JPH01231435A - Termination impedance setting circuit in 2 wire/4 wire converting circuit - Google Patents

Abstract

PURPOSE:To attain switching setting with high accuracy and to make the entire constitution small in size by forming a termination impedance matching with the characteristic impedance of a relay line according to an external command in response to the characteristic impedance of plural kinds of relay lines. CONSTITUTION:Transfer functions K, H of two amplifiers 12, 13, and a transfer function G of a voltage division circuit are calculated for each of plural kinds of characteristic impedances, and plural kinds of high resistance values are set to a resistance of each circuit, that is, ground resistors 23-26 of a feedback circuit of the amplifiers 12, 13 and each of branch resistors 21, 22 of a voltage division circuit and the plural kinds of resistances are selected switchingly by semiconductor switches 14, 15 by an external command. Thus, the termination impedance of a relay line 50 is always set stably. Thus, switching is set with high accuracy and the entire size is made small.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a telephone exchange system connected between a two-wire trunk line (or central office line) connected to an opposite converter and having various characteristic impedances, and a telephone exchange. The present invention relates to a terminal impedance setting circuit in a 2-wire/4-wire conversion circuit.

[Conventional technology]

In a conventional 2-wire/4-wire conversion circuit of this type, the transformer connected to the 2-wire relay line has a resistance of, for example, 600Ω/900Ω.
It has a switching terminal of Ω, and when connected to a relay line, it forms a terminal impedance according to the characteristics of this relay line.
Either the 00Ω/900Ω connection was manually switched or a switch circuit was installed and the switch was automatically switched according to instructions from the central control circuit of the exchange.

Such a conventional configuration will be explained with reference to FIG. In FIG. 7, a 2-wire/4-wire conversion circuit 80 matches the 2-wire trunk line 50 to a characteristic impedance of 600Ω or 900Ω under the control of the central control circuit 70 of the exchange, and converts the 4-wire A/ It is connected to a D (analog/digital) conversion circuit 60. The conversion circuit 80 includes a transformer 81.
Switch 82. Amplifiers 12 and 13. It has a resistor 100 and an echo cancellation circuit 83. The transformer 81 has a two-wire relay wire 50 connected to one winding, and a switch 82 from two terminals 811 and 812 that are matched to the characteristic impedance of the relay wire 50, that is, 600Ω and 900Ω, respectively, in the other winding. Connected. The switch 82 selects and connects matching terminals 811 and 812 of 600Ω and 900Ω according to instructions from the central control circuit 70. In this case, the difference in impedance is the transformer 8
It is determined by the difference in the number of windings. The 4-wire side of the switch 82 has a resistance of 100. The output of the A/D conversion circuit 60 is received via the amplifier 12 and transmitted to the trunk line 50, while the received signal from the A/D conversion circuit 3 is outputted via the amplifier 13. For example, an electromagnetic relay is used as the switch 82, and terminals are switched by mechanical contacts. The echo cancellation circuit 83 connects the output of the amplifier 12 to the amplifier 1.
This circuit assumes that the amount of sound looping around is 3, and subtracts this amount of signal from the output of the amplifier 13 to prevent the sound looping around.

[Problem to be solved by the invention]

In such a conventional configuration, one coil of the transformer 81 requires three terminals, and the switch 82 is also a mechanical relay, which inevitably increases the size of the entire circuit.

Further, in FIG. 7, it is possible to configure the switch 82 with a semiconductor element, but semiconductor switches generally have an internal conduction resistance value of approximately 50Ω to 200Ω, which varies widely. On the other hand, the resistor 100 is normally set to a resistance value of 400Ω to 600Ω for low load impedance. As a result, due to variations in the conduction resistance value of the semiconductor switch,
This was not practical because the impedance formed by the resistor 100 and the transformer 81 and the impedance of the relay line 50 would be mismatched.

The object of the present invention is to eliminate the above-mentioned conventional problems and to provide a 2-wire/4-wire conversion circuit connected to a trunk line.

