CA1171565A - Transformerless hybrid circuit - Google Patents
Transformerless hybrid circuitInfo
- Publication number
- CA1171565A CA1171565A CA000377972A CA377972A CA1171565A CA 1171565 A CA1171565 A CA 1171565A CA 000377972 A CA000377972 A CA 000377972A CA 377972 A CA377972 A CA 377972A CA 1171565 A CA1171565 A CA 1171565A
- Authority
- CA
- Canada
- Prior art keywords
- wire line
- resistor
- resistors
- hybrid circuit
- circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/54—Circuits using the same frequency for two directions of communication
- H04B1/58—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
- H04B1/583—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa using a bridge network
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M1/00—Substation equipment, e.g. for use by subscribers
- H04M1/58—Anti-side-tone circuits
- H04M1/585—Anti-side-tone circuits implemented without inductive element
Abstract
ABSTRACT OF THE INVENTION
The series arrangement of a current source controlled by a four-wire line in the incoming direction and a first resistor is connected in parallel to a two-wire line terminating shunt arm formed by a second resistor of double the value and a residual impedance, so that the associated two-wire line is terminated in reflection-free fashion. Voltages dependent upon the transmitted signal current which are equal in value but opposed in phase appear across the first and second resistors and in addition a voltage which is dependent upon the received signal current appears across the second resistor;
in the outgoing direction the four-wire line is subject to a voltage intermed-iate value which is independent of the transmitted signal. Instead of a four-wire line, separate go and return channels of any form may be utilized.
The series arrangement of a current source controlled by a four-wire line in the incoming direction and a first resistor is connected in parallel to a two-wire line terminating shunt arm formed by a second resistor of double the value and a residual impedance, so that the associated two-wire line is terminated in reflection-free fashion. Voltages dependent upon the transmitted signal current which are equal in value but opposed in phase appear across the first and second resistors and in addition a voltage which is dependent upon the received signal current appears across the second resistor;
in the outgoing direction the four-wire line is subject to a voltage intermed-iate value which is independent of the transmitted signal. Instead of a four-wire line, separate go and return channels of any form may be utilized.
Description
The present invention relates to transformerless hybrid circuits. To facilitate communication between two telecommun-ications stations in a telecommunications system ~
devices are required between the telecommunications stations in order to ensure adequately interference-free signal transmiss-ion in both directions of transmission. For this purpose, for each direction of transmission there can be provided a separate transmission line, and in the case of multiplex operation these lines are each multiply employed for a plurality of simultan-eously established connection paths between two telecommuni-cations stations; four-wire operatior, c~ this kind being preferably used in the higher levels of a telecomr;unications network. In the lower levels of a telecommunications network, and in particular in the subscriber connection lines, it is general practice to signal transmission carried out in duplex operation via two-wire lines. In this case the transmission signals belonging to the two directions of trans-mission can be isolated by means of a hybrid circuit which terminates the-two-wire line and consists of a bridge circuit which converts the two-wire line into a four-wire section of a subscriber terminal unit (and vice versa) for example. In order to achieve a complete decoupling of the receiving arm of a four-wire line, which leads away from the hybrid circuit, from the associated transmitting arm of the our-wire line, which leads into the hybrid circuit, the bridge circuit must be balanced, and for this purpose must contain an exact simulation
devices are required between the telecommunications stations in order to ensure adequately interference-free signal transmiss-ion in both directions of transmission. For this purpose, for each direction of transmission there can be provided a separate transmission line, and in the case of multiplex operation these lines are each multiply employed for a plurality of simultan-eously established connection paths between two telecommuni-cations stations; four-wire operatior, c~ this kind being preferably used in the higher levels of a telecomr;unications network. In the lower levels of a telecommunications network, and in particular in the subscriber connection lines, it is general practice to signal transmission carried out in duplex operation via two-wire lines. In this case the transmission signals belonging to the two directions of trans-mission can be isolated by means of a hybrid circuit which terminates the-two-wire line and consists of a bridge circuit which converts the two-wire line into a four-wire section of a subscriber terminal unit (and vice versa) for example. In order to achieve a complete decoupling of the receiving arm of a four-wire line, which leads away from the hybrid circuit, from the associated transmitting arm of the our-wire line, which leads into the hybrid circuit, the bridge circuit must be balanced, and for this purpose must contain an exact simulation
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of the input impedance of the two-wire line. However, in order to ensure a high trans~er quality by means of the hybrid circuit, in addition to the need for mutual decoupling between the transmitting and receiving arms of the four-wire line, 5 which is attained when the bridge circuit is properly balanced, it is also desirable to ensure freedom of re~lection between the hybrid circuit and two-wire line, which imposes further design demands with regard to the bridge circuit.
; In this respect a transformerless hybrid circuit is described in the German Patent Specification No. 1,762,849, which consists of a bridge circuit, serving as connecting element between a two-wire line and a foux-wire line, comprising an incoming and an outgoing component which are entirely decoupled from one another but are each connected to the two-wire line, one arm of which is formed by the surge impedance of the two-wire line, the second arm of which, adjoining the first arm~ is formed by a complex impedance which simulates the surge impedance of the two-wire line, and the third and fourth arms of which are each formed by a respective resistor, and whose bridge diagona~ contain~ those parts of the four-wire line which are to be decoupled, together with their input impedances for the outgoing and incoming.components. In this known bridge circuit the outgoing path o~ the four-wire line, for example the earphone of a telephone subscriber terminal unit, is preceded by an impedance converter which reduces the input impedance of the
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of the input impedance of the two-wire line. However, in order to ensure a high trans~er quality by means of the hybrid circuit, in addition to the need for mutual decoupling between the transmitting and receiving arms of the four-wire line, 5 which is attained when the bridge circuit is properly balanced, it is also desirable to ensure freedom of re~lection between the hybrid circuit and two-wire line, which imposes further design demands with regard to the bridge circuit.
