JPH0575675A - Speech circuit for analog telephone set - Google Patents

Abstract

PURPOSE:To facilitate the changeover of an AC impedance so as to use a line in common with a facsimile equipment or the like without provision of a line transformer and a switch for path changeover. CONSTITUTION:An operational amplifier section 2 has a 1st inverting input terminal (-) and plural 2nd noninverting input terminals (+) being differential inputs. Each of series connecting points among plural resistive elements R2a, R2b and a capacitive element C1 connected in series between 1st and 2nd subscriber terminals L1 and L2 is connected to each of the and input terminals (+). A resistive element R3 is connected between the 1st input terminal and an emitter of a bipolar transistor(TR) Q1. A selection changeover circuit 3 is provided to select one signal among the plural series connecting points by control signals CS1,CS2 and the selected signal is amplified by the operational amplifier section 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog telephone communication circuit, and more particularly to an analog telephone communication circuit that shares a line with a fax machine or the like.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional telephone circuit for analog telephones.

In this analog telephone communication circuit, a balance network element Z and an impedance element R are connected in series between the first and second subscriber terminals L1 and L2.
Z, and the hybrid circuit 1 including the first resistance element R1, and two second resistance elements R2a and R2b and a capacitance element C that are connected in series between the first and second subscriber terminals in series.
1 and a bipolar transistor Q1 having a collector connected to the first subscriber terminal L1 and an emitter connected to a series connection point of the impedance element RZ and the first resistance element R1;
The first and second input terminals (-) and (+) of the differential input are provided, the output terminal is connected to the base of the bipolar transistor Q1, and the first input terminal (-) is connected to the bipolar transistor Q1.
1 and an operational amplifier 2b that connects the second input terminal (+) to the series connection point of the second resistive elements R2a and R2b, and the operational amplifier for amplifying the signal of the microphone 4 for transmission. By amplifying the signal between the transmission amplifier 5 supplied to the second input terminal (+) of the section 2b, the series connection point of the balance network element Z and the impedance element RZ, and the second subscriber terminal L2. It has a configuration including a reception amplifier 6 which is supplied to the reception device 7.

Next, the output impedance Zo of the analog telephone communication circuit will be calculated. Subscriber terminal L
If the voltage between 1 and L2 is vo, and the current flowing from the subscriber terminal L1 into the interior is io, the output impedance Zo
Is Zo = vo / io. Further, the current flowing through the balance network element Z is i1, the current flowing through the collector of the transistor Q1 is i
2, and the current flowing through the resistance element R2d is i3, then io = i1 + i2 + i3. If the value of the balance network element Z is set so that i1 is sufficiently smaller than i2 and i3, R1 × i2 = vo−R2a × i3 = vo × (R2b + 1) from the condition of virtual grounding of the operational amplifier 2b. / JwC1) / (R2a + R2b + 1 / jwC1). However, w indicates the angular frequency, R1, R2a, R
2b and C1 represent the values of each resistance element and capacitance element. Therefore, the output impedance Zo is Zo = (R2a + R2b + 1 / jwC1) × R1 / (R2b + R1 + 1 / jwC1). Assuming that the capacitance element C1 has a sufficiently large value and the AC impedance can be ignored, Zo = R1 × (R2a + R2b) / (R1 + R2b) (1). Normally, the output impedance of an analog telephone is designed to be 600Ω, so R1 = 50Ω and R2a = 11.
If 1KΩ and R2b = 10KΩ, the output impedance Zo can be about 600Ω.

By the way, in recent years, a telephone terminal in which an analog telephone and a FAX or the like are integrated has appeared. Modems are often used in such telephone terminals. In the case of a device using a modem, since these are usually driven by a commercial power source, they must be galvanically isolated from the subscriber line. Therefore,
The specifications of AC impedance and DC resistance of the terminal are satisfied by using a line transformer. When a device that uses a modem using a line transformer and an analog telephone are simply combined, the line transformer and analog telephone each have their own function to meet the DC resistance and AC impedance specifications, and join each independently. In order to connect to the main line, a switch for path switching will be provided.

[0006]

Since the above-mentioned conventional telephone circuit for analog telephones has a fixed circuit configuration, when the line is shared with FAX or the like, in order to satisfy the regulation of the AC impedance or the like, the line transformer is used. There is a problem that a switch for switching the route and the route is required.

