JPH06141354A - Subscriber circuit - Google Patents

Abstract

PURPOSE:To reduce power consumption by keeping a transmission gain of the subscriber circuit constant independently of the length of a subscriber line and feeding power to a telephone set terminal with a constant current. CONSTITUTION:The subscriber circuit 9 connecting to a terminal equipment via a subscriber line 2 and receiving/outputting a signal is provided with a constant current feeding circuit 3 applying DC constant current feeding and a termination circuit 7 placed between signal input and a signal output to decide the impedance of the subscriber circuit and the termination circuit 7 variably sets the transfer coefficient of itself so that the impedance being the sum of that of the subscriber line and that of the subscriber circuit is a predetermined impedance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber circuit of an electronic exchange, and to a method of supplying power to a telephone terminal of a subscriber.

[0002]

2. Description of the Related Art Conventionally, the gain of a subscriber circuit of an exchange to which a telephone terminal is connected is fixed or manually set regardless of the line loss of a subscriber line to be connected. One that automatically optimizes the gain of the subscriber circuit is the subscriber circuit described in JP-A-63-54894.

The above conventional technique adopts a conventional constant resistance constant voltage power feeding method as a power feeding method in the subscriber circuit, and the subscriber line resistance changes depending on the line length of the subscriber line connected to the telephone terminal. The transmission and reception volume is automatically optimized by changing the call gain according to the DC power supply current flowing through the telephone terminal.

[0004]

However, although the above-mentioned prior art can optimize the transmission / reception volume, if the subscriber line length is short, the DC resistance of the subscriber line becomes small, so that the telephone terminal is There is a problem that the DC power supply current that flows increases and power consumption in the subscriber circuit on the power supply side increases. This becomes an obstacle to thermal problems such as heat dissipation in implementing the downsizing and weight saving of the subscriber circuit, and it is necessary to reduce the power consumption in the subscriber circuit.

As a countermeasure against the above-mentioned thermal problem, a method of changing the power feeding method from the constant resistance constant voltage power feeding method to the constant current power feeding method can be considered. However, if the power supply method is simply changed to the constant current power supply method, the circuit (usually called a pad) that adjusts the audio signal level by the power supply current built in the telephone terminal side does not work and the subscriber There is a problem that the attenuation of the voice signal due to the line length cannot be compensated on the telephone terminal side.

An object of the present invention is to provide a subscriber circuit in which the signal transmission gain is automatically made constant regardless of the subscriber line length and the power consumption in the subscriber circuit is reduced.

[0007]

In order to achieve the above object, in a subscriber circuit which is connected to a terminal through a subscriber line and inputs / outputs a signal, a constant current feeding circuit for feeding direct current with a constant current is provided. , A terminating circuit provided between the input side and the output side of the signal and determining the impedance of the subscriber circuit, and the terminating circuit has a combined impedance of the subscriber line and the subscriber circuit in advance. The transfer coefficient of the terminating circuit is variably set so as to obtain the defined impedance.

A direct current detection circuit for detecting a direct current voltage generated by the constant current feeding circuit is further provided, and the termination circuit sets the transfer coefficient of the termination circuit in accordance with the output voltage of the direct current detection circuit.

Further, in a switchboard which is connected to a terminal through a subscriber line and has one or two or more subscriber circuits for inputting / outputting signals, the subscriber circuit is a constant current feeding circuit for feeding direct current with a constant current. A voice signal output circuit for outputting a voice signal to the subscriber line, a voice signal detection circuit for detecting a voice signal generated on the subscriber line, and between the voice signal detection circuit and the voice signal output circuit. And a terminating circuit that determines the impedance of the subscriber circuit,
The termination circuit sets a transfer coefficient of the audio signal detected by the audio signal detection circuit so that the impedance between the subscriber line and the subscriber circuit becomes a predetermined impedance, and the audio signal output. The transfer coefficient of the audio signal output from the circuit can be set respectively.

[0010]

Since the DC call current from the subscriber circuit to the telephone terminal is constant, it is constant regardless of the length of the subscriber line, and the constant current value that becomes the DC call current is:
In the constant resistance constant voltage power supply method, the power consumption can be suppressed to a small value by setting the DC call current value when the subscriber line has the maximum length, which is the minimum value of the DC call current.

