Abstract:
A magnetics based hybrid circuit, comprising a receiver side transformer and a transmitter side transformer is described. Power is supplied via respective inductive elements coupled to respective first end of the receiver side transformer and the transmitter side transformer. A DC blocking element is further provided in series between the second end of the receiver side primary winding and the second end of the transmitter side primary winding.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of powering data terminal equipment and more particularly to providing power over data communication cabling constituted of a single pair. 
     Ethernet communication, also known as IEEE 802.3 data communication, is typically implemented over a structured cable having 4 twisted wire pairs. Power of Ethernet (PoE), as described in IEEE 802.3af—2003 and IEEE 802.3.at—2009, as published by the Institute of Electrical and Electronics Engineers, New York, the entire contents of each document is incorporated herein by reference, is superimposed over the data utilizing phantom powering. In particular, the existing data transformers of Ethernet are center-tapped, and thus the DC current through the two halves of the transformer are of equal magnitude and opposite direction leaving no net flux in the transformer core. 
     Ethernet communication for speeds less than 1000 megabits per second (Mbps) is typically supplied over 2 twisted wire pairs, one of the pairs being used as a transmit pair from the hub equipment to the data terminal equipment (DTE), which when powered by PoE is also known as a powered device (PD), and a second of the pairs being used as a transmit pair from the data terminal equipment to the hub equipment. The other two pairs were typically not used, and were known as spare pairs. The term transmit is typically abbreviated TX and the term receive is typically abbreviated RX for simplicity. In such an embodiment either spare powering, or data pair powering, may be implemented. 
       FIG. 1A  illustrates a high level block diagram of an arrangement  10  for powering a PD from a switch/hub equipment  30  using phantom powering in accordance with the above standards. Arrangement  10  comprises: switch/hub equipment  30  comprising a first and second data pair  20 , a power sourcing equipment (PSE)  40 , and a first and second data transformer  50 ; four twisted pair data connections  60  constituted in a single structured cable  65 ; and a powered end station  70  comprising a first and second data transformer  55 , a first and a second data pair  25 , and a PD  80 . Powered end station  70  is also known as the DTE. 
     The primary of each of first and second data transformers  50  are coupled to respective data pairs  20 . An output and return of PSE  40  are connected, respectively, to the center tap of the secondary of first and second data transformers  50 . The output leads of the secondary of first and second data transformers  50  are respectively connected to first ends of a first and a second twisted pair data connection  60  of structured cable  65 . The second ends of first and second twisted pair data connections  60  are respectively connected to the secondary of first and second data transformers  55  located within powered end station  70 . The center tap of the secondary of each of first and second transformers  55  is connected to a respective input of PD  80 . Third and fourth twisted pair data connections  60  of structure cable  65  are connected to respective inputs of PD  80  for use in an alternative powering scheme known to those skilled in the art. In another embodiment, as will be described further below, third and fourth twisted pair data connections  60  further carry data. First and second data pairs  25  are coupled to the primary winding of each of first and second data transformers  55  and represent data transmitted between powered end station  70 , particularly PD  80 , and switch/hub equipment  30 , each direction provided on a respected twisted pair data connection  60 . 
     In operation, PSE  40  supplies power over first and second twisted pair data connection  60 , thus supplying both power and data over first and second twisted pair data connections  60  to PD  80 . As described above, since power is transmitted and received via the center tap of the respective transformers  50 ,  55  DC flux does not build up in the respective transformers  50 ,  55  responsive to power from PSE  40 . 
     For speeds of 1000 Mbps, also known as Gigabit Ethernet, all 4 pairs are utilized for data communication, and each of the 4 pairs provide bi-directional communication. Thus, at both the hub equipment and at the DTE end, both a transmitter and a receiver are coupled to each pair. Arrangement  100  of  FIG. 1B  illustrates such an arrangement. Arrangement  100  is in all respects similar to arrangement  10 , with the exception that data pairs  20  are provided coupled to each of the four twisted pair data connections  60  via respective transformers  50  and similarly four data pairs  25  are coupled to respective twisted pair data connections  60  via respective transformers  55 . As indicated above each of data pairs  20 ,  25  are implemented as bidirectional transmitter receiver pairs as will be described further below, responsive to a respective hybrid circuit. 
