KR100391885B1 - Subscriber interface circuit of full electronic switching system - Google Patents

Abstract

The present invention relates to a subscriber matching circuit of an all-electronic exchange that provides a route and interacts with the subscriber so as to mutually transmit and receive voice band signals during the exchange. Conventional series regulators consume large amounts of power as heat in a subscriber line interface circuit (SLIC) integrated circuit (IC), resulting in high heat generation and power consumption. Switching mode regulators require complex circuits, are difficult to achieve stable operation, and have difficulty solving switching noise. Therefore, the SLIC IC has disadvantages such as a small size and various functions but difficult to integrate with semiconductor technology, requiring a peripheral component, and a strong protection circuit due to weak external shock. The present invention can be implemented in a smaller and simpler manner while providing the same functions as a transformer of the past or a widely used SLIC IC, and the circuit itself is simple. In addition, because the hybrid parts can be implemented in a hybrid and do not require peripheral parts, there is no need for peripheral parts. Therefore, when implemented with a transformer and a SLIC IC as a whole, components for adding peripheral circuits are not included. When included, it is possible to realize a lower material cost.

Description

Subscriber matching circuit of all-electronic exchange {SUBSCRIBER INTERFACE CIRCUIT OF FULL ELECTRONIC SWITCHING SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber interface circuit of a full electronic switching system. In particular, the present invention provides a path and an interface for mutual transmission and reception of voice band signals during an exchange with a subscriber. It relates to an analog subscriber matching circuit.

Analog subscriber matching circuits are one of the most classic technical fields that have remained intact since the invention of the telephone.

Analog subscriber matching circuits provide the ability to supply current to enable subscriber telephones and similar fax and modem operations. In addition, it provides a subscriber monitoring function that determines whether the subscriber has placed the handset on the phone (hook on) or picked up the handset (hook off) to attempt a call. It provides an auto ring trip function that transmits a ring signal to a subscriber and determines whether the handset is hooked off during the call to enable transmission and reception. In addition, the 2-wire voice signal transmitted from the telephone is converted into a 4-wire signal and provided to the switchboard. Line conversion function is provided as a basic function.

Conventionally, in order to implement these basic functions, a transformer is used to adhere to the most conceptual and basic principles. In order to overcome the shortcomings of the transformer, a subscriber matching circuit was constructed using a subscriber line interface circuit (SLIC) integrated circuit (IC) composed of semiconductor devices.

The transformer is the easiest and simplest to configure the subscriber matching circuit, but in order to ensure the faithful coupling between the two-wire side and four-wire side should have a high coupling rate and a large inductance (inductance). Since the talk current must be supplied through the transformer, it can be the magnetic saturation by the talk current. To prevent this, the volume of the trans is bound to be large. In addition, since the transformer is insulated from the primary side and the secondary side, it is very difficult to obtain an even frequency response in the voice band during the mutual transmission of the voice signals. In the subscriber matching circuit using a conventional transformer, a call current supplied to a subscriber is supplied up to 120 mA. This increases the power consumption of the exchange by supplying an excessively large current compared to the current required for the actual telephone to operate. Limiting excessive talk current can reduce the size of the transformer, but requires circuitry to limit the maximum talk current supply, which complicates the circuit. Thus, there is a limit to reducing the size of the transformer, which is not suitable for today's highly integrated exchanges.

In order to solve the shortcomings of these transformers, SLIC integrated circuits integrated using semiconductor design technology are used to provide high integration and various additional functions. However, SLIC integrated circuits are complex because low-power signal circuits and power amplification circuits are integrated in a limited size semiconductor. Since the subscriber matching circuit using the SLIC integrated circuit is directly connected to an external line, it is affected by various external shocks such as surge, lightning, and phase change. Therefore, it is vulnerable to external shocks, such as a large number of failures in the summer, due to the relatively weak protection performance compared to the case of implementing a transformer. Since SLIC integrated circuits consist of all the circuits in one semiconductor device, it is impossible to repair them in the event of a failure due to such destruction, thereby inevitably replacing expensive components.

