Impedance blocking filter circuit

Abstract

An impedance blocking filter circuit is provided for use in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances above 20 KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit. The filter circuit includes first, second, and third inductors connected in series between a first input terminal and a first common point. A first resistor has its one end connected also to the first common point and its other end connected to a first output terminal. Fourth, fifth and sixth inductors are connected in series between a second input terminal and a second common point. A second resistor has its one end also connected to the second common point and its other end connected to a second output terminal. A capacitor has its ends connected across the first and second common points. In other aspects, the filter circuit also includes switching means for eliminating shunt additive capacitance and/or correction circuit means reducing significantly return loss.An impedance blocking filter circuit is provided for use in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to block impedances above a desired frequency range due to the customer's terminal equipment from a DSL network unit and/or home networking interface unit. In one exemplary embodiment, the filter circuit includes first, second, and third inductors connected in series between a first input terminal and a first common point. A first resistor has its one end connected also to the first common point and its other end connected to a first output terminal. Fourth, fifth and sixth inductors are connected in series between a second input terminal and a second common point. A second resistor has its one end also connected to the second common point and its other end connected to a second output terminal. A capacitor has its ends connected across the first and second common points. In other configurations, the filter circuit also includes switching means for eliminating shunt additive capacitance and/or correction circuit means reducing significantly return loss.

1. An impedance blocking filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances from above 20 KHz due to the customer's terminal equipment from ASDL network unit and/or home networking interface unit, said filter circuit comprising:
 first, second, and third inductors connected in series between a first input terminal and a first common point,    said first inductor having its one end connected to said first input terminal and its other end connected to one end of said second inductor, said second inductor having its other end connected to one end of said third inductor, said third inductor having its other end connected to said first common point;    fourth, fifth, and sixth inductors connected in series between a second input terminal and a second common point;    said fourth inductor having its one end connected to said second input terminal and its other end connected to one end of said fifth inductor, said fifth inductor having its other end connected to one end of said sixth inductor, said sixth inductor having its other end connected to said second common point;    first switching means having a first end and a second end and being responsive to DC loop current for electrically connecting said first end to said second end;    a capacitor having a first end connected to said first common point and a second end connected to said first end of said switching means, said second end of said switching means being connected to said second common point; and    correction circuit means interconnected between said common points and said output terminals for significantly reducing return loss caused by inductive impedance when the customer's terminal equipment goes off-hook.    
     
     
       2. An impedance blocking filter circuit as claimed in  claim 1 , wherein said correction circuit means is comprised of a first tank circuit and a second tank circuit, said first tank circuit being formed of a first winding inductor, a first tank capacitors and a first tank resistor all connected in parallel and between said first common point and said first output terminal, second tank circuit being formed of a second winding inductor, a second tank capacitor, and a second tank resistor all connected in parallel and between said second common point and said second output terminal. 
     
     
       3. An impedance blocking filter circuit as claimed in  claim 2 , further comprising a seventh inductor having a first end connected to said first common point and a second end connected to said first tank circuit, and an eight inductor having a first end connected to said second common point and a second end connected to said second tank circuit. 
     
     
       4. An impedance blocking filter circuit as claimed in  claim 3 , further comprising second switching means having a first end and a second end and being responsive to said DC loop current for electrically connecting said first end to said second end, and a second capacitor having a first end connected said eighth inductor at a first node and a second end connected to said first end of said second switching means, said second end of said second switching means being connected to said seventh inductor at a second node. 
     
     
       5. An impedance blocking filter circuit as claimed in  claim 4 , further comprising a ninth inductor having a first end connected to said seventh inductor at said first node and a second end connected to said first tank circuit, and a tenth inductor having a first end connected to said eighth inductor at said second node and a second end connected to said second tank circuit. 
     
     
       6. An impedance blocking filter circuit as claimed in  claim 5 , wherein said first switching means includes a first reed switch and said second switching means includes a second reed switch. 
     
