DE2622568A1 - CIRCUIT FOR INTERFACE FORMATION - Google Patents

Description

BLUMBACH · WESER · BERGEN · KRAMER TWISTING DEER

PATENT LAWYERS IN MUNICH AND WIESBADEN

Postal address Munich: Patentconsult 8 Munich 60 Radeckestrasse 43 Telephone (089) 883603/883604 Telex 05-212313 Postal address Wiesbaden: Patentconsult 62 Wiesbaden Sonnenberger Straße 43 Telephone (06121) 562943/561998 Telex 04-186237

WESTERN ELECTRIC INCORPORATED James, D.B. 20-1 -4-1 -6

NEW YORK, N.Y. 10007 (USA)

Circuit for interface formation

The invention relates to a circuit for interfacing between two parts of a communication path.

When a conference call is to be established between a number of telephone lines, a four-wire operation is usually used used, in which the send and receive signals are transmitted via individual wire pairs. The wire pairs of each line are then selectively connected via a common amplifier by means of a Koppfelfeidmatrix whose cross points connect through all four wires of each line can. If electromechanical components are used, this is the case Switching matrix bulky and when electronic parts are used be to reduce the size so arise because of for each

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Line circuit required number of four cross points too high Costs.

Two-wire conference calls are associated with negative Series and parallel impedances are possible, but the negative impedance must be changed for different configurations and different sizes of conference calls. Controlling a negative Impedance can be extremely cumbersome.

Another problem arises when there are three or more telephone sets get together for a conference without a special conference call is used. Then there is one higher attenuation compared to a typical two-set connection. When joining every other intercom The signal strength is reduced proportionally during the conference. If the Crosspoints of the switching matrix have zero resistance the reduction in signal strength caused by the additional load impedance of each additional call station.

The invention has set itself the task of addressing the disadvantages of the known Avoid switching. The invention is aimed at solving the problem

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from a circuit of the type mentioned and is identified by means for supplying a signal stream representing the value of a signal on a first path part of the message path to a second path part of the message path and means for supplying a difference signal to the first path part which is the value represents a signal voltage on the second path portion minus a portion corresponding to the value of the signal current.

In a message switching system for establishing a communication link between selectable first message path parts can be a A large number of such interface circuits are used, each via a corresponding second message path part with a switching matrix are connected. The switching network can be controlled to connect selectable second path sections with a common bus, and the bus is connected to a facility on the Collector line generates a signal voltage which represents the sum of the signal currents which the collector line over the selected second Path parts supplied by the assigned interface circuits will.

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In a preferred embodiment of the invention, the interface circuit is a current source designed to deliver a current equivalent to the signal voltage available from the transmitting source is. The switching matrix provides a bus resistance, which is used jointly by the circuits serving the other connected transmission lines. The one generated by the power source Signal current is accordingly when flowing through the common bus resistance converted into a signal voltage, which is sent via the switching matrix to every further connected interface circuit is transmitted.

If the cross point resistance of the switching matrix is negligible the component measured at the output of the current source is the Bus voltage generated on one of each line Electricity is the opposite of that generated on the line Tension. On any given line, these voltages cancel each other out, causing the feedback signal to disappear.

As the output of each connection circuit for unbalanced operation can be a single wire, the switching matrix

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matrix on a single component per intersection without reducing the number of the lines that can be connected to each other at the same time is restricted. "

In applications where crosspoints with variable resistance are to be used, the voltage that is transmitted back from the bus resistance plus the cross-point resistance is correct does not exactly match the locally generated voltage, so that ' a feedback signal of unknown magnitude is applied to the telephone line. This feedback signal causes the back loss differs from the known case or the case in which the cross-point resistance is zero, and the transmission loss is changed by the resulting feedback signal.

In another embodiment of the invention, the Connections from the output of the high-impedance power source to the common busbar separated into transmission and reception paths and each path is connected to the manifold resistor by a separate cross point. This is how the tension is transmitted back more precisely adapted to the voltage on the bus, and changes of the cross-point resistance are compared to the high summation

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resistance negligible.

In the following, preferred exemplary embodiments of the invention will be described in more detail with reference to the drawings. Show it:

1 shows an exemplary embodiment of an interface circuit for use in a conference arrangement having a single core bus;

2 shows an exemplary embodiment of an interface circuit, which can then be used when crosstalk is to be reduced;

Fig. 3 shows an embodiment of an interface circuit that can be used when a DC bias the intersection is not wanted;

4 shows a switching network matrix with double cross points in Connection to a single manifold.