To limit the maximum talk current in small semiconductors, current limiting circuits are usually incorporated. Current limiting circuits use series regulators or switching mode regulators. The series regulators consume large amounts of power as heat in SLIC integrated circuits, resulting in high heat generation and power consumption. The switching mode regulator requires a complicated circuit, it is difficult to obtain stable operation, and there are difficulties in solving switching noise. Therefore, SLIC integrated circuits have disadvantages such as the disadvantage of requiring peripheral components due to the small size and various functions but difficult to integrate with semiconductor technology, and the need for a strong protection circuit due to external shock.

SUMMARY OF THE INVENTION The present invention has been made to solve such drawbacks of the prior art. In the subscriber matching circuit of an all-electronic exchange, the present invention accommodates both advantages such as impact resistance, which is an advantage of a transformer, and high integration of a SLIC integrated circuit. The purpose of the present invention is to provide a subscriber matching circuit of an all-electronic exchange which is not only simple but faithful to the basic concept, but also hybridizes individual components having high transmission characteristics.

In order to achieve the above object, the present invention provides an analog subscriber matching circuit of an all-electronic exchange: a transistor connected to each Darlington, supplying talk current to the subscriber through the tip terminal and the ring terminal, and amplifying the voice signal power. (Q3, Q31) (Q2, Q21); Transistors Q1 and Q11 connected to Darlington to limit the maximum talk current; A bias resistor R15 of the transistors Q1 and Q11; A transistor (Q4) for detecting a talk current to limit the base current of the transistor (Q11) to control the maximum talk current; The base-emitter of the transistor Q4 is connected to the Darlington connected transistors Q2 and Q21 and Q1 and Q11 to detect and convert a supplied current into a voltage to operate the transistor Q4. a resistor R12 providing an inter-emitter voltage; A transistor (Q5) for controlling the limit of the maximum talk current by controlling the potential of the resistor (R12) through the transistors (Q1, Q11); A bias resistor (R16) of the transistor (Q5); A transistor (Q7) for controlling an operation mode and a blocking mode of the transistors (Q3, Q31) by adjusting a base potential of the transistor (Q11) in response to a power-off control signal; A bias resistor R21 of the transistor Q7; An operational amplifier (U1A) for applying the voice signal received from the other side to the transistor (Q21); An operational amplifier (U1B) which inverts the output signal of the operational amplifier (U1A) again and inputs it to the transistor (Q31); Resistors R17 and R18 for determining an amplification degree of the operational amplifier U1B as a unit gain 1; Resistors R19 and R16 for adjusting the reception gain of the operational amplifier U1A; A coupling capacitor (C1) (C2) for coupling each output of the operational amplifier (U1A) (U1B) to each base of the transistors (Q31) (Q21), respectively; Connected between the transistors Q2 and Q21 Q3 and Q31 so that there is no alternating current (AC) load or direct current (DC) load between the tip and the ring, the transistors Q2 and Q21 (Q3 and Q31) Bias resistor (R3) to prevent () from operating in the blocking region; A bypass capacitor (C3) of the emitter resistors of the transistors (Q2, Q21) (Q3, Q31); Current / voltage conversion resistors R1 and R2 for detecting talk current; Bridge resistors (R4, R5, R6, R7) for comparing the voltages detected by the resistors (R1, R2); Bias and voltage feedback resistors R11 and R8 of the transistors Q2 and Q21 and Q3 and Q31; A capacitor (C4) connected between the base of the transistor (Q11) and the collector and coupling the alternating current impedance between the ring stage and the power supply to a low impedance when looking inside the circuit from outside the ring stage. It features.

