mechanical switches must be physically activated by the phone user, such as by depressing a button to activate line one. The need to physically depress a button to connect a line can cause confusion to a person using the phone. For example, if a switch is set in one position when the telephone is answered, the line indicated by that switch position will be connected to the voice circuit in the telephone, even if the incoming call is on another line. If the person answering the phone does not physically depress the correct line select button, the call will not be connected.
Multiline telephones are also known that have logic capabilities that allow the phone to recognize which line needs to be answered. In these phones, when the user picks up the handset, or presses the speaker phone button, the phone automatically switches to the line having the incoming call. A problem with these phones is that they use a microprocessor to execute the logic functions, and need an external power line to provide the power for the microprocessor. In many situations, such as in hotels and motel industry, running an additional power line to the telephone is very undesirable. Therefore, what is needed is a multiline telephone set having logic capabilities for allowing automatic line selecting functions, but which does not require an external power supply.
BRIEF SUMMARY OF THE INVENTION
Briefly, the present invention comprises a circuit in a multiline telephone set that automatically selects the correct telephone line to connect to a voice circuit in the telephone. The circuit includes an analog part and a digital part. The digital part is a logic circuit for generating a line connect signal that indicates which telephone line should be connected to the voice circuit. The logic circuit is powered by the line voltage associated with a tip and ring leads, so an external power cord is not needed.
The analog part of the circuit comprises a first switch means and a second switch means. The first switch means connects the voice circuit to the tip lead in response to the line connect signal generated by the logic circuit. The second switch means connects the voice circuit to the ring lead in response to the line connect signal. In the absence of the line connect signal, the first and second switch means are off, thereby ensuring that the tip and ring leads are not connected to the voice circuit (i.e. the telephone is on hook). When the first and second switch means are off, a pair of large resistors connected in parallel with the first and second switch means, allow a capacitor in the analog part of the circuit to be charged by the line voltage of the tip and ring leads. The charge in the capacitor is used to power the digital circuit.
The digital part of the circuit (i.e. the logic circuit), comprises a first AND gate and a second AND gate for outputting line connect signals that indicate whether line one or line two should be connected to the voice circuit. The first and second AND gates receive signals from a pair of flip-flop circuits that output high or low signals depending on whether line one or line two should be connected to the voice circuit. The output of the flip-flop circuits is controlled by data signals and clock signals inputted into the flip-flop circuits.
A third AND gate outputs a high data signal when line two should be connected to the voice circuit. The third AND gate outputs a high data signal when line one is busy or when line two is ringing, provided that the line one select button is not pushed. Clock signals are generated when the line one or line two select buttons are pushed, when the handset goes off-hook and when the speaker phone button is pushed. The net effect of the logic circuit is that a line connect signal is sent to the analog circuit when a line is to be connected to the voice circuit. The line connect circuit causes the first switch means and a second switch means to turn on and connect the tip and ring leads to the voice circuit.
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Bakaleynik Maxim
He Elaine C.
Hermanson Spencer L.
Jauregui Mario E.
Burns Doane , Swecker, Mathis LLP
Teledex Corporation
Woo Stella
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