POWER OVER COAXIAL CABLE

• US 20130187445A1
• Filed: 06/27/2012
• Published: 07/25/2013
• Est. Priority Date: 01/20/2012
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: MUTZABAUGH, Dennis M.
• Granted Patent: US 9,252,842 B2
• Time in Patent Office: Days
• US Class Current: 307/1
• CPC Class Codes: H04B 2203/547 via DC power distribution
• CPC Class Codes: H04B 2203/5487 cables
• CPC Class Codes: H04B 3/54 Systems for transmission via power distribution lines
• CPC Class Codes: H04B 3/548 the power on the line being DC arrangements for feeding power H04L12/10; extracting feeding power from signals H04L25/02

Abstract

An image communication system includes a coaxial cable having first and second ends. A monitor station is coupled to the first end and a camera is coupled to the second end. The monitor station provides power to the camera through the cable, while the cable is also used to carry communication signals transmitted by the camera to the monitor station. The image communication system includes a first active inductor coupled to the first end and a second active inductor coupled to the second end. A current-compensation circuit may also be provided.

Claims

1. A system, comprising:

a first active inductor coupled between an input power supply and a first end of a cable that is operable to carry a communication signal;

a current-compensation circuit coupled between the second active inductor a second end of the cable and an output power supply; and

a second active inductor coupled between the second end of the cable and the compensation circuit;

wherein the first and second active inductors are configured to enable power to pass through the cable from the input power supply to the output power supply, and

wherein the current-compensation circuit is configured to reduce voltage spikes across the active inductors.

2. The system of claim 1 wherein the cable includes a coaxial cable.

3. The system of claim 1, further comprising a camera coupled to the output power supply.

4. The system of claim 1, further comprising a monitor station coupled to the first end of the cable.

5. The system of claim 1 wherein the monitor station includes a recording device.

6. The system of claim 1 wherein the output power supply includes a switch mode power supply configured to down convert a voltage from the input power supply to a lower voltage.

7. The system of claim 1, further comprising:

over current sense circuitry coupled to the first active inductor, and configured to sense an over current in the first active conductor and configured to generate a signal in response to the sensed over current; and

control circuitry coupled to the over current sense circuitry to receive the generated signal, and configured to deactivate the first active inductor in response to the received generated signal.

8. The system of claim 1, further comprising:

no load sense circuitry coupled to the cable, and configured to sense disconnection of the cable and configured to generate a signal in response to the sensed disconnection; and

control circuitry coupled to the no load sense circuitry to receive the generated signal, and configured to deactivate the first active inductor in response to the received generated signal.

9. The system of claim 1, further comprising automatic reconnection circuitry coupled to the cable and configured to automatically attempt connection of power to the cable after disconnection of the cable is sensed.

10. The system of claim 1, further comprising surge protection circuitry coupled to either or both the first and second ends of the cable, and configured to reduce voltage spikes on the cable.

11. An apparatus, comprising:

a gyrator circuit configured as an active inductor to enable power to be passed along a coaxial cable, the gyrator circuit including;

an active device; and

first and second resistors and a capacitor coupled to the active device,

wherein an inductance provided by the gyrator circuit is approximated according to values of the first and second resistors and the capacitor, and

wherein the inductance enables the active inductor to have low impedance at a direct current frequency and high impedance at a higher frequency corresponding to a frequency of a video signal carried on the coaxial cable.

12. The apparatus of claim 11 wherein the inductance is approximated according to a relationship L˜

=Re*C1*R1, wherein Re, R1, and C1 are the values, respectively, of the first resistor, the second resistor, and the capacitor.

13. The apparatus of claim 11 wherein the gyrator circuit further includes a third resistor coupled to the active device to provide positive feedback to enable bootstrapping.

14. An apparatus, comprising:

a current-compensation circuit coupleable to a coaxial cable that carries both a power signal and a video signal, wherein the current-compensation circuit is configurable to reduce voltage spikes in the coaxial cable and in at least one active inductor coupled to the coaxial cable.

15. The apparatus of claim 14 wherein to reduce voltage spikes, the current-compensation circuit is configured to:

split an inductor current of the active inductor into a load current and a compensation current; and

in response to a change in the load current, offset the change in the load current with an equal and opposite change in the compensation current, such that a net change in the inductor current is approximately zero.

16. The apparatus of claim 15 wherein the current-compensation circuit includes:

a sense resistor;

a capacitor;

first and second voltage dividers; and

an operational amplifier having first input terminal coupled to the capacitor and to the first voltage divider, and having a second input terminal coupled to the second voltage divider,

wherein the change in the load current is sensed across the sense resistor, and a change in a voltage across the sense resistor affects a voltage at the second input terminal of the operational amplifier,

wherein a reference voltage is set using the capacitor and the first voltage divider at the first input terminal of the operational amplifier, and

wherein the operational amplifier is configured to control the compensation current according to the change in the load current at the first input terminal.

17. A method, comprising:

using first and second active inductors to pass power from a power supply coupled to a first end of a coaxial cable to a camera coupled to a second end of the coaxial cable, wherein the power is passed along the coaxial cable; and

compensating for a change in a load current drawn by the camera that may cause voltage spikes in either or both the active inductors and the coaxial cable, wherein said compensating including filtering the voltage spikes so as to reduce an effect of the voltage spikes on a video signal transmitted by the camera on the coaxial cable.

18. The method of claim 17 wherein said compensating further includes:

split an inductor current of the second active inductor into the load current and a compensation current; and

in response to the change in the load current, offset the change in the load current with an equal and opposite change in the compensation current, such that a net change in the inductor current is approximately zero.

19. The method of claim 17, further comprising using a surge protection circuit to protect the camera from voltage transients in response to connection or disconnection of the coaxial cable while power is being provided on the coaxial cable.

20. The method of claim 17, further comprising:

sensing an over current in the first active conductor and generating a signal in response to the sensed over current; and

deactivating the first active inductor in response to the generated signal.

21. The method of claim 17, further comprising:

sensing disconnection of the cable and generating a signal in response to the sensed disconnection; and

deactivating the first active inductor in response to the generated signal.

22. The method of claim 17, further comprising automatically attempting reconnection of power to the cable after disconnection of the cable is sensed.