For example, when the subscriber line length is zero and the DC resistance on the telephone terminal side is 50Ω in the constant voltage constant resistance power supply system of −48V, 440Ω, the DC power supply current is about 1
The power consumption at the subscriber circuit side is 00 mA, which is about 4 W. If this is supplied with constant current at about 25 mA, the power consumption on the subscriber circuit side can be reduced to about 1.2 W (about 1/3), and the heat dissipation plate required for the power supply circuit of the electronic subscriber circuit. From the perspective of, it is possible to reduce the size and weight of the power consumption.

Further, the voice signal level is controlled to be constant irrespective of the subscriber line length by the direct current detection circuit measuring the voltage between the subscriber lines to obtain the line length, and the line termination circuit in the termination circuit. It can be controlled by compensating for the increase / decrease in the subscriber line impedance corresponding to the length or by determining the terminating impedance of the subscriber circuit so as to correct the increase / decrease in the voice signal level due to the subscriber line impedance. The voltage between the subscriber lines in the DC detection circuit is measured because the DC call current is fed by a constant current, and therefore the voltage between the subscriber lines on the subscriber circuit side is proportional to the line length of the subscriber line. Is changing.

When the transfer coefficient of the terminating circuit is changed, the transfer coefficient is selected so that the combined impedance of the original terminating impedance of the subscriber circuit and the impedance of the subscriber line becomes constant as the transfer coefficient of the terminating circuit. , By increasing or decreasing the line length obtained from the voltage between the subscriber lines with respect to the transfer coefficient component that realizes the impedance of the subscriber line, thereby making the apparent subscriber line length from the telephone terminal side constant. Works like. As a result, even if the actual subscriber line length changes, the apparent subscriber line length is always constant, so that the audio signal level can be made constant.

Further, the transfer coefficient on the exchange side may be changed. In this case, the transmission / reception signal level on the exchange side is operated so as to correct the increase / decrease in the voice signal level due to the impedance of the line length of the subscriber line obtained from the voltage between the subscriber lines. Can be constant.

As described above, the DC call current to the telephone terminal is fed by the constant current circuit, and the DC detection circuit for detecting the DC voltage between the subscriber lines and the output voltage of the detection circuit are used for the subscriber circuit side. By providing a terminating circuit that changes the terminating impedance, or by changing the transfer coefficient on the exchange side, the power consumption on the subscriber circuit side is reduced and the audio signal level is automatically adjusted regardless of the line length. Can be kept constant.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a block diagram of a subscriber circuit in an embodiment of the present invention. FIG. 3 shows an equivalent circuit of the subscriber circuit.

In FIG. 1, a subscriber circuit 9 is connected to a subscriber line 2 to feed a constant current to a telephone terminal 1, and a terminating circuit 7 adjusts a transfer coefficient in accordance with an actual line length to simulate Specifically, a part of the subscriber line is realized in the subscriber circuit, the subscriber line length from the telephone terminal side, that is, the resistance component is equivalently made constant and is connected to the input of the voltage-current conversion circuit 4.

In the subscriber circuit 9, the constant current circuit 3 is
Perform constant current power supply. The voltage-current conversion circuit 4 serves as an audio signal output circuit for sending an audio signal component to the telephone terminal side. The differential voltage detection circuit 5 is a voice signal detection circuit that detects a voice signal component on the telephone terminal side. The DC voltage detection circuit 6 detects a DC voltage between two lines of the subscriber line. The termination circuit 7 varies the transfer coefficient in accordance with the DC voltage between the two lines detected by the DC voltage detection circuit 6. The power supply 8 is the power supply for the subscriber circuit.

In FIG. 1, a subscriber line 2 connected to a telephone terminal 1 has a constant current circuit 3, an input of a DC voltage detection circuit 6, an output of a voltage / current conversion circuit 4, and a differential voltage detection circuit. 5 inputs are connected. The output signal of the differential voltage detection circuit 5 and the signal v _4WR sent to the telephone from the exchange side are added to the input for the AC signal of the termination circuit 7, and the output signal of the termination circuit 7 is , The input signal of the voltage-current conversion circuit 4 and the signal v _4WS sent from the telephone terminal 1 to the exchange side are connected. The output signal of the DC voltage detection circuit 6 is connected to the control input for controlling the transfer coefficient of the termination circuit 7.

