WO2001076225A2

WO2001076225A2 - Video connection with power transfer

Info

Publication number: WO2001076225A2
Application number: PCT/US2001/010455
Authority: WO
Inventors: Gregor Said Jackson
Original assignee: Sony Electronics Inc.
Priority date: 2000-03-31
Filing date: 2001-03-30
Publication date: 2001-10-11
Also published as: AU2001249719A1; WO2001076225A3

Abstract

A method and apparatus for superimposing DC power on a baseband composite video signal. Negative DC power source (150) switches power into a composite video signal during a time period in which the composite video signal normally contains a horizontal and/or vertical synchronization pulse. The power signal is demultiplexed and supplied to a power storage element (150) such as a storage capacitor which supplies a switched mode power supply to supply power.

Description

VIDEO CONNECTION WITH POWER TRANSFER

FIELD OF THE INVENTION

This invention relates generally to the field of interfacing video devices to provide power along with a video signal. More particularly, this invention relates to a video connection system which transfers power from a target device such as a recorder to a source device such as a video camera or camcorder.

BACKGROUND OF THE INVENTION

When connecting a video camera or camcorder to a target device such as a video tape recorder or television set for purposes of transferring images to tape or viewing the images, it is desirable to minimize the complexity as much as possible. Minimizing the complexity facilitates enjoyment of the use of the camera or camcorder by not encumbering it with technical details. Therefore, it is desirable to minimize the number of wires and complexity of wiring to the extent possible for such interconnections.

For battery operated devices such as cameras and camcorders it is also desirable to minimize the drain on the battery or even provide charging to the battery when it is interconnected with a television or video tape recorder. Heretofore, separate connections were utilized between the camera and the target device for transferring baseband video signals from the camera or camcorder to the target device, and connections for supplying power to the camera. It would be desirable to supply power and baseband video signals over the same pair of wires so that the target device is supplying power to the camera while the camera supplies signals to the target device.

For purposes of this document, the term "baseband video" is intended to embrace both black and white baseband video, such as generally transmitted over a Y/C line (as in s-video connections provided on equipment manufactured by, for example Sony Corporation), as well as standard full color baseband composite video signals. So called, s-video connections include a Y/C connection and the color information is sent on a separate line, but such a connection can be considered baseband video nonetheless, for purposes of this document. In general, references herein to "baseband composite video" or simply "composite video" are equally applicable to other forms of baseband video as defined above.

Arrangements for having signals supplied over the same pair of wires as DC power supply signals are not new. One example of the classic technique for allowing DC and AC signals to share the same wires is shown in FIGURE 1.

FIGURE 1 represents a satellite receiver system in which a satellite receiver 10 receives RF signals from a low noise block/antenna arrangement 20 while simultaneously supplying the low noise block/antenna with DC current. As shown in FIGURE 1 , a pair of wires 24 interconnects the satellite receiver 10 with low noise block/antenna 20. The RF signal from low noise block/antenna 20 passes through a coupling capacitor 28 through wires 24 to an AC coupling capacitor 32 in the satellite receiver 10. The RF signal is thus AC coupled to permit the passage of the

RF signal. DC current, on the other hand, flows through an inductor 36 at satellite receiver 10 to the wires 24 and is similarly coupled through an inductor 40 at the low noise block/antenna 20. Thus, DC current flows through inductors 36 and 40 to supply DC current path and the RF signal passes through capacitors 28 and 32 to provide a NRF signal path. Inductors 36 and 40 serve as RF chokes to prevent RF current from flowing along the DC current path and capacitors 28 and 32 serve as DC blocking capacitors to keep the DC out of the RF signal path.

While this technique is very effective at high frequencies, it is hard to use with modern camcorder design in which the camcorder device is miniaturized to a very high degree. If the same technique were implemented in coupling a camera or camcorderto a video recorder ortelevision set, the analogous inductors to inductors 36 and 40 would have extremely high inductance value. The inductors would thus require many windings and probably a ferro-magnetic core in order to achieve suitable levels of inductance. Such inductors would negatively impact the cost and weight of both the camera and the target device. This is because the baseband video signal is a comparatively low frequency signal which will require large values of inductance to block effectively.

In some applications using 75 ohm characteristic impedance systems, a 75 ohm termination is connected to a DC voltage source instead of 75 ohms connected to ground. While this arrangement works without any need for inductors, the power that can be supplied is limited by the 75 ohm resistance at the source and at the sink, a total of 150 ohms.