; In this respect a transformerless hybrid circuit is described in the German Patent Specification No. 1,762,849, which consists of a bridge circuit, serving as connecting element between a two-wire line and a foux-wire line, comprising an incoming and an outgoing component which are entirely decoupled from one another but are each connected to the two-wire line, one arm of which is formed by the surge impedance of the two-wire line, the second arm of which, adjoining the first arm~ is formed by a complex impedance which simulates the surge impedance of the two-wire line, and the third and fourth arms of which are each formed by a respective resistor, and whose bridge diagona~ contain~ those parts of the four-wire line which are to be decoupled, together with their input impedances for the outgoing and incoming.components. In this known bridge circuit the outgoing path o~ the four-wire line, for example the earphone of a telephone subscriber terminal unit, is preceded by an impedance converter which reduces the input impedance of the
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outgoing component of the four-wire line to a value which is very low in relation to the surge impedance of the subscriber line, and the incoming component of the four-wire line, for example the microphone of the telephone subscriber terminal unit, is pxeceded by an impedance converter which raises the internal impedance of the incoming path of the four-wire line to a value which is very high relative to the surge impedance of the subscriber line.
A bridge circuit of this kind requires not only a transmitting path which is located in one diagonal arm of a ~alanced bridge circuit having a very high, virtually infinite, internal impedance, but also requires a receiving path which is located in the other diagonal arm of the bridge circuit and has a very low input impedance, approaching a value of zero, in . 15 order to achieve both decoupling between the transmitting and receiving paths of the four-wire line, and also a reflection-free termination of the two-wire line, which for a concrete construction of a hybrid circuit of this kind only approximately achieving the desired resistance values, would be relatively expensive, and also relatively critical in view of parasitic impedances which make it difficult to satisfy the condition of r :
decoupling (bridge compensation) and refle5ction fr~om fr2edom (matching) and, outside a relatively narrow band range, may render this impossible, whilst the active elements of an impedance converter, where the design has called for a resist-ance value approaching zero, may be overloaded by interference "
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signals occurring outside of the useful signal band, e.g, in ; the 50 Hz range.
One object of the present invention is to provide a transformerless hybrid circuit which not only achieves decoupling between the transmitting and receiving paths of the four-wire line but also a reflection-free termination of the two-wire line, without the need to provide~a four-wire line transmitting path exhibiting a high internal impedance ~ a four-wire line receiving path possessing an input impedance value approaching zero.
The invention consists in a transformerless hybrid circuit for connecting a two-wire line to a high impedance transmitting path and a receiving path whilst simultaneously decoupling the two paths from one another,-employing a two-wire line terminal impedance which at least approximately - simulates the surge impedance of the two-wire line, in which circuit there is a series arrangement of a signal current source and a first resistor connected -in parallel to a two-wire line terminating shunt arm formed by a series arrangement Of a second resistor and a further impedance, the signal current source being controlled by signals from the trans-mitting path, two terminals of the two resistors being connected together and to a~terminal of the two-wire line, at least for a.c., and the two other terminals of the two resistors being connected together via a series arrangement o~
two further resistors, the receiving path being connected between the junction of the first two resistors and the junction point of the two further resistors and supplied with a received signal which corresponds to an intermediate value, which is at least approximately proportional only to the received signal current, and lies between the voltage value which occurs across that resistor of the two-wire line terminating shunt arm which is traversed by a part of the transmitted signal current modulated in accordance with the transmitted signal occurring in the transmitting path and by the received signal current supplied from the opposite side via the two-wire line, and the voltage value which occurs across-that resistor of the current source arm which is traversed by the transmitted signal current.
The invention will now be described with reference to the drawings, in which:-Figure 1 is a simplified schematic circuit diagram of a_ two~wire ~ four-wire transmission system incorporating an exemplary embodiment of a hybrid circuit constructed in accordance with the invention; and Figure 2 illustrates further circuit details of one alternative exemplary embodiment.
In the transmission system illustrated in Figure 1, in which analogue signals (speech, video) or digital signals (data) can be transmitted, the connection of a two-wire line ZL to a four-wire line VL comprising a transmitting path VS
and a receiving path VE is effected via a transformerless s~
hybrid circuit G which simultaneously effects decoupling of the two four-wire line paths VS and VE from one another. The hybrid circuit G is provided with a ~wo-wire line terminating shunt arm containing an impedance Z2 and a second resistor R2 ~ Q~
in ser.ies, which together~approximately simulate~ the surge impedance of the two-wire line ZL. The hybrid circuit G
contains the series arrangement of a signal current source I and a first resistor R1, to the control input of the signal current source being connected ~ the transmitting path VS of the four-wire line VL, and this series arrangement is connected in parallel with the two-wire line terminating impedance path, which is formed by the series arrangement of the secona resistor R2 and the impedance Z2. The resistance value of the second ~ p~ y resistor R2 is at leas ~double that of the first resistor R1.
The free terminals of the two resistors R1 and R2, are connected together and to one two-wire line terminal a, at least for a~c., whereas the other terminals of the two resistors t R1 and R2 are connected together via a series arrangement of two resistors, R3 and R4, these two resistors having the same value, which i5 high relative to that of the second resistor R2. ~he receiving path VE of the ~our-wire line VL is connected between the junction point e of the two series-connected resistors, R3 and R4, and the terminal a to which the two resistors, R1 and R2 are connected.
