Telephone trunk interface circuit

• US 4,864,605 A
• Filed: 03/08/1988
• Issued: 09/05/1989
• Est. Priority Date: 03/08/1988
• Status: Expired due to Term

• Current Assignee: SER Solutions Incorporated (Atos SE)
• Original Assignee: International Telesystems Corp (Electronic Information Systems, Inc.)
• Inventors: Ramsay, John, Ouellette, Thomas
• Primary Examiner(s): Dwyer, James L.
• Application Number:
  US07/165,217
• Time in Patent Office: 546 Days
• Field of Search: 379/92, 379/93, 379/94, 379/95, 379/96, 379/97, 379/98, 379/99, 379/100, 379/102, 379/250, 379/257, 379/380, 379/379, 379/382, 379/399, 379/269, 379/377
• US Class Current: 379/379
• CPC Class Codes: H04M 7/0096 Trunk circuits

Abstract

A solid-state telephone trunk interface circuit provides high isolation between a central office and telephone equipment. Opto-isolator transistors and a transformer are used to isolate the central office and the local equipment portions of the circuit. A switching transistor (Q4) is connected between a ring connector (3) and turned on and off via an opto-isolator transistor connected to a control connector (9). A ring detector (11) comprising a first diode bridge is connected between tip and ring connectors (2 and 3) via an opto-isolator transistor to a ring signal connector (13). First and second parallel and opposite sign line condition detectors are respectively connected between tip and ring connectors and via opto-isolator transistors to battery-reverse and battery-forward signal connectors (19 and 17). The voice circuit includes a second diode bridge connecting tip and ring connectors to a first winding of a transformer (T1). The circuit between the diode bridge and the first winding is completed by a high voltage transistor (Q3) which is turned on and off via an opto-isolator transistor connected to an off-hook connector ( 21). A second winding of the transformer is connected to first and second operational amplifiers respectively connected to voice signal input and output connectors (23 and 25). A feedback cancelling circuit is connected between the voice signal input connector and the input of the second operational amplifier for cancelling a portion of the voice signal input to the voice signal output.

Claims

1. Telephone trunk circuit interface apparatus comprising tip and ring conductor connectors;

a ring detector having first and second inputs respectively connected to the tip and ring connectors and having a diode bridge connected between the ring detector inputs;

a first opto-isolator having an input portion connected to the diode bridge and having an output portion connected through a pull-up resistor to a voltage source and connected to a grounded capacitor and to an input of a first amplifier, an output of the first amplifier being connected to a ring signal connector, the interface further having first and second parallel and opposite line condition detectors respectively having first connections connected to the tip connector and second connections connected to the ring connector and having diodes as input portions of second and third opto-isolators, output portions of the second and third opto-isolators connected through pull-up resistors to reference voltage sources and connected to inputs of second and third amplifiers, and outputs of second and third amplifiers respectively connected to battery-reverse and battery-forward output signal connectors, the interface having a voice frequency signal diode bridge connected between the tip and ring connectors;

a transformer having first and second portions, the voice bridge being connected to the first portion of the transformer, a voice signal control transistor having power terminals, connected in series with the first portion of the transformer and the diode bridge for turning the transformer on and off, the voice transistor having a control terminal;

a fifth opto-isolator, the voice transistor control terminal being connected to an output portion of the fifth opto-isolator, the interface having an off-hook signal connector, an input portion of the fifth opto-isolator being connected between a voltage source and the off-hook signal connector, the transformer having a second portion, the interface having first and second operational amplifiers, the first operational amplifier having an input connected to the second portion of the transformer for amplifying the voice signal from the transformer, the interface having voice signal output and voice signal input connectors, the voice signal output connector being connected to an output of the first operational amplifier and the voice signal input connector being connected to an input of the second operational amplifier, and the second operational amplifier having an output connected to the second portion of the transformer for amplifying a voice signal from the voice signal input connector to the transformer.