While video signals could simply be offset by a DC voltage to permit the desired use of only two wires to interconnect to video equipment, the DC offset approach has a number of distinct disadvantages. In particular in the case of outdoor installations, the presence of a DC offset between the two lines can cause or exacerbate a corrosion problem. This problem can present itself in applications such as connection of recorder to an outside video surveillance camera. Corrosion can take place between connector terminals or between an exposed point of potential and nearby grounded metal (e.g. mounting brackets and the like).

In addition to the above problem with the DC offset approach, addition of a

DC offset renders the system incompatible with the composite video standard. Additionally, a DC offset can damage a device which is not designed to accept the offset if accidently connected, making it less suitable for amateur video use and may require special non-standard connectors. Moreover, the presence of a DC offset necessitates care in installation and possibly special conduit or insulators. The presence of a DC offset on the signal line can also be a shock or electrocution hazard to humans or animals that come in contact with the line. Under certain circumstances, 50 volts can be lethal to a human. Depending on the DC voltages required, a swing of 50 volts or more in this environment is not impossible to achieve.

This filtering technique, if applied to video, is also a poor approach since baseband video is comparatively low frequency. The filtering approach is likely to add some measure of distortion to video signal by virtue of the low-pass filtering effect which separates the DC from the signal.

SUMMARY OF THE INVENTION

Accordingly, a new technique is needed to permit a target device such as a television or video tape recorder to provide DC power to a camera or camcorder device.

The present invention relates generally, in certain embodiments, to a system and method for interfacing a camera or camcorder with a target device such as a video tape recorder, monitor or television set in which power is transferred to the camera or camcorder during a sync pulse (horizontal and/or vertical retrace interval). Objects, advantages and features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the invention.

In one embodiment of the present invention, a device for providing DC power to a source of baseband or other video video signals having blanking intervals, includes a baseband video receiver which receives baseband video signals over a signal wire and generates a. synchronization signal synchronized with a blanking interval. A source of DC current is provided. A switch, operates under control of the synchronization signal to selectively supply DC current from the source of DC current to the signal wire during the blanking interval.

In another embodiment of the present invention, a video signal source which receives DC power from a target device, has a baseband video transmitter which transmits baseband video signals over a signal wire and generates a synchronization signal synchronized with a blanking interval. A power storage element is provided. A switch operates to selectively supply DC current from the signal wire to the power storage element during the blanking interval. In another embodiment of the present invention, a two wire system for interconnecting a source of baseband video signals with a target device, has a ground wire and a signal wire. A baseband video receiver receives baseband video signals over the signal wire and generates a first synchronization signal synchronized with a blanking interval. A source of DC current is provided. A first switch, operating under control of the first synchronization signal selectively supplies DC current from the source of DC current to the signal wire during the blanking interval. A baseband video transmitter transmits baseband video signals over the signal wire to the baseband video receiver and generates a second synchronization signal synchronized with the blanking interval. A power storage element is provided. A second switch operates to selectively supply DC current from the signal wire to the power storage element during the blanking interval.

In a method according to an embodiment of the invention, DC power and baseband video are provided over a single pair of conductors. This method is carried out by: at a video transmitting end, transmitting a baseband video signal over the pair of conductors; receiving DC power over the pair of conductors during a blanking interval; and at a video receiving end, receiving the baseband video signal over the pair of conductors; and transmitting DC power over the pair of conductors during the blanking interval.

In another method according to an embodiment of the invention, a method of superimposing a DC power signal on a video signal is carried out by providing a video signal having a synchronization period forming a part thereof; providing a DC power signal; and multiplexing the DC power signal with the video signal so that the DC power signal occupies the synchronization period.

In yet another method according to embodiments of the invention, a method for starting a source of video, is carried out by: sending a pulse of DC power from a video target device to the source of video along a video signal path; receiving the pulse of DC power from the video target device and storing the DC power until enough power is stored to supply operating power to the source of video; and sending video signals from the source of video to the target of video.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however, both as to organization and method of operation, together with objects and advantages thereof, may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a diagram illustrating a DC transfer mechanism suitable for combination with RF signals.

FIGURE 2 is a baseband composite video signal.

FIGURE 3 is a power transfer system in accordance with an embodiment of the present invention.

FIGURE 4 is a schematic illustrating the interconnection of an exemplary capacitor storage element with a switch mode power supply.

FIGURE 5 is an illustration of a video source boot-up process using the present invention. DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail specific embodiments, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawing.