In the circuit arrangement illustrated in Figure 1, a transmitted signal current 2iS is supplied by the current source --I, which is controlled by the transmitting path VS Of the four-wire line VL, and.this current is substantially equally divided between the two-wire line ZL and the two-wire line terminating impedance path containing Z2 and R2 ~ respective proportions is Any received signal current ie supplied via the two-wire line ZL from the opposite station (not shown), which will be provided with a similar signal current source, flows through the two-wire line terminating shunt arm with the impedance Z2 and the resistor R2. Therefore a composite voltage composed of a component -e.R2 proportional to the received signal current and a component is.R2 proportional to the transmitted signal current appears across the resistor R2. The resistor R1 located in series with the signal current source I is traversed-only by the transmitted signal current 2.lS so that across this resistor there is a voltage 2~is.R1 proportional to the transmitted current aloneO The receiving path VE of the four-wire line VL, connected between the junction a of the two resistors R1 and R2, and th~e junction e of the two resistors R3 and R4, is supplied with a received signal which corresponds to an intermediate value proportional to the received signal current, lying between the voltage occurring across the resistor R2 and the voltage occurring across the resistor R1.
The mutual compensation of the voltages proportional to the transmitted signal current, which each occur across one of the two resistors, R1 and R2, is thus brought about as a result of this intermediate value formation, and is not, as previously . , , assumed/ dependent upon the fact that the resistance value of the second resistor R2 should be double that of the first resistor R1 and that the resistance value of the resistor R3 should be equal to that of the resistor ~4; instead it is sufficient for R2.R3 to~approximately equal 2.R1.R4, where the resistance values of the resistors R3 and R4 are high relative : to those of the resistors R1 and R2, so that any influence of the received signal current ~ via the resi~tors R3 and R4 upon the transmitted signal current source I is negligible.
In the event of a two-wire line terminal impedance which does not conduct d.c., the parallel arrangement of the two-wire line terminating shunt arm and the current source arm I
containing the source and resistor R1 can also be used as a feed filter for a feed current supplied via the two-wire line ZL, so that the signal current source-I is traversed by the feed current supplied via the two-wire line ZL. In this case.
the signal current source I can be formed by a transistor ~
which is traversed by feed current and which is controlled at . - its control electrode by the transmitting path VS of the four-wire line VS, as indicated in Figure 2. In the hybrid circuit G illustrated in Figure 2 the signal current source consists of a field effect transistor TI,Which lSarranged to be substant-ially temperature stable, and also exhibits dielectric . strength, the illustrated example em~loying a N-channel blocking layer field effect transistor preferably having a steep gradient, whose source f~e~=uY3~-~ ~L~ -~ the _ g _ , ,, .
, .
r-aforementioned first resistor R1 of Figure 1, and has a resistance value of 50Q, for example. A coupling element, formed ~y a series capacitor of 1OnF and a shunt resistor of 1Mn in *his example, provides a connection path for the field effect transistor T1 to be controlled from the transmitting path VS, for example by a microphone amplifier or a data source, so that the feed current is correspondingly modulated and a corresponding transmitted signal current produced.
The two-wire line terminating shunt arm with the impedance Z2 and resistor R2 of Figure 1 is replaced by a d.c.
blocking series arrangement of the second resistor R2, having a value of 100~in this example, and an impedance network Z2 ~,,~,, which ~=5y~Y~ simulation of-the two-wire line surge impedance, in accordance with the conductivity type, and which can advantageously be formed by an RC element, or an RC ladder circuit, as indicated in Figure 2. Between the junction e o~:
the two resistors, R3 and R4, which will each be assumed to have a resistance value of 100 k~L, and the junction a at which the two resistors R1 and R2 are directly connected together for a.c., the hybrid circuit G illustrated in Figure 2 contains the control path of a transistor TE, in the form of a depletion type N-channel IG field effect transistor, which operates as a simple source follower, from whose source resistor the received signal for the receiving path VE of the four-wire line VL is obtained via a capacitor. Although not shown in the drawing, the transistor TE may be replaced by an operational amplifier with negative feedback, connected by its inverting inpu~ to the received signal circuit junction e and by its other input to the ju~lction a, and whose output leads to the receiving path VE of the four-wire line VL; this then avoids ; 5 any residual influence of the received signal on the signal current sou~e transistor TI.
As can also be seen from Figure 2, there is connected in parallel to the resistor R3 an adaptive transversal filter F, which conducts an echo compensation signal to the received signal junction e in order to further increase the decoupling between ~he transmitting path VS and the receiving path VE of the four~wire line VL. As it is fundamentally described in FREQUENZ 28 (1974) 5, pages 118 to 122 and pages 155 to 161, the elimination of transmitted signal dependent interference signals which occur in the receiving arm of a hybrid circuit by the addition or subtraction of compensation signals using such echo compensation, such an arrangement does not require to be discussed in further detail here.
Between the terminals of the first resistor R1 and the second resistor R2, which are connected to one another for a.c.
there is inserted in the feed circuit a circuit element D
~hich is traversed by the feed current supplied via the two-wire line ZL, and from which a local operating voltage VB can be tapped (for transmitting and receiving circuits of the four-wire line and for the hybrid circuit itself). In the circuitarrangement illustrated in Figure 2 this circuit element is formed by a Zener diode; in contrast to the illustration in Figure 2 however the Zener diode can be replaced by a circuit which absorbs current only when the operating voltage UB has reached a given theo-retical value.
A hybrid circuit constructed in accordance with the inven-tion is not limited to comm~nications transmission in identical state processes, but can also be used in 2 transmission system employing two-wire line transmission channels which are separate frcm one another as regards time state and/or frequency state: the hybrid circuit is then connected to a four-wire line transmitting path or go-channel VS ~or the transmission of transmitted signal pulses at specific times and/or with a specific centre point for its frequency spectrum and to a four-wire line receiving path or return--channel UE for the reception of received signal pulses at other times, and/or with another centre point for its frequency spectrwm.
