4,173,714
`Nov.6, 1979
`
`] '
`
`
`且1
`
`[
`
`[45]
`
`United States Patent
`Bloch et al.
`
`[19]
`
`Inventors:
`
`Assignee:
`
`COMMUNICATION CIRCUIT WITH
`COMBINED POWER FEED AND DATA
`TRANSMISSION OVER A PHANTOM
`CHANNEL
`Alan Blocb, New York; Frank A.
`Coviello, Peekskill, both of N.Y.; Ira
`Guzik, Fairfield; Candido Puebla,
`Bridgeport, both of Conn.
`TIE/Communications, Inc.,
`Stamford, Conn.
`Appl. No.: 803,243
`Jun. 3, 1977
`Filed:
`Int. C1.2 …·………............................... H04Q 5/18
`U.S. C1. ..........…................. 179/99 R; 179/15 BB
`Field of Se缸ch .................…. 179/3, 4, 15 BB, 99
`References Cited
`U.S. PATENT DOCUMENTS
`Weissner ......................… 179/15 BB
`6/1940
`Anderson et a1. ..................... 179/99
`10/1972
`Lewis …"…..........…................ 179/99
`1/1974
`Ridley …........…..............….... 179/99
`10/1974
`Shiff ………....................………. 179/99
`8/1976
`Guntersdorfer ………........ 179/15 BB
`8/1976
`Huizinga et a1. ......….........…. 179/99
`9/1977
`
`ABSTRACf
`[57]
`The disclosure relates to a four conductor circuit ar(cid:173)
`rangement providing two communication channels be(cid:173)
`tween a control unit and a terminal device. Power feed
`and bi-directional signalling are accomplished simulta(cid:173)
`neously over the same four conductors used for the two
`commmunication channels without interference. The
`signalling from the control unit to the terminal is ac(cid:173)
`complished by means of a voltage modulator circuit in
`the control unit by which voltage pulses are transmitted
`via a phantom circuit arrangement over the four con(cid:173)
`ductors to the terminal unit. The voltage pulses are
`sensed from the phantom circuit in a data receiver
`which is located at the terminal unit. Connected to the
`phantom circuit in the terminal unit is a voltage regula(cid:173)
`tor circuit which receives power from the control unit
`via the four conductor phantom circuit interconnecting
`the control unit and the terminal. In series with the
`voltage regulator circuit is a constant current sink and
`an inductor. A current modulator circuit is provided in
`parallel for impressing current data pulses generated in
`the terminal onto the phantom circuit, which are, in
`turn, received by a receiver circuit in the control unit.
`A preferred data format is disclosed as a method for
`transmitting information between the control unit and
`the terminal.
`The preferred embodiment for the disclosed four con(cid:173)
`ductor communication circuit and the disclosed data
`format is in a key telephone system in which the control
`unit is a station card in a key service unit and the termi(cid:173)
`nal is a key telephone station set.
`
`12 C1aims, 8 Drawing Figures
`
`30
`
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`[75]
`
`[73]
`
`[21]
`
`[22]
`
`[51]
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`[58]
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`[56]
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`2,203,316
`3,701,854
`3,787,631
`3,843,845
`3,973,085
`3,975,594
`4,046,972
`FOREIGN PATENT DOCUMENTS
`5/1976 United Kingdom .
`1437032
`Primary Examiner-Bernard Konick
`Assistant Examiner-Randall P. Myers
`Attorney, Agent, or Firm-Francis N. Carten
`
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`u.s. Patent
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`Nov.6, 1979
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`Nov.6, 1979
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`1
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`4,173,714
`
`COMMUNICATION CIRCUIT WITH COMBINED
`POWER FEED AND DATA TRANSMISSION OVER
`A PHANTOM CHANNEL
`
`2
`The power feed and bi-directional signalling arrange-
`ment is described in British Pat. No. 1,437,032, also
`assigned to the Plessey Company. Power is transmitted
`from the control unit to the terminal by way of two
`5 conductors; simultaneously, data signals, generated in
`the control unit, are transmitted over the same two
`BACKGROUND OF THE INVENTION
`1.Field of the Invention
`conductors to the terminal where they are sensed by a
`This invention relates to a circuit arrmgemmt for
`data receiver and applied to the station set.At the sta-
`tion set itself, a series regulator senses the voltage im(cid:173)
`providing communication channels and power and sig-
`nalling circuits between a control unit and a terminal.10pressed on the two conductors and regulates that volt(cid:173)
`age in order to supply the terminal station set with d.c.
