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  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 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 ring and tip connector circuitry 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 receive opto - coupler having a receive signal input on a line side and a receive signal output on an equipment side;        a transmit opto - coupler having a transmit signal input on said equipment side and a transmit signal output on said line side, said receive opto - coupler and said transmit opto - coupler being connected in series on said line side;        said transmit signal output being connected to said tip output and to a gate input of said gated line switch;        a line side transmit signal and DC bias signal combining circuitry receiving a transmit communications signal and a DC bias signal and outputting a combined signal to said transmit signal input; and        a DC bias voltage generator responsive to a control signal to provide a low level DC signal as said DC bias signal, wherein sufficient current is generated on said transmit signal output to substantially saturate said gated line switch and seize said telephone line.     
     
     
       6. The circuit as claimed in  claim 5 , further comprising:
   AC ring signal detection circuitry connected to said telephone line ring and tip contacts and outputing a ring signal to said receive signal input.     
     
     
       7. The circuit as claimed in  claim 5 , wherein said ring and tip connector circuitry comprises a diode bridge. 
     
     
       8. The circuit as claimed in  claim 6 , further comprising a common band pass filter circuit connected to said receive signal output and switchable between a frequency band of said ring signal and a frequency band of a communications signal received over said telephone line, a switching of said filter circuit being in response to said control signal. 
     
     
       9. The circuit as claimed in  claim 6 , wherein said ring and tip connector circuitry comprises a diode bridge, said AC ring signal detection circuitry being connected to said ring and tip signal contacts before said diode bridge. 
     
     
       10. The circuit as claimed in  claim 8 , wherein said ring and tip connector circuitry comprises a diode bridge, said AC ring signal detection circuitry being connected to said ring and tip signal contacts before said diode bridge. 
     
     
       11. A method of isolating and connecting a transmit signal generated by subscriber electronic equipment to a telephone line, the method comprising:
   providing a transmit opto - coupler;        adding a DC bias to the electronic equipment transmit signal coming from the electronic equipment to obtain a combined signal and feeding the combined signal to the transmit opto - coupler, said DC bias being sufficient to generate a low level DC output on a line side of said transmit opto - coupler;        using said low level DC output to trigger a line seize circuit connected to said telephone line to draw a minimum current required by a central office to seize the telephone line;        transmitting an isolated copy of said transmit signal output from said transmit opto - coupler on said telephone line, using circuitry separate from the line seize circuitry;        providing a receive opto - coupler; and        connecting said transmit opto - coupler and said receive opto - coupler together in series on a telephone line side.     
     
     
       12. A method of isolating and connecting a ring signal and a communications receive signal on a telephone line to subscriber electronic equipment, the method comprising:
   providing a receive opto - coupler;        connecting said receive opto - coupler using first circuit elements to the telephone line to detect and isolate an incoming AC communications signal;        connecting said receive opto - coupler using second circuit elements to the telephone line to detect and isolate a ring signal;        providing a transmit opto - coupler;        connecting said transmit opto - coupler and said receive opto - coupler together in series on a telephone line side;        detecting the ring signal at an output of the receive opto - coupler in the subscriber electronic equipment when the subscriber electronic equipment is in an on - hook state; and        detecting the incoming AC communications signal at the output of the receive opto - coupler in the subscriber electronic equipment when the subscriber electronic equipment is in an off - hook state;        wherein said steps of detecting comprise using different filtering characteristics on said output of the receive opto - coupler depending on the on - hook/off - hook state.