       FIG. 2  illustrates a high level block diagram of an arrangement  100 , known to the prior art, to provide bidirectional communication over each twisted pair data connection  60 . At each end a transmitter  110 , a receiver  120  and a hybrid circuit  130  is provided. The output of each transmitter  110 , comprising a differential pair, is coupled to a respective differential input of the respective hybrid circuit  130  and the input of each receiver  120 , comprising a differential pair, is connected to a respective differential output of the respective hybrid circuit  130 . A bi-directional port of hybrid circuit  130  at the hub side, comprising a differential pair, is coupled to the primary winding of transformer  50  and presents data pair  20  and a bi-directional port of hybrid circuit  130  at the PD side, comprising a differential pair, is coupled to the primary winding of transformer  55  and presents data pair  25 . The secondary winding of transformer  50  is coupled to a first end of a respective twisted pair data connection  60  and the secondary winding of transformer  55  is coupled to a second end of the respective twisted pair data connection  60 . 
     Each hybrid circuit  130  is arranged to channel data transmitted by the coupled transmitter  110  towards twisted pair data connection  60  and away from the coupled receiver  120 . Hybrid circuit  120  may be implemented electronically or magnetically, as known to those skilled in the art, although typically electronic hybrid circuits are implemented. 
     The arrangement of  FIG. 2  thus provides bi-directional communication on each of the twisted pair data connection  60 . Data communication over a single pair, thus obviating the need for a structured cable of 4 twisted pairs, is similarly possible using arrangement  100 , has been commercially implemented, and is commonly known as single pair Ethernet. 
     Disadvantageously, the arrangement of  FIG. 2 , when utilized for single pair Ethernet does not provide a plurality of powering paths over twisted pair data connection  60  which would result in no net flux. This is particularly true, since with a single twisted pair, the power and return paths must be provided over only the 2 wires of twisted pair data connection  60 . 
     U.S. Pat. No. 8,044,747 issued Oct. 25, 2011 to Yu et al., entitled “Capacitor Coupled Ethernet”, the entire contents of which is incorporated herein by reference, provides a system and method for enabling power applications over a single conductor pair. In one embodiment, data transformers are coupled to a single conductor pair using one or more direct current (DC) blocking elements that preserve an alternating current path. Power is injected onto the single conductor pair after the DC blocking elements and power is extracted from the single conductor pair before the DC blocking elements. Disadvantageously, such a solution places the one or more DC blocking elements in the data path before the detecting element, which may lead to signal degradation. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the present invention to overcome at least some of the disadvantages of the prior art. This is provided in certain embodiments by a magnetics based hybrid circuit, comprising a receiver side transformer and a transmitter side transformer. Power is supplied via respective inductive elements coupled to respective first end of the receiver side transformer and the transmitter side transformer. A DC blocking element is further provided in series between the second end of the receiver side primary winding and the second end of the transmitter side primary winding. 
     Additional features and advantages of the invention will become apparent from the following drawings and description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings in which like numerals designate corresponding elements or sections throughout. 
       With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings: 
         FIG. 1A  illustrates a high level block diagram of an arrangement for powering a PD from a switch/hub equipment using phantom powering in accordance with the prior art; 
         FIG. 1B  illustrates a high level block diagram of an arrangement for powering a PD from a switch/hub equipment using phantom powering appropriate for Gigabit Ethernet in accordance with the prior art; 
         FIG. 2  illustrates a high level block diagram of an arrangement to provide bidirectional communication over each twisted data pair connection in accordance with the prior art; and 
         FIG. 3  illustrates a high level schematic of an exemplary arrangement providing bidirectional data communication and powering over a single twisted pair data connection. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. The term winding is particularly meant to mean a winding of electrically conducting wire forming an inductor. The winding may form a stand alone inductor, or be magnetically coupled to another winding forming a transformer. 
