Patent Application
20060215680
The present invention relates generally to power distribution, and more particularly, a solid state transformerless method for coupling high bandwidth data signals and power signals between a network and a network attached device.
Many networks such as local and wide area networks (LAN/WAN) structures are used to carry and distribute data communication signals between devices. The various network elements include hubs, switches, routers, and bridges, peripheral devices, such as, but not limited to, printers, data servers, desktop personal computers (PCs), portable PCs and personal data assistants (PDAs) equipped with network interface cards. All these devices that connect to the network structure require power in order to operate. The power of these devices may be supplied by either an internal or an external power supply such as batteries or an AC power via a connection to an electrical outlet.
Some network solutions offer to distribute power over the network in addition to data communications. The distribution of power over a network consolidates power and data communications over a single network connection to reduce the costs of installation, ensures power to key network elements in the event of a traditional power failure, and reduces the number of required power cables, AC to DC adapters, and/or AC power supplies which create fire and physical hazards. Additionally, power distributed over a network such as an Ethernet network may provide an uninterruptible power supply (UPS) to key components or devices that normally would require a dedicated UPS.
Additionally, the growth of network appliances, such as but not limited to, voice over IP (VOIP) telephones require power. When compared to their traditional counterparts, these network appliances require an additional power feed. One drawback of VOIP telephony is that in the event of a power failure, the ability to contact to emergency services via an independently powered telephone is removed. The ability to distribute power to network appliances or key circuits would allow network appliances, such as the VOIP telephone, to operate in a similar fashion to the ordinary analog telephone network currently in use.
The distribution of power over Ethernet network connections is in part governed by the IEEE Standard 802.3 and other relevant standards. These standards are incorporated by reference. However, these power distribution schemes within a network environment typically require cumbersome, real estate intensive, magnetic transformers. Additionally, power over Ethernet (PoE) requirements under 802.3 are quite stringent and often limit the allowable power.
There are many limitations associated with using these magnetic transformers. Transformer core saturation can limit the current that can be sent to a power device. This may further limit the performance of the communication channel. The cost and board space associated with the transformer comprise approximately 10 percent of printed circuit board (PCB) space within a modern switch. Additionally, failures associated with transformers often account for a significant number of field returns. The magnetic fields associated with the transformers can result in lower electromagnetic interference (EMI) performance.
However, magnetic transformers also perform several important functions such as providing DC isolation and signal transfer in network systems. Thus, there is a need for an improved approach to distributing power in a network environment that addresses limitations imposed by magnetic transformers while maintaining the benefits thereof.
Embodiments of the present invention provide a system and method operable to provide a voltage power feed on differential cable pairs to network attached powered devices (PD). This voltage power feed to PDs substantially addresses the above identified needs, as well as others. More specifically, one embodiment of the present invention provides a power feed circuit operable to supply power to a network attached PD. In one embodiment, this power feed circuit includes two differential transistor pairs wherein each transistor within the differential transistor pair is operable to pass a network power signal. Pairs of sense impedances couple to the differential transistors. Each sense impedance is operable to pass the network power signal received from the drain of the electrically coupled transistor. An amplifier couples to the drains of each differential transistor pair wherein this amplifier is operable to sense a differential voltage across the pair of impedances sensors. The amplifier then applies feedback signal(s) to the gate of individual differential transistors based on the differential voltage. This feedback system forces the network power signal passed by each transistor in a differential transistor pair to be equal. Other embodiments may balance the network power signal passed by each transistor based on other criteria. A pair of output nodes feed power to the network attached device. One output node is associated with each differential transistor pair and the pair of output nodes then feeds power to the network attached PD.
The power feed circuit may be implemented as a set of discrete components on a printed circuit board (PCB) or network interface card (NIC), or alternatively, the power feed circuit can be implemented in an integrated circuit (IC) that may contain other functional units or modules. This power feed circuit and additional embodiments may further include splitting circuitry operable to separate data signals from the network power signal and then pass the data signal to a network physical layer (PHY) module. This splitting circuitry may include direct current (DC) blocking capacitors in order to separate the data signal from the network power signal. Other embodiments of the power feed circuit may include or couple to a protection circuit and/or a rectifying/switching circuit. Such a protection circuit may provide surge protection (i.e. voltage spike and lightning protection) for incoming network signals. The rectifying/switching circuit may receive the output of the protection circuit and rectify or switch the power signal to ensure power with a proper polarity is applied to the IC. The protection and rectifying/switching circuits may not be required in a back plane application where the polarity of the power signal is known.