In the following explanation, the letter i is used to to designate the number of any particular connection circuit. Accordingly, it is the one associated with the connection circuit PCI

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Amplifier Αί-l around the name for the amplifier Al-I. Correspondingly, the transistor Qi-I assigned to the connection circuit PC2 is shown in the connection circuit PC2 as transistor Q2-1.

According to Fig. 1, each connection circuit is on Giund one over the associated telephone subscriber line, for example the Line LI, transmitted signal voltage, a signal to the busbar Bl in the form of a signal current from a current source that the transistors Contains Qi-I and Qi-2. The resulting signal voltage it on the The bus line Bl is the sum of all signal currents, multiplied by the resistor R4. In each connection circuit the amplifier subtracts Ai-I the port circuit's own contribution to the bus signal and gives the amplified result via the components Zi-I and Ti-I to the subscriber line. The operational amplifier Ai-2 represents together with the assigned components Zi-I, Ri-5 and Ri-3 an electronic hybrid circuit of the type disclosed in U.S. Patent 3,824 (July 16, 1974). This hybrid circuit separates the directions of transmission of the telephone set on 2 separate paths, namely the transmission path from the output of the amplifier Ai-2 and the reception path from the output of the amplifier Ai-I.

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The purpose of the bus circuit, also referred to below as the "monobus" circuit, is to restore the two transmission paths to one merge a single wire, while maintaining a four-wire transmission, i.e. separate and distinguishable Channels for the received and transmitted signals. This is achieved by separating the transmission directions in the form of Signal voltages or signal currents on the same wire.

Several connection circuits are used to establish a conference connected to a bus line terminated by resistor R4 is. Each connection circuit provides the bus with a high impedance and consists of a current source and a voltage amplifier. A signal voltage at the base of the transistor Qi-I appears at the emitter of the transistor Qi-2 as a voltage e3. This causes the A signal stream e3 / BRi-3 is fed to the bus line B1.

If resistor R4 is made equal to resistor BRi-3, the resulting signal voltage es across resistor R4 appears to be equal to -e3 on the bus. The total current flowing through the Resistance R4 flows is always equal to the sum of the current contributions from all connection circuits. The signal voltage es is then equal to that

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negative value of the sum of the voltages e3 from each connection circuit. In this way, each terminal circuit transmits a signal in the form of a signal stream to the bus.

Transmission from the bus to a connection circuit

The operational amplifier Ai-I forms with the associated components Ai-3, Ci-2, BAi-I and BRi-2 the voltage amplifier for the receive path. This amplifier senses the signal voltage on the bus and gives it to the hybrid circuit. The resistance BRi-I cancels the own contribution of the connection circuit to the signal voltage it out, so that the signal e2 only that contributed by further connection circuits Signals included. The resistor BRi-2 leads from the bus to the virtual earth potential at the input point of the amplifier Al-I, so that from the bus line Bl in the direction of the connection circuit impedance seen is equal to BRi-2 in parallel with the combined collector impedance of transistors Qi-I and Qi-2. This impedance is about equal to the resistance BRi-I. If this resistance is significantly greater than the resistance R4, the signal levels will not be noticeable impaired when new connections to a conference

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to be added. Using the "monobus" technology just described, many connection circuits can be used without Attenuation can be added to a conference.

DC voltage protection

Capacitor Ci-2 breaks the DC feedback loop in the connection circuit, which ensures the low-frequency stability and a small offset voltage in the amplifier Ai-I. aside from that changes when using a purely ohmic resistor for the Resistor R4 the DC voltage on the bus line Bl with the Number of connection circuits, because {every connection circuit both a direct current as well as a signal from across resistor R4 lets flow. The capacitor Ci-2 also prevents the DC voltage the bus overrides the amplifier Ai-I.

Conference interconnection stability

The stability of larger conference interconnections can be passed through Setting the ratio of the resistance BRl-2 to the resistance R4 to enhance. By decreasing this ratio, the manifold becomes

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: ■■ '■ "" 2822568

loaded in a controlled manner when adding new connections to a conference by adding the resistors BRi-2 to the Resistor R4 can be connected in parallel so that a smaller one gives an effective value for the resistor R4. This will increase the AC gain decreased and negative feedback introduced in small proportions when new connections were added to the conference to be added. For example, if the ratio of resistor BRI-1 to resistor R4 is 25, then the gain for each newly added connection circuit is reduced by approximately 0.4 dB.