1 is a circuit diagram showing an embodiment of a subscriber matching circuit of an all-electronic exchange according to the present invention;

FIG. 2 is a circuit diagram of a circuit for converting a 2-line signal on a line side into a 4-wire signal as part of a subscriber matching circuit of an all-electronic exchange according to the present invention; FIG.

3 is a part of the subscriber matching circuit of an electronic switch in accordance with the present invention, which detects a hook off when a subscriber picks up the handset, attempts to make a call, detects a dial pulse when dialing, and performs hook off during ring signal supply. A circuit diagram showing an embodiment of a circuit for detecting it when

FIG. 4 is a circuit diagram illustrating the ring trip function of FIG. 3. FIG. 4 is a diagram for describing a process in which a ring signal is supplied to a telephone and returned back by an operation of a relay.

FIG. 5 is a view showing the combination of FIGS. 1 to 3.

<Description of the symbols for the main parts of the drawings>

R: Resistor Q: Transistor

C: Capacitor UA, UB: Amplifier

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of a subscriber matching circuit of an all-electronic exchange according to the present invention, and includes a plurality of transistors, a plurality of resistors, a plurality of capacitors, and inverting amplifiers U1A and U1B.

In the figure, the power supply is the same as using a 48V power supply since the upper ground has a potential of 0V and the portion indicated by the lower Vbat has a -48V potential. Most exchanges and transmission equipment use a -48V supply rather than + 48V.

The power supply is as follows.

Current coming from the top ground is supplied through the transistors Q3 and Q31 through the resistor R1 to the tip end. At this time, a telephone (0 ohm to 2000 ohm) is connected between the tip and the ring. The configuration of the transistors Q3 and Q31 is a Darlington configuration and is an NPN transistor. The transistors Q3 and Q31 supply current to the base of the transistor Q31 by the resistor R8 to turn on the transistor Q3, and then return the emitter, which is the output terminal of the transistor Q31, to the transistor Q3. The transistor Q3 is turned on (in this case, the amplification margin of the transistor Q3 is maintained at about 2V so that an AC signal, which is a voice signal, can be transmitted). It flows to the tip end via Q3 and resistor R1. At this time, the resistor shown at the top is a resistor for balancing the impedance of the negative AC signal between the tip and ring ends. Similarly, capacitors C3 and resistors R3 are components for balancing the impedance of the voice AC signals at the tip and ring ends. The resistors R4, R5, R6, and R7 are configured to detect the case where a specific current or more flows using the potential difference between the resistors R1 and R2 when current flows through the tip and ring ends. The current IL introduced through the ring stage enters the PNP transistors Q2 and Q21 having the Darlington configuration as the tip stage through the resistor R2. In this case, the resistor Q21 is turned on through the bias resistor R11, and the resistor Q2 is turned on again. In this case, the amplification margin of the resistor Q2 is maintained at about 2V so that an AC signal, which is a voice signal, can be transmitted. The current IL enters the resistor R12 through the transistor Q2. At this time, a current flows through the resistor R12 to generate a voltage across the resistor R12. When the current is above a certain current, the voltage across the resistor R12 reaches the conduction voltage between the base of the transistor Q4 and the emitter. This causes transistor Q4 to be turned on. Here, transistors Q1 and Q11 are current limiting circuits. However, like the transistors Q2 and Q21, the transistor Q1 is turned on before the transistor Q4 is turned on. However, when the current continues to increase and the voltage across the resistor R12 reaches the energized voltage between the base of the transistor Q4 and the emitter, the potential of the base terminal of the transistor Q11 increases to decrease the turn-on current of the transistor Q11. In addition, the transistor Q11 reduces the turn-on current of the transistor Q1 to limit the flow of only a predetermined current. The emitter and base of the transistor usually have a potential difference of about 0.7V to make the transistor operate. The transistor Q7 is turned on when a power off control signal is input to raise the base potential of the transistor Q11 to turn off the transistor Q11 to cut off the current. The transistors Q5 and Q6 turn on the transistor Q5 when the signal enters the transistor Q6 to raise the base potential of the transistor Q11 by a predetermined potential to decrease the base current of the transistor Q11 to thereby reduce the transistor Q1. This reduces the current flowing into the furnace. Then, the current IL decreases by a certain amount as the base current of the transistor Q1 decreases. When the transistor Q7 is turned on by the power-off control signal, the transistor Q7 turns off the base current of the transistors Q11 and Q1 to turn off the transistors Q2 and Q21 (Q3 and Q31). to provide.