The typical field of application for this invention might be connection of a video camera or camcorder to a device such as a video tape recorder (e.g. VCR). However, the invention has general application any time it is desirable to simultaneously transfer DC power along a pair of wires which are also transferring baseband video signals or other video signals having blanking intervals. For purposes of this document, the sources of video, while discussed in terms of cameras and camcorders for ease of understanding, are not so limited. In accordance with the invention, other devices can also be supported and

The video signals that can be supported by the invention include but are not limited to s-video, PAL, Secam, ATSC (United States high definition television) and BS-DIGITA (Japanese high definition television). The present invention is applicable to any source and form of baseband video as well as to any source of video having blanking intervals. These include but are not limited to ITU-601 video, ITU-656 video, or other digital video having horizontal or vertical blanking intervals. The detail of the voltages and currents used may differ among the various video signals and particularly between analog and digital video, all are within the spirit and scope of the present invention. In some embodiments of the invention, it may preferable to keep the voltages and waveforms on the signal line within the specifications of the appropriate standards, so as to ensure compatibility, interoperability and the presence of a market that is ready for the present invention. In other embodiments, it may be preferable to use a non-standard video signal.

Further, while the invention is discussed in terms of a target device such as a video tape recorder, video cassette recorder, disc based video recorder, monitor or television set, any device receiving the video can be considered an equivalent target device. Moreover, while in the example to follow, the target device is the source of DC power, the source device could be arranged to be the source of DC power, or a device that is neither the video source nor the video target could be arranged to provide the DC power without departing from the invention.

Referring now to FIGURE 2, a baseband composite video signal 50 is illustrated (unsealed). In this signal, video information used to create screen images line by line appears above the broken line shown as 54. The period of the time between times T_{1 anc}| ₂ represent a synchronization pulse. This synchronization pulse is variously referred to as a synchronization pulse, blanking interval or retrace interval.

For standard NTSC baseband composite video, such pulses are used to control the synchronization of video equipment for both horizontal and vertical synchronization. Such pulses are extreme negative going pulses sometimes referred to as blacker than black since the composite video signal represents brightness information for the video signal being represented. In a standard NTSC composite video signal, these extreme negative going pulses occupy approximately 7.5% of the signal content. The broken line shown as 54 represents an approximate DC level, but those skilled in the art will recognize that the average DC value may fluctuate substantially in accordance with the overall brightness of the image being represented by the baseband composite video signal.

In accordance with embodiments of the present invention, the horizontal and/or vertical synchronization pulses can be advantageously utilized to transfer power from a target device to the video source. The mechanism for accomplishing this in one embodiment is shown in FIGURE 3

FIGURE 3 illustrates the interconnection of a target device 100 with a video source 110 such as a camera or camcorder. Target device 100 may represent, for example a video cassette recorder, a digital video recorder or television set. In the embodiment shown in FIGURE 3, composite video signals are transmitted by a composite video transmitter 114 along wire 116 to the target device 100. When the composite video signal reaches target device 100, it is coupled through a capacitor 120 to a composite video receiver 124. Synchronization signals 128 and 132 are derived from the composite video transmitter 114 and the composite video receiver

124 respectively. A common ground path 136 links camera 110 and target device

100 so that DC voltages enjoy a common reference point. A switch 140 at the video source side 110 is controlled by the synchronization signal 128. In a like manner, switch 144 is controlled by synchronization signal 132 at the target device 100.

A negative power source 150 supplies power through switch 144 to wire 116 during synchronization pulses. In a complimentary manner, switch 140 is synchronized to the synchronization pulse by synchronization signal 128 and the switch 140 closes to divert power from line 116 to a power storage element 150 during the occurrence of synchronization pulses. Those skilled in the art will understand that switch 140 may take many forms including that of a diode or a normally closed mechanical relay, each of which has the advantage of requiring no power during a boot-up process as will be described later. Use of a diode or normally closed relay as switch 140 permits charging of power storage element 150 without need for power when the video source 110 is being turned on. The diode implementation is also simpler and requires no sync signal from synchronization line 128 to properly function. Nonetheless, in either event, the diode operates as a switch which switches in synchronization with the synchronization pulses of the baseband video signal.

A baseband video signal can be readily derived from line 116 and 136 as illustrated by (optionally) coupling through a capacitor 156 to a conventional connector to have AC coupled composite video baseband signals available. Capacitive coupling is not needed provided that the negative power pulses substituted for the normal synchronization pulses remain within the baseband video specification of interest. In this case, the system appears to be a baseband video signal to a device which is non-compliant with the power supplying features of the present invention.

