JPH03231520A - Two-wire/four-wire conversion circuit - Google Patents

Abstract

PURPOSE:To improve the frequency characteristic of the bypass component of an output voice signal reaching a differential amplifier of a reception system via a bridge circuit from the amplifier of a transmission system by connecting the complex number impedance circuit to the input terminal of a differential amplifier of the reception system. CONSTITUTION:The noninverting input terminal of the differential amplifier OP1 is connected to a point (b) of a bridge circuit 24 via a complex number impedance R6 and complex number impedance R7 is connected between the noninverting input terminal and ground. The noninverting terminal of the differential amplifier OP1 is connected to ground via the complex number impedances R6, R7 and an input voice signal does not flow through the complex number impedances R6, R7. That is, the complex number impedances R6, R7 do not give the influence onto the frequency characteristic of the input voice signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention relates to a two-wire four-wire conversion circuit used in electronic private branch exchanges and the like.

(Prior Art) FIG. 4 shows a schematic configuration of an interface section in an electronic private branch exchange. A line consisting of two transmission lines (e.g.
A central office line or extension line 20 is connected to the primary side of the transformer 21 via a primary side circuit 22 . The secondary side of this transformer 21 is connected to a hybrid circuit 23, the input audio signal transmitted via the line 20 is taken out from the hybrid circuit 23, and the audio signal to be sent is added to the hybrid circuit 23 and sent to the line 20. Sent out. - The next circuit 22 includes a DC circuit that detects an incoming call, responds to an incoming call, opens a DC loop when making a call, opens and closes the DC loop when sending dial pulses, opens the DC loop when restoring, etc.

FIG. 5 shows the configuration of a conventional two-wire and four-wire conversion circuit in the hybrid circuit 23 shown in FIG. On the primary side of the transformer 21, an impedance R12 on the line 20 side with respect to the transformer 21 is connected between the terminal Tip and the terminal Ring, and a bridge circuit is connected from the secondary side coil of the transformer 21 and each impedance R1, R2, R3. 24 is formed.

In this bridge circuit 24, the impedance looking into the primary side of the transformer 21 is a complex impedance, so each impedance R1, R2, R3 needs to be constructed of a resistor, a capacitor, etc.

A point d of the bridge circuit 24 is grounded, and a point C is connected to the output side of an amplifier OP2 that amplifies the output audio signal. Note that the amplification factor of the amplifier OP2 is determined by the values of the resistors R8 and R9. In addition, the bridge circuit 24
The points a and b are respectively connected to the input side of the differential amplifier OPI, and the values of the respective resistors R4R5, R6, and R7A give the differential amplifier OP an amplification factor of 1 and a common mode rejection ratio CMRR (CMRR;
Common Mode Rejection Ra
tio> is determined.

When an input audio signal is transmitted from the line 20 to the electronic exchange side, this input audio signal is added to the primary side of the transformer 21 and reaches the bridge circuit 24, and from each point a, b of this bridge circuit 24. It is sent to differential amplifier OP1.

Here, assuming that the point d of the bridge circuit 24 is grounded and the output side impedance of the amplifier OP2 connected to the point C is zero, the input audio signal transmission circuit is shown in FIG. It can be expressed by an equivalent circuit like this. The signal source P1 outputs an input audio signal, and this input audio signal is applied to the primary side of the transformer 21 via an impedance R12. This transformer 21 is an ideal transformer, and its turns ratio is 1:1. Furthermore, if the value r12 of the impedance R12 and the value r1 of the impedance R1 are made equal and the primary and secondary sides of the transformer 21 are matched, the voltage V1 of the impedance R12 and the voltage 2 of the impedance R1 become equal. Become. The output voltage (3) of the differential amplifier 0'P1 can be expressed by the following equation (1).

VB=V2, r5/r4・(1) However, r4;
Value r5 of resistor R4; Value of resistor R5 On the other hand, when an output audio signal is transmitted from the electronic private branch exchange side to line 20, this output audio signal is amplified by amplifier OP2 shown in FIG. is added to point C and sent out from the primary side of the transformer 21 to the line 20. Here, transmission of the output audio signal will be explained with reference to FIG. FIG. 6 is a diagram showing the same circuit as FIG. 5, with necessary symbols added.

In FIG. 6, if the input voltage of amplifier OP2 is Vin, the output voltage VCd can be expressed by the following equation (2).

Vcd=Vin-r8/r9-(2) However,
r8; Value of impedance R8 r9; Impedance R
If the transformer 21 is an ideal transformer and its turns ratio is 1:1, then the following equation (3) holds true.

rl・r3=r2・rl2...(3) However, rl;
Value r2 of impedance R1: Value r3 of impedance R2; Value rl2 of impedance R3; Value of impedance R12. In this case, the voltage Vab between the point a and point A of the bridge circuit 24 becomes zero, and therefore the differential amplifier The output voltage (■3) of OP1 becomes zero.

However, in reality, the transformer 21 is not an ideal transformer, and the value r12 of the impedance R12 changes depending on the line length, so that equation (3) no longer holds, and the voltage Vab is generated. This voltage Vab generally has frequency characteristics, which is one of the causes of deteriorating the feedback from the output audio signal to the input audio signal.

(Problem to be Solved by the Invention) As mentioned above, in order to improve the frequency characteristics of the signal that the output audio signal wraps around as the input audio signal, conventional methods include giving frequency characteristics to the gain of the operational amplifier that amplifies the output signal. Although a filter has been provided to adjust the gain according to frequency, a problem has arisen in that the frequency characteristics of the audio signal sent between the Tip/Rinc+ terminals of the line are deteriorated.

