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bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 1 bel stewart connector may 1 2012 network connectors interfaces and differential to common mode conversion AN12012
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 2 network connector i nterfaces and differential to common m ode c onversion abstract the paper describes standard connector interfaces used in the networking including category 6a rj45 and category 7a arj45. it discusses the differences between connectors within the networking equipment and premise wiring channels that share the same interface. the paper provides data for the tra nsverse conversion loss contri bution of the interfaces within the twisted transmission media up to 2000 mhz . the effects of the differential to common mode conversion ( d c mc ) on the network performance are discussed . the tcl can be reduced by utilizing a balan ced rj45 interface and further improved by utili zing a higher level category 7a interface . the ethernet systems from 1 to 40 gbe shall benefit fro m the reduction of the tcl and corresponding common mode noise internet over copper wire channels close to 1 billion users are connected to the internet today. many of them are connected through copper - wire channels either leading to a final user or a part of the infrastructure. the internet is built upon the standardized ethernet protocols described in the ieee 802.3 standards. t he move toward the 40 and 100 gbe requires better and faster connectivity and lower noise. the ethernet signals utilize differential mode transmission. each differential channel consists of two conductors, and require s a balance wi thin the transmitter or receiving pair, or, in electrical terms , the characteristic impedance of each conductor within the channel shall be equal, typically 50 ohm. if the balance is violated that results in transformation of a portion of the original sig nal energy into the parasitic common mode noise. t he com mon mode conversion worsens the transmission by reducing the signal strength and adding to the noise. in order to focus on the relation between the interfaces and dcmc we limit this discussion to th e application spectra above 500 mhz . interfaces and c onnectors the interface between a network appliance and the premise wiring is an interface between the building cabling infrastructure and equipment such as a switch or computer. for the user , it is simply a port where a patch cord is plugged into the network device. unfortunately it is not simple. in fact, there are two networking interfaces, which have rather complex electrical and mechanical characteristics where the mechanical structures dire ctly impact the transmission performance . t he networking equipment connectors are not covered by the premise wiring standards .
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 3 the first interface is a connector; most often a n rj45 or arj45 (augmented rj45 . i t is usually a receptacle ( a jack ) at the network appliance side, and a plug a t the premise w iring cable side . the first interface is the interruption and disturbance of the twisted pair media . the second interface is a transformer that provides a safety barrier between cables and a n etworkin g appliance . often transformers , other magnetic elements and other signal conditioning components are incorporated into the connectors: such connectors are referred to as integrated connector modules (icm). as a result, the connectors spe cified by tia - 568 series and iso/ iec standards for the premise w iring have the same name as network equipment connectors but look and function differently. what they have in common are the interfaces . the interface is subject to mechanical stresses and abuse s . it is subj ect to electrical discharges due to connect and disconnect under the electrical load, in particular , in the power - over - ethernet (poe) applications. and yet the interfaces have to be inexpensive and therefore not complex, must be robust and be easy to use b y millions of people. figure 1 shows the most common connector inte rfaces for and applicable iso/iec standards. the jacks are shown. table 1 lists the transmission classes and typical applications. table 1 . transmission classes, categories and interfac es transmission cla ss iso/iec standards connector category frequency bandwidth typical application connecting hardware interface class c 3 16 mhz ieee 802.5 tokenring rj 45 class d 5e 100 mhz 10 to 1000baset ethernet rj45 class e 6 250 mhz 100 - 10 00 baset rj45 class ea 6a 500 mhz 1 to 10 gbe rj45, class f 7 600 mhz 1g be over single pair 10 gbe gg45, arj45 class fa 7a 1000 mhz 10 gigabit over 2 pairs 10 gbe over 100 m arj45, na na 2 000 mhz 10 to 40 gbe arj45