In the transmitting path VS the hybrid circuit can be preceded by a chain arrangement of a speech signal coder, formed for example by a delta m~dulator, and A digital signal transmitting circuit for the transmission of transmitted signal pulses for example at specific points of time, and in the receiving path UE the hybrid circuit can be follcwed by a chain arrangement of a corresponding digital signal receiving circuit and a speech signal decoder, possibly formed by a delta demGdulator. The aforementioned digital signal transmitting circuit can for example emit pseudo-ternary half-element signal pulses, so-called half-bauded AMI (alter-nate mark inversion) signal pulses, for which purpose, as proposed elsewhere, it can comprise a ROM which stores instantaneous values of the transmitted signal pulses in coded form and is operated in accordance with -the digital signals emitted from the speech signal coder and which conducts the corres-ponding instantaneous values in their coded form to a decoder which subsequ-ently forms the corresponding transmitted signal pulses. The digital signal receiving circuit can contain a regenerator such as is fundamentally known (for example from the Siemens publication "PCM- Die Pulscode-Modulation und ihre Anwendung im Fernmeldewesen", page 15 Fig. 21) and in which a pulse extractor is used to extract from the received signal pulses a received bit pulse train which serves to define the decision times at which the amplitude decision as regards the relevant status value of the bit in question is made in the digital signal receiving circuit; furthermore the digital signal receiving circuit can contain a received signal converter which can be constructed for example from a rectifier circuit and which converts the regenerated signals into correspond-ing L~M and PCM signals. As proposed elsewhere, the transmitted bit pulse train can be derived from the received bit pulse train and displaced in phase rela-tive to the latter by half a bit time interval. However such circuitry details of the transmitting path VS and the receiving path VE have not been shown ~ 13-~ ~ '7~
in the drawing and do not require to be considered in detail, as this is not essential for an understanding of the present invention.
A circuit constructed in accordance with the invention involves the advantage that a circuit which facilitates both decoupling between the transmitting and receiving paths of a four-wire line or the like over a wide band, and which provides a reflection-free termination of the two-wire line, nevertheless enables the value of the input impedance of the 1~ receiving path to be freely selected, and in particular does not require that it exhibits an extremely small value (zero), so that it is possible to avoid the special construction meas-ures otherwise required, and eliminates the need for overload protection of such an input impedance when having a value approaching ~ero, and so avoids associated difficulties with regard to the construction and dimensioning of the hybrid circuit, Advantageously the resistance value of the second resistor can be at least approximately double that of the first resistor, whereas the two further resistances, which are expediently high in value relative to the first or second resistors, are equal in value to one another, and this arrangement particularly expediently takes into account the division of the transmitted signal current supplied by the signal current source between the two-wire line and the two-wire line terminating shunt path.
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Preferably the signal current source can be traversed by a feed current which is supplied via the two~wire line, so that interference influences caused by any excess voltages which reach the hybrid circuit via the two-wire line are deactivated~ and an advantayeous construction of the signal current source is facilitated: the signal current source preferably being in the form of a transistor controlled at its control electrode by the transmitting path and traversed by feed current in its main circuit, and expediently being a field ~ ;~fir effect transistor whose source ~Y~U~ u~ acts as the first resistor. The control current taken by the field effect transistor is so low that it leaves the signal current prop-ortionality of the voltage occurxing across the resistor virtually unimpaired.
Advantageously~ the other two terminals of the first and second resistors are connected to one another for a.c. via~
a circuit element which is traversed by feed currents supplied via the two-wire line and from which there can be tapped a local operating voltage which permits a current supply of a four-wire line section formed, for example, by the four-wire component of a telephone subscriber terminal unit, where there can be provided a circuit element which does no~ absorb current until a theoretical operating voltage value has been exceeded.
The receiving path~may be connected to the hybrid circuit in floating fashion (possibly via opto-couplers), as may be possibly also the transmi-tting path, in order to achieve line symmetry of the two-wire line, may be directly connected be-tween the junction of the first and second resistors and the junc-tion of the further resistors; or alternatively, between the junc-tion of the first and second resistors and the junction of the further resistors it is possible to connect the control circuit of a transistor whose output circuit leads to the receiving path or it is possible to connect an operational amplifier provided with negative feedback having an output which leads to the receiving path.
If, in addition to the fulfilment of the requirement for decoupling and reflection from freedom, echo compensation is also to be achieved, an adaptive transversal filter can lead from the junction of the signal current source and the first resis-tor to the junction of the further resistors.
A hybrid d rcuit constructed in accordance with the inven-tion is not limited to use in a co~,munications transmission using identical state processes; in fact it can also be used in a transmis-sion sys-tem employing two-wire line transmission channels (go-channel and return channel) which æ e separate from one another as regards time state and/or frequency state, in which, in a further development of the invention, the hybrid circuit is connected to a transmitting path for the transmission of transmitted signal pulses at specific points of time and/or with a specific centre point for its frequency spectrum and to a receiving path for the ,,~
reception of received signal pulses at other times and/or with another centre point of its frequency spectrum.
,, ;
outgoing component of the four-wire line to a value which is very low in relation to the surge impedance of the subscriber line, and the incoming component of the four-wire line, for example the microphone of the telephone subscriber terminal unit, is pxeceded by an impedance converter which raises the internal impedance of the incoming path of the four-wire line to a value which is very high relative to the surge impedance of the subscriber line.
A bridge circuit of this kind requires not only a transmitting path which is located in one diagonal arm of a ~alanced bridge circuit having a very high, virtually infinite, internal impedance, but also requires a receiving path which is located in the other diagonal arm of the bridge circuit and has a very low input impedance, approaching a value of zero, in . 15 order to achieve both decoupling between the transmitting and receiving paths of the four-wire line, and also a reflection-free termination of the two-wire line, which for a concrete construction of a hybrid circuit of this kind only approximately achieving the desired resistance values, would be relatively expensive, and also relatively critical in view of parasitic impedances which make it difficult to satisfy the condition of r :
decoupling (bridge compensation) and refle5ction fr~om fr2edom (matching) and, outside a relatively narrow band range, may render this impossible, whilst the active elements of an impedance converter, where the design has called for a resist-ance value approaching zero, may be overloaded by interference "
:~ ~ '7~
signals occurring outside of the useful signal band, e.g, in ; the 50 Hz range.