The present invention was made to solve the problems of the conventional 2-wire 4-wire conversion circuit, and its purpose is to improve the frequency characteristics of the audio signal sent between the line Tip and Ring terminals without deteriorating the frequency characteristics of the audio signal. It is an object of the present invention to provide a two-wire and four-wire conversion circuit that can improve the frequency characteristics of a component that an output audio signal wraps around as an input audio signal.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a bridge circuit constituted by the secondary side of a transformer to which two transmission lines are connected to the primary side and three impedances; A transmission system amplifier that sends a signal to the transmission line side via a pair of opposing terminals of the circuit, and an amplifier that is connected to another pair of opposing terminals of the bridge circuit and receives the signal coming from the transmission line. and a complex impedance circuit that is connected to the input terminal side of the differential amplifier and improves the frequency characteristics of the loop signal from the transmission signal to the transmission line to the reception system. A four-wire conversion circuit was constructed.

(Function) According to the above configuration, the complex impedance circuit can improve the frequency characteristics of the wrap-around component of the output audio signal that reaches the differential amplifier of the receiving system from the differential amplifier of the sending system via the bridge circuit.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. Line TiD
The primary line of the transformer 21 is connected to the /R1n0 terminal, and the secondary coil has impedance R1, R
2 and R3 constitute a bridge circuit 24. The impedances R1°R2, R3 are generally configured by connecting a plurality of resistors, capacitors, etc. The d point of the bridge circuit 24 is grounded, and the 0 point is connected to the output terminal of a differential amplifier (operational amplifier) OF2. Differential amplifier O
The non-inverting input terminal of P2 is grounded, and the output audio signal arrives at the inverting input terminal via impedance R9. The output terminal and the inverting input terminal of the differential amplifier OP2 are connected through an impedance R8. Bridge circuit 24
The inverting input terminal of a differential amplifier (op-amp) OPl is connected to point a through an impedance R4, and the output terminal and the inverting input terminal of the differential amplifier OPI are connected through an impedance R5. Also, bridge circuit 2
A non-inverting input terminal of a differential amplifier OPI is connected to point b of 4 through a complex impedance R6, and a complex impedance R7 is connected between this non-inverting input terminal and the ground. As a result, the input audio signal arriving from the line is amplified by the differential amplifier OPI and output. Note that the gains of the differential amplifiers OPI and OP2 are determined by impedances R4°R5, R8, and R9.

In such a circuit, the case where a voice signal is transmitted from the electronic private branch exchange side to the line will be explained with reference to FIG. FIG. 2 is the same as the circuit in FIG. 1, with necessary symbols inserted. The output terminal of the differential amplifier OP2 is connected to the 0 point of the bridge circuit 24, and the output signal of the differential amplifier OP2 generates a voltage VOUT between the Tip/R1n9 terminals of the line via the bridge circuit 24 and the transformer 21. Here, if the transformer 21 is an ideal transformer and the number of windings thereof is 1:1, the following equation (4) holds true.

rl・r3=r2・rl2...(4) However, rl:
Value r2 of impedance R1; Value r3 of impedance R2; Value rl2 of impedance R3; Value of impedance R12. If this equation (4) holds, then Vab becomes zero.

However, in reality, the transformer 21 is not an ideal transformer, and the value r12 of the impedance R12 appears to change depending on the line length, so the Vab does not become zero and wraparound occurs. - For boat fishing, since VCd has frequency characteristics, by setting the complex impedance of R6 and R7 to appropriate values, the frequency characteristics can be improved and appropriate communication can be guaranteed.

Next, considering the case where a voice signal is transmitted from the line side to the electronic exchange side, this transmission circuit can be equivalently represented as shown in FIG. As is clear from this equivalent circuit, the non-inverting terminal of the differential amplifier OPI is grounded via the complex impedances R6 and R7, and no input audio signal flows via the complex impedances R6 and R7. That is, the complex impedances R6 and R7 do not affect the frequency characteristics of the input audio signal.

[Effects of the Invention] As explained above, according to the present invention, since the complex impedance circuit is connected to the input terminal side of the differential amplifier of the receiving system, the complex impedance circuit is connected to the input terminal side of the differential amplifier of the receiving system. It is possible to improve the frequency characteristics of the wraparound component of the output audio signal that reaches the differential amplifier.

[Brief explanation of drawings]

1 and 2 are block diagrams of an embodiment of the present invention, FIG. 3 is an equivalent circuit diagram of FIG. 1, FIG. 4 is a block diagram showing a line interface section in an electronic private branch exchange, and FIG. 5 , FIG. 6 is a block diagram of a conventional two-line/four-line conversion circuit, and FIG. 7 is an equivalent circuit diagram of FIG. 5. 21...Transformer 24...Bridge circuit OPl, OF2...Differential amplifier R1, R2, R3, R4, R5, R8, R9...Impedance R6, R7...Complex impedance

Claims (1)

[Claims] A bridge circuit constituted by three impedances and a secondary side of a transformer whose primary side is connected to two transmission lines, and a pair of opposing terminals of this bridge circuit, a transmission system amplifier that sends a signal to the transmission line side; a reception system differential amplifier that is connected to the other pair of opposing terminals of the bridge circuit and receives the signal arriving from the transmission line; A 2-wire 4-wire conversion circuit comprising: a complex impedance circuit connected to an input terminal side of an amplifier for improving frequency characteristics of a wraparound signal to a reception system of a signal transmitted to the transmission line.