Transmission of ethernet signals and power over coaxial cable

System, apparatus and method for transmission of 10/100Base-T Ethernet signals and electrical power over a coaxial cable are disclosed. The system includes a first media converter and a second media converter which are connected by the coaxial cable. The first media converter is connectable to a power sourcing equipment (PSE) and the second media converter is connectable to a powered device (PD). The two media converters are configured to enable transmission of 10/100Base-T Ethernet signals between the first network device and the second network device over the coaxial cable, and the two media converters are further configured to provide a passive DC circuit path between the PSE and PD for the PSE to deliver electrical power to the PD over the coaxial cable. According to one embodiment of the invention, the two media converters are swappable and are passive devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from U.S. Provisional Application No. 62/287,606 filed Jan. 27, 2016, which is incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to the Ethernet, in particular, relates to transmission of 10/100Base-T Ethernet signals and electrical power over a coaxial cable.

BACKGROUND OF THE INVENTION

10Base-T and 100Base-TX (hereafter referred to as 10/100Base-T Ethernet) are Ethernet protocols defined in the IEEE 802.3 Ethernet specification for transmission of Ethernet signals over a network cable at 10 Mbps and 100 Mbps respectively. The network cable (e.g., Cat5E cable) usually consists of four twisted pairs, of which one twisted pair carries Ethernet signal sent from one network device to a connected network device and another twisted pair carries Ethernet signal sent in the opposite direction between the two connected network devices. The remaining two twisted pairs are left unused. The two twisted pairs that carry bi-directional Ethernet signals are usually referred to as data pairs and the two unused twisted pairs are usually referred to as spare pairs.

With the advent of Power-over Ethernet (PoE) technology, electrical power from a network device can also be delivered to a connected network device over a shared network cable so that the connected network device can be advantageously powered without a separate power cord. According to the PoE technology as defined in the IEEE 802.3af and 802.3at specification, the network device which outputs electrical power onto the shared network cable is referred to as a Power Source Equipment (PSE) such as an Ethernet switch with the PoE capability, and the connected network device which receives electrical power from the PSE over the shared network cable is referred to as a Power Device (PD) such as a PoE powered IP (Internet Protocol) phone. Specifically, there are two power delivery modes referred to as “Mode A” and “Mode B” for delivering electrical power over the shared network cable according to the PoE specification. “Mode A” uses the two data pairs of a network cable for delivering electrical power, and “Mode B” uses the two spare pairs of a network cable for delivering electrical power; a PSE usually supports either “Mode A” or “Mode B”, and a PD must support both “Mode A” and “Mode B”. “Mode A” and “Mode B” are also commonly referred to as Endspan and Middlespan, respectively. It can be seen that for a 10/100Base-T PSE operating in “Mode A”, only the two data pairs of a network cable are used.

Although 10/100Base-T Ethernet technology and the PoE technology were originally developed for transmission of Ethernet signals and electrical power over a network cable of four twisted pairs or at least two twisted pairs, there have been great commercial interests in techniques for transmission of 10/100Base-T Ethernet signals (4-wire based signals) and electrical power over a coaxial cable which is a 2-wire transmission medium. For example, as more and more video surveillance systems worldwide are migrating from analog video systems to IP camera based digital video systems, techniques of transmission of 10/100Base-T Ethernet signals and electrical power over a coaxial cable can make it possible to reuse the existing coaxial cables in a retired analog video system for transmission of IP videos and for delivering electrical power to power IP cameras, which can bring down overall system costs significantly by not having to install new network cables.

In view of the foregoing, there is a need for improved and more cost-effective system, apparatus and method for transmission of Ethernet signals and electrical power over a coaxial cable.

DETAILED DESCRIPTION OF THE INVENTION

Several aspects of the present invention are described below with reference to examples for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the present invention. One skilled in the relevant art, however, will readily recognize that the present invention can be practiced without one or more of the specific details, or with other methods, etc. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the features of the present invention.