One object of the present invention is to provide a transformerless hybrid circuit which not only achieves decoupling between the transmitting and receiving paths of the four-wire line but also a reflection-free termination of the two-wire line, without the need to provide~a four-wire line transmitting path exhibiting a high internal impedance ~ a four-wire line receiving path possessing an input impedance value approaching zero.
The invention consists in a transformerless hybrid circuit for connecting a two-wire line to a high impedance transmitting path and a receiving path whilst simultaneously decoupling the two paths from one another,-employing a two-wire line terminal impedance which at least approximately - simulates the surge impedance of the two-wire line, in which circuit there is a series arrangement of a signal current source and a first resistor connected -in parallel to a two-wire line terminating shunt arm formed by a series arrangement Of a second resistor and a further impedance, the signal current source being controlled by signals from the trans-mitting path, two terminals of the two resistors being connected together and to a~terminal of the two-wire line, at least for a.c., and the two other terminals of the two resistors being connected together via a series arrangement o~
two further resistors, the receiving path being connected between the junction of the first two resistors and the junction point of the two further resistors and supplied with a received signal which corresponds to an intermediate value, which is at least approximately proportional only to the received signal current, and lies between the voltage value which occurs across that resistor of the two-wire line terminating shunt arm which is traversed by a part of the transmitted signal current modulated in accordance with the transmitted signal occurring in the transmitting path and by the received signal current supplied from the opposite side via the two-wire line, and the voltage value which occurs across-that resistor of the current source arm which is traversed by the transmitted signal current.
The invention will now be described with reference to the drawings, in which:-Figure 1 is a simplified schematic circuit diagram of a_ two~wire ~ four-wire transmission system incorporating an exemplary embodiment of a hybrid circuit constructed in accordance with the invention; and Figure 2 illustrates further circuit details of one alternative exemplary embodiment.
In the transmission system illustrated in Figure 1, in which analogue signals (speech, video) or digital signals (data) can be transmitted, the connection of a two-wire line ZL to a four-wire line VL comprising a transmitting path VS
and a receiving path VE is effected via a transformerless s~
hybrid circuit G which simultaneously effects decoupling of the two four-wire line paths VS and VE from one another. The hybrid circuit G is provided with a ~wo-wire line terminating shunt arm containing an impedance Z2 and a second resistor R2 ~ Q~
in ser.ies, which together~approximately simulate~ the surge impedance of the two-wire line ZL. The hybrid circuit G
contains the series arrangement of a signal current source I and a first resistor R1, to the control input of the signal current source being connected ~ the transmitting path VS of the four-wire line VL, and this series arrangement is connected in parallel with the two-wire line terminating impedance path, which is formed by the series arrangement of the secona resistor R2 and the impedance Z2. The resistance value of the second ~ p~ y resistor R2 is at leas ~double that of the first resistor R1.
The free terminals of the two resistors R1 and R2, are connected together and to one two-wire line terminal a, at least for a~c., whereas the other terminals of the two resistors t R1 and R2 are connected together via a series arrangement of two resistors, R3 and R4, these two resistors having the same value, which i5 high relative to that of the second resistor R2. ~he receiving path VE of the ~our-wire line VL is connected between the junction point e of the two series-connected resistors, R3 and R4, and the terminal a to which the two resistors, R1 and R2 are connected.
In the circuit arrangement illustrated in Figure 1, a transmitted signal current 2iS is supplied by the current source --I, which is controlled by the transmitting path VS Of the four-wire line VL, and.this current is substantially equally divided between the two-wire line ZL and the two-wire line terminating impedance path containing Z2 and R2 ~ respective proportions is Any received signal current ie supplied via the two-wire line ZL from the opposite station (not shown), which will be provided with a similar signal current source, flows through the two-wire line terminating shunt arm with the impedance Z2 and the resistor R2. Therefore a composite voltage composed of a component -e.R2 proportional to the received signal current and a component is.R2 proportional to the transmitted signal current appears across the resistor R2. The resistor R1 located in series with the signal current source I is traversed-only by the transmitted signal current 2.lS so that across this resistor there is a voltage 2~is.R1 proportional to the transmitted current aloneO The receiving path VE of the four-wire line VL, connected between the junction a of the two resistors R1 and R2, and th~e junction e of the two resistors R3 and R4, is supplied with a received signal which corresponds to an intermediate value proportional to the received signal current, lying between the voltage occurring across the resistor R2 and the voltage occurring across the resistor R1.
The mutual compensation of the voltages proportional to the transmitted signal current, which each occur across one of the two resistors, R1 and R2, is thus brought about as a result of this intermediate value formation, and is not, as previously . , , assumed/ dependent upon the fact that the resistance value of the second resistor R2 should be double that of the first resistor R1 and that the resistance value of the resistor R3 should be equal to that of the resistor ~4; instead it is sufficient for R2.R3 to~approximately equal 2.R1.R4, where the resistance values of the resistors R3 and R4 are high relative : to those of the resistors R1 and R2, so that any influence of the received signal current ~ via the resi~tors R3 and R4 upon the transmitted signal current source I is negligible.
In the event of a two-wire line terminal impedance which does not conduct d.c., the parallel arrangement of the two-wire line terminating shunt arm and the current source arm I
containing the source and resistor R1 can also be used as a feed filter for a feed current supplied via the two-wire line ZL, so that the signal current source-I is traversed by the feed current supplied via the two-wire line ZL. In this case.
the signal current source I can be formed by a transistor ~
which is traversed by feed current and which is controlled at . - its control electrode by the transmitting path VS of the four-wire line VS, as indicated in Figure 2. In the hybrid circuit G illustrated in Figure 2 the signal current source consists of a field effect transistor TI,Which lSarranged to be substant-ially temperature stable, and also exhibits dielectric . strength, the illustrated example em~loying a N-channel blocking layer field effect transistor preferably having a steep gradient, whose source f~e~=uY3~-~ ~L~ -~ the _ g _ , ,, .