When DC power is supplied from the constant current source 3 connected to the subscriber line 2, the DC voltage generated between the two lines of the subscriber line 2 on the subscriber circuit side is the DC resistance of the telephone terminal 1 and the subscriber. The voltage drops with the DC resistance of the line. Assuming that the subscriber line is a resistance that increases in proportion to the line length L as shown in FIG. 2, and the line resistance is R _Line (L),

[0021]

[Equation 1]

Then, if the DC voltage between the lines is V _L , V _L is given by the following equation.

[0023]

[Equation 2]

Here, R _TEL is the DC resistance of the telephone terminal 1, R _L0 is the line resistance per unit length of the subscriber line, L is the line length of the subscriber line, and I _L is the current of the constant current source 3. It is a value.

Therefore, by detecting the DC voltage V _L generated on the subscriber line 2 by the DC voltage detection circuit 6, the line length L of the subscriber line 2 can be obtained.

In FIG. 1, if the transfer coefficient of the differential voltage detection circuit 5 of the subscriber circuit 9 is A, the transfer coefficient of the voltage-current conversion circuit 4 is G, and the transfer coefficient of the terminating circuit 7 is β (V _L ). ,
The termination impedance Z _in (V _L ) of the subscriber circuit 9 is given by the following equation.

[0027]

[Equation 3]

As shown in FIG. 3, as the termination impedance of the subscriber circuit 9, in addition to the termination impedance originally required for the subscriber circuit 9 by the resistor R _S and the capacitor C _S , the voltage V _L between the subscriber lines is also present. In order to realize the impedance component R _X (V _L ) equivalent to that of the subscriber line 2 correspondingly,
_{so that in} ( _VL ) is obtained.

[0029]

[Equation 4]

Here, the sum of the impedance component R _X (V _L ) to be equivalently realized and the impedance R _Line (L) of the connected subscriber line 2 is predetermined as shown in Equation 5. It should be a constant value R _Lall .

[0031]

[Equation 5]

As described above, the total impedance of the subscriber line 2 is defined by the impedance R _Line (L) of the subscriber line 2 and the subscriber line impedance component R _X (V _L ) equivalently realized by the subscriber circuit 9. By keeping
The impedance component of the apparent subscriber line length from the subscriber terminal 1 is always constant regardless of the line length L of the subscriber line 2. The transfer coefficient β (V
_L ) is obtained from the equations 2 to 5 by the following equation 6.

[0033]

[Equation 6]

Here, R _S1 , R _S2 and C _S 'are arbitrary constants that determine the terminating impedances R _S and C _S inherent in the subscriber circuit.

The transfer coefficient β of the termination circuit 7 shown in Equation 6
The apparent termination impedance Z _in 'on the subscriber circuit side including the subscriber line 2 viewed from the telephone terminal end by ( _VL ) is always a constant value Z _const as in the following equation.

[0036]

[Equation 7]

FIG. 4 shows a specific circuit configuration of an equivalent circuit of the termination circuit 7 shown in FIG. FIG. 5 shows an equivalent circuit of the voltage control termination circuit. As shown in FIG. 5, in the voltage control termination circuit, the resistance R _X 'is changed by the output voltage V _CONT from the DC voltage control circuit 6, thereby changing the output current. FIG. 4 is a configuration example of the termination circuit 7 for realizing the transfer function β (V _L ) in the equation 7. _{Reference numeral} 11 is a voltage control resistor R _X '(V _CONT ), the resistance value of which can be varied by the control voltage V _CONT , and the transistors Q _{1 to} Q ₁₂ and the resistors R ₁ to
It is composed of R ₃ , R _E and a current source I ₁ . 12 is a current output circuit, formed by transistors Q ₁₃ to Q ₁₄ and the current source I _2, a current mirror circuit for outputting a current that flows in the voltage control resistor 11. Reference numeral 13 is an input terminal of the termination circuit 7, 14 is an output terminal of the termination circuit 7, and 15 is an input terminal for inputting a control input voltage V _CONT that changes the transfer coefficient of the termination circuit. The voltage control resistor R _X '(V
_CONT ), if the resistors R _{1 to} R ₃ have the same resistance value and if the transistors Q _{1 to} Q ₃ , Q ₄ and Q ₅ , Q _{6 to} Q ₁₀ , and Q ₁₁ and Q ₁₂ have the same characteristics, respectively, As shown by, the resistance value can be changed by the control input voltage V _CONT .