Voice signal transmission is as follows.

A voice signal, which is an AC signal, enters through the resistor R19. In this case, U1A is an operational amplifier which is an inverting amplifier. (The signal gain of the inverting amplifier is determined by the resistors R19 and R16.) The voice signal passing through the inverting amplifier U1A is a direct current cut off from the capacitor C2 and is pure. Only the AC signal goes to the base end of the transistor Q21 which is the next stage. In this case, the base current of the transistor Q21 is changed to add an audio signal to the ring end. U1B is also an operational amplifier that is an inverting amplifier. Like the inverting amplifier U1A, the output signal of the inverting amplifier U1A is received through the resistor R17, and the unit gain is changed 180 degrees only to send a voice signal through the capacitor C1 to the base terminal of the transistor Q31. Add a signal at the tip end.

Looking at such an embodiment of Figure 1 as follows.

The transistors Q2 and Q21 (Q3 and Q31) serve to supply current for the call to the subscriber station and superimpose the received voice signal on the call current. In other words, the transistors Q2 and Q21 (Q3 and Q31) together with the resistors R3, R8 and R11 form an emitter follower power amplification circuit to power amplify. The emitter follower power amplifier circuit constituted by the transistors Q2 and Q21 (Q3 and Q31) does not have a constant direct current bias. Because transistors Q2 and Q21 (Q3 and Q31) must supply current to the tip and ring through their respective emitters, and the magnitude of the current varies depending on the load condition of the line, so that they do not have a fixed bias. This requires proper design of the bias to ensure the circuit's operation is stable in all load regions.

The resistors R8 and R11 increase or decrease the base current of the transistors Q2 and Q21 Q3 and Q31 according to the changing DC load conditions so that the transistors Q2 and Q21 and Q3 and Q31 operate in a stable bias region at all times. It ensures a role. The resistors R8 and R11 are voltage feedback resistors while supplying the base bias currents of the transistors Q3 and Q31 and Q2 and Q21, and when the load resistance between the tip and the ring increases and the current I _L decreases. The emitter potentials of the transistors Q3 and Q31 approach the ground potential, and the emitter potentials of the transistors Q2 and Q21 approach the Vbat side. As the load resistance gradually increases and the current I _L approaches zero, the transistors Q2 and Q21 and Q3 and Q31 saturate, but the voltage is fed back by the resistors R8 and R11 and the transistors Q3 and Q31 and Q2, The base current of Q21 is reduced to prevent the transistors Q2 and Q21 (Q3 and Q31) from saturating. However, when an extreme load, i.e., no load state, the transistors Q2 and Q21 Q3 and Q31 enter the blocking region, the resistor R3 serves as a load resistor to prevent this.

The resistor R3 acts as a direct current and alternating current load, but the characteristic impedance of the subscriber matching circuit and the line has a value of about 600 ohms, so the resistor R3 cannot be selected unconditionally. Selecting an excessively small value of resistor R3 results in a reduction in the talk current supplied to the line resistance, including the subscriber terminal present between the tip and ring ends, and also affects matching with the characteristic impedance of the line. R3) is a value of several tens of KOhm.

In the normal call state, the call current flows and the transistor Q2, Q21 (Q3, Q31) is operated in the operating area. However, the subscriber matching circuit cannot transmit the signal even under the DC load state, that is, on hook state. It should be possible. Therefore, the on-hook state should have the same AC characteristics as the off-hook state. In the on-hook state, the DC and AC load impedances of the transistors Q2 and Q21 Q3 and Q31 are reduced, and the capacitor C3 acts as an AC load to ensure stable operation.