, .
r-aforementioned first resistor R1 of Figure 1, and has a resistance value of 50Q, for example. A coupling element, formed ~y a series capacitor of 1OnF and a shunt resistor of 1Mn in *his example, provides a connection path for the field effect transistor T1 to be controlled from the transmitting path VS, for example by a microphone amplifier or a data source, so that the feed current is correspondingly modulated and a corresponding transmitted signal current produced.
The two-wire line terminating shunt arm with the impedance Z2 and resistor R2 of Figure 1 is replaced by a d.c.
blocking series arrangement of the second resistor R2, having a value of 100~in this example, and an impedance network Z2 ~,,~,, which ~=5y~Y~ simulation of-the two-wire line surge impedance, in accordance with the conductivity type, and which can advantageously be formed by an RC element, or an RC ladder circuit, as indicated in Figure 2. Between the junction e o~:
the two resistors, R3 and R4, which will each be assumed to have a resistance value of 100 k~L, and the junction a at which the two resistors R1 and R2 are directly connected together for a.c., the hybrid circuit G illustrated in Figure 2 contains the control path of a transistor TE, in the form of a depletion type N-channel IG field effect transistor, which operates as a simple source follower, from whose source resistor the received signal for the receiving path VE of the four-wire line VL is obtained via a capacitor. Although not shown in the drawing, the transistor TE may be replaced by an operational amplifier with negative feedback, connected by its inverting inpu~ to the received signal circuit junction e and by its other input to the ju~lction a, and whose output leads to the receiving path VE of the four-wire line VL; this then avoids ; 5 any residual influence of the received signal on the signal current sou~e transistor TI.
As can also be seen from Figure 2, there is connected in parallel to the resistor R3 an adaptive transversal filter F, which conducts an echo compensation signal to the received signal junction e in order to further increase the decoupling between ~he transmitting path VS and the receiving path VE of the four~wire line VL. As it is fundamentally described in FREQUENZ 28 (1974) 5, pages 118 to 122 and pages 155 to 161, the elimination of transmitted signal dependent interference signals which occur in the receiving arm of a hybrid circuit by the addition or subtraction of compensation signals using such echo compensation, such an arrangement does not require to be discussed in further detail here.
Between the terminals of the first resistor R1 and the second resistor R2, which are connected to one another for a.c.
there is inserted in the feed circuit a circuit element D
~hich is traversed by the feed current supplied via the two-wire line ZL, and from which a local operating voltage VB can be tapped (for transmitting and receiving circuits of the four-wire line and for the hybrid circuit itself). In the circuitarrangement illustrated in Figure 2 this circuit element is formed by a Zener diode; in contrast to the illustration in Figure 2 however the Zener diode can be replaced by a circuit which absorbs current only when the operating voltage UB has reached a given theo-retical value.
A hybrid circuit constructed in accordance with the inven-tion is not limited to comm~nications transmission in identical state processes, but can also be used in 2 transmission system employing two-wire line transmission channels which are separate frcm one another as regards time state and/or frequency state: the hybrid circuit is then connected to a four-wire line transmitting path or go-channel VS ~or the transmission of transmitted signal pulses at specific times and/or with a specific centre point for its frequency spectrum and to a four-wire line receiving path or return--channel UE for the reception of received signal pulses at other times, and/or with another centre point for its frequency spectrwm.
In the transmitting path VS the hybrid circuit can be preceded by a chain arrangement of a speech signal coder, formed for example by a delta m~dulator, and A digital signal transmitting circuit for the transmission of transmitted signal pulses for example at specific points of time, and in the receiving path UE the hybrid circuit can be follcwed by a chain arrangement of a corresponding digital signal receiving circuit and a speech signal decoder, possibly formed by a delta demGdulator. The aforementioned digital signal transmitting circuit can for example emit pseudo-ternary half-element signal pulses, so-called half-bauded AMI (alter-nate mark inversion) signal pulses, for which purpose, as proposed elsewhere, it can comprise a ROM which stores instantaneous values of the transmitted signal pulses in coded form and is operated in accordance with -the digital signals emitted from the speech signal coder and which conducts the corres-ponding instantaneous values in their coded form to a decoder which subsequ-ently forms the corresponding transmitted signal pulses. The digital signal receiving circuit can contain a regenerator such as is fundamentally known (for example from the Siemens publication "PCM- Die Pulscode-Modulation und ihre Anwendung im Fernmeldewesen", page 15 Fig. 21) and in which a pulse extractor is used to extract from the received signal pulses a received bit pulse train which serves to define the decision times at which the amplitude decision as regards the relevant status value of the bit in question is made in the digital signal receiving circuit; furthermore the digital signal receiving circuit can contain a received signal converter which can be constructed for example from a rectifier circuit and which converts the regenerated signals into correspond-ing L~M and PCM signals. As proposed elsewhere, the transmitted bit pulse train can be derived from the received bit pulse train and displaced in phase rela-tive to the latter by half a bit time interval. However such circuitry details of the transmitting path VS and the receiving path VE have not been shown ~ 13-~ ~ '7~
in the drawing and do not require to be considered in detail, as this is not essential for an understanding of the present invention.