As is shown inFIG. 1, a first media converter10-1is connected via its twisted-pair cable interface110-1to a PSE50by a network cable55, the twisted-pair cable interface110-1transmits Ethernet signal to the PSE50using one of the two data pairs of the network cable55and receives Ethernet signal from the PSE50using the other data pair of the network cable55. If the PSE50operates in “Mode A” of the PoE technology, it delivers electrical power using the same two data pairs of the network cable55into the twisted-pair cable interface110-1; if the PSE50operates in “Mode B” of the PoE technology, it delivers electrical power using two spare pairs of the network cable55into the twisted-pair cable interface110-1. The first media converter10-1is also connected to a second media converter10-2by a coaxial cable65via their respective coaxial cable interfaces120-1and120-2, one at each end of the coaxial cable65. The second media converter10-2is further connected via its twisted-pair cable interface110-2to a PD60by a network cable75, the twisted-pair cable interface110-2transmits Ethernet signal to the PD60using one of the two data pairs of the network cable75and receives Ethernet signal from the PD60using the other data pair of the network cable75. The PD60also receives electrical power output from the twisted-pair cable interface110-2using at least two twisted pairs of the network cable75selected from either two data pairs or two spare pairs or all the four twisted pairs, depending on how electrical power is delivered from the PSE50.

According to the present invention as depicted inFIG. 1, the first media converter10-1and the second media converter10-2are configured to enable transmission of bi-directional 10/100Base-T Ethernet signals between the PSE50and the PD60over the coaxial cable65.

According to one aspect of the present invention, the first media converter10-1and the second media converter10-2are configured to establish a passive direct-current (DC) circuit path so that the PSE50can directly send electrical power over the coax cable65to the PD60. The passive DC circuit path is an uncontrolled circuit path for the flow of electrical power without any control means using active components which need electrical power to operate. Typical active components may include power gating components such as power MOSFETs (metal-oxide semiconductor field-effect transistors) which can be used to enable or disable the flow of electrical power and DC/DC converters which are commonly used to adjust or boost voltage levels of electrical power. On the other hand, diodes are not considered actives components.

According to another aspect of the present invention, the first media converter10-1and the second media converter10-2are functionally identical and therefore the two media converters10-1and10-2are swappable directly. In other words, any of the two media converters10-1and10-2can be used to connect to either the PSE50or the PD60without being reconfigured by a hardware or software means. As a result, the DC circuit path allows bi-directional flow of electrical power. Using two identical media converters in the system ofFIG. 1offers a very desirable advantage for making product manufacturing/management more cost-effective and also simplifying system installations and maintenance.

According to another aspect of the present invention, both of the first media converter10-1and the second media converter10-2are passive devices which do not need power to operate, and each of which is made of passive components such as resistors, capacitor, inductors, electrical magnetic coils and etc.

In addition, the first media converter10-1may be integrated into the PSE50according to the present invention.

FIG. 2shows a first example of a media converter in accordance with one or more embodiments of the present invention. The media converter10A shown inFIG. 2is an implementation for use with a PSE compatible with “Mode A” of the PoE specification. As such, the media converter10A can be used as the media converter10-1ofFIG. 1when the PSE inFIG. 1operates in “Mode A” of the PoE specification.

As shown inFIG. 2, the media converter10A includes a signal converter100, a RJ45 connector110as the twisted-pair cable interface110-1inFIG. 1and a coaxial connector120as the coaxial cable interface120-1inFIG. 1. The RJ45 connector110has 8 conductor pins 1-8 for engaging with four twisted pairs of a connected network cable which connects a network device such as the PSE50or PD60inFIG. 1. According to the Ethernet technology, pin 1 and pin 2 of the RJ45 connector110engages with one of the two data pairs which carries 10/100Base-T Ethernet signal being transmitted from the network device to the media converter10A, pin 3 and pin 6 of the RJ45 connector110engages with the other data pair which carries 10/100Base-T Ethernet signal being transmitted to the network device from the media converter10A.

The coaxial connector120is a 2-wire connector such as a BNC or F-type coaxial connector for connecting with a coaxial cable. The coaxial cable carries bi-directional 10/100Base-T Ethernet signals and electrical power as described with reference toFIG. 1.