`Specifically, the invention relates to such a circuit ar-
`voltage. In series with the series regulator is a constant
`rmgement in a key telephone system-current source, which is modulatBd by a current modu-
`2.Description of the Prior Art
`lator in response to data generated by the terminal.The
`There has been a continuing effort on behalf of the 15 data generated by the terminal gives information about
`telephone industry to reduce the cabling and cross-con-the characteristicBof the terminal itself;and these data
`necting equipment requirements for key telepho甲 sys-
`are transmitted over the two conduct~rs back to the
`c。ntrol unit where they are sensed by a receiver respon-
`tems.These requirements are based in the deSIre to
`allow a key telephone set to be interchangeable, and
`sive to the current pulses and are used in the terminal to
`also for the desire to reduce service assignments at the 20CZMEtrol the terminal itBelt
`telephone sets-So called electronic key telephone sys·In modern communication systems, such as key tele-
`phone systems，也ere is often a requirement that there be
`tems have been proposed in recent yeus in anpffort to
`reduce the cabling and cross-connectmg reqmremepts
`two communication channels connecting the control
`of the older key telephone systems, .and in additIOIl
`unit and the terminal.For example, in a key telephone
`provide features not possible in the pnor systems-25system it is often desirable that a user ofa key telephone
`For example, in amm of papers publi?heht the
`sution seb who is communicating over a first channel,
`1970 International Conference on COInmumeat1OIls, an(for example on m outside call over ac咽tral office line)
`electronic key telephone system is descubed iqwhich
`be able to simultaneouslyulk over a second communi(cid:173)
`the control unit and each telephone statIOn set lsmte?·cation channel to someone connected to the key tele(cid:173)
`connectedbymansofsixco!由lc~ors:.Two oft~ese.six 30 ph~~~ ~y;t~~-o-~e;-~~-~ï~r~~;-l~~~ Th~;:-th~;e is--a
`requirement that there be provided not one, but two
`conductors are used for a VOICE CIre111t COInmUIncat1on
`audio communication ch~~~ls o~~r the fo~~ ~~~duc~
`channel. The other four conductors are used for data
`tors connecting the control unit and the terminal, with
`transmission:two conductors for transmission in ope
`direction;the other two conductors for data tmnSEEMS-the simultaneous provision of data signalling in both
`mon in the other dhction-One paper pmenteqat-the 35directions (from the contml unit to tktemind and
`1970 Intemational Conference on Communications
`from the teiminal to the control unit) with simultaneous
`entitled "Exploratory Common Control Key Tele-provisionofpowerbeingsuppliedfmmthecontrolm山
`to the termi~al over the-fo.ir-conductors.
`phone System: 8ystem and Functional Dωcription"， by
`L.P.FabianoJr.ofBellTelephone-LaEomon郎， Inc.,
`Thus this ir附ntion provides a circuit arrangement in
`describes how the six conductor circuit arrangement 40 which a control unit aÌJ.d a terminal are interconnected
`by means of only four conductors and in which two
`among fou! _of the s~x co~ductors is_ ~sed ~o tran~n_lÎt
`communication channels, bi-directional signalling be-
`data to and from each station set and how 岛ur of the
`cond~ctors are conne~te~ in! p.hantom' pair a~r~ge-
`tween the control unit and the terminal-and põwer
`ment for power transmission. Each conductor pair has a
`transmission from the control unit to the termlnal is
`center tapped transformer conneeted both at_the ~on- 45 provided.
`trol unit and at the station set. Power is supplied from
`This invention also provides a method for transmit-
`the control unit to the station set over the phantom pair
`ting control data over -the four conductor arrangement
`arrangement, while_ data _ in one direction is being _sup-
`by which various circuits in a key telephone statïon set
`may be controlled and/or monitored. The invention
`plied on one pair of the four conductors and data from
`the station set to the control unit is being_retumed over 50 further provides a method of dial pulse signalling simul-
`taneously with control data transmission.
