Telephone line coupler

Abstract

The telephone line coupler circuit has a single transmit opto-coupler whose output includes a DC bias component connected to a gate of a line seize switch for connecting a DC line seize load across the ring and tip contacts of the telephone line. The line seize switch is saturated by the transmit opto-coupler bias output and the AC component of the transmit opto-coupler output is sent over the telephone lines. The receive opto-coupler is used both for receiving communications signal and for detecting the ring signal. The band pass filter connected to the output of the receive opto-coupler may be switched to pass a ring signal frequency band or a communications frequency band. The circuit operates using two opto-coupler devices while conventional circuits require four opto-coupler devices.

1. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 ring and tip connector means for connecting to telephone line ring and tip contacts and providing ring and tip signal outputs;   a high impedance DC load and a gated line switch connected in series between said ring and tip signal outputs for controllably conducting an “off-hook” current between said ring and tip signal outputs;   a transmit opto-coupler means having a transmit signal input and output;   means for connecting said transmit signal output to said tip output and to a gate input of said gated line switch;   means for controllably providing a low level DC bias signal to said transmit signal input and generating sufficient current on said transmit signal output to substantially saturate said gated line switch and seize said telephone line;   means for providing an outgoing AC signal to said transmit signal input; and   AC signal receive means connected to said ring and tip outputs for detecting an incoming AC signal and producing an incoming AC signal output.   
     
     
       2. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 ring and tip connector means for connecting to telephone line ring and tip contacts and providing ring and tip signal outputs;   a high impedance DC load and a gated line switch connected in series between said ring and tip signal outputs for controllably conducting an “off-hook” current between said ring and tip signal outputs;   a transmit opto-coupler means having a transmit signal input and output;   means for connecting said transmit signal output to said tip output and to a gate input of said gated line switch;   means for controllably providing a low level DC bias signal to said transmit signal input and generating sufficient current on said transmit signal output to substantially saturate said gated line switch and seize said telephone line;   means for providing an outgoing AC signal to said transmit signal input;   AC communications signal receive means connected to said ring and tip outputs for detecting an incoming AC communications signal and producing an incoming AC communications signal output; and   AC ring signal detect means connected to said ring and tip outputs for detecting a telephone ring signal on said telephone line and generating a ringing output signal; wherein:   said AC communications signal receive means and said AC ring signal detect means share a common receive opto-coupler device.   
     
     
       3. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 ring and tip connector means for connecting to telephone line ring and tip contacts and providing ring and tip signal outputs;   a high impedance DC load and a line switch connected in series between said ring and tip signal outputs for controllably conducting an “off-hook” current between said ring and tip signal outputs;   signal transmit means having a transmit signal input and being connected to said ring and tip outputs for transmitting AC signal;   AC communications signal receive means connected to said ring and tip outputs for detecting an incoming AC communications signal and producing an incoming AC communications signal output; and   AC ring signal detect means connected to said ring and tip outputs for detecting a telephone ring signal on said telephone line and generating a ringing output signal;   
       wherein said AC communication signal receive means and said AC ring signal detect means share a common receive opto-coupler device and a common band pass filter circuit switchable between a frequency band of said ring signal and a frequency band of communications signal received over said telephone line, a switching of said filter circuit being in response to a control signal for said line switch. 
     
     
       4. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 ring and tip connector means for connecting to telephone line ring and tip contacts and providing ring and ti-p signal outputs;   a high impedance DC load and a gated line switch connected in series between said ring and tip signal outputs for controllably conducting an “off-hook” current between said ring and tip signal outputs;   a transmit opto-coupler means having a transmit signal input and output;   means connecting said transmit signal output to said tip output and to a gate input of said gated line switch;   means for controllably providing a low level DC bias signal to said transmit signal input and generating sufficient current on said transmit signal output to substantially saturate said gated line switch and seize said line;   means for providing an outgoing AC signal to said transmit signal input;   AC communications signal receive means connected to said ring and tip outputs for detecting an incoming AC communications signal and producing an incoming AC communications signal output; and   AC ring signal detect means connected to said ring and tip outputs for detecting a telephone ring signal on said telephone line and generating a ringing output signal;   
       wherein said AC communications signal receive means and said AC ring signal detect means share a common receive opto-coupler device and include a shared band pass filter circuit switchable between a ring signal frequency band and a communication signal frequency band, said filter circuit being switched by a line seize signal fed to said low level DC bias signal providing means. 
     