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 4 figure 1. t he connector interfaces and applicable international standards the basic connector is a 1 2 - contact category 7 connector described in the iso/iec 60603 - 7 - 7. its opening?s dimensions and contact positions were derive d from the traditional rj45 jack . t he 8 - contact rj45 and ar45 connectors are its subsets. with an exception of the presence of bottom contacts all the dimensions of arj45 are identical to rj45. the category 7 connector has a mechanical switch inside that w ould redirect the signals from traditional split pairs 3/6 and 4/5 to new pairs located on the opposite side of the cavity. a catego r y 7 jack can accept either category 6a or lower rj45 plugs or category 7a and 7a plugs. the same plug is used for categor y 7 and 7a connectors. this plug has a k eying feature that prevents them from mating with cat egory 5e, 6 and 6a jacks. a c ategory 7 and 7a plug has the front protrusion that activates a mechanical switch within the category 7 connector , shown in figure 2 . t he same patch cord can have a category 6a plug on one side and a category 7a plug on another. standard con nector interfac es iec standard 60603-7 - 7 contains a switch iec standard 61076-3 - 110 arj45 600 to 1000 to 2000 mhz iec standard 60603- 7 rj45 3 to 500 mhz
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 5 the category 7a con nector arj45 (augmented rj45) does not have any split pair s. an alternative category 7a connector that was not derived from the rj45 int erface is described by iso 61076 - 3 - 114 . figure 2. c ategory 7a to 6a plugs combined in a single patch cord compensation vs. isolation the major difference between category 7a and lesser c ategories . the major difference between rj45 and arj45 co nnectors and interfaces is how the differential near end cross talk is attenuated. that issue was one of the prime factors why the international standards organization decided to chang e to a new interface for applications above 500 mhz in the iec/iso standard 60603- 7 - 7 . the rj45 connector categories 5e to 6a use compensation to cancel the differential next. the compensation is a method of purposefully creating the crosstalk in the ne ar vicinity of the interface that is equal in amplitude but opposite in phase to the next ? native ? to the interface. in practice , it calls for adding capacitive and some inductive elements and creating complex structures within the connectors. the compen sation in the rj45 connectors is used in both: shielded and unshielded designs. the category 7a connectors rely on isolation to attenuate the next. category 7a connectors are always shielded. a far aday cage is built around each differential pair that i solates them from each other , thus reducing next. the arj45 category 7a category 6a
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 6 interface design allows the isolat ion to be extended through a plug and a receptacle. an additio nal and valuable benefit of an isolation method design is a dramatic improvement in the transverse c onversion l oss in comparison to lesser interfaces . transverse conversion loss . the measure of the balance and differential to common mode conversion applicable to the interface is described in the connecting hardware standards as the transverse con version loss (tcl), or sdc 11 as an s - parameter . it is useful to keep in mind that tcl is the measure of the quality of the interface a s a source of common mode . table 2 . tcl in the s tandards expression frequency range, mhz tia 28 - 20log (f/100) 1 to 500 iso/iec 68 - 20 log(f) 1 to 1000 both standard expressions yield the same values shown in table 3 below. tcl (db) = 20 log common mode voltage differential mode voltage (measured at the same end)
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 7 table 3 . tcl values (db) as specified in the iec/iso standards frequ ency tcl mhz db 1 68.0 10 48.0 50 34.0 100 28.0 150 24.5 200 22.0 250 20.0 300 18.5 400 16.0 500 14.0 600 12.4 700 11.1 800 9.9 900 8.9 1000 8.0 balanced twisted pair environment o utside the connector contacts proper, that form the mech anical interface, the r egions directly adjacent to the interface are twisted pairs. on one side it is a patch cord, on another side it is a high performance lan transformer. the transformer winding s made of twisted pairs are shown in figure 3 figure 3 . high performance 10gbe lan transformer utilizes twisted pairs
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 8 the differential pairs of the high performance 10gbe lan transformer winding are twisted. in addition to reducing the inter - winding capacitance which is always parasitic, the twisting directly improves the dcmc. also, the highest performing lan magnetics both chokes and transformers tend to use a control led media, such as ferrite , on all sides of the channels within the windings . the i mpedance of a balanced twisted pair is derived fro m the impedances of two conductors, as shown in figure 4. the differential impedance in this case does not have a resistive component and consists of the inductance and capacitance. z 1 = z 2 and z d = z 1 + z 2 figure 4. differential impedance of a balanced twisted p air