`the other pair of the four conductors. The other two
`leads of the total of six leads, as mentioned above, are
`~-s~~l ~~ly--~s -~ ~~~~~~ic~ti~~ channel.
`SUMMARY OF THE INVENTION
`This invention relates to a circuit arrangement in
`Key telephone systems have been known in which
`station sets are controlled and powered from a control 55 which first and second communication channels are
`unit via only four conductors connecting the control
`provided over two conductor pairs which are simulta-
`unit and each station set. For example, British Pat. No.
`neously used for power feed and bi-directional signal-
`1,437,031, assigned to the Plessey Compan:y Limited of
`ling between first and second equipment units. These
`Great Britain, describes a four conductor circuit ar-
`first and second equipment units, in a preferred embodi-
`rangement which connects the control unit for a tele- 60 ment, are a control unit and key telephone station sets in
`phone system to each station set. This British patent
`a key telephone system.
`describes a "house telephone system" in which the four
`A frrst pair of conductors is used as one information
`channel. The other pair of conductors provides the
`conductors connecting the control unit to the terminal
`are divided into two pairs of conductors, one pair being
`second information channel. Each conductor pair is
`used for power feed and bi-directional signalling, the 65 terminated at the control unit and at the terminal unit
`other pair being used solely as a communication channel
`with a transformer. Each transformer has one center tap
`winding, the ends of the center tapped winding being
`or voice circuit path between the station set and the
`control unit.
`connected to the conductor pair.
`
`JUNIPER Ex 1005-pg. 6
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`4,173,714
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`4
`current pulse from the key telephone station set to the
`key service unit.
`
`3
`The communication channels, typically audio chan-
`nels, are created by using each pair of conductors via
`transformer coupling to the terminal and to the control
`BRIEF DESCRIPTION OF THE DRA WINGS
`unit, there being a; information receiver (typically a
`The invention will be described by referring to the
`small speaker) and generator (typically a microphone) 5
`accompanying drawings, in which:
`fòr each channel in the terminal and there being means
`FIG~ 1 shows in block diagram form the circuit ar-
`to receive and transmit information for each channel at
`rangement by which two communication channels and
`thc:_ cont_ro) unit.
`_
`Data information now between the control unit and
`means for supp1ying power from the control unit to the
`the terminal and power feed 仕om the control unit 飞o the 10 terminal, tra~s~itti;g data from the control unit to the
`terminal is acCOInp1ished via a phantom paIrqrcuuterminal, and transmitting data from the terminal to the
`arrangement in which the control unit circuitry mcop-control unit are provided over four conductors con(cid:173)
`nected to the two center tapsofthe transformers tem-Electing the controlunit and the terminal;
`IEating the two pair of conductors at the control umt.FIG.2shows the d.c.supp1y circuit and modIdating
`Connections to the center tap connections of the trans-15circuit within the control unit for applying d.c.power
`formers terminating the two conductor pairs at the
`and data signals to the four conductors connecting the
`terminal complete the phantom pair circuit.A d.c.volt-control unit and terminal,
`age source is connected at the control unit to the phan-
`FIG. 3 shows details of the voltage regulator circuit
`tom pair circuit arrangement. The d.c. voltage is ap-
`p1ied to the phantom circuit arrangement, and is sensed 20located in the terminal for receiving the d.c.power
`and regulated by a voltage regulator in the terminal
`from the four conductors and for providing different
`connected in series at the terminal end of thephantom
`voltage levels with which to power the terminal logic
`p a i r . c i r cu i t s and components,
`Data signals are applied to the phantom pair at the
`FIG.4shows the detailed circuit of the receiver
`control unit by means of a voltage modulator.These 25located in the terminal which is responsive to the data
`data signals, transmitted from the control unit to the
`signals generated in the control unit and applied to the
`terminãl, are sensed at the terminal end of the phantom
`four . co~ductors connecting the control unit and the
`terminal,
`pair by means of a data receiver. Information-is trans-
`Înitted to the control unit from the terminal by modulat-
`FIG. 5 shows the details of the current modulator
`ing a resistor in parallel with a constant current sink at 30 circuit located in the terminal, responsive to dáta from
`the logic circuitry in the terminal, for applying current
`the terminal end of the circuit arrangement. This pro-
`vides current modulation of the constant current in the
`modulated pulses onto the four conductors connecting
`the control unit and the terminal,
`terminal circuit connected to the phantom pair. Current
`pulses therefore are applied via the phantom pair, the
`FIG. 6 shows the circuit in the control unit which
`pulses being sensed in the control unit by means of a 35 senses the current modulation from the terminal which
`data receiver. An additional feature of the invention
`is applied to the four conductors connecting the control
`provides at the terminal end of the circuit arrangement,
`unit and the terminal, and
`an inductor selected so that the terminal circuit presents
`FIGS. 7A and 7B show the data format with which
`a very high impedance to the phantom pair line as
`the modulators in the control unit and the terminal
`viewed from the control unit end of the arrangement, 40 provide information to and from the control unit ánd
`the terminal.