An object of the present invention is to provide a telephone circuit for an analog telephone which can share a line with a FAX or the like without providing a line transformer or a switch for switching a route.

[0008]

The analog telephone communication circuit of the present invention comprises a balance network element, an impedance element, and a first resistance element which are connected in series between first and second subscriber terminals. A hybrid circuit, a plurality of second resistance elements and capacitance elements serially connected between the first and second subscriber terminals, a collector connected to the first subscriber terminal, and an emitter connected to the impedance. A bipolar transistor connected to a series connection point of the element and the first resistance element, an operational amplifier having first and second input terminals for differential input, and an output terminal connected to the base of the bipolar transistor; A third resistance element connected between a first input terminal of the amplifier and the emitter of the bipolar transistor; and the plurality of second resistance elements.
Selection switching for selecting one of the signals at the series connection point of the resistance elements and the series connection point of one of these second resistance elements and the capacitance element by the control signal and amplifying by the operational amplifier. Means, a transmission amplifier for amplifying a signal of the transmission microphone and supplying the amplified signal to the first input terminal of the operational amplifier, a series connection point of the balance network element and the impedance element, and the second connection. A receiver amplifier for amplifying a signal between the receiver terminal and the receiver terminal and supplying the amplified signal to the receiver.

[0009]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

This embodiment differs from the conventional analog telephone communication circuit shown in FIG. 5 in that the operational amplifier 2 is
A first input terminal (-) of the differential amplifier is used and three inputs having two second input terminals (+) are provided.
A third resistance element R3 is connected between the input terminal (-) and the emitter of the bipolar transistor Q1 and the output end of the transmitting amplifier 5 is connected to the first input terminal (-).
One of the second input terminals (+) is connected to the second resistance element R2a,
R2b is connected to the series connection point, the other of the second input terminal (+) is connected to the series connection point of the second resistance element R2b and the capacitance element C1, and the selection switching unit 3 is provided to provide the control signal CS.
1 and CS2 select a signal input to one of the two second input terminals (+) and the signal is amplified by the operational amplifier 2.

FIG. 2 shows a concrete circuit example of the operational amplification section 2 and the selection switching section 3.

The operational amplifier 2 includes a plurality of first transistors T1 whose base is connected to one end of the third resistance element R3.
a and T1b and the bases of the second resistance elements R2a and R2b.
And a series connection point and a second resistance element R2b and a capacitance element C1.
A plurality of second transistors T2a and T2 corresponding to the respective series connection points of the first and second transistors T1a and R1b.
2b, transistors T4, T5 connected between the collectors of the first transistors T1a, T1b and the collectors of the second transistors T2a, T2b, and the ground potential point to form a load circuit of the current mirror circuit type; Of the transistors T2a and T2b of the transistor T2a, T2b, and outputs the amplified output to the base of the bipolar transistor Q1.
1, I2.

The selection switching unit 3 also flows into a plurality of third transistors T3a and T3b which are turned on and off by inputting control signals CS1 and CS2 respectively corresponding to their bases, and these third transistors T3a and T3b. A first and a second transistor T1a, which respectively correspond to a current,
It comprises transistors T8, T9, T10, T11 forming a plurality of current mirror circuit type current supply sources for supplying to the emitters of T2a, T1b, T2b, and a current source I3.

When one of the control signals CS1 and CS2 is set to a high level, one of the third transistors T3a and T3b is turned on, and the current of the turned-on transistor is formed by the transistors T8, T9, T10 and T11. A current is supplied to one of the differential amplifier circuits formed by the first and second transistors (T1a, T2a) and (T1b, T2b) to activate the current.
The input of the operational amplifier 2 is switched and amplified.

Next, the output impedance Z of this embodiment.
Calculate o.

When one (T2a side) of the second input terminal (+) of the operational amplifier 2 is made active and the other is made non-active by the control signals CS1 and CS2, the output impedance Zo becomes the same as the conventional example. ..