Another embodiment provides a method to at least partially power a network attached PD from a network power signal fed through the network connection. This will involve physically coupling the network attached PD to an available network. Then a network signal that includes power signals and/or data signals may be received by the network attached PD. This power signal may be passed through optional protection and/ or rectifying/switching circuits/modules. Then the power signal is passed to a power feed circuit implemented as discrete components on a board or within an IC. The power feed circuit separates the data signal from the network signal and then passes the data signal to the network PHY. The power signal also separated from the network signal is passed to a power management module in order to at least partially power the network attached device.
Yet another embodiment provides a method to at least partially power a network attached device from a power signal feed from the attached network. First network power signals are received with an appropriate polarity. These network power signals can then be passed through differential transistor pairs. The drain voltage of each drain of each differential transistor may be sensed and then compared. The result of this comparison may be used to generate a pair of control signals for each differential transistor pair. These control signals may be then be applied to the gate of each transistor in order to force the network power signal passed by each transistor of the differential transistor pair to be equal or balanced based on other criteria. The power signal may then be passed from a pair of output nodes associated with the differential transistors in order to feed power to the network attached device.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings wherein:
Preferred embodiments of the present invention are illustrated in the FIGS., like numerals being used to refer to like and corresponding parts of the various drawings.
The 802.3 Ethernet network Standards, which is incorporated herein by reference, allow loop powering of remote Ethernet network devices (802.3af). The Power over Ethernet (PoE) standard and other like standards intends to standardize the delivery of power over Ethernet network cables in order to have remote client devices powered through the network connection. The side of link that supplies the power is referred to as Powered Supply Equipment (PSE). The side of link that receives the power is referred to as the Powered device (PD).
Replacing the magnetic transformer of prior systems while maintaining the functionality of the transformer has been subsumed into the embodiments of the present invention. In order to subsume the functionality of the transformer, the circuits provided by embodiments of the present invention, which may take the form of ICs or discrete components, are operable to handle these functions. These functions may include, in the case of an Ethernet network application:
In a solid-state implementation, common mode isolation between the earth ground of the device and the cable is not necessarily required. Fixed common mode offsets of up to 1500V are possible in traditional telephony systems. Embodiments of the present invention deliver power via cable and the earth ground is used solely for grounding of the device chassis. As there is no electrical connection between the earth and PoE ground, large voltage offsets are allowable.
Second, another transformer function provides surge and voltage spike protection from lightning strike and power cross faults. Wires inside the building comply with the ITU recommendation K.41 for lightning strikes. Lines external to the building must comply with IEC60590. Lightning strike testing as specified in these Standards consists in a common mode voltage surge applied between all conductors and the earth or chassis ground. As embodiments of the present invention uses the earth ground only for chassis protection, minimal stress will occur across the device, thus simplifying the circuits required by embodiments of the present invention.
In the case of 802.3.af, power is delivered via the center tap of the transmit transformer and receive signal transformers for transformer based designs. The embodiments of the present invention may take up to 400 ma DC from the common mode of the signal pair without disturbing the AC (1 MHz-100 MHz) differential signals on the transmit/receive pairs.
Embodiments of the present invention are operable to support PoE side applications as well. As several functions are integrated together, the entire IC ground will track the Ethernet line ground. This means that the IC potential will vary significantly (1500V) from the chassis ground. As no power is necessary from the local supply, the voltage drop will occur across an air gap.
Although the description herein may focus and describe a system and method for coupling high bandwidth data signals and power distribution between the IC and cable that uses transformer-less ICs with particular detail to the 802.3af Ethernet network standard, these concepts may be applied in non-Ethernet network applications and non 802.3af applications. Further, these concepts may be applied in subsequent standards that supersede the 802.3af standard.