`thereby preventing signal reflections returning to the
`control unit from the terminal end. A very high impe-
`dance also aids in the generation of ctirreit pulses
`which result from modulation of the constant current
`sink in the terminal circuit.
`A缸c∞c∞or时硝din昭g tωoa削n∞.ot仙he缸r fc阳二卢卢a创ture of t巾he i即n盯:ve圳n川t阳i
`~创spectωs of this invention. Four conductors. 1,2,3,4 are
`data to each terminal i沁s provi泊ded by means of dividing
`time into N segments, where N is preferably sdected to
`shown connecting a control unit 10and a terminal 20.
`be the integer 34.Each of these N segments, called a
`Although the preferred application for the invention is
`~o;d~ i~-i~rthe; ~Íi~d~d i;t~-fi~~ ~~b:ti;_;-~i~~~~t~~ Ã 50 in a key telcph(Jne s~~te~， the inventive_circuit arrange-
`pulse卢Iring the Erst ofthese time ekmenuofa word is
`ment cm End app1ication in many difterent ∞ntrol
`unit/terminal applications.
`~;~d- ~-~~~h :;~;d-to-indi~~teth~ ~tart-~i~ -~ew ~orci~
`A second element is used to transmit pulses from the
`Each conductor pair is terminated by a transformer.
`∞EUrol unit to the terminal indicating control informa-Transformers T1and T2teEInmate the conductor pair
`tion about a particular terminal circuit. A third time 55 1, 2 ~d con~~tor.p~i: 3, 4.in te~inal unit 20 while
`element during each word is used to transmit status
`transformers T3and T4terminate the conductor pair I
`information abóut a particular terminal circuit from the
`an~ 2 ~nd cOI!-ductor_ pair 3 and 4 in control unit 10.
`terminal to the control unit. The other time elements are
`Each transformer has a center tap connection on the
`left idle in each word. Typically the first word, labeled
`t!ansformer winding connected to the conductor pair.
`the Oth word is used as a -synchronizing word, and the 60 Center tap connections are located at the control unit 10
`(C3 and C的 and at the terminal unit 20 (Cl and C2). A
`following N-l words are used to convey information
`between the control unit and the terminal about individ-
`"phantom circuit" is created via the center tap connec-
`tions Cl and C2, through the conductors 1,2,3,4, to the
`ual terminal circuits.
`center taps c3 and C4 of transfo口ners T3 and T4. This
`When the inventive data format is used in the pre-
`ferred embodiment of a key telephone system, informa- 65 arrangement is known as a phantom pair because in a
`closed circuit connected to taps c3 and C4 ofT3 and T4
`tion concerning the condition ofthe hookswitch and the
`and to taps Cl and C2 of Tl and T2, the current sup-
`presence of a dial pulse during signalling is transmitted
`during the first time interval of each word by sending a
`plied at a center tap point will divide at the center tap
`
`DESCRIPTION OF THE INVENTION
`General Description of The Circuit Arrangement
`
`45
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`4,173,714
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`8
`7
`and the modulated voltage caused by the data pulses on
`Data Receiver in Terminal
`lead 103.