The signal converter100is a 3-port circuit module with an input port (T+, T−)106, an output port (R+, R−)108and a bi-directional I/O port (TR+, TR−)112. The two terminals of the input port (T+, T−)106are wired with one side of a first transformer105and pin 1 and pin 2 of the RJ45 connector110are wired with the other side of the first transformer105. As such, a transformer-based alternating current (AC) signal coupling is provided for the input port106to receive Ethernet signal carried by the data pair of the network cable which engages with pin 1 and pin 2 of the RJ45 connector110.

The two terminals of the output port (R+, R−)108are wired with one side of a second transformer115and pin 3 and pin 6 of the RJ45 connector110are wired with the other side of the second transformer115. As such, a transformer-based AC signal coupling is provided for the output port108to output Ethernet signal to the data pair of the network cable which engages with pin 3 and pin 6 of the RJ45 connector110.

The two terminals of the bi-directional I/O port (TR+, TR−)112are wired with two capacitors135respectively which provides a capacitor-based AC signal coupling between input/output signals at the bi-directional I/O port112and the bi-directional Ethernet signals on the coaxial cable which is connected to the coaxial connector120.

The signal converter100operates in such a way that it enables 4-wire based signals, i.e., the transmit signal and receive signal of 10/100Base-T Ethernet carried respectively by two separate data pairs of the network cable, to be communicated over the 2-wire coaxial cable. Technically, the signal converter100includes circuitry to perform functions such as 4/2-wire signal conversions between two channels of balanced twisted-pair signals and one channel of unbalanced coaxial cable signals, impedance matching between the a twisted-pair (e.g., 100 ohm) and a coaxial cable (e.g., 75 ohm), echo cancellation and etc.

According to the PoE technology, a PSE operating in “Mode A” delivers electrical power using two data pairs of a network cable. As such, if the media converter10A is connected to a PSE of “Mode A”, the voltage of the electrical power from the PSE operating in “Mode A” will be presented between the center tap102of the first transformer105and the center tap104of the second transformer115. As is shown inFIG. 2, the voltage of the electrical power is sent to and is filtered by a low-pass filter (LPF)125. The output of LFP125is connected directly to the coaxial connector120so that the filtered electrical power is applied onto the connected coaxial cable. Use of the LPF125is to prevent any noises of higher frequencies associated with the electrical power from interfering or “polluting” the bi-directional Ethernet signals which is AC-coupled from the bi-directional I/O port112to the coaxial connector120and is superimposed with the electrical power for transmission over the coaxial cable connected to the coaxial connector120. In other words, use of LPF125is to provide an effective isolation of noises of electrical power from the Ethernet signals. The LPF125can be implemented as simple as a circuit with an inductor.

Being a portion of the passive DC circuit path for delivering electrical power, which is previously described with reference toFIG. 1, the media converter10A presents itself as a segment of the passive DC-circuit path for electrical power to pass between the RJ45 connector110and the coaxial connector120. Furthermore, current flow of electrical power along the segment of the passive DC circuit path may be bi-directional, either from the RJ45 connector110to the coaxial cable connector120or from the coaxial connector120to the RJ45 connector110.

As can be further appreciated, the media converter10A as described with reference toFIG. 2can be used for connecting to either a PSE operating in “Mode A” or a PD. When the media converter10A is connected to a PSE of “Mode A”, the electrical power is received at the RJ45 connector110and is output at the coaxial connector120. When the media converter10A is connected to a PD, the electrical power is received at the coaxial connector120and is output at the RJ45 connector110.

In addition, both the signal converter100and the LPF125can be implemented with purely passive components, making the whole media converter10A a passive device.

FIG. 3shows a second example of a media converter in accordance with one or more embodiments of the present invention. The media converter10B shown inFIG. 3is an implementation for use with a PSE compatible with “Mode B” of the PoE specification. Therefore, the media converter10B can be used as the media converter10-1ofFIG. 1when the PSE inFIG. 1operates in “Mode B” of the PoE specification.

The media converter10B as shown inFIG. 3includes a signal converter100, a RJ45 connector110, a coaxial connector120, two AC-coupling capacitors135and a low-pass Filter LFP125which are exactly the same as their counterparts inFIG. 2and therefore are referenced with the same reference numbers as those inFIG. 2.