Symmetrical connection circuit

Fig. 2 shows a modification of the connection circuit with a symmetrical bus for applications in which crosstalk or induced interference represent a problem. Amplifier 2Ai-3 and resistors 2Al -12, 2Rl-20 were added to generate a signal out of phase with the signal from amplifier 2AI-2. This out-of-phase signal is sent to transistors 2Qi-3 and 2Qi-4 and resistor 2Rl-9, which act as the signal current source for the second path of the symmetrical bus pair

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to serve. The signal is sent to a second bus 2B2 via the Cross point 2XPi-I created. The resistors 2BRPi-I, 2BRPi-2 and 2Ri-11 and the capacitor 2Ci-3 convert the amplifier 2Ai-I to an amplifier with a balanced input. Then the circuit is only for the difference signal between the bus lines 2Bl and 2B2 sensitive. Common mode signals that are in phase with one another, such as induced interference, are passed through the balanced amplifier 2Ai-I rejected, making a high security circuit against crosstalk and interference.

The connection circuit 2PCN shown in Fig. 2 is for one Four-wire operation designed in which the transmission from the call station via the receiving wire pair TR, RR and the transmission to Intercom station takes place via the wire pair TT, RT. · Since the transmission directions are separate, it is not necessary to use the Representation for the connection circuit 2PCl the output of the amplifier 2AN-1 with the input of the amplifier 2AN-2. The resistors 2RN-31 and 2RN-32 close the connection circuit for the from the transformer 2Tl 1-N coming input signal, while the resistor 2RN-30 terminates the output of the transformer 2Tl-N.

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"2622508

The connection circuit 2PCN works on all other points the same way as the connection circuit 2PC1. Note that all or some of the connection circuits shown in FIG separated between the amplifiers Ai-I and Ai-2 and resistors added according to the representation in the connection circuit 2PCN will.

Connection circuit without direct current bias

The connection circuits according to FIG. 3 operate in the same way Manner as described in connection with Figs. 1 and 2, with the exception that the transistor current source is provided by an operational amplifier current source with the operational amplifier 3Ai-3 and the associated resistors 3Ri-6, 3Ri-7, 3Ri-8, 3Ri-3 is replaced. This power source can then should be used if only the signal current is desired and a direct current is undesirable. Different types of intersection points, for example CMOS crosspoints work satisfactorily in conjunction with this connection circuit.

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14th
Cross point with variable resistance

A cross point XPl-O (Fig. 1) with a non-zero resistance leads to the fact that the resistors BRl-I and BRl-2 because of of the voltage drop at the intersection XPl-O are different, so that incomplete cancellation results, leading to gain fluctuations the bus circuit and also changes the back loss. Although there is usually an impedance mismatch in the System, it may be desirable to control the effects of cross-point resistance fluctuations. By The use of an additional cross point for each connection circuit reduces the gain difference and the back loss of the system is made independent of the cross-point resistance fluctuations.

Double cross point switching

The main connections of the double cross point connection circuits are shown in FIG. The connection circuits IPCl and 1PC2 are via cross points 1 XPl-O, 1 XPl-I, 1XP2-0 and 1XP2-1 with

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a common manifold Bl connected. With this new arrangement there is an almost perfect extinction, since the
Voltage drop across the cross point 1 XPl-I does not affect the voltage drop across the resistor 1R4 and the voltage drop across the cross point IXPl -0 is negligible, since the value of the resistor IBRl-I is significantly greater than the resistance value of the cross point IXPl-O. With perfect extinction, this leads
Circuitry for transmission gains and back loss, which are identical to those which are present in a structure with a single cross point and a cross point resistance of zero.

Ana I yj

Referring to Fig. 1, at a cross point with a a resistance different from zero and a mismatch express the signal arriving at the connection circuit 1PC2 as follows:

"s + R / Λ Ί Γ PA

(1)

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Zg-ZI-I
where ρ = Zg + Zi-1 and rs is the cross point resistance.

Correspondingly, the return signal can be sent to the connection circuit

Express IPCl to:

• "' C ■ r 2 _n 2

_ _e g "~ ^Λ '■ ⁿ ^ -

'T'v & vY-f, - *

where Ar = R4 + rs - BRl -3 the amount of the cross-point resistance change is. The value of the resistor BRl-3 is selected in this circuit so that it is equal to R4 = rsn, where rsn is the nominal cross-point resistance is.