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 9 figure 5 . interface geometry vs. electrical structure the prime source of tcl is change in the geometry defining the characteristic impedance on the interface. compare figures 4 and 5 . the f igure 5 is an electrical structure of rj45 - o ne the most popular connector in the world where differential pairs defined as contacts 1 - 2, 3 - 6 , 4 - 5, 7 - 8 . t he positions of the contacts in the rj45 interface are such as there is explicit imbalance. the pair 45 is intr insically better balanced as well as 36, though their impedance is hard to match to each other. the intra - pair balance of differential pairs 1 - 2 and 7 - 8 are affected by their position s where contacts 2 and 7 capaci tive ly coupled to adjacent contacts, and z 1 z 2 the r esult is a skew and the degradation of the tcl. there are other sources of imbalance . a ll category 6a connectors are supposed to meet the minimum tcl requi re ments . within the plug the patch cord is changed from the twisted to the interface geometry. the balanced plug incorporates the d esign where at least a portion of the transmission channel within the plug is balanced or controlled. the technology , sometime s referred to as a wire guide f ilter , in which pairs are guided through the plug to mimic the balance of a twisted pair cable. rj45 contacts
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 10 thus, within the category 6a connectivity there are subsets of balanced and unbalanced connectors. the categor y 7a connecto rs main tain the balance and low tcl to the spectra well above 1000 mhz negative effects of h igh tcl the high tcl causes greater common mode noise. the common mode noise reduces the signal energy . the common mode signal generally has a different prop agation velocity from the differential signal . i t also has an arbitrary phase. t wo common noise signals can form an effectively parasitic differential signal superimposed on the original useful transmission . the common noise causes emi and jitter. as a c ontributor to the alien next it may cause bit errors. the shorter the channel length the greater are negative effects of the tcl the reduction in the tcl and corresponding dcmc is translated in a lower noise and potential increases in the useful channel length. the direct contribution of the tcl to the channel length heavily depends on the cable quality, specifically the cable?s insertion loss. though the experimental evaluation is still in progress, t he estimated improvement in length due to 10 db reduc tion in the tcl can be as high as 10m for 500 mh z applications transverse conversion loss: comparative test d ata the computer modeling co nducted by bel?s r& d , using the coaxial structures , established a theoretical limit for sdc11 as 98 db at 1000 mhz . table 4 provides a comparison of the tcl values for balanced and unbalanced category 6a connectors a nd category 7a arj45 connectors. the tcl limit is used instead of data of unbalanced category 6a connectors. table 4. test data: selected (worst) tcl values of network connectors, db frequency, mhz category 6a category 7a unbalanced balanced rj45 rj45 arj45 50 34 45 58 100 28 40 53 250 20 32 56 500 14 26 42 1000 - 16 31 2000 --- 14 19
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 11 figure 6 . tcl of balanced category 6a conne ctor with a wire guide filter figure 7 tcl of category 7a arj45 connector
bel stewart connector 11118 susquehanna trail s outh glen rock, pa 17327 tel: 717.235.7512 page 12 summary the transverse c onversion loss defines the interface as a source of diff erential to common mode c onversion. the common mod e noise negatively affects the n etwork transm ission. the internet traffic from 1 gbe to 10 gb e and, in particular , new 40 gbe system s should benefit from balanced category 6a con n ectors. in th e frequency spectra above 500 mh z the category 7a connectors can provide improvement of over 15 db in comparison to category 6a and extend the channel bandwidth to 2000 mh z and above authors yakov belopolsky , manage r, research & development , m ember of the us tag and a member of the iso/iec committees on connect ors and cabling. y akov published over 30 technical papers and awarded 78 us patents. rich marowsky , principal electrical engineer , member of the tia committee s. rich has over 35 years experience in development, simulation, and testing high speed con nector products for computer systems and the premise wire industry bel stewart connector, glen rock, pa , usa

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