       FIG. 3  illustrates a high level schematic of an exemplary arrangement  200  providing bidirectional data communication and powering over a single twisted pair data connection  60 . Arrangement  200  comprises: a PSE  40 ; a twisted pair data connection  60 ; a first transmitter  110 ; a first receiver  120 ; a first combination DC blocking and hybrid circuit  210 ; a first inductive element  220 ; a second inductive element  220 ; a PD  240 ; a second transmitter  110 ; a second receiver  120 ; a second combination DC blocking and hybrid circuit  210 ; a third inductive element  220 ; and a fourth inductive element  220 . Each of first and second combination DC blocking and hybrid circuit  210  comprise a first and a second transformer  250 , a first, second and a third resistor  260  and a DC blocking capacitor  270 . Each transformer  250  comprises a first and a second primary winding  252  and a first and a second secondary winding  254 , arranged about a common core and magnetically inter-coupled. 
     Each transformer  250  is described as having a first and a second primary winding  252  primarily for ease of understanding, it being understood that first and second primary windings  252  may be combined into a single primary winding  252  without limitation. 
     A first lead of the differential output of first transmitter  110  is connected via first resistor  260  of first combination DC blocking and hybrid circuit  210  to a first end of first primary winding  252  of first transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of first primary winding  252  of first transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a first end of second primary winding  252  of first transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of second primary winding  252  of first transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a second lead of the differential output of first transmitter  110 . 
     A first lead of the differential input of first receiver  110  is connected to a first end of first primary winding  252  of second transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of first primary winding  252  of second transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a first end of second primary winding  252  of second transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of second primary winding  252  of second transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a second lead of the differential input of first receiver  120 . Second resistor  260  of first combination DC blocking and hybrid circuit  210  is connected across the differential inputs of first receiver  120 . 
     A first end of first secondary winding  254  of first transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity, is connected to a first end of third resistor  260  of first combination DC blocking and hybrid circuit  210 . A second end of first secondary winding  254  of first transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a first end of first secondary winding  254  of second transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of first secondary winding  254  of second transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a second end of second resistor  260  of first combination DC blocking and hybrid circuit  210 . 
     A first end of second secondary winding  254  of first transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity, is connected via DC blocking capacitor  270  to a first end of second secondary winding  254  of second transformer  250  of first combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of second secondary winding  254  of first transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a first output of PSE  40  via first inductive element  220 , the first output of PSE  40  denoted as the positive output for clarity, without limitation, and to a first end of a first wire of twisted pair data connection  60 . A second end of second secondary winding  254  of second transformer  250  of first combination DC blocking and hybrid circuit  210  is connected to a second output of PSE  40  via second inductive element  220 , the second output of PSE  40  denoted as the return for clarity, without limitation, and to a first end of a second wire of twisted pair data connection  60 . In particular, as will be apparent, combination DC blocking and hybrid circuit  210  is polarity insensitive. 
     A first lead of the differential output of second transmitter  110  is connected via first resistor  260  of second combination DC blocking and hybrid circuit  210  to a first end of first primary winding  252  of first transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of first primary winding  252  of first transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a first end of second primary winding  252  of first transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of second primary winding  252  of first transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a second lead of the differential output of second transmitter  110 . 
     A first lead of the differential input of second receiver  110  is connected to a first end of first primary winding  252  of second transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of first primary winding  252  of second transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a first end of second primary winding  252  of second transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of second primary winding  252  of second transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a second lead of the differential input of second receiver  120 . Second resistor  260  of second combination DC blocking and hybrid circuit  210  is connected across the differential inputs of second receiver  120 . 
     A first end of first secondary winding  254  of first transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity, is connected to a first end of third resistor  260  of second combination DC blocking and hybrid circuit  210 . A second end of first secondary winding  254  of first transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a first end of first secondary winding  254  of second transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of first secondary winding  254  of second transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a second end of third resistor  260  of second combination DC blocking and hybrid circuit  210 . 
     A first end of second secondary winding  254  of first transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity, is connected via DC blocking capacitor  270  to a first end of second secondary winding  254  of second transformer  250  of second combination DC blocking and hybrid circuit  210 , denoted with a dot for polarity. A second end of second secondary winding  254  of first transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a second end of the first wire of twisted pair data connection  60  and via third inductive element  220  to a first input of PD  240 , denoted as the positive input for clarity, without limitation. A second end of second secondary winding  254  of second transformer  250  of second combination DC blocking and hybrid circuit  210  is connected to a second end of second wire of twisted pair data connection  60  and via fourth inductive element  220  to a second input of PD  240 , denoted as the return for clarity, without limitation. 