Embodiments of the present invention may provide solid state (non-magnetic) transformer circuits operable to couple high bandwidth data signals and power signals with new mixed-signal IC technology in order to eliminate cumbersome, real-estate intensive magnetic-based transformers 34 and 52 as pictured in
Modern communication systems use transformers 34 and 52 to provide common mode signal blocking, 1500 volt isolation, and AC coupling of the differential signature as well as residual lightning or electromagnetic shock protection. These functions are replaced by a solid state or other like circuits in accordance with embodiments of the present invention wherein the circuit may couple directly to the line and provide high differential impedance and low common mode impedance. High differential impedance allows separation of the PHY signal form the power signal. The low common mode impedance removes the need for a choke. This allows power to be tapped from the line. The local ground plane may float in order to eliminate the need for 1500 volt isolation. Additionally through a combination of circuit techniques and lightning protection circuitry, it is possible to provide voltage spike or lightning protection to the network attached device. This eliminates another function performed by transformers in traditional systems or arrangements. It should be understood that the technology may be applied anywhere where transformers are used and should not be limited to Ethernet network applications.
Specific embodiments of the present invention may be applied to various powered network attached devices or Ethernet network appliances. Such appliances include, but are not limited to VOIP telephones, routers, printers, and other like devices known to those having skill in the art. Such exemplary devices are illustrated in
In an Ethernet network application, the 802.3af standard (PoE standard) provides for the delivery of power over Ethernet cables to remotely power devices. The portion of the connection that receives the power may be referred to as the powered device (PD). The side of the link that provides the power is referred to as the power sourcing equipment (PSE). Two power feed options allowed in the 802.3af standard are depicted in
Returning to
In the instance where network interface 60 is used to couple the network attached device or PD to an Ethernet network, network physical layer 36 may be operable to implement the 10 Mbps, 100 Mbps, and/or 1 Gbps physical layer functions as well as other Ethernet data protocols that may arise. The Ethernet PHY 36 may additionally couple to an Ethernet media access controller (MAC). The Ethernet PHY 36 and Ethernet MAC when coupled are operable to implement the hardware layers of an Ethernet protocol stack. This architecture may also be applied to other networks. Additionally, in the event that a power signal is not received but a traditional, non-power Ethernet signal is received the nonmagnetic power feed circuitry 62 will still pass the data signal to the network PHY.
The power signal separated from the network signal within non-magnetic transformer and choke power feed circuit 62 by the power feed circuit is provided to power converter 38. Typically the power signal received will not exceed 57 volts SELV (Safety Extra Low Voltage). Typical voltage in an Ethernet application will be 48-volt power. Power converter 38 may then further transform the power as a DC to DC converter in order to provide 1.8 to 3.3 volts, or other voltages as may be required by many Ethernet network attached devices.
Network interface 60 and power sourcing switch 64 may be applied to an Ethernet application or other network-based applications such as, but not limited to, a vehicle-based network such as those found in an automobile, aircraft, mass transit system, or other like vehicle. Examples of specific vehicle-based networks may include a local interconnect network (LIN), a controller area network (CAN), or a flex ray network. All of these may be applied specifically to automotive networks for the distribution of power and data within the automobile to various monitoring circuits or for the distribution and powering of entertainment devices, such as entertainment systems, video and audio entertainment systems often found in today's vehicles. Other networks may include a high speed data network, low speed data network, time-triggered communication on CAN (TTCAN) network, a J1939-compliant network, ISO11898-compliant network, an ISO11519-2-compliant network, as well as other like networks known to that having skill in the art. Other embodiments may supply power to network attached devices over alternative networks such as but not limited to a HomePNA local area network and other like networks known to those having skill in the art. The HomePNA uses existing phone wires to share a single network connection within a home or building. Alternatively, embodiments of the present invention may be applied where network data signals are provided over power lines.