     
       7. An impedance blocking filter circuit as claimed in  claim 6 , wherein said first winding of said first tank circuit, said second winding of said second tank circuit, said first reed switch, and said second reed switch are arranged in a dual winding inductor structure. 
     
     
       8. An impedance blocking filter circuit as claimed in  claim 6 , wherein said first winding of said first tank circuit and said first reed switch is arranged in a first current sensor unit, said second winding of said second tank circuit and said second reed switch is arranged in a second current sensor unit. 
     
     
       9. An impedance blocking filter circuit as claimed in  claim 1 , further comprising a metal-oxide varistor connected to series with said capacitor and in parallel with said first switching means. 
     
     
       10. An impedance blocking filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances from above 20 KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit, said filter circuit comprising:
 first, second, and third inductors connected in series between a first input terminal and a first common point;    said first inductor having its one end connected to said first input terminal and its other end connected to one end of said second inductor, said second inductor having its other end connected to one end of said third inductor, said third inductor having its other end connected to said first common point;    fourth, fifth, and sixth inductors connected in series between a second input terminal and a second common point;    said fourth inductor having its one end connected to said second input terminal and its other end connected to one end of said fifth inductor, said fifth inductor having its other end connected to one end of said sixth inductor, said sixth inductor having its other end connected to said second common point;    first switching means having a first end and a second end and being responsive to DC loop current for electrically connecting said first end to said second end;    a capacitor having a first end connected to said first common point and a second end connected to said first end of said switching means, said second end of said switching means being connected to said second common point; and    bobbin means including at least a first narrow section on which is wound said second inductor, first wider sections on which are wound said third inductor, a second narrow section on which is wound said fifth inductor; and second wider sections on which are wound said sixth inductor for reducing interwinding capacitance so as to increase the useful frequency range, said bobbin means having a center portion for receiving said first switching means.    
     
     
       11. An impedance blocking filter circuit as claimed in  claim 10 , further comprising correction circuit means interconnected between said common points and said output terminals for significantly reducing return loss caused by inductive impedance when the customer's terminal equipment goes off-hook. 
     
     
       12. An impedance blocking filter circuit as claimed in  claim 11 , wherein said correction circuit means is comprised of a first tank circuit and a second tank circuit, said first tank circuit being formed of a first winding inductor, a first tank capacitor, and a first tank resistor all connected in parallel and between said first common point and said first output terminal, second tank circuit being formed of a second winding inductor, a second tank capacitor, and a second tank resistor all connected in parallel and between said second common point and said second output terminal. 
     
     
       13. An impedance blocking filter circuit as claimed in  claim 12 , further comprising a seventh inductor having a first end connected to said first common point and a second end connected to said first tank circuit, and an eighth inductor having a first end connected to said second common point and a second end connected to said second tank circuit. 
     
     
       14. An impedance blocking filter circuit as claimed in  claim 13 , further comprising second switching means having a first end and a second end and being responsive to said DC loop current for electrically connecting said first end to said second end, and a second capacitor having a first end connected said eighth inductor at a first node and a second end connected to said first end of said second switching means, said second end of said second switching means being connected to said seventh inductor at a second node. 
     
     
       15. An impedance blocking filter circuit as claimed in  claim 14 , further comprising a ninth inductor having a first end connected to said seventh inductor at said first node and a second end connected to said first tank circuit, and a tenth inductor having a first end connected to said eighth inductor at said second node and a second end connected to said second tank circuit. 
     
     
       16. An impedance blocking filter circuit as claimed in  claim 15 , wherein said first switching means includes a first reed switch and said second switching means includes a second reed switch. 
     
     
       17. An impedance blocking filter circuit as claimed in  claim 16 , wherein said first winding of said first tank circuit, said second winding of said second tank circuit, said first reed switch, and said second reed switch are arranged in a dual winding inductor structure. 
     
     
       18. An impedance blocking filter circuit as claimed in  claim 16 , wherein said first winding of said first tank circuit and said first reed switch is arranged in a first current sensor unit, said second winding of said second tank circuit and said second reed switch is arranged in a second current sensor unit. 
     
