JPH07193618A - Off-hook detection circuit - Google Patents

Abstract

PURPOSE:To detect a hooked-off of a telephone set without being affected of dispersion in components or a temperature change with respect to the off- hook detection circuit of a terminal equipment use network controller. CONSTITUTION:The circuit is provided with a differential operational amplifier 1 whose output signal level differs from the quantity of two input voltages, a 1st resistor 2 connected between power supply and a 1st input of the differential operational amplifier 1, a reference resistor 3 connected between the 1st input of the differential operational amplifier 1 and a ground point, and a 2nd resistor 4 connected between the power supply and a 2nd input of the differential operational amplifier. The off-hook of a telephone set connected between the 2nd resistor 4 and the ground point is detected. Moreover, a 1st constant current source is provided in place of the 2nd resistor. Or a 2nd constant current source is provided in place of the 1st resistor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal network control device which is connected between a telephone line and a terminal device and has a function of making a call operation from the terminal device. The present invention relates to an off-hook detection circuit for a telephone connected to a terminal network controller.

[0002]

2. Description of the Related Art When a terminal network controller calls a telephone line for communication, a telephone connected to the terminal network controller is disconnected from the telephone line. During communication, it is necessary to monitor the off-hook of the telephone and, when off-hook, stop the communication and connect the telephone to the telephone line. In order to detect the off-hook of the telephone, it is sufficient to monitor the impedance of the telephone because the impedance at both ends of the telephone decreases when the telephone is off-hook.

FIG. 4 shows a conventional off-hook detection circuit. As shown in FIG. 4, the telephone is connected between the resistor R ₁ connected to the base of the transistor and the ground point. When the telephone is on-hook, the impedance of the telephone is high and almost no current flows in the base, so the transistor is off and the collector output of the transistor is at low level. When the phone goes off-hook, the impedance across the phone drops, the base current of the transistor increases, the transistor turns on, and the collector output goes high. The collector output of this transistor may be monitored by the controller to determine that the telephone is off-hook when the collector output goes high.

[0004]

However, the above-mentioned conventional structure has a problem in that the output characteristics greatly change due to variations in the resistances and transistors and the temperature change.

Further, depending on the model of the telephone, the impedance may not be sufficiently lowered even when off-hook when a small current is supplied to the telephone, and the transistor may not be turned on.

Further, if a circuit is constructed by using a high resistance to reduce the current consumption, there is a problem that the area becomes large in the IC process.

Further, in the above-mentioned conventional example, the current flowing to the base of the transistor is calculated from the impedance when the telephone is off-hook and the resistance that constitutes the other, so that the transistor is switched from off to on when the telephone is on-hook and off-hook. Therefore, it is complicated to set the value of the resistance.

SUMMARY OF THE INVENTION The first object of the present invention is to provide an off-hook detection circuit for detecting that a telephone is off-hook without being affected by variations in parts and temperature changes. It was done.

In addition, the current flowing to the telephone remains constant,
A second object is to provide an off-hook detection circuit that detects that the telephone has gone off-hook.

A third object of the present invention is to provide an off-hook detecting circuit for detecting that the telephone is off-hook without using high resistance.

A fourth object of the present invention is to provide an off-hook detection circuit which can easily set the constants of constituent parts.

[0012]

In order to achieve the first object of the present invention, a first embodiment of a differential arithmetic unit having different output signal levels depending on the magnitude of two input voltages, a power supply and the differential arithmetic unit. A first resistor connected to the input of the differential calculator, a reference resistor connected to the first input of the differential calculator and the ground point, a power supply and a second resistor of the differential calculator. A second resistor connected to the input is provided to detect off-hook of the telephone connected between the second resistor and ground.

Further, in order to achieve the second object, in the above first structure, a first constant current source is provided instead of the second resistor.

In order to achieve the third object, in the first configuration, a second constant current source is provided instead of the second resistor, and a second constant current source is provided instead of the first resistor. I am trying.

Further, in order to achieve the fourth object, the second constant current source in the above third configuration is configured to flow the same current as the first constant current source.

[0016]

According to the first aspect of the present invention, the voltage value of the first input of the differential calculator is determined by the ratio of the sum of the resistance value of the reference resistance to the resistance value of the reference resistance. Similarly, the voltage value of the second input of the differential calculator is determined by the ratio of the second resistance to the resistance value of the telephone and the sum of the resistance values of the telephone. Therefore, the voltage value of the first input of the differential operation unit is set to the voltage value of the second input of the differential operation unit when the telephone is on-hook and the voltage value of the second input of the differential operation unit when the telephone is off-hook. By setting in between, when the telephone is off-hook, the output of the differential calculator is inverted.