From equations (I) and (2) it follows that _r when P = 0, rs = 0 and ^ r = 0, ie the system has a perfect impedance match and the cross point has zero resistance when switched on, BRl applies -3 = R4and

el =} _ eg, 2

e2 = 0.

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Accordingly, the system is transparent and the back loss is infinite great as expected.

If rs, Ar and ρ deviate from zero, problems arise in the system with regard to gain differences, back loss and transmission loss. By using an additional A different feedback arrangement than that shown in FIG. 1 can be achieved at the cross point per connection circuit. With this feedback arrangement improves the properties of the system in terms of gain differences, back loss and transmission losses.

This can be explained physically in the following way. From Fig. 4 it is seen that the KonstantstromqueIjenwiderstand 4BRI-3 equal to the resistance 4R4 _r namely made the manifold resistance. is. Accordingly, the signal appearing across resistor 4R4 is equal to -Ie3. This value differs from the value in the arrangement in FIG. 2, in which the voltage across the resistor R4 is equal to the output current of the transistor pair Ql multiplied by the resistance ratio R4 / BR1-3 (where BRl-3 = R4 + rsn). When this signal is transmitted to the other terminal circuit, it is found that according to FIG

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Fig. 4 is in the feedback path of the cross point in series with the resistor 4BRl -2. This resistance has a value of 100 kA, while the resistance of a cross point when switched on is around 100 A. Accordingly, the change in the cross-point resistance is covered by the very large resistance 4BRl-2, so that an almost complete cancellation takes place at the input of the amplifier IALl. The gain fluctuations are reduced because the fluctuations in rs have only a very small influence on rs + 4BRl -2. For the same reason, since the feedback cancellation is hardly affected by fluctuations in rs, the back loss becomes independent of rs changes. The transmission loss is also reduced because the ratio rs-4BRl-l is very small. - -.- .. '' ■■

Mathematically, this can be confirmed as follows. From Fig. 4 it follows:

= eg - ^ + 4e2 ^ Ln '' »

= 2 (4ei) -

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-2 ~ (Ie6)

Combining these equations gives

¹ "^ SBR = Sj-

(Ι) Γ λ ) ο

Equations (1), (2), (3) and (4) can be used to improve the with regard to the gain change, the transmission loss and the back loss in the system.

Assuming that the system has an impedance mismatch of -12 dB (P = 0.25) and the cross point has a resistance rs = 100 - 60 / I, then in the worst case the gain change for a single cross point is 0.91 dB and for a double cross point 0.0175 dB. Since the transmission loss for a single cross point is -2.2 dB and for a double cross point is -0.023 dB, while the return loss for a single cross point is -12.9 dB and for a double cross point is -14.2 dB.

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From the above results it can be seen that improvements in gain change, transmission loss and return attenuation of the system by using a double cross point connection to a monobus interconnect circuit can be achieved with high impedance.

In a typical keypad telephone system, the requirements are for the gain change when connecting a subscriber line to subscriber line 0.5 dB at 1 kHz. With the feedback arrangement with a single cross point, the gain change of 0.91 dB does not meet the requirement. The double cross point method described above however, it can alleviate this problem. The total number of crosspoints in the system can be reduced if additional crosspoints can only be used for those line connection circuits that are sensitive to gain fluctuations.

Note that the use of two cross points per connection circuit the mode of operation of the bi-directional monobus circuit not impaired, but only serves to expand the usefulness of such a connection circuit. For example, you can

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Single cross point and double cross point circuits in connection use with the same monobus. The double cross point circuit is assigned to those subscriber lines that are sensitive to gain fluctuations. Such an arrangement reduces the number of the intersection points required in the system. In addition, the Embodiment in connection with the symmetrical transmission arrangement according to FIG. 2 and the asymmetrical transmission arrangement use according to FIG.

The operation of the connection circuit is in connection with a Multiple port conference system has been described, but the port circuit can also be used in cases where the separation of the transmission directions on a single path is important. For example it is with: switching matrices that for a Two-wire operation are set up, sometimes required two Four-wire connections, for example connecting lines, via a only way to interconnect. According to the prior art, such an interconnection is effected by a hybrid circuit. The connection circuit according to the invention can have such a fork

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replace circuit. In such a case, the common Summing impedance be assigned to one of the connection circuits or the switching arrangement.