     
       19. An impedance blocking filter circuit as claimed in  claim 10 , further comprising a metal-oxide varistor connected in series with said capacitor and in parallel with said first switching means. 
     
     
       20. An impedance blocking filter circuit as claimed in  claim 10 , further comprising a thermo-fuse connected in series with said first, second and third inductors. 
     
     
       21. An impedance blocking filter circuit used in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances from above  20  KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit, said filter circuit comprising:
   first, second, and third inductors connected in series between a first input terminal and a first common point;        said first inductor having its one end connected to said first input terminal and its other end connected to one end of said second inductor, said second inductor having its other end connected to one end of said third inductor, said third inductor having its other end connected to said first common point;        fourth, fifth, and sixth inductors connected in series between a second input terminal and a second common point;        said fourth inductor having its one end connected to said second input terminal and its other end connected to one end of said fifth inductor, said fifth inductor having its other end connected to one end of said sixth inductor, said sixth inductor having its other end connected to said second common point;        first switching means having a first end and a second end and being responsive to DC loop current for electrically connecting said first end to said second end;        a capacitor having a first end connected to said first common point and a second end connected to said first end of said switching means, said second end of said switching means being connected to said second common point; and        correction circuit means interconnected between said common points and said output terminals for significantly reducing return loss caused by inductive impedance when the customer's terminal equipment goes off - hook.      
     
     
       22. An impedance blocking filter circuit in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances from above  20  KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit, said filter circuit comprising:
   first, second, and third inductors connected in series between a first input terminal and a first common point;        said first inductor having its one end connected to said first input terminal and its other end connected to one end of said second inductor, said second inductor having its other end connected to one end of said third inductor, said third inductor having its other end connected to said first common point;        fourth, fifth, and sixth inductors connected in series between a second input terminal and a second common point;        said fourth inductor having its one end connected to said second input terminal and its other end connected to one end of said fifth inductor, said fifth inductor having its other end connected to one end of said sixth inductor, said sixth inductor having its other end connected to said second common point;        first switching means having a first end and a second end and being responsive to DC loop current for electrically connecting said first end to said second end;        a capacitor having a first end connected to said first common point and a second end connected to said first end of said switching means, said second end of said switching means being connected to said second common point; and        bobbin means including at least a first narrow section on which is wound said second inductor, first wider sections on which are wound said third inductor, a second narrow section on which is wound said fifth inductor, and second wider sections on which are wound said sixth inductor for reducing interwinding capacitance so as to increase the useful frequency range, said bobbin means having a center portion for receiving said first switching means.      
     
     
       23. An impedance blocking filter circuit as claimed in  claim 21 , wherein said correction circuit means is comprised of a first tank circuit and a second tank circuit, said first tank circuit being formed on a first winding inductor, a first tank capacitors and a first tank resistor all connected in parallel and between said first common point and said first output terminal, second tank circuit being of a second winding inductor, a second tank capacitor, and a second tank resistor all connected in parallel between said second common point and said second output terminal.  
     
     
       24. An impedance blocking filter circuit as claimed in  claim 23 , further comprising a seventh inductor having a first end connected to said first common point and a second end connected to said first tank circuit and an eighth inductor having a first end connected to said second common point and a second end connected to said second tank circuit.  
     
     
       25. An impedance blocking filter circuit as claimed in  claim 24 , further comprising second switching means having a first end and a second end and being responsive to said DC loop current for electrically connecting said first end to said second end, and a second capacitor having a first end connected said eighth inductor at a first node and a second end connected to said first end of said switching means, said second end of said second switching means being connected to said seventh inductor at a second node.  
     
     
       26. An impedance blocking filter circuit as claimed in  claim 25 , further comprising a ninth inductor having a first end connected to said seventh inductor at said first node and a second end connected to said first tank circuit, and a tenth inductor having a first end connected to said eight inductor at said second node and a second end connected to said second tank circuit.  
     