[0038]

[Equation 8]

Here, V _T = about 26 mV. Therefore, the transfer coefficient β (V _CONT ) of the termination circuit 7 in FIG.
Is as shown in Equation 9 below.

[0040]

[Equation 9]

Here, in order to make Expression 9 the same as Expression 7, the variable range of the voltage control resistor R _X '(V _{CON T} ) is set to R _X ' _{(MIN) to} R _X ' _(MAX) . Then, the transfer coefficient β (V _L ) of the terminating circuit 7 can be realized such that V _CONT and R _S1 'become equations 10 and 11.

[0042]

[Equation 10]

[0043]

[Equation 11]

As described above, the voltage between the subscriber lines corresponding to the resistance component due to the actual line length of the subscriber line is measured, and the transfer coefficient of the termination circuit in the subscriber circuit is changed to an apparent value. Keep track resistance constant.

In the conventional example, if the telephone terminal 1 is simply fed with direct current at a constant current, the voice signal level adjusting circuit such as the pad circuit in the telephone terminal 1 does not operate and the voice signal is attenuated. In this embodiment, DC power is fed to the telephone terminal 1 at a constant current, but since the transfer coefficient is changed as described above, the transmission gain of the voice signal becomes constant as described below. That is, the transmission gain G ₂₄ from the exchange side to the telephone terminal side and the transmission gain G from the telephone side to the exchange side.
₄₂ is as follows respectively. The voltage of the AC signal at the telephone terminal v _2W ', when the voltage of the AC signal sent to the exchange side and v _4WS, v _2W' relationship between v _4WS is as shown in the following equation,

[0046]

[Equation 12]

Here, R _Line (L) + Z _in (V _L ) is
It is controlled by the terminating circuit 7 so as to have a constant value Z _const , Z _in (V _L ) becomes as shown in Expression 3, and the transmission gain G ₂₄ becomes constant as shown in Expression 13.

[0048]

[Equation 13]

Next, when the AC signal sent from the exchange side is v _4WR , the AC voltage on the subscriber circuit side of the subscriber line is v _2W , and the impedance of the telephone terminal 1 is Z _TEL , v _4WR and v _2W are obtained. The relationship is as follows.

[0050]

[Equation 14]

[0051] Here, the relationship of the phone terminal-side AC signal v _2W 'and the AC signal v _2W of the subscriber circuit side,

[0052]

[Equation 15]

It becomes Therefore, the transmission gain G ₄₂ is constant as shown in the equation 16 from the equations 14 and 15.

[0054]

[Equation 16]

As described above, the DC call current to the telephone terminal 1 is supplied by the constant current circuit 3 to detect the DC voltage between the subscriber lines, and the subscriber circuit based on the output voltage of the detection circuit 6. By providing the terminating circuit 7 that varies the terminating impedance on the side, the transmission gains G ₂₄ and G ₄₂ can be automatically kept constant regardless of the line length, and the voice signal level can be kept constant.

In the present embodiment, as described above, the termination circuit 7
Thus, a part of the subscriber line is artificially realized in the subscriber circuit corresponding to the actual line length, and the subscriber line length from the telephone terminal side is equivalently made constant. Therefore, it is possible to use the constant current power supply as the DC power supply method from the subscriber circuit side. In the conventional constant resistance constant voltage power supply, so as to meet when the subscriber line length is the minimum of the power supply current,
It is possible to reduce power consumption on the subscriber circuit side by selecting the subscriber line impedance and the power supply current realized in the subscriber circuit. By reducing the power consumption on the subscriber circuit side, it is possible to reduce the size of the heat dissipation plate required for heat dissipation of the electronic power supply circuit, and it is possible to reduce the size and weight of the subscriber circuit.

Further, as the constant current feeding circuit 3, DC /
Power consumption can be further reduced by using a power conversion circuit such as a DC converter.