Transistors Q1 and Q11 serve to limit the maximum load between the tip and ring ends, i.e., the current flowing in the short circuit state. The talk current I _L flows into the resistor R12 and a potential difference is formed across the resistor R12. The current increases and the current increases in the current I _L such that the potential difference formed at both ends is equal to V _BE of the transistor Q4. Will be limited. The desired maximum call current may be calculated from the equation of Equation 1 below.

In the present invention, the maximum talk current can be selected in two ways according to the RB selection signal. This reduces the power of the exchange in situations where the subscriber has left the handset or the line has been shorted abnormally. Equation 1 shows the maximum talk current in the low power mode. The maximum call current I _{L (MAX)} in a normal call state is expressed by Equation 2 below.

At this time, the transistor Q5 is turned on in a saturated state by the RB control signal.

Power consumed by the transistor is represented by Equation 3 below.

The transistors Q2 and Q21 (Q3 and Q31) constitute an emitter follower power amplifying circuit in which the outputs of the inverting amplifiers U1A and U1B are input as base currents and output to the emitters, respectively. The emitter follower power amplification circuit provides low output impedance to drive the load connected between the tip and ring ends. The load becomes the characteristic impedance of the line and is finally delivered to the terminal.

The inverting amplifiers U1A and U1B output signals that are mutually inverted, and output the signals whose phases are inverted from each other at the tip and ring ends.

Resistors R1 and R2 provide current detection for monitoring the direct current of the line. The talk current I _L flowing through the resistors R1 and R2 causes a potential difference in the resistor to be formed, and the potential difference is divided by the voltage Vdet (+) distributed between the resistors R4 and R7, and the resistors R5 and R6. Outputs the voltage Vdet (-) divided between Compare Vdet (+) and Vdet (-) to each other to determine whether it is greater than or less than the minimum threshold current value when hooking off. Vdet (+) and Vdet (-) are about half the size of VTR between the tip and the ring. Therefore, since the input range of the comparator is exceeded, the voltage is increased with the resistors R26, R28, R27, and R29.

The output of the comparator U2B is output as + 5V or -5V, which is converted into logic '1' or logic '0' by the transistor Q8 so that this information can be utilized by a processor.

FIG. 2 is a circuit diagram showing an embodiment of a circuit for converting a two-line signal on a line side into a four-line signal as part of a subscriber matching circuit of an all-electronic exchange according to the present invention. The voice signal transmitted from the subscriber is transmitted to the counter side. To do this, the amplifier comparator (U2A) for converting a 2-wire voice signal into a 4-wire signal, the resistors (R22, R23, R24, R25), the DC potential of the tip and the ring for operating the comparator (U2A) in a differential amplification mode DC blocking capacitors C5 and C6 for blocking the AC signal and inputting the AC signal to the differential amplifier, and a coupling capacitor C7 for AC coupling the output signal of the comparator U2A with the input terminal of the next stage.

In the figure, the differential amplifier circuit detects the difference between the voice signal input to the tip and the ring stage and provides the signal to a code / decode converter which is the next step. Capacitors C5 and C6 serve to remove direct current potential at the tip and ring ends.

As a voltage comparator, the difference between the voice signal at the tip and ring ends is made into a single signal. Capacitors C5 and C6 block the DC voltage at the tip and ring ends and allow only pure AC signals to enter the voltage comparator. The comparator (U2A) compares the voltages of the tip and ring ends to cut off the DC voltage at the capacitor (C7) and outputs only pure AC audio signals. At this time, the output gain is adjusted by the resistors R23, R24, R25, and R26, and the gain of the tip and the ring can be adjusted.

