JPH0444862B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a communication current supply circuit that supplies direct current to subscriber lines, and particularly relates to a communication current supply circuit that is less affected by external noise. It is.

(b) Technical Background Generally, in a digital electronic exchange, a subscriber circuit is installed on the subscriber line that connects the subscriber telephone.
Provides an interface between subscriber telephones and exchanges.

This subscriber circuit has various functions in addition to supplying communication current to subscriber telephones, and as the main body of the exchange shifts from a space-division type to a digital time-division type, its peripheral circuits have changed. In addition, IC technology has been widely adopted, leading to miniaturization and high-density packaging.

FIG. 1 shows an example of the configuration of a subscriber circuit, and this subscriber circuit has a function commonly called BORSCHT.

In the figure, 1 is a subscriber telephone, 2 is a subscriber circuit, and 3
indicates that it is connected to the electronic exchange main body side, 4 is the subscriber line, O is the overvoltage protection circuit, TST is the test circuit, RING is the calling signal sending circuit, B is the call current supply circuit, H is the hybrid circuit, CODEC is a codec circuit, and S is a status monitoring circuit. The same symbols represent the same objects throughout all the figures below.

In FIG. 1, a subscriber circuit 2 is provided between a subscriber telephone 1 and an electronic exchange main body 3, and provides an interface with the subscriber telephone 1 via a subscriber line 4.

The above BORSCHT function includes subscriber line 4
An overvoltage protection circuit O that prevents overvoltage, etc. applied from the side from being transmitted to the subscriber circuit 2 and the electronic exchange main body 3 side, and a test circuit that enables separation tests between the subscriber line 4 side and the electronic exchange main body 3 side. TST, a ring signal sending circuit RING that sends a ring signal CR to the subscriber telephone 1, a call current supply circuit B that supplies a call current to the subscriber line 4, a hybrid circuit H that converts from 2 wires to 4 wires, analog → It is equipped with a codec circuit CODEC that performs digital conversion and digital to analog conversion, and a status monitoring circuit S that has a function of detecting the on-hook and off-hook states of the subscriber telephone 1.

The present invention provides a communication current supply circuit B of the subscriber circuit.
It is related to.

(c) Conventional technology and problems Conventional communication current supply circuits that supply direct current to subscriber lines have been supplied with power from a direct current power source via a chiyoke coil, but this method is difficult to miniaturize. For this reason, electronic communication current supply circuits have come to be widely used in recent electronic exchanges.

FIG. 2 is a block diagram showing an embodiment of a conventional electronic communication current supply circuit.

In the figure, Tr1 and Tr2 are transistors, respectively, and R1
-R8 are resistors, C1 and C2 are capacitors, AMP1 and AMP2 are operational amplifiers, T is a chip line of a communication line, R is a ring line of a communication line, and E is a DC power supply. In addition, the ring wire R is the A wire, and the tip wire T
is also called the B line.

A conventional communication current supply circuit will be explained below with reference to the drawings.

As shown in FIG. 2, the route of ground, resistor R1, transistor Tr1, chip line T, telephone set, ring line R, transistor Tr2, resistor R2, and power supply (-E) constitutes a power supply loop.

Furthermore, resistors R5 and R7, resistors R6 and R8 constitute a voltage dividing circuit, respectively, resistor R3 and capacitor C1, resistor R4 and capacitor C2 constitute a low-pass filter, respectively, and resistor R1, transistor Tr1 and operational amplifier AMP1 constitute a voltage divider circuit. It constitutes a current conversion circuit, and also includes a resistor R2, a transistor Tr2, and an operational amplifier AMP2.
also constitutes a voltage-current conversion circuit, and the transistor Tr
1 supplies current to the chip line T, and transistor Tr2 supplies current to the ring line R.

This configuration is based on the patent application filed by the applicant earlier.
For details, refer to No. 57-38053.

That is, for DC signals, voltage dividing circuits R5 and R
7, and has a resistance value determined by the resistance ratio of R6 and R8 and the resistor R1, and exhibits high impedance for audio signals by a low-pass filter (capacitor C1 and resistor R3) and (capacitor C2 and resistor R4).

However, this configuration exhibits high impedance not only to audio signals (differential signals) but also to external noise (common-mode signals) picked up by subscriber lines and the like.

Therefore, this communication current supply circuit does not attenuate the voice signal, but at the same time it does not attenuate the noise. This caused a new problem: noise was easily picked up.