It is an object of the present invention to provide a characteristic impedance setting circuit which can switch and set characteristic impedance with high accuracy, and which enables miniaturization of the overall configuration.

[Means to solve the problem]

The present invention provides a 2-wire/4-wire conversion circuit connected to an analog/digital conversion circuit that accommodates a 2-wire trunk line and mutually converts an analog signal transmitted on the trunk line and a digital signal transmitted within an exchange. A terminal impedance setting circuit that sets a terminal impedance that matches the characteristic impedance of the relay line, the terminal impedance setting circuit comprising: a DC blocking section to which the relay line is connected that blocks direct current and passes alternating current; and an analog output signal of the conversion circuit. a first amplifier that amplifies and transmits the amplified signal to the relay line via the DC blocking unit; and a first amplifier that receives and amplifies the received input from the relay line via the DC blocking unit and transmits the amplified signal to the analog input of the conversion circuit. 2
a series resistor inserted between the first amplifier and the analog output of the conversion circuit; a series resistor inserted and connected between the input of the first amplifier and the output of the second amplifier; A plurality of branch resistors each having a predetermined resistance value related to each of the plurality of types of characteristic impedance expected for the relay line and forming a voltage divider circuit with the series resistor, and these plurality of types of branch resistances. a first semiconductor switch that forms the voltage divider circuit by selecting according to a terminal impedance value specified from the outside, and each of the first and second amplifiers corresponds to the characteristic impedance of each of the trunk lines. a negative feedback circuit having a plurality of types of grounding resistances each having a predetermined resistance value; and a negative feedback circuit that selects a combination of the grounding resistances according to the instruction from the outside to form a grounding resistance corresponding to the characteristic impedance of the relay line. 2 semiconductor switches, the first and second semiconductor switches operate according to an external instruction according to the characteristic impedance of the plurality of types of the trunk line, and match the characteristic impedance of the trunk line. It is characterized by forming a terminal impedance.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

Referring to FIG. 1, in one embodiment of the present invention, a terminal impedance setting circuit 10 connected to a trunk line 50 inserted
and an echo cancellation circuit 30 connected to an A/D conversion circuit 60 of the digital exchange.

The termination impedance setting circuit 10 receives termination impedance setting information C0NT (
For example, the relay line (600Ω/900Ω distinction)
2 wire) Matching is performed for the characteristic impedance of the wire 50. This circuit 10 has a transformer 11, an amplifier (op-amp) 12, 13, electronic switches 14, 15, 16, and resistors 17-26.

The transformer 11 functions as a DC blocking section, with one winding connected to two wires of the relay wire 50, one terminal of the other winding connected to the earth, and the other terminal connected to the A/D conversion circuit 60. Connected to the input/output circuit. The transmission path from the A/D conversion circuit 60 to the trunk line 50 includes an echo cancellation circuit 30 and a series resistor 17.
- Input terminal "+" of amplifier 12 - Resistor 18 - Transformer 1
Via 1.

Further, the reception path from the trunk line 50 to the A/D conversion circuit 60 passes through the transformer 11 - input terminal "+" of the amplifier 13 - echo cancellation circuit 30 . The resistor 17 and the input terminal "+" of the amplifier 12 are further connected to one terminal of each of two branch resistors 21 and 22. These resistors 21.
The other terminal of the switch 22 is connected to two selection terminals A and ff of the switch 16, and the common terminal C of the switch 16 is connected to the output terminal of the amplifier 13.

The input terminal "-" and the output terminal of the amplifier 12 are connected to the feedback resistor 1.
9, and one terminal of two ground resistors 23 and 24 is further connected to the input terminal "-". The other terminals of the grounding resistors 23 and 24 are connected to two selection terminals A and B of the switch 14, respectively, and the common terminal C of the switch 14 is connected to the ground.

The amplifier 13 also connects the input terminal "-" and the output terminal with the feedback resistor 2.
0, and one terminal of two grounding resistors 25 and 26 is further connected to the input terminal "-". The other terminals of the grounding resistors 25 and 26 are connected to two selection terminals A and B of the switch 15, respectively, and the common terminal C of the switch 15 is connected to the ground.