The capacitor 156 can be eliminated to provide standard baseband video provided all standards of the ratio of voltages of the video to the sync are maintained (e.g. to the NTSC specification). If this capacitor 156 is eliminated, no black-clamping is needed in a signal receiver connected thereto. Although most signal receivers have this circuitry built in, it becomes unnecessary in the present invention since the signal at the conductor pair 116 and 136 is essentially ideal to modern signal processing devices.

The power storage element 150 may, for example, include a large charge storage capacitor which supplies energy to a switching mode power supply in one embodiment. In another embodiment, power storage element 150 is converted to an appropriate voltage and current level for charging an internal battery of camera

110.

For a standard NTSC composite video signal, the negative going synchronization pulses occupy about 7.5% of the time as approximately calculated in below:

pulse time per second = [15750 X 4.7μS ] + [ 10 X 63.5μS ] = 0.0755 S

Therefore, power can be transferred approximately 7.5% of the time and the power transferred in this time needs to be approximately 14 times as large as the steady state power consumption of the video source in order to assure that a highly efficient power conversion technique can supply all of the energy required by the video source 110 for an NTSC composite video embodiment. For other embodiments (e.g. Secam, PAL and those that transfer power during only a portion of the blanking interval), these times may not be applicable and should be recalculated.

Some embodiments of the invention make power available to the video source during essentially all of the blanking intervals present in the video signal. Video source device 110 can control the rate at which power is transferred to it by varying its effective resistance during the blanking intervals and power source or storage device 150 operates to maintain the voltage on the signal line at a substantially constant level.

Other embodiments of the invention transfer power during only a portion of the blanking intervals, so as to allow other portions of the blanking intervals to transfer information. Such information can include but is not limited to electronic program guide (EPG) information. This can be accomplished in a variety of ways, including but not limited to transferring power only during horizontal blanking intervals, only during vertical blanking intervals, only during a portion of a blanking interval, or only during a subset (e.g. every other one) of the blanking intervals. For tape based camcorders, it may be desirable to supply somewhat more energy so that transient conditions such as ejecting tapes, fast forwarding, etc. to not overload the power supply mechanism. It is also desirable that a backup power source such as the video source's battery be available for short term heavy demands. It should be noted that tape based camcorders require substantially more power to operate than cameras. Therefore, it is likely that some embodiments of the present invention may not be able to supply all of the DC power required to power the source device. Nonetheless, the present invention can be utilized to extend the battery life of such devices.

Referring now to FIGURE 4, the basic arrangement for conversion of the received pulses of power into a usable supply source is illustrated. A baseband composite video signal is received by synchronization generator 114A which forms a part of composite video transmitter 114 of FIGURE 3. This synchronization signal 114 controls the switching of switch 140 so that pulses of negative voltage are supplied to power storage element 150 which in FIGURE 4 is illustrated as a large storage capacitor 150A. The stored energy in capacitor 150A is supplied to a switch mode power supply which uses it to generate positive pulses of energy which are rectified and then filtered to produce a positive supply voltage.

In the manner described above, power is essentially time division multiplexed with the image conveying portion of a composite video signal so that the time periods utilized for horizontal and/or vertical synchronization pulses are advantageously utilized to supply power. A power timing signal or synchronization can be used to control when the time is to be used for power transfer and when the power source and sink are to stay off of the signal lines so that the video signal or other information can be transferred.

Those skilled in the art will recognize that either horizontal pulses or vertical pulses could potentially be utilized for implementation of the present invention in an NTSC system. However, the preferred technique is to utilize both horizontal and vertical synchronization. Other video formats may have similar synchronization pulse times that can be utilized to transfer power without departing from the present invention.

Turning now to FIGURE 5, a camera boot-up process in accordance with an embodiment of the invention is illustrated. In this embodiment, a camera or other video source device can be turned on via the target device. At time T,, the target device is turned on or enabled. The target device 100 closes switch 144 between times T₂ and T₃ to begin sending power to the source device 110. Thus, initially, the target device is In control of the startup process. In this embodiment, switch 140 of source device 110 is normally closed so that the pulse of negative power is transferred to the power storage element 150. The pulse duration between times T₂ and T₃ may be longer than a normal horizontal or vertical synchronization pulse width in order to provide initial charge to power storage element 150, or multiple pulses could be sent in place of the single pulse illustrated.