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Claims (10)

BLUMBACH · WESER · BERGEN · KRAMER PATENT LAWYERS IN MUNICH AND WIESBADEN Postal address Munich: Patentconsult 8 Munich 60 Radeckestrasse 43 Telephone (089) 883605/883604 Telex 05-212313 Postal address Wiesbaden: Patentconsult 62 Wiesbaden Sonnenberger Straße 43 Telephone (06121) 562943/561998 Telex 04-186237 £ AIiJ ± l ^A J ± sEJLü £! JL ^E - 1;' Circuit for creating interfaces between two parts of a message path,
marked by a device (Ql-2; 2Ql-2; 2Ql-4; 3A2-3; 4Ql-2) for supplying a value of a signal on a first path part (Tl-1; 2TIrI; 3Tl-1; 4Tl-1) of the Signal stream representing the message path to a second Wegtei I (XPl -0; 2XPl -0; 2XPl -1J 3XPl-0; 4XPl-0) of the message path and
a device (Al-I; 2Al-1; 3Al- 1; 4Al-1) for supplying a difference signal to the first path part (Tl -1J 2Tl-1J
3Tl -1; 4Tl -1), which is the value of a signal voltage on the
represents the second part I (XPl -0; 2XPl -0; 3XPl -0; 4XPl -0) minus a component corresponding to the value of the signal current. 609850/0259 2. Circuit according to claim I ₁ . characterized in that the device (3A2-3) for supplying a signal current has a symmetrical bridge has high impedance. 3. Circuit according to claim 1, characterized in that the device (Ql-2; 2Ql-2; 2Ql-4; 4Q1-2) at least one power source higher Has impedance. 4. Circuit according to one of the preceding claims, characterized by a device (Cl-2 ^ 2Cl-2; 2Cl-3; 3Ci-2; 4Cl-2), which prevents a direct current bias the device (Al-1; 2Al -Ij 3Al-1; 4Al-1) influenced to deliver a difference signal. 5. Circuit according to one of the preceding claims, characterized in that the delivery devices (Ql -2 and Al -1 / 3A2-3 and 3A-1) to a common terminal for the purpose of connection to a second single wire path part (XPl-O; 3XPl -0) are connected. 609850/0259 6. Circuit according to one of claims 1- 4, characterized in that the delivery devices (2Ql-1, 2Ql-4) are designed so that they have a symmetrical signal current and a differential signal representing a symmetrical voltage to a second two-wire path part (2XPl-0, 2XPl-1). 7. Circuit according to one of claims 1 -4 ,. characterized in that the delivery devices (4Ql -2, 4Al-1) with corresponding connections for the purpose of connection corresponding parts (4XP2-1, 4XP2-0) of the second path parts are coupled are. . 8. Message switching equipment for establishing a message connection between selectable first message path files with a large number of interface connections that are connected to corresponding first message path file can be switched on and are each connected to a switching network via a corresponding second message path part, characterized, that the interface circuits (PGI; 2PCl, 3PCl, 4PC1) are each designed according to one of claims 1-7, that the switching network (XPl -0 to XPN-O; 2XPl -0 to 2 XPN-I ', 609850/0259 3XPl -O to 3XPN-0; 4XPl -0 to 4XPN-1) for connection selectable second path parts can be controlled with a common collecting line (Bl; 2BT; 2B2; 3Bl; 4Bl), and that the manifold is connected to a device (R4; 2R4-1; 2R4-2; 3R4; 4R4) is switched on, which is on the manifold a signal voltage is generated which is the sum of the signal currents represents which of the manifold over the selected second Parts of the path supplied by the associated Schnitfstellenschalfungen will. 9. Message switching system according to claim 8, characterized in that the interface circuits are designed according to claim 6 and that the switching network (2XPl -0 to 2XPN-1) is controllable so that it is each of the two wires of the selected second message path parts with corresponding bus lines (2Bl , 2B2), each of which has a device (2R4-1, 2R4-2) for generating the signal voltage. 10. message switching system according to claim 8, characterized in that the interface circuit 609850/0259 is designed according to claim 7, and that the switching matrix (4XPl -0 to 4XPN-0) can be controlled in such a way that each of the connects the two wires of the second message path part separately with a single collecting line (4Bl). 60 98 50/0259