The media converter10B as shown inFIG. 3differs from the media converter10A inFIG. 2in two aspects as will be described in the following.

First, the two terminals of the input port (T+, T−)106of the signal converter100are wired directly to pin 1 and pin 2 of the RJ45 connector110, and the two terminals of the output port (R+, R−)108of the signal converter100are wired directly to pin 3 and pin 6 of the RJ45 connector110. As such, Ethernet signals on the two data pairs of a network cable connected to the RJ45 connector110are directly coupled to the input port106and the output port108of the signal converter100respectively.

Secondly, pin 4 and pin 5 of the RJ45 connector110are wired together, and pin 7 and pin 8 of the RJ45 connector110are wired together. This is done for the media converter10B to receive electrical power from a connected PSE operating in the “Mode B” of the PoE specification which uses two spare pairs of the connected network cable to deliver electrical power. According to the Ethernet technology, one spare pair of the connected network cable engages with pin 4 and pin 5 of the RJ45 connector110, and the other spare pair of the connected network cable engages with pin 7 and pin 8 of the RJ45 connector110. As shown inFIG. 3, the voltage of the electrical power, which is presented between pin 4/5 and pin 7/8 of the RJ45 connector110, is sent to and filtered by the LPF125and then applied onto the coaxial connector120.

As can be appreciated, the media converter10B provides all the functionality and inventive features as the media converter10A inFIG. 2does except for that the media converter10B is compatible only with a PSE operating in “Mode B”.

The media converter10B can also be used as the second media converter10-2inFIG. 1which connects with the PD60. In such a case, it receives electrical power from the coaxial cable65and delivers the received electrical power to the PD60over the network cable75.

Furthermore, according to one embodiment of the present invention, a media converter10A inFIG. 2and a media converter10B inFIG. 3are used as the two media converters10-1and10-2inFIG. 1. Such a combination of media converters10A and10B for the communication system depicted inFIG. 1can advantageously support a PSE of either “Mode A” or “Mode B” of the PoE specification. In other words, if the PSE50inFIG. 1operates in the “Mode A” of the PoE specification, the media converter10A will be used as the first media converter10-1and the media converter10B will be used as the second media converter10-2; If the PSE50inFIG. 1operates in the “Mode B” of the PoE specification, the media converter10B will be used as the first media converter10-1, and the media converter10A will be used as the second media converter10-2.

FIG. 4shows a third example of a media converter in accordance with one or more embodiments of the present invention. The media converter10C shown inFIG. 4is an implementation for use with a PSE compatible with either “Mode A” or “Mode B”. Therefore, the media converter10C can be used as the media converter10-1ofFIG. 1regardless of the power delivery modes of the PSE inFIG. 1

The media converter10C as shown inFIG. 4includes a signal converter100, a RJ45 connector110, a coaxial connector120, two transformers105and115with respective center taps102and104, two AC-coupling capacitors135and a low-pass Filter LFP125which are exactly the same as their counterparts inFIG. 2and therefore are referenced with the same reference numbers as those inFIG. 2.

The only difference between the media converter10C as shown inFIG. 4and the media converter10A as shown inFIG. 2is that pin 4 and pin 5 of the RJ45 connector110are wired together with the center tap102of the first transformer105, and pin 7 and pin 8 of the RJ45 connector110are wired together with the center tap104of the second transformer115.

As such, the media converter10C is able to receive electrical power from a connected PSE that operates in either “Mode A”, which uses the two data pairs of a connected network cable to deliver electrical power, or “Mode B”, which uses the two spare pairs of a connected network cable to deliver electrical power.

As can be appreciated, the media converter10C provides all the functionality and inventive features as the media converter10A inFIG. 2does in addition that the media converter10C is also compatible with a PSE operating in either “Mode A’ or “Mode B”.

As can be further appreciated, the media converter10C can also be used as the second media converter10-2inFIG. 1which connects with the PD60. In such a case, it receives electrical power from the coaxial cable65and delivers the received electrical power to the PD60over the network cable75.

Although the present invention has been described in terms of various embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all changes and modifications as fall within the true spirit and scope of the invention. As a result, the invention is not limited to the specific examples and illustrations discussed above, but only the following claims and their equivalents.