2. A trunk interface method comprising supplying a ground start signal on a ground start connector to a first optical diode, turning on a first optical isolator with the first optical diode, turning on a transistor with the first optical isolator, and connecting a ring connector to ground with the first transistor, supplying power to a first diode bridge from a ring connector and a tip connector, energizing a second optical diode with the first diode bridge, turning on a second opto-isolator with the second optical diode and supplying the signal to a ring indicator connector with the second opto-isolator, sensing line conditions with third and fourth optical diodes connected respectively in parallel with oppositely connected zener diodes in ring and tip circuits, respectively, and turning on a third opto-isolator with the third optical diode and supplying a forward condition indication with the third opto-isolator, turning on a fourth opto-isolator with the fourth optical diode and supplying a reverse line condition indication with the fourth opto-isolator, supplying an off-hook signal to a fifth optical diode, turning on a fifth opto-isolator with the fifth optical diode, turning on a second transistor with the fifth optical diode and connecting a first portion of a transformer with a second diode bridge, supplying voice signals from the ring and tip lines through the second diode bridge and the first portion of the transformer to a second portion of the transformer and supplying voice signals through a first operational amplifier to a voice signal output, supplying input voice signals through a second operational amplifier to the second portion of the transformer and to the first portion of the transformer, and through the diode bridge to the tip and ring connectors and cancelling feedback of a portion of the voice signal input to an input of the first operational amplifier to cancel feedback of a portion of the voice signal input to the voice signal output.

3. A solid-state trunk interface circuit for a telephone system comprising:

tip and ring connectors on a telephone side of the circuit;

a diode bridge connected across the tip and ring connectors;

a transformer and a transistor having power terminals connected in series across the diode bridge;

an off-hook connector on a telephone equipment side of the circuit;

a control terminal of the transistor being connected to said off-hook connector via a first opto-isolator;

a voice signal input circuit and a voice signal output circuit connected to the transformer;

the voice signal input circuit having a voice signal input connector and a first operational amplifier connected to the voice signal input connector and the first operational amplifier having an output connected to the transformer;

the voice signal output circuit comprising a second operational amplifier having an input connected to the transformer and a voice signal output connector connected to an output of the second operational amplifier;

forward and reverse line condition signal connectors on the equipment side of the circuit;

first and second amplifiers having outputs respectively connected to the forward and reverse line condition signal connectors;

second and third opto-isolators respectively having outputs connected to inputs of the first and second amplifiers;

an input of the second opto-isolator being connected between the ring connector and the diode bridge to indicate a forward condition in the ring circuit;

an input of the third opto-isolator being connected between the diode bridge and the tip connector to indicate a reverse line condition;

the inputs to the second and third opto-isolators comprising diodes;

first and second zener diodes connected in parallel with the first and second input diodes in opposite direction;

the first zener diode being connected between the ring connector and the diode bridge; and

the second zener diode being connected between the tip connector and the diode bridge.

4. The apparatus of claim 3 further comprising a feedback cancelling circuit connected between the voice signal input connector and the input of the second operational amplifier for cancelling feedback of a portion of the voice signal input to the voice signal output.

5. The apparatus of claim 3 further comprising a second diode bridge connected between the tip and ring connectors and a fourth opto-isolator, an input of the fourth opto-isolator connected to the second diode bridge and an output of the fourth opto-isolator connected through a third amplifier to a ring indicator connector.

6. The apparatus of claim 3 further comprising a second transistor having power terminals connected between ground and the ring connector and a fifth opto-isolator, the fifth opto-isolator having a an input connected to a control terminal of the second transistor and having an input connected to a ground start connector.

7. A trunk interface method comprising the steps of:

turning on a first light-emitting diode with an off-hook signal indication;

turning on a first opto-isolator with the first light-emitting diode;

turning on a first transistor with the first opto-isolator and forming a series connection of a first portion of a transformer to a first diode bridge with the first transistor;

supplying voice signals from tip and ring indicators to the first diode bridge and to the first portion of the transformer and supplying voice signals through the transformer to a second portion of the transformer;

amplifying the voice signals and supplying the amplified voice signals to a voice signal output;

supplying voice signals in a voice signal input;

amplifying the input voice signals and supplying the amplified input voice signals to the second portion of the transformer, through the transformer to the first portion, and through the diode bridge to the tip and ring connectors;

cancelling a portion of the voice signal input and amplifying a remaining portion of the voice signal input to the voice signal output;

sensing a first line condition with a second diode connected in series between the first diode bridge and the ring connector and turning on a second opto-isolator with the second diode;

enabling a forward condition indication with the second opto-isolator;

supplying a voice signal through a third diode connected between the diode bridge and the tip connector;

turning on a third optical isolator with the third diode and enabling a line reverse signal indication with the third opto-isolator;

supplying a signal from the tip and ring indicators to a second diode bridge;

supplying a signal to a fourth diode from the second diode bridge;

turning on a fourth opto-isolator with the fourth diode;

enabling a ring indication signal with the fourth opto-isolator;

supplying power to a fifth diode from a start input;

turning on a fifth opto-isolator with a fifth diode;

turning on a second transistor with the fifth diode; and

grounding the ring connector with the second transistor.