Next, when the transistor T2a side is made non-active and the other is made active, the output impedance Zo becomes R2a (R2a + R2) in the equation (1).
b) and R2b = 0, Zo = R2a + R2b. Therefore, the output impedance Zo is (1). Zo = R1 × (R2a + R2b) / (R1 + R2b) (2). Zo = R2a + R2b can be controlled in two ways, and the resistance elements R1 and R2 can be controlled.
By properly setting the values of a and R2b, it is possible to use FA without a line transformer or a switch for path switching.
The line can be shared with X and the like.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention, and FIG. 4 is a circuit diagram showing a concrete example of the operational amplification section and the selection switching section.

In this embodiment, the output impedance Zo can be switched in the following three ways. The basic structure and operation are the same as in the first embodiment.

(1). Zo = (R2a + R2b + R2c) × R1 / (R1 + R2b + R2c) (In the formula (1), R2b is defined as R2b + R2c) (2). Zo = (R2a + R2b + R2c) × R1 / (R1 + R2c) (In the formula (1), R2a is R2a + R2b and R2b is R2c) (3). Zo = (R2a + R2b + R2c) (In the formula (1), R2a is set as R2a + R2b + R2c and R2b = 0.)

As described above, according to the present invention, the operational amplifier has the first input terminal (-) for differential input and the plurality of second input terminals (+). Connecting each series connection point of a plurality of second resistance elements and capacitance elements connected in series between two subscriber terminals to a second input terminal (+),
A first resistance element is connected between the emitter of the bipolar transistor and the first input terminal (-), and a selection switching circuit selects one of a plurality of series connection points by a control signal to perform operational amplification. With the configuration in which the amplification is performed in one part, one of the plurality of output impedances can be selected by the control signal, so that the line can be shared with the FAX or the like without providing a line transformer or a switch for path switching. There is an effect that can be. Further, since this line can be easily realized by a single manufacturing process, it is easy to form an IC and there is an effect that the number of parts of the device can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific example of an operational amplifier section and a selection switching circuit of the embodiment shown in FIG.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a specific example of an operational amplification unit and a selection switching circuit of the embodiment shown in FIG.

FIG. 5 is a circuit diagram showing an example of a conventional analog telephone communication circuit.

[Explanation of symbols]

1 Hybrid Circuit 2, 2a, 2b Operational Amplifier 3, 3a Selection Switching Circuit 4 Microphone 5 Transmitter Amplifier 6 Receiver Amplifier 7 Receiver C1, C2 Capacitance Element I1 to I3 Current Source Q1 Bipolar Transistor R1, R2a to R2c, R3 Resistance element RZ Impedance element T1a to T1c, T2a to T2c, T3a to T3c, T
4-T13 transistor Z balance network element

Claims (2)

[Claims] 1. A hybrid circuit including a balance network element, an impedance element, and a first resistance element, which are sequentially connected in series between first and second subscriber terminals, and the first and second subscribers. A plurality of second resistance elements and capacitance elements sequentially connected in series between terminals, a collector connected to the first subscriber terminal, and an emitter connected to a series connection point of the impedance element and the first resistance element. A bipolar transistor, an operational amplifier having first and second differential input terminals and an output terminal connected to the base of the bipolar transistor, a first input terminal of the operational amplifier and an emitter of the bipolar transistor. A third resistance element connected between the second resistance element and the second resistance element.
Selection switching for selecting one of the signals at the series connection point of the resistance elements and the series connection point of one of these second resistance elements and the capacitance element by the control signal and amplifying by the operational amplifier. Means, a transmitting amplifier for amplifying a signal of a transmitting microphone and supplying the amplified signal to the first input terminal of the operational amplifier, a series connection point of the balance network element and the impedance element, and the second subscriber. A telephone call circuit for an analog telephone, comprising: a reception amplifier for amplifying a signal between the terminal and the receiver. 2. An operational amplifier and a selection switching means, a plurality of first transistors whose bases are connected to a third resistance element, a base of a plurality of second resistance elements connected in series, and these second resistances. An operational amplifier section including a plurality of second transistors, each of which is connected to a serial connection point of one of the elements and a capacitive element, and the emitter of which is connected to the emitter of the first transistor. When,
A plurality of third transistors that turn on and off by inputting corresponding control signals to the bases, and a plurality of currents that flow through these third transistors to the emitters of the corresponding first and second transistors, respectively. 2. The analog telephone communication circuit according to claim 1, further comprising a selection switching unit formed with a current supply source.