FIG. 6 shows a second configuration example of the termination circuit 7 of this embodiment. In the above description, the subscriber line 2 is assumed to be only resistance as shown in FIG. 2 for simplification, but the actual subscriber line is C between the subscriber lines as shown in FIG. It is represented by a distributed constant circuit having capacitances of C _AG and C _BG between _AB and ground. Therefore, the transfer function β (V _L ) of the terminating circuit 7 is required to have a more complicated function than the equation (7). Therefore, digital signal processing (DS
The terminal circuit 7 can be realized by P) and signal processing can be performed. The voltage V _CONT of the output signal 15 from the DC voltage detection circuit 6 and the audio signal of the output signal 13 from the differential voltage detection circuit 5 are converted into digital values by an AD converter, and the formula and the capacitance shown in Formula 7 are used. Is processed by the digital signal processing (DSP) according to the equation taking into account

In the subscriber circuit described above, as a method of terminating the voice signal, the differential voltage detection circuit 5 detects the voice signal voltage of the subscriber line 2, and the voltage / current conversion circuit 4 passes the termination line 7 to the subscriber line 2. This is a subscriber circuit of a voltage detection current supply system for supplying a voice signal to the subscriber circuit. The termination method according to this embodiment detects the current of the voice signal flowing through the subscriber line 2 and outputs a voltage to the subscriber line 2 through the termination circuit. It is also possible to implement the current detection voltage output method.

Next, the second embodiment will be described. Figure 8
FIG. 7 is a configuration diagram of a subscriber circuit according to a second embodiment of the present invention. In the subscriber circuit according to the second embodiment, instead of the DC voltage detection circuit 6 in FIG. 1, a DC voltage detection circuit 2 that detects a DC voltage from the output of the differential voltage detection circuit 5 is used.
1 is provided, instead of the constant current circuit 3 that feeds the subscriber circuit, a voltage source 20 that sets the feeding current value is provided, and is added to the output signal of the termination circuit 7 that determines the termination impedance,
It is a subscriber circuit connected to the input of the voltage-current conversion circuit 4.

In FIG. 1, the DC voltage detection circuit 6 detects the DC voltage V _L generated between the subscriber lines by performing balanced / unbalanced conversion directly from the subscriber line side. Then, the differential voltage between the subscriber lines is balanced / unbalanced converted by the differential voltage detection circuit 5, and then the DC voltage is detected. As a result, the circuit required for the DC voltage detection circuit can be realized by a simple CR filter including resistors and capacitors as shown in FIG. 9 as a configuration example. Further, when it is realized by the operation amplifier 22 and the transistor 23 as shown in FIG. 10 as one example of the configuration of the voltage-current conversion circuit 4 (showing the current discharge side), the feeding current should be used as the bias current of the transistor. Thus, the circuit can be simplified.

Further, the high withstand voltage circuit required on the subscriber line side to which a high voltage such as lightning is applied can be eliminated and the circuit can be simplified.

Next, a third embodiment will be described with reference to FIG. The subscriber line 2 connected to the telephone terminal 1 receives a constant current circuit 3 for supplying a constant current and an input of a DC voltage detection circuit 6 for detecting a DC voltage between two lines of the subscriber line, and an audio signal component. The output of the voltage-current conversion circuit 4 serving as an audio signal output circuit to be sent to the telephone terminal side and the input of the differential voltage detection circuit 5 serving as an audio signal detecting circuit for detecting an audio signal component on the telephone terminal side are connected. The termination circuit 70 can be configured by a conventional termination circuit, unlike the above termination circuit. The output of the differential voltage detecting circuit 5 is connected to the input of the terminating circuit 70 and the input of the gain adjusting circuit 32 for adjusting the voice level of the signal v _4WS sent to the exchange side, and the signal sent from the exchange side. The v _4WR is input to the gain adjusting circuit 31, and the output of the gain adjusting circuit 31 and the output of the terminating circuit 70 are added to be connected to the input of the voltage-current conversion circuit 4. The output of the DC voltage detection circuit 6 is
It is connected to the input for gain control of the gain adjusting circuits 31 and 32. The power supply 8 is the power supply for the subscriber circuit.