`FIG. 4 shows the detai!s of receiver 150 in terminal
`Transistors Ql and Q2 are of a kind denominated
`MPS U05 and MPS U55, manufactured by the Motor-
`20. Data pulses are sensed on the line at terminals Cl
`ola Co. and are described at pages 1087 and 1107 in a 5 and C2 which are the center tap connections of trans-
`former Tl and T2. Voltage pulses modulated at the
`publication by Motorola Semiconductor Products Inc.
`entit1ed "Semiconductor Data Library", Series A, Vol-
`control unit by modulator 100 appear across the termi-
`ume 3, 1974. Differential amplifiers 151 and 152 are of a
`nals Cl, C2. These voltage pulses are then applied to
`type denominated LM 1458 manufactured by the Na-
`operational amplifier 180 through resistor-capacitor
`tional Semiconductor Company and are described at 10 paths created by resistors R160 and R161 and capacitors
`pages 2-238 in a publication by National Semiconduc-
`C162 and C163.
`tor Company entit1ed "Linear Integrated Circuits",
`Operational amplifier 180 is connected as a differen-
`published February, 1975. Biasing for the differentia1
`tial amplifier such that the difference in voltages ap-
`amplifiers is shown as in FIG. 2, and is provided by . _ pearing at its plus and minus terminals are measured.
`resistors R6 and R7 to provide the proper bias to the 15 Differential amplifier 180 operates to sense only the
`differences in voltage appearing at its input terminals,
`negative input of differential amplifier 151 and by resis-
`tors R15 and R16 in conjunction with voltage source 14
`yet it is not sensitive to any common mode voltages
`which appear on both of its input termina1. This feature
`to the positive input terminal of differential amplifier
`151. In a similar fashion, the biasing for differential ~^ insures that any common mode voltages which appear
`~~plifier152 inputs is pr~vided by r~istor R18 to the 20 on the conductors 1,2,3 and 4 conne7:ting the c~~trol
`positive input and by resistors R8 and R9 to the nega-
`unit and the terminal will be rejected.
`tive input termina1.
`Operational amplifier 180 has a feedback resistor
`RI66 connected from its output terminal to its negative
`input terminal thereby providing negative feedback and
`Detailed Description of the Voltage Regulator 500in
`Terminal 20
`25 an overal1 gain across the amplifier from input to out-
`put. The signal appearing at point 190 thus represents
`Connected to the center tap connections Cl and C2
`in terminal 20 is a transformer T3, voltage regulator
`the ampli负ed difference in voltages appearing from
`500, and constant current sink 300, as shown in FIG. 3.
`center-tap points Cl and C2.
`T~.e_ sigl_l~l. at P?i?t. P190 is app!ied to the operational
`The vo~tage _r~gula!?r cir~ui~ 5~_ c~~pri~e~_ a se.rie~ 30
`connection ofthree Zener diodes ZI, Z2 and Z3 each of -- amplifier 181 which is connected as a comparator am-
`plifier. Amplifier 181 has a resistor R171 connected
`which has a capacitor connected in parallel with it. The
`Zener diodes sense the current flowing through the line
`from its output terminal P191 back to its positive input
`from C2 to Cl. With sufficient voltage applied across
`terminal thereby insuring that voltage pulses applied to
`Cl to C2, each Zener diode breaks down having a con- 35 its negative terminal wil1 not cause osci1lation at its
`stant voltage across it. The capacitors, CI0, C20 and
`input. The output of the receiver 150 appears at point
`C30 connected across Zener diodes ZI, Z2 and Z3,
`P191 from which the data pulses are applied to logic
`provide ftltering so as to provide a substantially con-
`circuitry in the terminal for controlling various func-
`stant voltage at points Pl, P2, P3 and P4. The Zener
`tions and apparatus in terminal 20. Operational amplifi-
`diodes preferred in this invention are lN4737A and 40 ers 180, 181 may be Motorola 1458 operational amplifi-
`lN4733A diodes manufactured by Motorola Semicon-
`ers identified above.
`ductor Products, Inc. and are described at page 1-101 of
`a publication entitled "Semiconductor Data Library",
`Degcription of the Current Modulator 200in Terminal
`20
`Volume 1, Series A, 1974, by Motorola Semiconductor
`Products.
