Telephone line interface circuit with voltage switching

• US 5,323,461 A
• Filed: 04/02/1992
• Issued: 06/21/1994
• Est. Priority Date: 01/31/1991
• Status: Expired due to Term

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Sutherland, Brian A. F. S., Rosenbaum, Stanley D., Rosch, Reinhard W.
• Primary Examiner(s): Dwyer, James L.
• Assistant Examiner(s): FOURNIER, PAUL
• Application Number:
  US07/862,478
• Time in Patent Office: 810 Days
• Field of Search: 379/252, 379/253, 379/254, 379/255, 379/324, 379/340, 379/399, 379/400, 379/401, 379/413, 363/21, 363/127
• US Class Current: 379/399.01
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence
• CPC Class Codes: H04M 19/02 providing ringing current or supervisory tones, e.g. dialling tone or busy tone

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.

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.

2. An interface circuit as claimed in claim 1 and including means for monitoring direct current on the line.

3. An interface circuit as claimed in claim 2 and including 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.

4. An interface circuit as claimed in claim 2 and including means for supplying a source voltage as the supply voltage for the driver means when the monitored current is below a predetermined threshold.

5. An interface circuit as claimed in claim 2 and including means for selectively supplying either the controlled voltage or a source voltage as the supply voltage for the driver means in dependence upon whether the monitored current is respectively above or below a predetermined threshold, 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.

6. An interface circuit as claimed in claim 1 and including means for selectively supplying a source voltage as the supply voltage for the driver means.

7. An interface circuit as claimed in claim 6 and including means for monitoring direct current on the line.

8. An interface circuit as claimed in claim 7 and including 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.

9. An interface circuit as claimed in claim 7 wherein the source voltage is supplied as the supply voltage for the driver means when the monitored current is below a predetermined threshold.

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.

11. An interface circuit as claimed in claim 10 wherein the source voltage is supplied as the supply voltage for the driver means when the monitored current is below a predetermined threshold.

12. An interface circuit for a two-wire telephone line, comprising:

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.

13. An interface circuit as claimed in claim 12 wherein the switching means is further 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.

14. An interface circuit as claimed in claim 12 wherein the switching means comprises first to sixth switches respectively for selectively connecting the source voltage to a supply voltage line of the driver means, the controlled output voltage to the supply voltage line of the driver means, a first output of the driver means to a first wire of the line, a second output of the driver means to a second wire of the line, the controlled output voltage to the first wire of the line, and the controlled output voltage to the second wire of the line.

15. An interface circuit as claimed in claim 14 wherein the third and fifth switches are constituted by first and second contacts of a first relay, the fourth and sixth switches are constituted by first and second contacts of a second relay, each relay has its second contact phased oppositely to the first contact and includes a third contact having the same phase as the first contact, and the third contacts of the two relays are connected in series with one another and together constitute the second switch.

16. An interface circuit as claimed in claim 12 and including means for monitoring direct current on the line, the control means being responsive to the monitored current.

17. An interface circuit as claimed in claim 16 wherein the control means is arranged to control the output voltage of the voltage generator in dependence upon the monitored current when this output voltage is supplied as the supply voltage for the driver means.

18. An interface circuit as claimed in claim 16 wherein the control means is arranged to control the switching means to supply the source voltage as the supply voltage for the driver means when the monitored current is below a predetermined threshold.

19. An interface circuit as claimed in claim 16 wherein the control means is arranged to control the switching means to selectively supply either the controlled voltage or the source voltage as the supply voltage for the driver means in dependence upon whether the monitored current is respectively above or below a predetermined threshold, and to control the output voltage of the voltage generator in dependence upon the monitored current when this output voltage is supplied as the supply voltage for the driver means.

20. An interface circuit for a two-wire telephone line, comprising:

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.

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.

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.

23. A telephone line interface circuit comprising:

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.