In this embodiment, as in the first embodiment, DC power is supplied by the constant current circuit 3, and the DC voltage detection circuit 6 is used.
Since the voltage shown in the equation 2 is obtained as the output voltage of, the line length L of the subscriber line 2 can be obtained, and the impedance R _Line (L) of the subscriber line 2 can also be obtained.

Similarly, in FIG. 11, if the transfer coefficient of the differential voltage detection circuit 5 of the subscriber circuit 9 is A, the transfer coefficient of the voltage-current conversion circuit 4 is G, and the transfer coefficient of the termination circuit 70 is β, The termination impedance Z _in of the subscriber circuit 9 is given by
It becomes the value shown in.

[0066]

[Equation 17]

In this embodiment, unlike the first embodiment, the transfer coefficient of the termination circuit 70 is not changed, so that the termination impedance Z _in shown in Equation 17 is always constant.

Since the telephone terminal 1 is supplied with a constant current, the pad circuit inside the telephone terminal 1 does not operate and the terminating impedance Z _in of the subscriber circuit 9 is the same as in the first embodiment.
Is fixed as shown in Expression 16, so that if the line length L and the impedance R _Line (L) of the subscriber line 2 are obtained,
It is possible to obtain the attenuation amount of the voice signal transmission between the subscriber terminal 1 and the subscriber circuit 9 by the subscriber line 2. Therefore, the gain adjustment circuit 31 is configured to correct this attenuation amount.
By controlling and 32, the transfer gain between the exchange side and the subscriber terminal 1 can be made constant regardless of the line length.

FIG. 12 shows a configuration example of the gain adjusting circuits 31 and 32. By changing the control voltage V _CONT by changing the control voltage V _CONT by resistance division of the voltage control resistor 11 and the fixed resistor R _Y used in the configuration example of the voltage control termination circuit shown in FIG. Since the resistance value of is changed, the gain can be adjusted.

As described above, according to the present embodiment, the resistance component can be made constant regardless of the subscriber line length, and it is possible to supply power to the telephone terminal by the constant current circuit, thereby reducing the current value of the constant current circuit. By doing so, the power consumption associated with the power supply on the subscriber circuit side can be reduced. Therefore, thermal problems such as heat dissipation are reduced, and high-density mounting of subscriber circuits is possible.
It is possible to make it small, lightweight and thin.

As shown in the above embodiment, the injection points and the extraction points of the audio signals v _4WR and v _{4 WS} before and after the input / output of the termination circuit 7 are not limited to this, but the gain adjusting circuits 31 and 3 are used.
It goes without saying that the circuit configuration of 2 is not limited to this.

As described above, in the method of changing the transfer coefficient of the terminating circuit, the subscriber line is artificially realized in the subscriber circuit, and the impedance on the subscriber circuit side seen from the telephone terminal side is equivalently constant. Therefore, the transmission gain of the voice signal can be made constant regardless of the subscriber line length.

Further, in the method using the gain adjusting circuit, since the attenuation due to the impedance of the subscriber line is corrected for the voice signal level transmitted to and received from the exchange side, it can be made constant regardless of the subscriber line length. Therefore, power can be supplied to the telephone terminal by the constant current circuit, and by reducing the current value of the constant current circuit, the power consumption due to the power supply on the subscriber circuit side can be reduced. Therefore, thermal problems such as heat radiation are alleviated, and the subscriber circuit can be mounted at a high density, small in size, lightweight, and thin.

The transmission coefficient of the termination circuit or the transmission coefficient of the transmission / reception signal can be automatically changed by obtaining the line length from the DC voltage, and the transmission gain can be made constant regardless of the line length of the subscriber line. It is possible to supply direct current with current and reduce power consumption.

[0075]

According to the present invention, the transmission gain of a voice signal can be automatically made constant regardless of the subscriber line length, and the power consumption in the subscriber circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a principle diagram of a subscriber circuit according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit 1 of a subscriber line.

FIG. 3 is an equivalent circuit at the end of a subscriber circuit.

FIG. 4 is a configuration diagram of a voltage control termination circuit.

FIG. 5 is an equivalent circuit of a voltage control termination circuit.

FIG. 6 is a configuration diagram of a voltage control termination circuit.

FIG. 7 is an equivalent circuit 2 of a subscriber line.