(d) Object of the Invention The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a communication current supply circuit that is resistant to in-phase external noise and is effective for computerization.

(e) Structure of the Invention According to the present invention, the above object is achieved by connecting first and second operational amplifiers connected between one of the subscriber lines and the ground, and between the other subscriber line and a DC power source, respectively. ,
first and second voltage-current conversion circuits each consisting of a second transistor;
first and second resistor voltage divider circuits each connected to the input terminal of the operational amplifier, and each of which has both ends connected between one of the subscriber lines and the ground, and between the other subscriber line and the DC power supply; The respective output terminals are connected to the input terminals of the first and second operational amplifiers through first and second capacitors constituting a low-pass filter, respectively, and are connected to the DC power source and the input terminals of the first and second operational amplifiers through series resistance circuits, respectively. third and fourth operational amplifiers are connected to the ground, and have their respective negative input terminals connected to the midpoint of the series resistor circuit; a third resistive voltage divider circuit connected to the positive input terminals of the third operational amplifier and the fourth operational amplifier via a capacitor; and a common voltage divider circuit connected to the positive input terminals of the third operational amplifier and the fourth operational amplifier. This is achieved by a communication current supply circuit characterized by comprising a resistor bias circuit and a resistor bias circuit.

(f) Embodiment of the Invention FIG. 3 is a circuit diagram showing an embodiment of a communication current supply circuit having a function of preventing in-phase noise according to the present invention.

In the figure, R9 and R10 are resistors, respectively.

As shown in FIG. 3, the communication current supply circuit according to the present invention has a resistive voltage divider circuit R between the chip wire T and the ground.
5, R7, and is connected to the operational amplifier AMP1 of the first voltage-current conversion circuit from the midpoint between the resistor voltage dividing circuits R5 and R7 via the resistor R3, and the output of the transistor Tr1 of the voltage-current conversion circuit is connected to the chip line. T
Similarly, the operational amplifier AMP of the second voltage-current conversion circuit is connected via the resistor R4 from the midpoint of the resistor voltage divider circuits R6 and R8 between the ring wire R and the power supply -E.
1, the output of the transistor Tr2 of the voltage-current conversion circuit is connected to the ring line R, and two identical resistors R are connected between the chip line T and the ring line R.
9 and R10 are connected in series, and the circuit configuration is such that the midpoint thereof is connected to the operational amplifier input terminals of the first and second voltage-current conversion circuits via capacitors C1 and C2, respectively.

In this circuit configuration, the same resistors R5 and R7 and resistors R6 and R8 as in the case of FIG. 2 constitute a voltage dividing circuit, respectively, and the resistor R1, transistor Tr1, and operational amplifier AMP1 constitute a current-voltage conversion circuit. Resistor R2, transistor Tr2, and operational amplifier
AMP2 also constitutes a current-voltage conversion circuit, and resistor R3
, capacitor C1, resistor R4, and capacitor C2 constitute a low-pass filter, respectively. With these two low-pass filters, the circuit presents a high impedance to the audio signal, but a low impedance to the noise of the in-phase signal.

That is, when an audio signal is applied to the chip wire T and the link wire R, the chip wire T and the ring wire R are in opposite phases, so the potential at point x remains unchanged due to the application of the audio signal, and the chip wire T and the ring wire R are in opposite phases. Since both wires R maintain high impedance, no loss is caused to the audio signal.

However, when the noise applied to the chip line T and the noise applied to the ring line R are in the same phase, the potential at point x changes in the same way due to the application of the in-phase noise, and the capacitors C1 and C2 cause differential amplifiers AMP1 and AMP1, respectively.
Since it is input to AMP2, transistors Tr1 and
Since both Tr2 exhibit low impedance, they absorb the influence of such external noise.

Although the conventional problems can be solved by the circuit configuration of the present invention shown in FIG. 3, if noise is mixed in from the power supply E side, that is, power supply noise can be mixed into the subscriber line and carried over to the voice signal.

That is, in FIG. 3, earth-resistance R7-resistance R3-capacitor C1-capacitor C2-resistance R
A power supply noise current flows in the path of 4-resistor R8-power supply-E, and since the noise voltage in this case has an opposite phase, there is a possibility that it will mix into the other subscriber line.

FIG. 4 is a circuit diagram showing another embodiment of the communication current supply circuit having a function of preventing power supply noise according to the present invention.

In the figure, R11 to R18 are resistors, AMP3,
AMP4 is an operational amplifier, and C3 is a capacitor.