3 is a part of the subscriber matching circuit of an electronic switch in accordance with the present invention, which detects a hook off when a subscriber picks up the handset, attempts to make a call, detects a dial pulse when dialing, and performs hook off during ring signal supply. Is a circuit diagram showing an embodiment of detecting a circuit, and receives the Vdet (+) and Vdet (-) outputs in FIG. 1 and compares the potentials of Vdet (+) and Vdet (-) to + 5V or −. Comparator U2B outputs 5V and resistors R26, R27, R28 that enhance the potentials of Vdet (+) and Vdet (-) existing between the tip and ring DC potentials of FIG. R29 and the transistor Q8 for converting the output voltage to the TTL (Transistor-Transistor Logic) voltage level as a result of the comparison in the comparator U2B and the hook-off detection signal when the transistor Q8 is in the off state. And a pull-up resistor R33 for holding at 1 '.

In the figure, the voltage comparator U2A detects the voltage difference due to the current flowing through the resistors R1 and R2 in FIG. Comparator U2A detects the voltage between Vdet (-) and Vdet (+) as a voltage comparator. At this time, the resistors R28 and R29 are resistors for matching the input voltage range of the comparator U2A. When the voltage difference between Vdet (-) and Vdet (+) becomes more than the voltage between the emitter and the base of transistor Q8, transistor Q8 operates. The resistors R31, R32, R30 and the capacitors C8, C40, R40 of the ring feedback signal are low pass filters. After removing the alternating current through the low pass filter, the ring current entering the ring feedback signal stage is input to the direct current comparator (U2B), and the magnitude of the DC current of the ring feedback signal stage is compared with Vdet (+).

The embodiment of FIG. 3 is as follows.

The ring return signal of FIG. 3 is fed through the ring end when supplying the ring signal to call the subscriber as shown in FIG. 4 which is returned back to the tip end via the telephone. The return signal is input to monitor whether the subscriber has hooked the handset off while supplying the ring signal. The ring signal supplied is generally an AC signal of 20 to 25 Hz with a magnitude of 70 to 90 Vrms, and is superimposed on a direct current for hook-off monitoring. The ring trip is used to make a call when hooked off while supplying a ring signal. In order to detect a ring trip, an AC component is removed from a ring signal returned and only a DC component is detected. Resistor R32 is a current detection resistor for forming a potential difference from the feedback ring signal to ground. Since the ring feedback signal detected by the resistor R32 is a superimposed signal of direct current and alternating current, the alternating current is removed by passing through a Π type low pass filter composed of resistors R30, R31, and R40 and capacitors C8 and C40. Is input to the comparator. The input signal is compared with the Vdet (+) potential. During the ring signal supply, the Vdet (+) signal has a fixed potential.

FIG. 4 is a circuit diagram illustrating the ring trip function of FIG. 3. FIG. 4 is a diagram for describing a process in which a ring signal is supplied to a telephone and returned again by an operation of a relay.

FIG. 5 is a view showing a combination of FIGS. 1 to 3, wherein the added TH1 and TH2 are tip and ring terminal overvoltage protection diodes. Transistor Q15, diode D1, and resistor R36 are additional circuits for driving an external relay. Transistor Q20 is used to control transistor Q15 using the output from comparator U2A.

As described above, the present invention can be implemented in a smaller and simpler while providing the same functions as the transformer of the past, the SLIC integrated circuit which is widely used now, and the circuit itself is simple. In addition, since the hybridized peripheral components can be implemented in the hybrid, and do not require peripheral components, the effects of high density and overall, for example, when implemented in a transformer and SLIC integrated circuit, may include components for adding peripheral circuits. In this case, a lower material cost can be realized. In addition, based on the implementation of the basic functions required in the subscriber matching circuits of all exchanges, additional functions such as an on-hook transmission function, a remote charging function, and a sender transmission function can be provided. Because they use individual devices, low power components designed as SLIC integrated circuits are used as individual high power components, which is resistant to external shocks such as lightning strikes. Thus, for example, in the case of an extreme ground fault, repair is possible even in case of damage caused by a very strong lightning strike and surge.