According to the second structure, the voltage value of the first input of the differential calculator is determined by the ratio of the resistance value of the reference resistance to the sum of the resistance value of the reference resistance.
Further, the voltage value of the second input of the differential calculator is determined by the product of the current flowing by the first constant current source and the resistance value of the telephone. Therefore, the voltage value of the first input of the differential operation unit is set to the voltage value of the second input of the differential operation unit when the telephone is on-hook and the voltage value of the second input of the differential operation unit when the telephone is off-hook. By setting in between, when the telephone is off-hook, the output of the differential calculator is inverted.

According to the third or fourth configuration,
The voltage value of the first input of the differential calculator is determined by the product of the current flowing by the second constant current source and the resistance value of the reference resistance. Further, the voltage value of the second input of the differential calculator is determined by the product of the current flowing by the first constant current source and the resistance value of the telephone. Therefore, the voltage value of the first input of the differential arithmetic unit is set to the second value of the differential arithmetic unit when the telephone is on-hook.
When the telephone is off-hook, the output of the differential calculator is inverted by setting it between the voltage value of the input of the input terminal and the voltage value of the second input of the differential calculator during the off-hook.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 1 is a differential calculator, and 2 is a first.
Resistance, 3 is a second resistance, 4 is a reference resistance, and 5 is a telephone.

The operation of this embodiment when the power supply voltage is Vcc will be described below. Assuming that the input impedance of the differential calculator 1 is sufficiently large, most of the current flowing through the first resistor 2 will flow through the reference resistor 4. Therefore, the resistance value of the first resistor 2 is RA and the resistance value of the reference resistor 4 is R
Let S be the input voltage V of the first input a of the differential calculator 1.
1 can be represented by V1 = Vcc × RS / (RA + RS).
Similarly, most of the current flowing through the second resistor 3 will flow into the telephone 5. Therefore, if the resistance value of the second resistor 3 is RB and the resistance value of the telephone is RT, the differential calculator 1
Input voltage V2 of the second input b of V2 = Vcc × RT
/ (RB + RT).

Here, the impedance of the telephone 5 when the telephone 5 is on-hook is RT1, the voltage value of the second input b of the differential calculator 1 is V21, and the impedance of the telephone when the telephone 5 is on-hook is RT2, and the difference is RT2. The second of the dynamic calculator 1
The voltage value of the input b of is set to V22. Generally RT> RT2
RT1 / (RB + RT1)> RT2
Since / (RB + RT2) is established, V21> V22. Therefore, by using the reference resistor 4 having the resistance value RS that satisfies V21>V1> V22, the magnitude of the input voltage of the differential calculator 1 is reversed between the off-hook state and the on-hook state of the telephone. The output will be inverted.

According to the structure of the first embodiment, assuming that the resistance changes or variations in the resistance value due to temperature are the same as in the IC process, the first input a of the differential calculator 1 is the same.
Since the input voltage V1 of is obtained by the relative ratio of RA and RS, there is almost no voltage change due to temperature, and since the differential calculator 1 is operated only by the voltage, the resistance values of the first resistor 2 and the reference resistor 4 are By increasing each other, the current flowing for the reference voltage can be reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same components as those in the first embodiment are designated by the same reference numerals, and the different components are the first constant current source 6 in FIG.

In the following, in the present embodiment, the power supply voltage is Vc
The operation when c is shown. Assuming that the input impedance of the differential calculator 1 is sufficiently large, most of the current flowing through the first resistor 2 will flow through the reference resistor 4. Therefore, assuming that the resistance value of the first resistor 2 is RA and the resistance value of the reference resistor 4 is RS, the input voltage V1 of the first input a of the differential calculator 1 is V1 = Vcc × RS / (RA + RS) Can be expressed as Further, most of the current I1 flowing through the first constant current source 6 flows into the telephone 5. Therefore, assuming that the resistance value of the telephone 5 is RT, the input voltage V2 of the second input b of the differential calculator 1 is obtained by V2 = I1 × RT.

Here, when the current I1 flows through the telephone set 5, the impedance of the telephone set 5 when on-hook is RT1, the voltage value of the second input b of the differential calculator 1 is V21, and the telephone set when the telephone set 5 is off-hook is set. Impedance of RT
2. The voltage value of the second input b of the differential calculator 1 is V22. Generally, there is a relation of RT> RT2, so V21> V
22. Therefore, by using the second resistor 3 having the resistance value RA satisfying V21>V1> V22 and the reference resistor 4 having the resistance value RS, the input voltage of the differential calculator 1 can be reduced when the telephone is off-hook and on-hook. Since the magnitude is reversed, the output will be reversed when the phone goes off-hook.

According to the configuration of the second embodiment, the current flowing through the telephone is constant regardless of the type and state of the telephone, so that the impedance of the telephone can be determined stably. The input voltage V1 of the first input a of the differential calculator 1 is RA
Since there is almost no change in voltage due to temperature since it is obtained as a relative ratio between RS and RS, the resistance values of the first resistor 2 and the reference resistor 4 must be made large in order to operate the differential calculator 1 only by the voltage. Therefore, the current flowing for the reference voltage can be reduced.

