Telephone line interface circuit with voltage switching
First Claim
1. An interface circuit for a telephone line, comprising driver means for supplying direct current on the line, generating means for generating a controlled voltage, and means for selectively supplying the controlled voltage either as a voltage on the line or as a supply voltage for the driver means.
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Accused Products
Abstract
A two-wire telephone line interface circuit comprises a driver circuit for supplying direct current on the line, a controlled voltage generator, a sensing circuit for monitoring the line current, a control circuit for controlling an output voltage of the voltage generator, and a switching circuit. The control circuit controls the switching circuit to supply, as a supply voltage for the driver circuit, a battery voltage in an on-hook state of the line or the controlled output voltage of the voltage generator in an off-hook state of the line, this output voltage being controlled to provide off-hook current limiting. The control circuit also controls the switching circuit to selectively supply the controlled output voltage of the voltage generator as a signalling voltage to at least one wire of the line for high voltage signalling, e.g. ringing, on the line. Desirable forms of the switching circuit are described.
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Citations
23 Claims
- 1. An interface circuit for a telephone line, comprising driver means for supplying direct current on the line, generating means for generating a controlled voltage, and means for selectively supplying the controlled voltage either as a voltage on the line or as a supply voltage for the driver means.
- 10. An interface circuit for a telephone line, comprising driver means for supplying direct current on the line, generating means for generating a controlled voltage, means for selectively supplying either the controlled voltage or a source voltage as a supply voltage for the driver means, means for monitoring direct current on the line, and means for controlling the controlled voltage generated by the generating means in dependence upon the monitored current when the controlled voltage is supplied as the supply voltage for the driver means.
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12. An interface circuit for a two-wire telephone line, comprising:
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driver means for supplying direct current on the line; a controlled voltage generator; control means for controlling an output voltage of the voltage generator; and switching means controlled by the control means for deriving a supply voltage for the driver means selectively from either the controlled output voltage of the voltage generator or a source voltage. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. An interface circuit for a two-wire telephone line, comprising:
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driver means for supplying direct current on the line; a controlled voltage generator; control means for controlling an output voltage of the voltage generator; and switching means controlled by the control means for selectively supplying the controlled output voltage of the voltage generator either as a signalling voltage to at least one wire of the line or as the supply voltage for the driver means.
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21. A telephone line interface circuit comprising a line drive circuit, a controlled voltage generator, switches for coupling the controlled voltage generator selectively to a telephone line or to the line drive circuit to provide a supply voltage thereto, and a control circuit for controlling the switches and the controlled voltage generator.
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22. A telephone line interface circuit comprising a line drive circuit, a controlled voltage generator, a voltage source, at least one switch for deriving a supply voltage for the line drive circuit selectively from either the controlled voltage generator or the voltage source, and a control circuit for controlling the switch and the controlled voltage generator.
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23. A telephone line interface circuit comprising:
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a line drive circuit; a control circuit; a controlled voltage generator for producing a voltage controlled by the control circuit; a voltage source; and switches controlled by the control circuit for selectively coupling; a telephone line to either the line drive circuit or the controlled voltage generator; and
either the controlled voltage generator or the voltage source to the line drive circuit to provide a supply voltage thereto.
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Specification