     
       27. An impedance blocking filter circuit as claimed in  claim 26 , wherein said first switching means includes a first reed switch and said second switching means includes a second reed switch.  
     
     
       28. An impedance blocking filter circuit as claimed in  claim 27 , wherein said first winding of said first tank circuit, and second winding of said second tank circuit, said first reed switch, and said second reed switch are arranged in a dual window inductor structure.  
     
     
       29. An impedance blocking filter circuit as claimed in  claim 27 , wherein said first switching of said first tank circuit and said first reed switch is arranged in a first current sensor unit, said second winding of said second tank circuit and said second reed switch is arranged in a second current sensor unit.  
     
     
       30. An impedance blocking filter circuit as claimed in  claim 21 , further comprising a metal- oxide varistor connected in series with said capacitor and in parallel with said first switching means.    
     
     
       31. An impedance blocking filter circuit as claimed in  claim 22 , further comprising correction circuit means interconnected between said common points and said output terminals for significantly reducing return loss caused by inductive impedance when the customer's terminal equipment goes off- hook.    
     
     
       32. An impedance blocking filter circuit as claimed in  claim 31 , wherein said correction circuit means is comprised of a first tank circuit and a second tank circuit, said first tank circuit being formed of a first winding inductor, a first tank capacitor, and a first tank resistor all connected in parallel and between said first common point and said first output terminal, second tank circuit being formed of a second winding inductor, a second tank capacitor, and a second tank resistor all connected in parallel between said second common point and said second output terminal.  
     
     
       33. An impedance blocking filter circuit as claimed in  claim 32 , further comprising a seventh inductor having a first end connected to said first common point and a second end connected to said first tank circuit, and an eighth inductor having a first end connected to said second common point and a second end connected to said second tank circuit.  
     
     
       34. An impedance blocking filter circuit as claimed in  claim 33 , further comprising second switching means having a first end and a second end and being responsive to said DC loop current for electrically connecting said first end to said second end, and a second capacitor having a first end connected said eighth inductor at a first node and a second end connected to said first end of said second switching means, said second end of said second switching means being connected to said seventh inductor at a second node.  
     
     
       35. An impedance blocking filter circuit as claimed in  claim 34 , further comprising a ninth inductor having a first end connected to said seventh inductor at said first node and a second end connected to said first tank circuit, and a tenth inductor having a first end connected to said eighth inductor at said second node and a second end connected to said second tank circuit.  
     
     
       36. An impedance blocking filter circuit as claimed in  claim 35 , wherein said first switching means includes a first reed switch and said second switching means includes a second reed switch.  
     
     
       37. An impedance blocking filter circuit as claimed in  claim 36 , wherein said first winding of said first tank circuit, said second winding of said second tank circuit, said first reed switch, and said second reed switch are arranged in a dual winding inductor structure.  
     
     
       38. An impedance blocking filter circuit as claimed in  claim 36 , wherein said first winding of said first tank circuit and said first reed switch is arranged in a first current sensor unit, said second winding of said second tank circuit and the second reed switch is arranged in a second current sensor unit.  
     
     
       39. An impedance blocking filter circuit as claimed in  claim 22 , further comprising a metal- oxide varistor connected in series with said capacitor and in parallel with said first switching means.    
     
     
       40. An impedance blocking filter circuit as claimed in  claim 22 , further comprising a thermo-fuse connected in series with said first, second and third inductors.  
     
     
       41. A telecommunications filter circuit comprising:
 at least one first inductor electrically disposed between a first input terminal and a first common point;    at least one second inductor electrically disposed between a second input terminal and a second common point;    a first switch responsive to DC loop current for selectively passing therethrough;    first and second tank circuits, each of said circuits being formed of respective ones of a winding inductor, capacitor and resistor all disposed in parallel and between respective ones of said first and second common points and output terminals, said tank circuits being adapted to reduce return loss when equipment connected to said filter circuit changes state;    third and fourth inductors disposed electrically between respective ones of said first and second common points, and said first and second tank circuits;    a second switch responsive to DC loop current; and    a capacitor disposed in electrical series with said second switch, said second switch and capacitor being disposed substantially between said third and fourth output.    
     