The switches 14, 15, and 16 are semiconductor switches that receive the specification of characteristic impedance type (600Ω/900Ω) from the central control circuit 70 and connect the common terminal C to one of the two selection terminals A and B.

This semiconductor switch is, for example, 0 as shown in FIG.
MO8) Analog switches composed of transistors,
This can be realized using a field effect transistor or the like. In the circuit shown in Figure 2, the switching control terminal C0NT is set to “H”.
When input, terminals B and C become conductive and terminals A and C are cut off.

The A/D conversion circuit 60 sends an analog output to the resistor 17 of the conversion circuit 1 via an amplifier 69 with an internal impedance of approximately 0Ω.

FIG. 3 is an equivalent circuit diagram in which the three switch portions in FIG. 1 are each replaced with variable resistors. In FIG. 3, the variable resistor 27 is composed of the two resistors 21 and 22 of FIG. 1 and the switch 16, and has a characteristic impedance of 600Ω/9.
The resistance value is set to match 00Ω. The variable resistors 28 and 29 are also constituted by two grounded resistors 23.24 and 25.26, respectively, and switches 14 and 15 connected to them, and are set to a resistance value that matches the characteristic impedance of 600Ω/900Ω.

Next, with reference to FIG. 4, an example of numerical calculation that is the basis for setting each resistance value will be explained. FIG. 4 is a circuit diagram showing an example of a basic circuit for numerical design. In FIG. 4, in the 2-wire/4-wire conversion circuit 10, a resistor 18 and an amplifier 1 are connected to a terminal 51.
The input terminal of the resistor 18 is connected to the output terminal of the amplifier 12. The input terminal of the amplifier 12 and the output terminal of the amplifier 13 are connected through a resistor 27, and the input terminal of the amplifier 12 is further connected to the output of the amplifier 69 through the resistor 17, and the impedance when looking into the amplifier 69 from the terminal 52 is It becomes almost 0. The output terminal of amplifier 13 is further connected to terminal 53. If you look into the right side (circuit 10 side) from terminal 51, you will see amplifier 13. Resistance 27.17
．． Amplifier 12. The resistor 18 constitutes a feedback system. Let us assume that the amplifiers 12 and 13 each have a transfer coefficient of H (that is, amplification factor=output/input), and that the transfer coefficient of the feedback circuit formed by the resistors 17 and 27 forming the voltage divider circuit is G. In addition, the resistance values of resistors 17, 18, and 27 are R
17, R18, R27, transfer coefficient G=R17/
(R17+R27).

The input voltage of amplifier 13 at terminal 51 is ■.

When the output voltage of the amplifier 12 is vo, the input impedance of the amplifier 13 is very large and the inflow current can be ignored, so the internal impedance Zin as viewed from the terminal 51 toward the circuit 10 can be obtained from the following equation.

On the other hand, V, = V-H-G-. /V=H-G-K
(1) Further, when the characteristic impedance of the trunk line 50 is set to 202 and the transmission voltage is set to 28, the voltage level R at the receiving terminal 53 is obtained from the following equation.

(2) Furthermore, if the input of the amplifier 12 is set as vl, the transmission terminal 52
When the level T in is transmitted to the trunk line 50, the following equation (3) holds between V and T.

=a-H・V+(1-G) ・T V,=ni-V,=K [G-H-V+ (1-G)-T
] Therefore, ......(3) Here, 28 is a signal source of the opposite exchange located at the other end of the trunk line 50, and when a signal is sent at voltage 2S, circuit 1
At the receiving terminal 53 of 0, a signal of ' is obtained.