The initial pulse or pulses may be supplied for a predetermined period of time by the target device 100, or the target device 100 may detect the presence of baseband video to complete the boot process. In any event, at time T₄, the source device 110 (e.g. camera) has stored enough energy to begin outputting a baseband video signal. Between times T₄ and T₅, and between T₆ and T₇, baseband video is transferred from the source device 110 to the target device 100. Between times T₅ and T₆, and between times T₇ and T₈, DC power is transferred in the form of negative pulses from the target device 100 to the source device 110. During this period, the video source device 110 reverts to acting as the source of synchronization pulses. In this manner, the video source device 110 can be automatically "booted up" from the video target device 100. As described, the power source 150 starts the transfers by emitting synchronization pulses. The video source 110 can synchronize itself to these synchronization pulses to maintain synchronization lock, for example, in broadcast equipment where all cameras are sync-locked to each other. The system may communicate on a periodic basis where both the target and the source will resynchronize on a periodic, pre-determined basis. Thus, a system using the present invention can be designed to have a built in synchronization or gen-locking mechanism.

In certain embodiments, power control of the camera can be implemented by simply denying power transfers to the camera to turn it off. The camera will be power starved in a short period of time and turn off. Power can be restored at will by simply re-supplying the camera with power pulses as previously described.

Those skilled in the art will recognize that certain embodiments of the present invention may be equivalently implemented using a programmed processor within the video transmitter and receiver. However, the invention should not be so limited, since the present invention could be implemented using hardware component equivalents such as special purpose hardware and/or dedicated processors which are equivalents to the invention as described and claimed. Similarly, microprocessors, microcontrollers, analog circuits, dedicated processors and/or dedicated hard wired logic may be used to construct alternative equivalent embodiments of the present invention.

Moreover, while the present invention has been specifically described in terms of a standard NTSC composite video signal, the present invention is applicable to any scanning video signal including Y/C, black and white baseband signals, s-video signals, Secam format video and PAL format video which has similar synchronization periods which could be adapted to carry DC power using the time multiplexing scheme of the present invention. The invention has been described in terms of synchronized switches 140 and 144. These switches can be implemented in any number of ways, as will be apparent to those skilled in the art. Semiconductor switches such as transistor switches and diode switches can be used as well as mechanical relays as will be understood by those skilled in the art. For systems in which the video signal is always a positive voltage and the synchronization pulses are always negative voltages, the system can advantageously use diodes as inexpensive switches which may require no synchronization signals 128 to operate per se. This has the advantage of operating without any standby power requirements at the signal source (power sink) as previously described.

While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.

Claims

What is claimed is:

5. A device for providing DC power over a video signal wire, comprising: a video receiver configured to receive a video signal over a signal wire and to generate a power timing signal synchronized with a blanking interval of the video signal; a source of DC current; and a switch, configured to selectively supply, according to the power timing signal, DC current from the source to the signal wire during at least a portion of the blanking interval.

2. The device of claim 1 , wherein the blanking interval comprises an interval selected from a horizontal blanking interval, a portion of a horizontal blanking interval, a subset of a plurality of horizontal blanking intervals, a vertical blanking interval, a portion of a vertical blanking interval, and a subset of a plurality of vertical blanking intervals.

3. The device of claim 1 , wherein the video signal is selected from an analog video signal, an NTSC video signal, a Secam video signal, a PAL video signal, a ATSC video signal, a BS-DIGITA video signal, a digital video signal, an ITU-601 video signal, an ITU-656 video signal, and a non-standard video signal.

4. A device for providing DC power over a video signal wire, comprising: a means for receiving a video signal over a signal wire and for generating a power timing signal synchronized with a blanking interval of the video signal; a means for sourcing DC current; and a means for selectively supplying, according to the power timing signal, DC current from the source to the signal wire during at least a portion of the blanking interval.

5. A video signal source which receives DC power over a video signal wire, comprising: a video signal transmitter which transmits a video signal over a signal wire and generates a control signal synchronized with a blanking interval of the video signal; a power storage element; and a switch which selectively supplies DC current from the signal wire to the power storage element according to the control signal.

6. The signal source of claim 5, wherein the blanking interval comprises an interval selected from a horizontal blanking interval, a portion of a horizontal blanking interval, a subset of a plurality of horizontal blanking intervals, a vertical blanking interval, a portion of a vertical blanking interval, and a subset of a plurality of vertical blanking intervals.

7. The signal source of claim 5, wherein the video signal is selected from an analog video signal, an NTSC video signal, a Secam video signal, a PAL video signal, a ATSC video signal, a BS-DIGITA video signal, a digital video signal, an ITU-601 video signal, an ITU-656 video signal, and a non-standard video signal.