Claims (7)

delete In the analog subscriber matching circuit of the all-electronic exchange, Transistors Q3 and Q31 and Q2 and Q21, respectively, connected to Darlington and supplying talk current to the subscriber through the tip terminal and the ring terminal and amplifying the voice signal power; Transistors Q1 and Q11 connected to Darlington to limit the maximum talk current; Bias resistors R15 of the transistors Q1 and Q11; A transistor (Q4) for detecting a talk current to limit the base current of the transistor (Q11) to control the maximum talk current; The Darlington-connected transistors Q2 and Q21 (Q1 and Q11) are connected to each other, and the supplied current is detected and converted into a voltage so that the transistor Q4 operates the base-to-emitter voltage of the transistor Q4. Providing a resistor R12; Connected between the transistors Q2 and Q21 Q3 and Q31 to prevent the transistors Q2 and Q21 Q3 and Q31 from operating in the blocking region when there is no alternating current or direct current load between the tip and the ring. A bias resistor R3; Current / voltage conversion resistors R1 and R2 for detecting talk current; Bridge resistors (R4, R5, R6, R7) for comparing the voltages detected by the resistors (R1, R2); An operational amplifier (U1A) for applying the voice signal received from the other side to the transistor (Q21); An operational amplifier (U1B) which inverts the output signal of the operational amplifier (U1A) again and inputs it to the transistor (Q31); A transistor (Q5) for controlling the limit of the maximum talk current by controlling the potential of the resistor (R12) through the transistors (Q1, Q11); And An analog subscriber matching circuit of an all-electronic exchange comprising a bias resistor (R16) of said transistor (Q5). The method of claim 2, A transistor (Q7) for controlling an operation mode and a blocking mode of the transistors (Q3, Q31) by adjusting a base potential of the transistor (Q11) in response to a power-off control signal; A bias resistor R21 of the transistor Q7; Resistors R17 and R18 for determining an amplification degree of the operational amplifier U1B as a unit gain 1; Resistors R19 and R16 for adjusting the reception gain of the operational amplifier U1A; And And an coupling capacitor (C1) (C2) for coupling each output of said operational amplifier (U1A) (U1B) to each base of said transistors (Q31) (Q21), respectively. The method of claim 2, A bypass capacitor (C3) of the emitter resistors of the transistors (Q2, Q21) (Q3, Q31); And And an bias and voltage feedback resistor (R11) (R8) of each of the transistors (Q2, Q21) (Q3, Q31). The method of claim 2, And a capacitor (C4) connected between the base and the collector of the transistor (Q11) and coupling the alternating current impedance between the ring stage and the power supply to a low impedance when looking inside the circuit from outside the ring stage. Analog subscriber matching circuit. The method of claim 2, An operational amplifier (U2A) for converting a 2-wire audio signal into a 4-wire audio signal for transmitting the voice signal transmitted from the subscriber to the counterpart; Resistors R22, R23, R24 and R25 patterned around the operational amplifier U2A to operate the operational amplifier U2A in a differential amplification mode; DC blocking capacitors C5 and C6 that respectively block the DC potential of each tip and ring and input an AC signal to the differential amplifier, respectively; And And an capacitor (C7) for alternating-coupling the output signal of the operational amplifier (U2A) with an input of a next stage. The method of claim 2, The subscriber detects the hook-off when attempting to make a call with the handset, detects the dial pulse when dialing, and receives two potentials respectively inputted to detect the hook-off during ring signal supply. Comparing comparator U2B; Resistors R26, R27, R28, R29 that drop the two potentials of the tip and ring ends to the supply voltage range of the comparator; A transistor (Q8) for converting an output voltage of the comparison result in the comparator (U2B) to a TTL voltage level; And And an pull-up resistor (R33) for holding a hook-off detection signal at a logic '1' when the transistor (Q8) is turned off.