FIG. 8 is a principle diagram of a subscriber circuit according to a second embodiment of the present invention.

FIG. 9 is a configuration diagram of a DC voltage detection circuit.

FIG. 10 is a configuration diagram of a voltage-current conversion circuit.

FIG. 11 is a principle diagram of a subscriber circuit according to a third embodiment of the present invention.

FIG. 12 is a configuration diagram of a gain adjustment circuit.

[Explanation of symbols]

1 ... Telephone terminal, 2 ... Subscriber line, 3 ... Constant current circuit, 4
... voltage-current conversion circuit, 5 ... differential voltage detection circuit, 6 ... DC voltage detection circuit, 7.70 ... termination circuit, 8 ... power supply, 9 ... subscriber circuit, 11 ... voltage control resistor, 12 ... current output circuit,
13 ... Input terminal, 14 ... Output terminal, 15 ... Control input terminal, 16 ... Current mirror circuit, 20 ... Power supply, 21 ...
DC voltage detecting circuit, 22 ... Operational amplifier, 23 ... Transistor, 31 ... Gain adjusting circuit, 32 ... Gain adjusting circuit. C _AB
… Line capacitance of subscriber line per unit length, C _AG … Ground capacitance of subscriber line per unit length, C _BG … Ground capacitance of subscriber line per unit length, R _Line (L)… Line resistance at subscriber line length L, R _L0 ... Line resistance per unit length, V _L ... DC voltage between subscriber lines on the subscriber circuit side,
V _BB ... Power supply, v _2W ... AC voltage between subscriber lines on the subscriber circuit side, v _2W '... AC voltage between subscriber lines on the telephone terminal side, v _4WS ... AC signal sent to the exchange side, v _4WR ... AC signal sent from the exchange side, C _S ... capacitance component of termination impedance, C _S '... capacitance determining termination impedance, R _S ... resistance component of termination impedance, R _S1 ... resistance determining termination impedance, R _S2 ... A resistance for determining the terminating impedance, R _X ... Equivalently for the subscriber line impedance realized in the subscriber circuit, R _X '... Determining the subscriber line impedance equivalently realized in the subscriber circuit Resistance, _RY ... Resistance, V _CC ... Power supply, V _EE ... Power supply, Q ₁
To Q ₁₆ ... transistor, R ₁ ~R ₃ ... resistor, I ₁ ~I ₂ ... current source.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Ishizawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (4)

[Claims] 1. A subscriber circuit connected to a terminal through a subscriber line for inputting and outputting a signal, wherein a constant current feeding circuit for feeding a direct current with a constant current and an input side and an output side of the signal. And a terminating circuit that determines the impedance of the subscriber circuit, the terminating circuit transmitting the terminating circuit such that the impedance of the subscriber line and the subscriber circuit is a predetermined impedance. A subscriber circuit characterized in that a coefficient is variably set. 2. The direct current detection circuit according to claim 1, further comprising a direct current detection circuit for detecting a direct current voltage generated by the constant current power supply circuit, wherein the termination circuit corresponds to an output voltage of the direct current detection circuit. A subscriber circuit, characterized in that the transfer coefficient of is set. 3. A switch, which is connected to a terminal through a subscriber line and comprises one or more subscriber circuits for inputting / outputting signals, wherein the subscriber circuit is a constant-current power supply circuit for supplying direct current with a constant current. A voice signal output circuit for outputting a voice signal to the subscriber line, a voice signal detection circuit for detecting a voice signal generated on the subscriber line, and between the voice signal detection circuit and the voice signal output circuit. A termination circuit for determining the impedance of the subscriber circuit, wherein the termination circuit is such that the combined impedance of the subscriber line and the subscriber circuit is a predetermined impedance. The setting of the transfer coefficient of the audio signal detected in step 1 and the setting of the transfer coefficient of the audio signal output from the audio signal output circuit are performed.換機. 4. A subscriber line power feeding method in a subscriber circuit which is connected to a terminal via a subscriber line and inputs and outputs signals, wherein the impedance is viewed from the terminal side so that the impedance becomes a predetermined value. A subscriber line power feeding method, characterized in that the impedance in the subscriber circuit is set corresponding to the impedance of the main line, and DC power is fed at a constant current.