As shown in FIG. 4, the communication current supply circuit according to the present invention has a resistive voltage divider circuit R between the chip wire T and the ground.
5, R7, and the operational amplifier of the voltage-current conversion circuit is connected from the midpoint of the resistor voltage divider circuit through the resistor R3.
AMP1, the output of the transistor Tr1 of the voltage-current conversion circuit is connected to the chip line T,
Similarly, the resistive voltage divider circuit R between the ring wire R and the power supply
6, R8 is connected to the operational amplifier AMP2 of the voltage-current conversion circuit via the resistor R4 from the midpoint of R8, and the output of the transistor Tr2 of the voltage-current conversion circuit is connected to the ring wire R. Two identical resistors R17 and R18 are connected in series between R, and a capacitor C3 is connected to the midpoint of them.
The other end of the capacitor C3 is connected to the connection point of two resistors R11 and R12 connected in series between the power source -E and the ground, and the first and second operational amplifiers AMP3 and AMP.
A series circuit of two resistors R13 and R14 is connected between the output terminal of the first operational amplifier AMP3 and the power supply -E, and a connection point between R13 and R14 of the two resistors is is connected to the − input terminal of the first operational amplifier, and a series circuit of two resistors is connected between the output terminal of the second operational amplifier and the power supply, and the connection point of the two resistors is connected to the − input terminal of the second operational amplifier. - connected to the input terminal of the first operational amplifier;
The output terminal of AMP3 is connected to the input of operational amplifier AMP1 of the voltage-current conversion circuit through capacitor C1, and the output terminal of the second operational amplifier AMP4 is connected to the input of operational amplifier AMP2 of the voltage-current conversion circuit through capacitor C2. I am working on the circuit configuration.

In this circuit configuration, the output terminals of the third and fourth operational amplifiers AMP3 and AMP4 have low impedance with respect to the earth, so for audio signals (differential signals), resistor R3, capacitor C1, and resistor R
4. Capacitor C2 operates as a low pass filter.

Therefore, the differential signal is transferred to the first and second operational amplifiers that constitute the voltage-current conversion circuit, as in the case of Fig. 2.
It is not input to the input terminals of AMP1 and AMP2, and exhibits high impedance for differential signals.

Next, external noise (in-phase signal) picked up by the subscriber line etc. also appears at the midpoint of the third resistive voltage divider circuit made up of resistors R17 and R18.

This in-phase signal is input to the positive input terminals of the third and fourth operational amplifiers AMP3 and AMP4 via a common capacitor C3. This positive input terminal is biased to an appropriate voltage by a bias circuit consisting of a resistor R11 and a resistor R12.

An in-phase signal that has the same phase as the input and is expanded (amplified) is output to the output terminals of the third and fourth operational amplifiers AMP3 and AMP4.

This expansion consists of resistor R13 and resistor R of the series resistor circuit.
It is determined by a ratio of 14.

This expanded common-mode signal is transmitted to the first and second operational amplifiers via capacitor C1 and capacitor C2.
The output signals that are applied to the input terminals of AMPM1 and AMP2 control the first and second transistors Tr1 and Tr2 with the same phase as the input, so the subscriber line is controlled in phase opposite to the external noise and the external noise is canceled out. works.

Therefore, it presents a low impedance to common mode signals.

In addition, if noise from the power supply E is mixed in, the power supply noise will enter the communication current supply circuit together with the direct current.
The DC potential at each point, which is supposed to be at a predetermined voltage with respect to the ground, fluctuates, and power supply noise is caused by subscriber line R line -
It appears as a differential signal between the T lines, but with respect to the ground, the R and T lines are in phase, and it appears as large amplitude noise on the R line and small amplitude noise on the T line. .

Now, if the resistors R17 and R18 have the same value, there will be a noise between the midpoint between the resistors R17 and R18 and the ground that has an amplitude approximately halfway between the R line and the T line, that is, 1/2 the amplitude of the power supply noise. appears.

Also, if resistors R11 and R12 have the same value,
Resistors R11 and R from the power supply -E through resistor R12
Noise with an amplitude half the power supply noise also appears at the midpoint of 12.

These power supply noises are caused by the third and fourth operational amplifiers.
Input to the positive input terminals of AMP3 and AMP4.

On the other hand, the negative input terminal of the fourth operational amplifier AMP4 is connected to the resistor R15 of the series resistor circuit and the resistor R1.
6 from the output terminal, and the resistor R
If 15 and R16 are the same value, the op amp
The amplification factor of AMP4 is twice, and power supply noise having the same amplitude as the power supply noise is output as an output signal to the output terminal.

