Cable network interface circuit
View Patent ↗An input section of an RF interface is shown in conjunction with a tuner circuit. The input, in one embodiment, is constructed using co-planner wave guide techniques and serves to provide low return loss, low insertion loss, high voltage protection, all within a single housing without causing RF interference problems.
1. An interface device for use as a front end to an RF processing circuit, said device comprising:
an input coaxial connector, said input connector having a center conductor and an outer shield;
an output coaxial connector, said output connector having a center conductor and an outer shield;
a housing for containing said device, said outer shields connected to said housing;
an inductance having one of its terminals connected to said input center conductor, and the other of its terminals connected to a second capacitor and also connected to a power bias tap;
a capacitance having one of its terminals connected to said input center conductor and the other of its terminals connected to the input of a directional coupler, said directional coupler having low insertion loss; and
said directional coupler having an output connected to said center conductor of said output coaxial connector, aid having a connection to said RF processing circuit.
2. The interface device of claim 1 wherein said directional coupler is connected also to one terminal of a second capacitance and a second terminal of said second capacitance connected to said output center conductor.
3. The interface device of claim 2 wherein at least a portion of the connections between said input connector, said output connector, said first capacitor, said inductance and said directional coupler is constructed using co-planar wave guides.
4. The interface device of claim 2 wherein said capacitors are safety caps.
5. The interface device of claim 3 wherein said housing also includes therein an RF transmitter for transmitting RF signals to said input coaxial cable via said directional coupler, said directional coupler operational for preventing transmitted ones of said RF signals from said RF transmitter from going to said output coaxial connector.
6. The interface device of claim 5 wherein said housing includes a digital connector for delivering digital signals to said RF transmitter and for receiving digital signals from said RF receiver.
7. An interface device for use as a front end to an RF processing circuit, said device comprising:
an input connector, said input connector having a first conductor;
an output connector, said output connector having a first conductor;
a directional coupler disposed in a signal path between said input connector and said output connector, wherein an input of said directional coupler is coupled to said input connector first conductor and an output of said directional coupler is coupled to said output connector first conductor, and wherein said directional coupler provides a connection to said RF processing circuit;
an inductor having a plurality of terminals, wherein one of said plurality of terminals is coupled to said input connector first conductor, and another of said plurality of terminals is coupled to a first capacitor and to a power bias tap; and
a capacitor having a plurality of terminals, wherein one of said plurality of terminals is coupled to said input connector first conductor and another of said plurality of terminals is coupled to said input of said directional coupler.
8. The interface device of claim 7 , wherein said inductor comprises a radio frequency choke.
9. The interface device of claim 7 , wherein said input connector and said output connector comprise coaxial connectors.
10. The interface device of claim 9 , further comprising:
a housing for containing said device, wherein an outer shield of each of said input connector and said output connector are coupled to said housing.
11. The interface device of claim 7 , wherein said directional coupler has a low insertion loss associated therewith as disposed in said signal path.
12. The interface device of claim 7 , wherein said directional coupler taps off radio frequency signals input to said input connector.
13. The interface device of claim 7 , wherein said power bias tap provides power isolated from said radio frequency signals input to said input connector.
14. The interface device of claim 13 , further comprising:
a surge protection circuit coupled to said power bias tap.
15. The interface device of claim 7 , further comprising:
a signal denial circuit disposed in said signal path between said input connector and said output connector.
16. The interface device of claim 7 , wherein said signal path comprises a co-planer waveguide.
17. The interface device of claim 7 , wherein said interface device comprises a cable television front end interface device.
18. The interface device of claim 7 , wherein said interface device comprises a cable modem front end interface device.
19. An interface for use as a front end to an RF processing circuit, said device comprising:
a directional coupler disposed in a signal path between an input to said interface and an output of said interface, wherein an input of said directional coupler is coupled to said input of said interface and an output of said directional coupler is coupled to said output of said interface, and wherein said directional coupler provides a signal input at said input of said interface to said RF processing circuit; and
a power bias tap coupled to said signal path, wherein said power bias tap provides an alternating current bias power signal isolated from said signal input at said input of said interface.
20. The interface of claim 19 , wherein said power bias tap is coupled to said input of said interface via an inductance.
21. The interface of claim 19 , wherein said directional coupler is coupled to said input of said interface via a capacitance.