     
       42. A telecommunications filter circuit as claimed in  claim 41 , further comprising fifth and sixth inductors disposed electrically between respective ones of said third and fourth inductors and said first and second tank circuits.  
     
     
       43. A telecommunications filter circuit as claimed in  claim 42 , wherein said first switch includes a first reed switch and said second switch includes a second reed switch.  
     
     
       44. A telecommunications filter circuit as claimed in  claim 43 , wherein said winding inductors of said first and second tank circuits and said first and second reed switches are arranged in a dual winding inductor structure.  
     
     
       45. A telecommunications filter circuit as claimed in  claim 43 , wherein said winding inductor of said first tank circuit and said first reed switch are arranged in a first current sensor unit, and said winding inductor of said second tank circuit and said second reed switch are arranged in a second current sensor unit.  
     
     
       46. A telecommunications filter circuit comprising:
 at least one first inductor electrically disposed between a first input terminal and a first common point;    at least one second inductor electrically disposed between a second input terminal and a second common point;    a first switch responsive to DC loop current for selectively passing therethrough;    a varistor connected in series with at least one capacitor and in parallel with said first switch; and    a correction circuit interconnected between said common points and output terminals, said correction circuit being adapted to reduce return loss when equipment connected to said filter circuit changes state.    
     
     
       47. The telecommunications filter circuit as claimed in  claim 46 , wherein said varistor and first switch are disposed in electrical parallel with one another to form a first circuit, said first circuit being disposed in electrical series with at least one capacitor.  
     
     
       48. The telecommunications filter circuit as claimed in  claim 46 , wherein said first circuit and said at least one capacitor are disposed in electrical series substantially between said first and second common points.  
     
     
       49. The telecommunications filter circuit as claimed in  claim 46 , wherein said at least one first and second inductors each comprise three inductors disposed in electrical series between respective ones of said first and second input terminals and said first and second common points.  
     
     
       50. The telecommunications filter circuit as claimed in  claim 48 , wherein said at least one first and second inductors each comprise three inductors disposed in electrical series between respective ones of said first and second input terminals and said first and second common points.  
     
     
       51. A telecommunications filter circuit comprising:
 at least one first inductor electrically disposed between a first input terminal and a first common point;    at least one second inductor electrically disposed between a second input terminal and a second common point;    a correction circuit adapted to reduce return loss when equipment connected to said filter circuit changes state, said correction circuit comprising first and second tank circuits disposed in parallel and interconnected between said common points and output terminals, said first and second tank circuits each comprising at least one winding;    a first reed switch responsive to DC loop current for selectively passing current therethrough, said first switch being disposed in a dual winding inductor structure comprising said at least one windings of said first and second tank circuits; and    a second reed switch disposed in said dual winding inductor structure.    
     
     
       52. The telecommunications filter circuit as claimed in  claim 51 , wherein said at least one first and second inductors each comprise three inductors disposed in electrical series between respective ones of said first and second input terminals and said first and second common points.  
     
     
       53. The telecommunications filter circuit as claimed in  claim 51 , wherein said dual winding inductor structure comprises a bobbin, and said first and second reed switches are disposed substantially within a central region of said bobbin.  
     
     
       54. A impedance blocking filter circuit comprising:
 at least one first inductor disposed in electrical series between a first input terminal and a first common point;    at least one second inductor disposed in electrical series between a second input terminal and a second common point;    a first switch being responsive to DC loop current;    at least one capacitor disposed in electrical series with said first switch between said first and second common points;    at least one bobbin including at least first and second portions on which are wound corresponding ones of said at least one first and second inductors, said at least one bobbin being adapted to reduce intertwining capacitances so as to increase the useful frequency range of said filter circuit, said at least one bobbin further having a center portion for receiving at least a portion of said first switch;    at least one correction circuit interconnected between said common points and respective output terminals of said filter circuit, said at least one correction circuit being adapted to reduce return loss caused by inductive impedance when a customer's terminal equipment connected to said filter circuit changes state; and    a second switch and a second capacitor, said second capacitor and second switching being disposed in electrical series between third and fourth common points of said filter circuit.    
     