This output signal is given to the input terminal of the second operational amplifier AMP2 via the capacitor C2, and the second transistor Tr2 connected to its output terminal
is controlled so that it has the same magnitude and opposite phase as the power supply noise at the emitter of the transistor Tr2, and operates so as not to output power supply noise to the collector of the transistor Tr2.

In this way, the transistor closest to the power supply -E
Since power supply noise is blocked by Tr2, it does not appear on the subscriber line.

Also, since power supply noise is input from the power supply -E to the negative input terminal of the third operational amplifier AMP3 via the resistor R13, if the resistors R13 and R14 have the same value, the power supply noise will be 1/1/2 from the midpoint. Noise with an amplitude of 2 is input.

Therefore, since exactly the same signal is input to both inputs of the operational amplifier AMP3, the amplification factor is 0, that is, there is no output signal.

As a result, the first operational amplifier AMP1 and the first transistor Tr1 are not controlled in any way by the power supply noise component, but this is because the power supply noise is already blocked by the second transistor Tr2 as described above, so control is not necessary. There isn't.

The above operation provides low impedance against power supply noise.

In this case, to eliminate power supply noise, resistors R1 and R
2 have the same resistance value, resistors R17 and R18 have the same resistance value, resistor R13. It is desirable that R14, R15, and R16 have the same resistance value.

As described above, the communication current supply circuit of the present invention uses an operational amplifier for a voice signal which is a differential signal.
Since the output terminals of AMP3 and AMP4 are low impedance, resistor R3, capacitor C1 and resistor R4,
Capacitor C2 operates as a resistance filter and presents high impedance to audio signals.

However, since capacitor C1 and capacitor C2 transmit the signal to the input terminals of operational amplifiers AMP1 and AMP2 against the common-mode signal and power supply noise generated at the positive input terminals of operational amplifiers AMP3 and AMP4, It exhibits low impedance.

(g) Effects of the Invention As described above in detail, the present invention has the great effect of realizing a communication current supply circuit that is resistant to in-phase external noise and power supply noise.

[Brief explanation of drawings]

FIG. 1 shows an example of the configuration of a subscriber circuit. Second
The figure is a block diagram showing one embodiment of a conventional electronic communication current supply circuit. FIG. 3 is a circuit diagram showing an embodiment of a communication current supply circuit having a function of preventing in-phase noise according to the present invention. FIG. 4 is a circuit diagram showing an embodiment of a communication current supply circuit having a function of preventing power supply noise according to the present invention. In the figure, 1 is a subscriber telephone, 2 is a subscriber circuit, and 3
indicates that it is connected to the electronic exchange main body side, and 4
is a subscriber line, O is an overvoltage protection circuit, TST is a test circuit, RING is a calling signal sending circuit, B is a power supply circuit, H is a hybrid circuit, CODEC is a codec circuit, S is a status monitoring circuit, Tr1 and Tr2 are transistors respectively. , R1 to R18 are resistances, C
1 to C2 are capacitors, AMP1 to AMP4 are operational amplifiers, T is a chip line of a communication line, R is a ring line of a communication line, and E is a DC power supply.

Claims (1)

[Scope of Claims] 1. A first device comprising first and second operational amplifiers and first and second transistors connected between one of the subscriber lines and the ground, and between the other subscriber line and a DC power supply, respectively. , a second voltage-current conversion circuit, and the respective midpoints are connected to the first and second voltage-current conversion circuits via resistors.
first and second resistor voltage divider circuits each connected to the input terminal of the operational amplifier, and each of which has both ends connected between one of the subscriber lines and the ground, and between the other subscriber line and the DC power supply; The respective output terminals are connected to the input terminals of the first and second operational amplifiers through first and second capacitors constituting a low-pass filter, respectively, and are connected to the DC power supply and the input terminals of the first and second operational amplifiers through series resistance circuits, respectively. third and fourth operational amplifiers are connected to the ground, and have their respective negative input terminals connected to the midpoint of the series resistor circuit; a third resistor voltage divider circuit connected to the positive input terminals of the third operational amplifier and the fourth operational amplifier via a capacitor; and a common voltage divider circuit connected to the positive input terminals of the third operational amplifier and the fourth operational amplifier. A calling current supply circuit comprising a resistor bias circuit and a resistor bias circuit.