Further, a third embodiment of the present invention will be described with reference to FIG. In FIG. 3, the same components as those in the first embodiment are designated by the same reference numerals. The configuration is different between the first constant current source 6 and the second constant current source 7.

Below, the current I flowing through the first constant current source 6 will be described.
The operation in this embodiment will be described for the case where the currents I2 flowing through the first and second constant current sources 7 are equal.

Assuming that the input impedance of the differential calculator 1 is sufficiently large, the current I2 flowing through the second constant current source 7
Will flow to the reference resistor 4. Therefore,
When the resistance value of the reference resistor 4 is RS, the input voltage V1 of the first input a of the differential calculator 1 is obtained by V1 = I2 × RS. Similarly, most of the current I1 flowing through the first constant current source 6 flows into the telephone 5. Therefore, assuming that the resistance value of the telephone 5 is RT, the input voltage V2 of the second input b of the differential calculator 1 is obtained by V2 = I1 × RT. Here, since I1 = I2, V1: V2 = RT: RS holds. If the impedance of the telephone when on-hook when the current I1 flows is RT1 and the impedance of the telephone when off-hook is RT2, there is a relation of RT> RT2. Therefore, the resistance value R is such that RT>RS> RT2.
By using the reference resistor 4 having S, the magnitude of the input voltage of the differential calculator 1 is inverted when the telephone is off-hook and on-hook, so that the output is inverted when the telephone is off-hook.

According to the structure of the third embodiment, the first constant current source 6 and the second constant current source 7 have the same structure so that the flowing current does not flow even if the temperature or the power supply voltage changes. Since the two constant current sources are the same, the currents flowing through the reference resistor 4 and the telephone 5 can be exactly the same. Therefore, by simply setting the resistance value of the reference resistor 4 to a resistance value between the on-hook resistance value and the off-hook resistance value of the telephone 5, the telephone 5
Off-hook can be detected. Further, according to the IC process, the area of the constant current source can be reduced as compared with the case of forming a high resistance.

[0032]

As described above, according to the off-hook detection circuit of the present invention, the first input a is realized by the first configuration.
When the voltage value of is the reference voltage, this reference voltage is determined by the relative ratio of the resistance values of the first resistance and the reference resistance, so there is almost no effect from temperature changes, so the reference voltage is stable and consumes less power. Obtained by electric current.

Further, by adopting the second configuration, the current flowing in the telephone is always made constant by the first constant current source, so that the change in the impedance of the telephone due to the change in current is eliminated.

Further, by adopting the third configuration, the current flowing through the telephone by the first constant current source is always constant, so that the impedance change of the telephone due to the current change is eliminated and the second constant current source is kept small. In the case of an IC process, by using a current, it is possible to reduce the area compared to using a high resistance to reduce the current.

Further, by adopting the fourth configuration, since the current values of the first constant current source and the second constant current source are equal, the voltage value of the first input a of the differential calculator is different from the differential value. The magnitude of the voltage value of the second input b of the arithmetic unit is not affected by the power supply voltage and is proportional only to the magnitude of the resistance value of the reference resistor and the resistance value of the telephone. Therefore, by simply setting the resistance value of the reference resistance between the on-hook resistance value and the off-hook resistance value of the telephone, it is possible to detect that the telephone is off-hook, which makes it very easy to set constants in circuit design. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of an on-hook detection circuit according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of an on-hook detection circuit according to the second embodiment.

FIG. 3 is a configuration diagram of an on-hook detection circuit according to the third embodiment.

FIG. 4 is a block diagram of a conventional on-hook detection circuit.

[Explanation of symbols]

 1 Differential Calculator 2 First Resistance 3 Reference Resistance 4 Second Resistance 5 Telephone 6 First Constant Current Source 7 Second Constant Current Source

Claims (5)

[Claims] 1. A voltage comparison section having different output signal levels depending on the magnitude of two input voltages, a reference voltage generation section for generating a constant voltage and giving it to a first input of the voltage comparison section, and the voltage comparison section. And a comparison voltage generator for determining the voltage of the second input of the voltage comparator by connecting a telephone between the second input of the voltage comparator and the ground point. And an off-hook detection circuit for detecting an off-hook of the telephone connected between the second input of the voltage comparator and the ground point. 2. A differential operation unit is used as a voltage comparison unit, a reference voltage generation unit is connected between a power supply and a first input of the differential operation unit, and the differential operation unit and the differential operation unit. A second resistor connected between the power supply and the second input of the differential operation unit, the reference voltage generating unit being constituted by a reference resistor connected between the first input and the ground point. The off-hook detection circuit according to claim 1, wherein the off-hook detection circuit comprises: 3. The off-hook detection circuit according to claim 2, further comprising a first constant current source instead of the second resistor. 4. The off-hook detection circuit according to claim 2, further comprising a first constant current source instead of the second resistor and a second constant current source instead of the first resistor. 5. The off-hook detection circuit according to claim 4, wherein the second constant current source is configured to flow a current equal to that of the first constant current source.