A circuit constructed in accordance with the invention involves the advantage that a circuit which facilitates both decoupling between the transmitting and receiving paths of a four-wire line or the like over a wide band, and which provides a reflection-free termination of the two-wire line, nevertheless enables the value of the input impedance of the 1~ receiving path to be freely selected, and in particular does not require that it exhibits an extremely small value (zero), so that it is possible to avoid the special construction meas-ures otherwise required, and eliminates the need for overload protection of such an input impedance when having a value approaching ~ero, and so avoids associated difficulties with regard to the construction and dimensioning of the hybrid circuit, Advantageously the resistance value of the second resistor can be at least approximately double that of the first resistor, whereas the two further resistances, which are expediently high in value relative to the first or second resistors, are equal in value to one another, and this arrangement particularly expediently takes into account the division of the transmitted signal current supplied by the signal current source between the two-wire line and the two-wire line terminating shunt path.
.t7.~.S~
Preferably the signal current source can be traversed by a feed current which is supplied via the two~wire line, so that interference influences caused by any excess voltages which reach the hybrid circuit via the two-wire line are deactivated~ and an advantayeous construction of the signal current source is facilitated: the signal current source preferably being in the form of a transistor controlled at its control electrode by the transmitting path and traversed by feed current in its main circuit, and expediently being a field ~ ;~fir effect transistor whose source ~Y~U~ u~ acts as the first resistor. The control current taken by the field effect transistor is so low that it leaves the signal current prop-ortionality of the voltage occurxing across the resistor virtually unimpaired.
Advantageously~ the other two terminals of the first and second resistors are connected to one another for a.c. via~
a circuit element which is traversed by feed currents supplied via the two-wire line and from which there can be tapped a local operating voltage which permits a current supply of a four-wire line section formed, for example, by the four-wire component of a telephone subscriber terminal unit, where there can be provided a circuit element which does no~ absorb current until a theoretical operating voltage value has been exceeded.
The receiving path~may be connected to the hybrid circuit in floating fashion (possibly via opto-couplers), as may be possibly also the transmi-tting path, in order to achieve line symmetry of the two-wire line, may be directly connected be-tween the junction of the first and second resistors and the junc-tion of the further resistors; or alternatively, between the junc-tion of the first and second resistors and the junction of the further resistors it is possible to connect the control circuit of a transistor whose output circuit leads to the receiving path or it is possible to connect an operational amplifier provided with negative feedback having an output which leads to the receiving path.
If, in addition to the fulfilment of the requirement for decoupling and reflection from freedom, echo compensation is also to be achieved, an adaptive transversal filter can lead from the junction of the signal current source and the first resis-tor to the junction of the further resistors.
A hybrid d rcuit constructed in accordance with the inven-tion is not limited to use in a co~,munications transmission using identical state processes; in fact it can also be used in a transmis-sion sys-tem employing two-wire line transmission channels (go-channel and return channel) which æ e separate from one another as regards time state and/or frequency state, in which, in a further development of the invention, the hybrid circuit is connected to a transmitting path for the transmission of transmitted signal pulses at specific points of time and/or with a specific centre point for its frequency spectrum and to a receiving path for the ,,~
reception of received signal pulses at other times and/or with another centre point of its frequency spectrum.
,, ;
Claims (13)
1. A transformerless hybrid circuit for connecting a two-wire line to a high impedance transmitting path and a receiving path whilst simultaneously decoupling the two paths from one another, employing a two-wire line terminal impedance which at least approximately simulates the surge impedance of the two-wire line, in which circuit there is a series arrange-ment of a signal current source and a first resistor connected in parallel to a two-wire line terminating shunt arm formed by a series arrangement of a second resistor and a further impedance, the signal current source being controlled by signals from the transmitting path, two terminals of the two resistors being connected together and to a terminal of the two-wire line, at least for a.c., and the two other terminals of the two resistors being connected together via a series arrangement of two further resistors, the receiving path being connected between the junction point of the first two resistors and the junction point of the two further resistors and supplied with a received signal which corresponds to an intermediate value, which is at least approximately proportional only to the received signal current, and lies between the voltage value which occurs across that resistor of the two-wire line terminating shunt arm which is traversed by a part of the transmitted signal current modulated in accordance with the transmitted signal occurring in the transmitting path and by the received signal current supplied from the opposite side via the two-wire line, and the voltage value which occurs across that resistor of the current source arm which is traversed by the transmitted signal current.
2. A hybrid circuit as claimed in Claim 1, in which the resistance value of said second resistor is substantially double that of said first resistor and the two further resistors are of substantially the same value.
3. A hybrid circuit as claimed in Claim 1 or Claim 2, in which said two further resistors are high in value relative to the first or second resistor.
4. A hybrid circuit as claimed in Claim 1, in which said further impedance is in the form of a RC network.
5. A hybrid circuit as claimed in Claim 1, in which said signal current source is traversed by feed current supplied via the two-wire line.
6. A hybrid circuit as claimed in Claim 5, in which said signal current source is a transistor controlled at its control electrode by signals from the transmitting path.
7. A hybrid circuit as claimed in Claim 6, in which said transistor is a field effect transistor whose source resistor acts as said first resistor.
8. A hybrid circuit as claimed in Claim 5, in which said other two terminals of the first and second resistors are connected to one another for a.c. via a circuit element which is traversed by feed current supplied via the two-wire line and from which a local operating voltage can be tapped.
9. A hybrid circuit as claimed in Claim 8, in which a circuit element is provided which does not absorb current until a nominal operating voltage value is exceeded.
10. A hybrid circuit as claimed in Claim 1, in which the junction of the first and second resistors and the junction of the further resistors are connected by the control circuit of a further transistor whose output circuit leads to the receiving path.
11. A hybrid circuit as claimed in Claim 1, in which the junction of the first and second resistors and the junction of the further resistors are connected to inputs of an operational amplifier with negative feedback whose output feeds the receiving path.
12. A hybrid circuit as claimed in Claim 1, in which an adaptive trans-versal filter additionally leads from the junction of the signal current source and the first resistor to the junction of the further resistors.