     
       55. An impedance blocking filter circuit as claimed in  claim 54 , wherein said first switch comprises a first switch magnetically coupled to at least one inductor of said at least one correction circuit.  
     
     
       56. An impedance blocking filter circuit as claimed in  claim 54 , wherein said at least one correction circuit comprises first and second tank circuits.  
     
     
       57. An impedance blocking filter circuit as claimed in  claim 54 , wherein the filter circuit is used in telecommunication systems for interconnecting between incoming telephone lines and customer's terminal equipment so as to unconditionally block impedances from above  20  KHz due to the customer's terminal equipment from an ADSL network unit and/or home networking interface unit.  
     
     
       58. A telecommunications filter circuit comprising:
 first inductor means electrically disposed between a first input terminal and a first common point;    second inductor means electrically disposed between second input terminal and a second common point;    first means, responsive to DC loop current, for selectively passing current therethrough;    first and second tank circuits, each of said circuits being formed of respective ones of a winding inductor, capacitor and resistor all disposed in parallel and between respective ones of said first and second common pints and output terminals, said tank circuit being adapted to reduce return loss when equipment connected to said filter circuit charges state;    third and fourth inductor means disposed electrically between respective ones of said first and second common points, and said first and second tank circuits;    second means, responsive to DC loop current, for selectively passing current; and    means for storing electrical charge disposed in electrical series with said second switch, said second switch and means for storing electrical charge being disposed substantially between said third and fourth inductor means.    
     
     
       59. A telecommunications filter circuit comprising:
 first inductor means electrically disposed between a first input terminal and a first common point;    second inductor means electrically disposed between a second input terminal and a second communication point;    first means, responsive to DC loop current, for selectively passing current therethrough;    means for providing transient suppression connected in series with at least one means for storing electrical charge, and in parallel with said first means for selectively passing current; and    correction circuit means interconnected between said common points and output terminals, said correction circuit means being adapted to reduce return loss when equipment connected to said filter circuit changes state.    
     
     
       60. A telecommunications filter circuit comprising:
 first means for providing inductance electrically disposed between a first input terminal and a first common point;    second means for providing inductance electrically disposed between a second input terminal and a second common point;    means for reducing return loss when equipment connected to said filter circuit changes state, said means for reducing return loss comprising first and second tank circuits disposed in parallel and interconnected between said common points and output terminals, said first and second tank circuits each comprising at least one winding means;    first means for switching responsive to DC loop current and adapted to selectively passing current therethrough, said first means for switch being disposed in a means for receiving at least two winding means, said at least two winding means comprising said at least one winding means of said first and second tank circuits; and    a second means for switching disposed in said means for receiving.    
     
     
       61. A impedance blocking filter circuit comprising:
 first inductive means disposed in electrical series between a first input terminal and a first common point;    second inductive means disposed in electrical series between a second input terminal and a second common point;    first means for switching, responsive to DC loop current;    at least one capacitor disposed in electrical series with said first means for switching between said first and second common points;    means for receiving including at least first and second portions on which are wound corresponding ones of said first and second inductive means, and means for receiving being adapted to reduce interwinding capacitance so as to increase the useful frequency range of said filter circuit, said at least one means for receiving further having means for receiving at least a portion of said first means for switching;    at least one correction circuit means interconnected between said common points and respective output terminals of said filter circuit, said at least one correction circuit being adapted to reduce return loss caused by inductive impedance when a customer's terminal equipment connected to said filter circuit changes stage; and    second means for switching and a second capacitor, said second capacitor and second means for switching being disposed in electrical series between third and fourth common points of said filter circuit.