When setting the level for converting an analog signal to a digital signal, the maximum dynamic range of the transmission system is C, C, 1, T,
T (International Telegraph
aphand Te1ephon Con5ulti
3.1 according to the standards of
When it is 7dbm, 2S=3. in Zo=600Ω system.
156V, 2S=3.86 in Zo=900Ω system
It becomes 52V. At this point, the level R is the maximum dynamic range of the A/D conversion circuit 60 (for example, upper 2°5V).
The respective constants of the transfer coefficients H and G are determined so that On the other hand, when setting the level for conversion from digital signals, the maximum dynamic range of the transmission system is set to 3.17 dbm.
Then, the voltage V across the impedance Zo is 60
In the 0Ω system, V=1.578V (=S), and in the 900Ω system, V=1.9328V. Specifically, for example, let R18=400Ω, and in the 600Ω system Zin=Zo=
In the 600, 900Ω system, the three transmission coefficients H, G, and K can be calculated by applying the equations (1), (2), and (3) above with Zin=Zo=900. Based on the calculation results of these three transfer coefficient values, each amplifier 12.1
3 and the parallel resistance values required for the voltage divider circuit are calculated, and the resistance values of the branch resistance and ground resistance connected to each switch can be calculated.

For example, in amplifier 12, Zo=600Ω and 9
Assuming that the transmission coefficients obtained by the above formulas at 00Ω are 1 and 2, respectively, in Fig. 2, the resistance values R19, R of resistors 19, 23, and 24 are as follows.
23 and R24, and connect the terminals A and C using the switch 14 in response to the designation of Zo=600Ω, while connecting the terminals B and C when Zo=900Ω.

These resistance values R23°R24 obtained by calculation can be set to a high resistance value of 50Ω or more, so the internal resistance value of the semiconductor switch 14 connected in series is 100Ω to 20Ω.
A variation of 0Ω does not pose a problem when setting the characteristic impedance and can be ignored.

This also applies to switches 15 and 16.

Next, FIG. 5 shows an embodiment in which a part of FIG. 1 is changed and will be described. In Fig. 1, for two amplifiers 12°13,
The ground resistors 23.24 and 25.26 are connected to the ground resistors 23.24 and 25.26 by switches 14.15, respectively, but in FIG. As a resistance value, the parallel resistance value of two grounding resistors 61.62 connected directly to the ground is Zin=
The design resistance value is 900Ω. Further, in the amplifier 13, a grounding resistor 64 is directly connected to the earth as a design resistance value when Zin=900Ω, and a parallel resistance value R634 of the two grounding resistors 63 and 64 has a designed resistance value when Zin=600Ω. The two grounding resistors 62 and 63 are the switch 6
The common terminal C of the switch 65 is connected to the earth, and the switching operation of the switch 65 is executed according to instructions from the central control circuit 70. That is,
When Zin=600Ω, only terminals A and C of the switch 65 are connected, and the transmission amount H of the amplifier 12 becomes □. In this embodiment, the two switches 14 and 15 in FIG. 1 can be replaced with one switch 65. In addition, the above-mentioned transfer coefficients H, G
, strictly speaking, losses in the transformer and DC loop circuit are taken into consideration.

In the above-mentioned embodiment, the direct current blocking section is illustrated and described as being formed by the transformer 11, but it may be formed of a semiconductor element.

In addition, when switching semiconductor switches, when connecting multiple relay wires with the same characteristic impedance to multiple 2-wire/4-wire conversion circuits housed in a single package, the switch can be connected to multiple circuits in the same package. The switching commands may be issued all at once. Further, the central control circuit that gives switching commands to the switch may be a central processor of the exchange or a processor that controls a package equipped with a trunk line accommodation circuit. According to this embodiment, since there is no mechanical operating mechanism, the reliability is higher than that of a mechanically configured circuit.

Further, as shown in FIG. 6, a plurality of sets of 2-wire/4-wire conversion circuits 1 are formed in one package 100, and the impedance changeover switches 14 to 16 of these conversion circuits 1 are
It may also be configured such that impedance setting instructions are issued all at once using a dip switch or key switch 101. In this configuration, the impedance of a plurality of 2-wire and 74-wire transformer circuits can be switched at once for a plurality of relay lines having the same impedance by a single operation.

Further, in the above-described embodiment, a switch having two types of load impedance of the relay line, 600Ω and 900Ω, can be used.