Non-magnetic transformer and choke power feed circuitry 62 and 66 eliminate the use of magnetic transformers with integrated system solutions that provide the opportunity to increase system density by replacing magnetic transformers 34 and 52 with solid state power feed circuitry in the form of an IC or discreet component such as the power feed circuit of
The Ethernet PHY may support the 10/100/1000 Mbps data rate and other future data networks such as a 10000 Mbps Ethernet network. The non-magnetic transformer and choke power feed circuitry 62 will supply the line power minus the insertion loss directly to the power converter 38. This will convert the power first to a 12v supply, then subsequently to the lower supply levels. This circuit may be implemented in the 0.18 or 0.13 micron process or other like process known to those having skill in the art.
The non-magnetic transformer and choke power feed circuitry 62 implements three main functions: 802.3.af signaling and load compliance, local unregulated supply generation with surge current protection and signal transfer between the line and integrated Ethernet PHY. As the devices are directly connected to the line, the circuit may be required to withstand a secondary lightning surge.
In order for the PoE to be 802.3af standard compliant, the PoE may be required to be able to accept power with either power feeding schemes illustrated in
The non-magnetic transformer and choke power feed circuitry when applied to PSE may take the form of a single or multiple port switch in order to supply power to single or multiple devices attached to the network.
The 802.3af Standard is intended to be fully compliant with all existing non-line powered Ethernet network systems. As a result, the PSE is required to detect via a well defined procedure whether or not the far end is PoE compliant and classify the amount of needed power prior to applying power to the system. Maximum allowed voltage is 57 volts to stay within the SELV (Safety Extra Low Voltage) limits.
In order to be backward compatible with non-powered systems the DC voltage applied will begin at a very low voltage and only begin to deliver power after confirmation that a PoE device is present. In the classification phase, the PSE applies a voltage between 14.5V and 20.5V, measures the current and determines the power class of the device. In one embodiment the current signature is applied for voltages above 12.5V and below 23 Volts. Current signature range is 0-44 mA.
The normal powering mode is switched on when the PSE voltage crosses 42 Volts. At this point the power MOSFETs are enabled and the large bypass capacitor begins to charge.
The maintain power signature is applied in the PoE signature block—a minimum of 10 mA and a maximum of 23.5 kohms may be required to be applied for the PSE to continue to feed power. The maximum current allowed is limited by the power class of the device (class 0-3 are defined). For class 0, 12.95 W is the maximum power dissipation allowed and 400 ma is the maximum peak current. Once activated, the PoE will shut down if the applied voltage falls below 30V and disconnect the power MOSFETs from the line.
The power feed devices in normal power mode provide a differential open circuit at the Ethernet signal frequencies and a differential short at lower frequencies. The common mode circuit will present the capacitive and power management load at frequencies determined by the gate control circuit.
Additional circuits may be used to implement specific functions in accordance with various embodiments of the present invention. One embodiment of a power feed circuit diagram is provided in
Active control circuits 125 and 126 may be employed to ensure that the power signals passed through the transistors are of equal magnitude or balanced based on other criteria. Active control circuits 125 and 126 are operable to provide common mode suppression, insertion loss control, and current balancing by controlling the gate by control signals 105, 106, 111 and 112 which are applied to the gates of differential transistors M1, M2, M3 and M4. Additionally, the active control circuits may provide temperature and load control, or other signal conditioning functions.
The active control circuit may receive inputs 107, 108, 109, and 110 from the sense impedances, inputs from common mode suppression circuits 123 and 124, inputs from L1P, L1N, L2N and L2P. Common mode suppression circuits may be placed between conductors 1, 2, 3 and 6 as shown to sample signals 101, 102, 103 and 104 upstream of RX PHY 128 and TX PHY 127. Additionally this circuitry shows for an Ethernet network connection the connection of conductors 1 and 2 to receive side PHY and conductors 3 and 6 on the transmit side PHY with DC locking capacitors that act to only pass the AC portion of the signal. Power feed portion of the circuit as well as the splitting circuitry as exemplified by the DC blocking capacitors and the diode bridge network may be implemented within an integrated circuit. At a minimum the power feed circuit may be implemented as a discreet integrated circuit. Wherein the discreet or several discreet integrated circuits may be utilized on a printed circuit board in order to realize a network interface as provided by the embodiments of the present invention.