     In one embodiment, each of first, second, third and fourth inductive elements  220  are constituted of a stand-alone inductor. In another embodiment, each of first, second, third and fourth inductive elements  220  are constituted of ferrite beads which provide high AC resistance at data frequencies instead of reactive impedance. In one particular embodiment, the ferrite beads of first, second, third and fourth inductive elements  220  are constituted of nickel zinc which provide ohmic resistance at high frequencies, and thus do not present phase changes. In yet another embodiment first and second inductive element  220  are constituted of a pair windings on a single core arranged to offer impedance to differential signals appearing on single twisted pair data connection  60 . Additionally, or optionally, third and fourth inductive element  220  are similarly constituted of a pair windings on a single core arranged to offer impedance to differential signals appearing on single twisted pair data connection  60 . Each of first, second and third resistors  260  of the respective combination DC blocking and hybrid circuit  210  are preferably matched to provide impedance matching. DC blocking capacitor  270  is selected to pass frequencies of data transmission without appreciable impedance. 
     In operation, each combination DC blocking and hybrid circuit  210  provides DC blocking and echo cancellation. For clarity, operation of first combination DC blocking and hybrid circuit  210  will be detailed, it being understood by those skilled in the art that the identical explanation is to be applied to second combination DC blocking and hybrid circuit  210 . In the event that first transmitter  110  is active, the differential signal creates a current flow through first windings  252  of first transformer  250 , which is mirrored in second windings  254  of first transformer  250 . Due to the crossed connections via third resistor  260 , the current flow through first windings  252  of second transformer  250 , responsive to the differential signal from first transmitter  110 , cancel current flow responsive thereto reflected back from second combination DC blocking and hybrid circuit  210  via twisted pair data connection  60 . In some further detail, the polarity of current flow experienced by first receiver  120  responsive to the output of first transmitter  110 , received via first and second primary windings  252  and first secondary winding  254  of second transformer  250  is 180° out of phase with the polarity of current flow experienced by first receiver  120  responsive to the reflected signal received via twisted pair data connection  60  and reflected to receiver  120  via second secondary winding  254  of second transformer  250 . DC blocking capacitor  270  prevents a short circuit for current injected by PSE  40 . Inductive elements  220  prevent PSE  40  from appearing as a capacitive load to data signals traversing twisted pair data connection  60 . 
     Similarly, current flow caused by a differential signal received over twisted pair data connection  60 , originating in second transmitter  110 , creates a current flow through second windings  254  of first and second transformers  250 , which is mirrored in first windings  252 . Due to the crossed connections via third resistor  260 , the current flow through first windings  252  of first transformer  250  experienced by first transmitter  110  are cancelled by current flow reflected back from the current flow experienced by first receiver  120 . In some further detail, the polarity of current flow experienced by first transmitter  110  responsive to the current flow received via twisted pair data connection  60  is 180° out of phase with the polarity of current flow experienced by first transmitter  110  reflected by the cross connection. 
     The operation of combination DC blocking and hybrid circuit  210 , in the absence of DC blocking capacitor  270 , which as described above does not impact operation in relation to high frequency signals, is known to those skilled in the art. 
     Referring to PD  240 , power is received from the second ends of secondary windings  254 , and inductive elements  220  prevent PD  240  from appearing as a capacitive load to data signals traversing twisted pair data connection  60 . PD  240  typically comprises a diode bridge input circuit thus providing the above mentioned polarity insensitivity, and a under voltage lockout circuit to prevent startup of any load circuitry until sufficient voltage appears across the input leads of PD  240 . Such a PD  240  is known to those skilled in the art, and in the interest of brevity is not further detailed. 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meanings as are commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods are described herein. 
     All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the patent specification, including definitions, will prevail. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. Rather the scope of the present invention is defined by the appended claims and includes both combinations and sub-combinations of the various features described hereinabove as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not in the prior art.