〔Effect of the invention〕

As explained above, according to the present invention, the transfer coefficients of two amplifiers and the transfer coefficient of one voltage divider circuit are calculated for each of a plurality of types of characteristic impedance, and one resistance value of each circuit, that is, a feedback In the grounding resistance of the circuit and the voltage divider circuit, multiple types of high resistance values can be set for each of the branch resistors, and these multiple types of resistance values can be switched and selected using a semiconductor switch based on an external instruction. The impedance at the end of the line can always be set to be stable, and the switching configuration can be made into a semiconductor circuit, making the entire circuit smaller.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an embodiment of the present invention, Fig. 2 is a detailed circuit diagram of a part of Fig. 1, Fig. 3 is an equivalent circuit diagram of the rain explained in Fig. 1, and Fig. 4 is a circuit diagram of a part of Fig. 1. FIG. 1...2-wire/4-wire conversion circuit, 10...
Termination impedance setting circuit, 11...Transformer, 12゜13...Amplifier, 14, 15.16
...Semiconductor, switch, 30...Echo cancellation circuit, 60...A/D conversion circuit, 70.
...Central control circuit. Agent Patent Attorney Uchihara Oto) F3Z Figure Xun 3 Figure 4

Claims (1)

[Claims] (1) Two wires connected to an analog/digital conversion circuit that accommodates a two-wire trunk line and mutually converts the analog signal transmitted on the trunk wire and the digital signal transmitted within the exchange. / A termination impedance setting circuit that sets a termination impedance that matches the characteristic impedance of the relay line in a four-wire conversion circuit, comprising: a DC blocking section to which the relay line is connected, which blocks direct current and allows alternating current to pass; and the conversion path. a first amplifier that amplifies an analog output signal of the conversion circuit and transmits the analog output signal to the relay line via the DC blocking unit; the second to transmit to the input
a series resistor inserted between the first amplifier and the analog output of the conversion circuit; a series resistor inserted and connected between the input of the first amplifier and the output of the second amplifier; A plurality of branch resistors each having a predetermined resistance value related to each of the plurality of types of characteristic impedance expected for the relay line and forming a voltage divider circuit with the series resistor; A first semiconductor switch that is selected to form the voltage divider circuit according to a terminal impedance value specified from the outside, and each of the first and second amplifiers corresponds to the characteristic impedance of each of the trunk lines. a negative feedback circuit having a plurality of types of grounding resistors having predetermined resistance values; and a second circuit that selects a combination of the grounding resistors according to the instruction from the outside to form a grounding resistor corresponding to the characteristic impedance of the relay line. a semiconductor switch, wherein the first and second semiconductor switches operate according to an external instruction according to the characteristic impedance of the plurality of types of the trunk line, and a termination that matches the characteristic impedance of the trunk line. A terminal impedance setting circuit in a 2-wire/4-wire conversion circuit, characterized in that it forms an impedance. (2) The second semiconductor switch is two semiconductor switches that selectively ground the plurality of ground resistances of the two feedback circuits of the first and second amplifiers, and 2. The terminal impedance setting circuit in a 2-wire/4-wire conversion circuit according to claim 1, wherein the three semiconductor switches work together to set a plurality of types of terminal impedance. (3) One grounding resistor of each of the feedback circuits of the first and second amplifiers is fixedly grounded, and the other grounding resistors of each of the feedback circuits of the first and second amplifiers are fixedly grounded.
The terminating impedance in the 2-wire/4-wire conversion circuit according to claim 1, wherein two types of terminating impedance are set by being respectively connected to the selection terminals of the semiconductor switches and selectively grounded. Setting circuit. (4) A plurality of the above two wires/wires on one electronic circuit package
A 4-wire conversion path and at least one manual switch are installed, and each manual switch is equipped with a plurality of 2-wire/4-wire conversion paths.
The two-wire/wire conversion circuit according to claim (1), characterized in that the terminal impedance of the line conversion circuit is configured to be set at one time.
Termination impedance setting circuit in 4-wire conversion circuit.