13. A hybrid circuit as claimed in Claim 1, in which there is connected a transmitting path for the transmission of transmitted signal pulses at specific points of time and/or with a specific centre point for its frequency spectrum and to a receiving path for the reception of received signal pulses at other points of time and/or with another center point for its frequency spectrum.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3019835A DE3019835C2 (en) | 1980-05-23 | 1980-05-23 | Transformer-free hybrid connection |
| DEP3019835.7 | 1980-05-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1171565A true CA1171565A (en) | 1984-07-24 |
Family
ID=6103195
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000377972A Expired CA1171565A (en) | 1980-05-23 | 1981-05-21 | Transformerless hybrid circuit |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US4418249A (en) |
| EP (1) | EP0040785B1 (en) |
| JP (1) | JPS5713825A (en) |
| AT (1) | ATE3487T1 (en) |
| CA (1) | CA1171565A (en) |
| DE (1) | DE3019835C2 (en) |
| DK (1) | DK151997C (en) |
| SU (1) | SU1371514A3 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5010399A (en) | 1989-07-14 | 1991-04-23 | Inline Connection Corporation | Video transmission and control system utilizing internal telephone lines |
| US6243446B1 (en) | 1997-03-11 | 2001-06-05 | Inline Connections Corporation | Distributed splitter for data transmission over twisted wire pairs |
| JPH0375370U (en) * | 1989-11-27 | 1991-07-29 | ||
| NL1000486C2 (en) * | 1995-06-02 | 1996-12-03 | Nederland Ptt | Fork circuit for twisted pair transmission line |
| DE19828337A1 (en) * | 1998-06-25 | 1999-12-30 | Bosch Gmbh Robert | Telecommunication device |
| US6532279B1 (en) | 1999-06-11 | 2003-03-11 | David D. Goodman | High-speed data communication over a residential telephone wiring network |
| US8385538B2 (en) * | 2008-12-10 | 2013-02-26 | Utc Fire & Security Americas Corporation, Inc. | Method, system, and apparatus for a differential transformer-free hybrid circuit |
Family Cites Families (15)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3453395A (en) * | 1965-12-01 | 1969-07-01 | Gen Electric | Solid-state hybrid |
| US3529099A (en) * | 1967-05-10 | 1970-09-15 | Itt | Telephone subset with resistive hybrid network |
| GB1241037A (en) * | 1968-07-26 | 1971-07-28 | Telefongyar | A circuit arrangement |
| DE1762849B2 (en) * | 1968-09-10 | 1980-02-07 | Telefunken Patentverwertungsgesellschaft Mbh, 7900 Ulm | Transformer-free bridge circuit |
| DE1963507A1 (en) * | 1969-12-18 | 1971-06-24 | Licentia Gmbh | Transformerless hybrid circuit for connecting a two-wire and a four-wire line |
| US3751602A (en) * | 1971-08-13 | 1973-08-07 | Bell Telephone Labor Inc | Loudspeaking telephone |
| DE2159149C3 (en) * | 1971-11-29 | 1978-08-31 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Circuit arrangement for centrally fed subscriber stations with speech circuits containing a resistor bridge |
| BE792329A (en) * | 1971-12-09 | 1973-06-06 | Int Standard Electric Corp | ELECTRONIC TRANSMISSION CIRCUIT FOR TELEPHONE STATION |
| DE2607480C2 (en) * | 1976-02-20 | 1982-11-25 | Deutsche Telephonwerke Und Kabelindustrie Ag, 1000 Berlin | Circuit arrangement for a fork |
| FR2404344A1 (en) * | 1977-09-27 | 1979-04-20 | Jeumont Schneider | SUBSCRIBER ELECTRONIC EQUIPMENT, WITH TWO-WIRE-FOUR-WIRE CONVERSION CIRCUIT, FOR TELEPHONE CENTER |
| DE2807785A1 (en) * | 1978-02-23 | 1979-08-30 | Siemens Ag | DIGITAL NEWS TRANSMISSION SYSTEM |
| US4174470A (en) * | 1978-10-10 | 1979-11-13 | Bell Telephone Laboratories, Incorporated | Electronic hybrid |
| US4228323A (en) * | 1979-01-31 | 1980-10-14 | Bell Telephone Laboratories, Incorporated | Variable loop length compensated barrier circuit |
| DE2916576C3 (en) * | 1979-04-24 | 1981-12-10 | Siemens AG, 1000 Berlin und 8000 München | Digital telecommunication system for two-wire remote location operation |
| DE2921019C2 (en) * | 1979-05-23 | 1981-06-19 | Siemens AG, 1000 Berlin und 8000 München | Digital telecommunications system with at least one four-wire line section |
-
1980
- 1980-05-23 DE DE3019835A patent/DE3019835C2/en not_active Expired
-
1981
- 1981-05-12 JP JP7028181A patent/JPS5713825A/en active Granted
- 1981-05-18 AT AT81103807T patent/ATE3487T1/en not_active IP Right Cessation
- 1981-05-18 EP EP81103807A patent/EP0040785B1/en not_active Expired
- 1981-05-21 CA CA000377972A patent/CA1171565A/en not_active Expired
- 1981-05-22 SU SU813290849A patent/SU1371514A3/en active
- 1981-05-22 DK DK226381A patent/DK151997C/en active
- 1981-05-22 US US06/266,210 patent/US4418249A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0040785B1 (en) | 1983-05-18 |
| EP0040785A1 (en) | 1981-12-02 |
| DE3019835C2 (en) | 1983-12-01 |
| JPS5713825A (en) | 1982-01-23 |
| US4418249A (en) | 1983-11-29 |
| DK151997C (en) | 1988-07-18 |
| SU1371514A3 (en) | 1988-01-30 |
| DE3019835A1 (en) | 1981-12-03 |
| ATE3487T1 (en) | 1983-06-15 |
| DK151997B (en) | 1988-01-18 |
| JPS6342977B2 (en) | 1988-08-26 |
| DK226381A (en) | 1981-11-24 |
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