Additional circuits may be used to implement specific functions in accordance with various embodiments of the present invention. These circuits may absorb power sent on differential cable pairs.
A specific circuit diagram is provided in
To ensure that the power signals passed by each transistor are of equal magnitude, amplifier A1 on the receive side and A2 on the transmit side each sense the voltage at the drain of each transistors of the differential transistor pair to which the amplifier is coupled. This voltage equates to the voltage dropped across the sense impedances R1 and R2 or R3 and R4 respectively. The amplifiers A1 and A2 are operable to amplify the difference in voltage between the two voltages and then apply a feedback signal to the gate of individual transistors M1. M2, M3 and M4. This feedback signal forces the Ethernet power signal passed by each transistor of a differential transistor pair to be equal. (i.e. the current of M1 and M2 (or M3 and M4) are equal.)
The power feed portion of circuit 120 as well as the splitting circuitry as exemplified by the DC blocking capacitors shown in
Other embodiment may include additional elements to further provide for dynamic insertion loss control. Minimizing insertion loss allows the delivered power to be maximized. This may be applied to 10/100/1000/10000 megahertz Ethernet signaling, as well as signaling for other network protocols. In one embodiment, the transistors of the differential pair may have a control signal applied to the gate dynamically adjusted depending on what type of signal of 10/100/1000/10000 megahertz. This may be implemented such that the minimal drop is realized from the source to drain of that device as experienced for that particular mode of operation. The insertion loss may be based on the actual received data signal or by determining the type of signaling and applying a predetermined insertion loss for a given type of signal. Mode detection may be performed within the higher level network protocol to determine the type of signal received and associated predetermined insertion loss.
Specific circuit applications for a portion of the non-magnetic transformer and choke power circuit 46 may utilize source degenerated differential pair of transistors wherein the well is floated relative to the substrate of the silicon devices. This allows the differential high impedance and the common mode short.
In summary, the embodiments of present invention may provide a network powered device operable to receive a network signal that may include both power and data from a coupled network. This network device includes a network connector, an optional protection circuit, an optional switching/rectifying circuit, and an integrated circuit. The network connector physically couples the network device to the network. The protection circuit provides surge protection (if needed) for incoming network signals received by the network device through the network connector. The switching/rectifying circuit (if needed) receives the output of the protection circuit and is operable to rectify a power signal when contained within the network signal. The integrated circuit further includes a power feed circuit conductively coupled to the protection circuit and the rectifying circuit. This power feed circuit is operable to separate and pass the received data signal to a network physical layer and separate and pass the received power signal to a power management module. The power feed circuit may balance the power signal or otherwise control/limit the power feed within the power circuit. The power management module electrically couples to the integrated circuit but is not necessarily part of the integrated circuit. The power management module is operable to at least partially power the network device for specific circuits within the network device from the received power signal.
As one of average skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. As one of average skill in the art will further appreciate, the term “operably coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of average skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “operably coupled”. As one of average skill in the art will further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal 1 has a greater magnitude than signal 2, a favorable comparison may be achieved when the magnitude of signal 1 is greater than that of signal 2 or when the magnitude of signal 2 is less than that of signal 1.
Although embodiments of the present invention are described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention.
This application claims the benefit of priority to and incorporates herein by reference in its entirety for all purposes, U.S. Provisional Patent Application No. 60/665,766 entitled “SYSTEMS AND METHODS OPERABLE TO ALLOW LOOP POWERING OF NETWORKED DEVICES,” by John R. Camagna, et al. filed on Mar. 28, 2005. This application is related to and incorporates herein by reference in its entirety for all purposes, U.S. patent application Ser. Nos.: XX/XXX,XXX entitled “SYSTEMS AND METHODS OPERABLE TO ALLOW LOOP POWERING OF NETWORKED DEVICES,” by John R. Camagna, et al.; XX/XXX,XXX entitled “A METHOD FOR DYNAMIC INSERTION LOSS CONTROL FOR 10/100/1000 MHZ ETHERNET SIGNALLING,” by John R. Camagna, et al., which have been filed concurrently.
| Number | Date | Country | |
|---|---|---|---|
| 60665766 | Mar 2005 | US |