`The detailed circuitry of the modulator 200 shown in
`FIG. 1 is illustrated in FIG. 5. Terminallogic circuitry
`Point P4 between Zener diodes ZI and Z2 is taken as
`in termina1 20 applies data to the modulator 200 which
`an arbitrary reference point from which the voltage of
`other points Pl, P2 and P3 may be measured. In the
`is to be transmitted to the control unit for sensing infor-
`preferred embodiment as shown in FIG. 3, point Pl is
`mation about the termina1. The data is applied to the
`7.5 volts higher than point P4; P2 is 7.5 volts negative 50 negative termina1 through resistor R220 of amplifier 201
`with respect to P4; and P3 is 12.6 volts negative with
`which is connected as a comparator amplifier. A large
`respect to P4. Points Pl, P2 and P3 provide a supply of
`resistor R222 is connected from the output of amplifier
`d.c. voltages to operate circuitry within terminal 20;
`201 back to the positive input which is connected via
`resistor R221 to a common point. This large resistor
`ihey also provide power for biasing and powering the
`modulator 200, receiver 150 and the constant current 55 connected around the positive feedback path of ampli-
`source 300.
`fier 201 insures that the output of amplifier 201 at point
`Transformer T3, acting as an indicator, is inserted in
`P250 wil1 not osci1late when the leading edges of pulses
`the series line between points C2 and Cl in order to
`are applied to the negative input terminal of amplifier
`provide a high impedance for the pulse transmission
`201.
`The pulses appearing at point P250 are applied first to
`circuit in the control unit 10 in order to substantially 60
`a transistor Q212 via resistor R223 for inverting the
`prevent reflections from the terminal 20 as the pulses
`pulse, which is then applied via resistor 226 to the posi-
`are transmitted from the control unit 10 to the terminal
`20. In this regard the constant current sink 3ωhas an
`tive input of amplifier 202. The pulse at point P250 is
`interna1 high impedance and therefore the impedance of
`also applied to amplifier 203 at its positive terminal via
`transformer T3, as inserted into the line between points 65 resistor R227. The amplifiers 202 and 203 are connected
`Cl and C2 and the impedance of constant current sink
`as level shifting negative feedback amplifiers whereby
`300 create a balanced line, thereby substantially pre-
`the outputs of amplifiers 202 and 203 at points P251 and
`venting reflections when pulses are transmitted.
`P252 serve to bias the transistors Q210 and Q211 to their
`
`45
`
`JUNIPER Ex 1005-pg. 9
`
`

`
`4;173,714
`
`5ω
`
`10
`Description of the Data Pulses Applied to the Line
`FIG. 7 illustrates a preferred format for the data
`pulses which are applied to conductors 1,2,3,4 by the
`control unit 10 and the terminal 20. Each period of time
`T, typically 20.4 milliseconds, is broken up into thirty(cid:173)
`four 6∞ microsecond segments. The first word, called
`
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`JUNIPER Ex 1005-pg. 10
`
`

`
`10
`
`11
`of key telephone station sets. In such an embodiment,
`each particular word of the time period T is used to
`provide information for the control of and/or status of
`line keys, indicators, hold keys, speaker-phone circuit,
`etc. Although thirty-four words are shown in this speci- 5
`fication for purposes of demonstrating the preferred
`embodiment of the data format of this invention, any
`number of words may be used to correspond with the
`number of keys indicators and auxiliary circuits existing
`in a particular key telephone system.