     
       5. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 a diode bridge having an input and a rectified output;   an interconnect structure coupled to an opto-coupler, wherein the interconnect structure and the opto-coupler are configured to detect signals on a telephone line side and produce corresponding signals on an equipment side;   a diode connected across said opto-coupler on said telephone line side and configured to conduct current opposed to a bias of said opto-coupler; and   a ring signal detection circuit provided on said telephone line side and configured to provide an AC signal from said diode bridge input across said opto-coupler in response to a ring signal, said opto-coupler configured to be biased to operate in response to a forward part of said AC signal, a negative part of said AC signal being conducted through said diode.   
     
     
       6. The coupler circuit as claimed in claim 5, wherein said coupler circuit is configured to receive communications signals on said line side through said optocoupler, said coupler circuit comprising a receive opto-coupler bias circuit responsive to an off-hook signal provided by said subscriber equipment, said forward part of said AC signal is biasing said opto-coupler to operate when said off-hook signal is not provided and said bias circuit is not operating. 
     
     
       7. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 ring and tip connector means for connecting to telephone line ring and tip contacts and providing ring and tip signal outputs;   a high impedance DC load and a gated line switch connected in series between said ring and tip signal outputs for controllably conducting an “off-hook” current between said ring and tip signal outputs;   a transmit opto-coupler having a transmit signal input and output;   means for connecting said transmit signal output to said tip output and to a gate input of said gated line switch;   means for controllably providing a low level DC bias signal to said transmit signal input and generating sufficient current on said transmit signal output to substantially saturate said gated line switch and seize said telephone line;   means for providing an AC signal to said transmit signal input in the presence of the DC bias signal; and   AC signal receive means connected to said ring and tip outputs for detecting an incoming AC signal and producing an incoming AC signal output.   
     
     
       8. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 ring and tip connector means for connecting to telephone line ring and tip contacts and providing ring and tip signal outputs;   a high impedance DC load and a gated line switch connected in series between said ring and tip signal outputs for controllably conducting an “off-hook” current between said ring and tip signal outputs;   a transmit opto-coupler means having a transmit signal input and output;   means for connecting said transmit signal output to said tip output and to a gate input of said gated line switch;   means for controllably providing a low level DC bias signal to said transmit signal input and generating sufficient DC current on said transmit signal output to substantially saturate said gated line switch and seize said telephone line;   means for providing an outgoing AC signal to said transmit signal input;   AC communications signal receive means connected to said ring and tip outputs for detecting an incoming AC communications signal and producing an incoming AC communications signal output; and   AC ring signal detect means connected to said ring and tip outputs for detecting a telephone ring signal on said telephone line and generating a ringing output signal;   wherein said AC communications signal receive means and said AC ring signal detect means share a common receive opto-coupler device.   
     
     
       9. The telephone line coupler circuit of claim 8 wherein said receive opto coupler is connected in series to said transmit opto-coupler to provide a bias level to said receive opto-coupler placing said receive opto-coupler in operational mode. 
     
     
       10. The telephone line coupler circuit of claim 9 wherein said transmit opto-coupler includes an output that is connected to a gate input of said gated line switch. 
     
     
       11. A telephone line coupler circuit for connecting telephone subscriber equipment to a telephone line, the circuit comprising:
 ring and tip connector means for connecting to telephone line ring and tip contacts and providing ring and tip signal outputs;   a high impedance DC load and a line seize circuit connected between the ring and tip signal outputs and configured to controllably conduct an “off-hook” current between the ring and tip signal outputs;   a receive opto-coupler having a receive signal input and a receive signal output and configured to receive an AC receive signal if the receive opto-coupler is biased;   a transmit opto-coupler having a transmit signal input and a transmit signal output and configured to receive an AC transmit signal if the transmit opto-coupler is biased; and   a circuit configured to controllably provide a low-level DC bias signal to the transmit opto-coupler to generate sufficient current to substantially saturate the line seize circuit and to seize the telephone line.