8. The signal source of claim 5, wherein the power storage element is selected from a charge storage capacitor and a battery.

9. The signal source of claim 5, further comprising a switching mode power supply configured to receive power from the power storage element.

10. A two wire system for interconnecting a source of a video signal with a target device, comprising: a ground wire and a signal wire; a video receiver configured to receive a video signal over the signal wire and to generate a receiver synchronization signal synchronized with a blanking interval of the video signal; a source of DC current; a receiver switch, operating under control of the receiver synchronization signal, configured to selectively supply DC current from the source to the signal wire; a video transmitter configured to transmit the video signal over the signal wire to the video receiver and to generate a transmitter synchronization signal synchronized with the blanking interval; a power storage element; and a transmitter switch configured to selectively supply DC current from the signal wire to the power storage element according to the transmitter synchronization signal.

11. The device of claim 10, wherein the blanking interval comprises an interval selected from a horizontal blanking interval, a portion of a horizontal blanking interval, a subset of a plurality of horizontal blanking intervals, a vertical blanking interval, a portion of a vertical blanking interval, and a subset of a plurality of vertical blanking intervals.

12. The signal source of claim 10, wherein the video signal is selected from an analog video signal, an NTSC video signal, a Secam video signal, a PAL video signal, a ATSC video signal, a BS-DIGITA video signal, a digital video signal, an ITU-601 video signal, an ITU-656 video signal, and a non-standard video signal.

13. The signal source of claim 10, wherein the power storage element is selected from a charge storage capacitor and a battery.

14. A method for providing DC power and video over a single pair of conductors, comprising: transmitting a video signal over the pair of conductors; receiving DC power over the pair of conductors during a blanking interval of the video signal; receiving the video signal over the pair of conductors; and transmitting DC power over the pair of conductors during the blanking interval.

15. The method of claim 14 wherein the transmitting of the video signal and the receiving of the DC power occur at one end of the pair of conductors, and the receiving of the video signal and the transmitting of the DC power occur at another end of the pair of conductors.

16. The method of claim 14 wherein the transmitting of the video signal and the transmitting of the DC power occur at one end of the pair of conductors, and the receiving of the video signal and the receiving of the DC power occur at another end of the pair of conductors.

17. The method of claim 14, further comprising storing the DC power in a storage element at a video receiving end of the pair of conductors.

18. The method of claim 14, wherein the blanking interval comprises at least one interval selected from of a vertical blanking interval, a portion of a vertical blanking interval, a horizontal blanking interval and a portion of a horizontal blanking interval.

19. The method of claim 14, wherein the video signal is selected from an analog video signal, an NTSC video signal, a Secam video signal, a PAL video signal, a ATSC video signal, a BS-DIGITA video signal, a digital video signal, an ITU-601 video signal, an ITU-656 video signal, and a non-standard video signal.

20. A method of superimposing a DC power signal on a video signal, comprising: providing a video signal having a synchronization period forming a part thereof; providing a DC power signal; and multiplexing the DC power signal with the video signal so that the DC power signal occupies at least a portion of the synchronization period.

21. The method of claim 20, further comprising storing the DC power in a storage element.

22. The method of claim 20, wherein the blanking interval comprises at least one interval selected from a vertical blanking interval, a portion of a vertical blanking interval, a horizontal blanking interval and a portion of a horizontal blanking interval.

23. The method of claim 20, wherein the video signal is selected from an analog video signal, an NTSC video signal, a Secam video signal, a PAL video signal, a ATSC video signal, a BS-DIGITA video signal, a digital video signal, an ITU-601 video signal, an ITU-656 video signal, and a non-standard video signal.

24. A method for starting a source of video, comprising: sending at least one initialization pulse of DC power along a video signal path from a video target device to a video source device; receiving the initialization pulse from the video signal path and storing the DC power in the video source device; and starting to send a video signal from the video source device to the video device.

25. The method of claim 24, further comprising sending a subsequent pulse of DC power to the video source device during a synchronization period of the video signal.

26. The method of claim 24, wherein the target device sends the initialization pulse for a predetermined period of time before receiving the video signal.

27. The method of claim 24, wherein the target device sends the initialization pulse until enough power is stored to supply operating power to the video source device.

28. The method of claim 24, wherein the video signal is selected from an analog video signal, an NTSC video signal, a Secam video signal, a PAL video signal, a ATSC video signal, a BS-DIGITA video signal, a digital video signal, an ITU-601 video signal, an ITU-656 video signal, and a non-standard video signal.