`Another feature of the data format part of this inven(cid:173)
`tion relates to the manner in which information relating
`to the status of the hookswitch and dial pulsing of the
`telephone station set is transmitted to the key service
`unit (as a specific embodiment of the control unit 10) 15
`from the telephone station set (as a specific embodiment
`of the terminal 20). As illustrated in FIG. 7B, during
`each word, short width current pulses during time inter-
`val two, are transmitted from the telephone station set
`over the phantom circuit of conductors 1,2,3,4 to the 20
`key service unit, whenever the hookswitch is open and
`the speaker phone is not operational. Time interval two
`is selected in the preferred embodiment ofthe invention
`so that the frequently occurring hookswitch current
`pulses are generated during the long time interval two 25
`of each word which is 3/2 L in the time length. This
`design f注cilitates reception of the hookswìtch pulses in
`the key service unit since the relatively short hook(cid:173)
`switch pulses do not overlap the ends of the time inter(cid:173)
`val. A hookswitch signal is applied from the key tele- 30
`phone station set under two conditions: (1) when the
`status ofthe telephone station set is "on hook" (on hook
`status occurs when the hookswitch is open and the
`speakerphone is not operational) or (2) when a dial
`pulse from a rotary dial associated with the telephone 35
`station set is generated.
`Thus, when the station set has an "on hook" condi(cid:173)
`tion, current pulses during the second interval of each
`word are transmitted and continue to be transmitted
`until the on-hook status is terminated (by the handset 40
`being taken "ofιhook" or by the speakerphone being
`tumed on). During dial pulse signalling, the current
`pulses are applied during the second interval of each
`word during, but only during, the generation of each
`dial pulse. The time period for each word of the data 45
`format, illustrated in FIG. 7A, is sufficiently short with
`respect to the length of a dial pulse that many "hook-
`switch" current pulses are transmitted, one each during
`each of the words of the data format. The presence or
`absence of current pulses received by the key service 50
`unit in the second time interval indicate that a dial pulse
`is being transmitted from the key telephone set.
`Thus, the novel data format of this invention, in com-
`bination with the four wire communication circuit,
`allows either telephone stations adapted for dial pulse 55
`signalling, or telephone stations adapted for frequency
`signalling to be connected to the key service unit by
`means of the communication circuit. Frequency signals
`are applied over one of the communication channels,
`1,2, or 3,4 while dial pulse signals are transmitted överω
`the four conductor phantom circuit 1,2,3,4 by meaÌls of
`the data format as discussed above.
`The advantages of the present invention, as well as
`certain changes and modifications to the disclosed em-
`bodiment thereof, will be readily apparent to those 65
`skilled in the art. It is the applicants' intention to cover
`all those changes and modifications which could be
`made to the embodiment of the invention herein chosen
`
`4,173,714
`
`12
`for the purposes of the disclosure without departing
`from the spirit and scope of the invention.
`What is claimed is:
`1. A circuit arrangement providing first and second
`communication channels, power feed and bi-directional
`signalling between first and second equipment units
`compnsmg,
`four conductors the ends of which are connected
`between the first and second equipment units, a
`first pair of said conductors providing a first infor(cid:173)
`mation channel between the first and second equip(cid:173)
`ment units, and a second pair of said conductors
`providing a second information channel between
`the first and second equipment units,
`first and second transformers for inductively cou(cid:173)
`pling associated first communication channels in
`the first and second equipment units via said first
`conductor pair; each of the windings of said first
`and second transformers connected to said first
`conductor pair having a center tap connection,
`third and fourth transformers for inductively cou(cid:173)
`pling associated second communication channels in
`the first and second equipment units via said second
`conductor pair, each of the windings of said third
`and fourth transformers connected to said second
`conductor pair having a center tap connection,
`means in the first equipment unit connected via said
`center taps of said first and third transformers to
`said first and second conductor pairs at the first
`equipment unit for
`(a) applying voltage to said four conductors,
`(b) applying voltage-modulated data signals to said
`four conductors for transmission from the first
`equipment unit to the second equipment unit, and
`(c) receiving current-modulated data signals transmit(cid:173)
`ted from the second equipment unit on said four
`conductors, and means in the second equipment
`unit connected via said center taps of said second
`and fourth transformers to said first and second
`conductor pairs at the second equipment unit for
`(a) receiving and regulating said voltage applied to
`said four conductors in the first equipment unit and
`applying said voltage to power the se心ond equip(cid:173)
`ment unit,
`(b) receiving voltage-modulated data signals on said
`four conductors from the frrst equipment unit, ai1d
`(c) applying current-modulated data signals to said
`four conductors for transmission from the second
`equipment unit to the frrst equipment unit.
`2. The circuit of claim 1 wherein:
`a first winding of said