JPH0296436A - Call set - Google Patents

Abstract

PURPOSE:To suppress a sidetone with a simple balancing circuit and to improve a call quality by connecting a hybrid transformer through an isolation amplifier to a two-wire type calling line and setting the impedance value of a balancing circuit to the nominal impedance value of the line. CONSTITUTION:A hybrid transformer 9 is connected through an isolation amplifier I.I10 to calling lines L1 and L2. The input impedance of the amplifier I.I10 is not influenced by the impedance of the lines L1 and L2 and set to a constant value equal to the nominal impedance on the lines L1 and L2. The impedance of a balancing circuit 11 is matched to the nominal impedance. Thus, with a simple circuit 11, the impedance matching condition is always maintained, the generation of the sidetone can be prevented and the calling quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a telephone set, such as an telephone, which is capable of carrying out simultaneous bidirectional telephone calls via a two-wire telephone line without DC superimposition, such as an telephone.

[Conventional technology]

Currently, intercoms that enable simultaneous two-way communication are hybrid intercoms that are interposed between the transmitter/receiver and the line in order to prevent the transmission signal sent from the transmitter from going around to the receiver, that is, to suppress the generation of sidetone. It is generally known that a transformer is provided with a balancing circuit having the same nominal impedance as the nominal impedance of the line.

[Problem to be solved by the invention]

In the above conventional technology, if the impedance of the balancing circuit and the nominal input impedance of the line are perfectly matched, it is possible to completely suppress the generation of sidetone in principle, but the input impedance of the line side is In reality, it is not possible to sufficiently match the impedance of the balancing circuit, as it varies depending on the line length and the input impedance of your telephone, and therefore a good sidetone prevention effect could not be expected. .

Further, the circuit configuration of the balancing circuit has to be complicated in order to accommodate the line-side impedance component, resulting in an increase in cost.

The present invention was made in view of the above-mentioned problems, and aims to provide a telephone device that is inexpensive and has excellent speech quality, which can sufficiently suppress the generation of sidetone by using a simplified balance circuit. .

In the communication device of the present invention having the above means, since the line and the hybrid transformer are separated by an isolation amplifier, it is assumed that the actual input impedance on the line side varies depending on the line length, the other party's communication device, etc. However, the input impedance of the isolation amplifier as seen from the hybrid transformer is always constant. Therefore,
There is no mismatch between the input impedance of this isolation amplifier and the impedance of the balancing circuit.
No side sounds occur.

[Means to solve the problem]

This invention connects a humbrid transformer to which a transmitter/receiver is connected to a two-wire communication line via an isolation amplifier, and adjusts the impedance value of a balance circuit connected to the humbrite transformer to the line. is set to a predetermined nominal impedance value.

[For production]

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a block diagram showing the overall circuit configuration of this embodiment.

In the figure, 1 is a unidirectional microphone that converts the call sound into an audio electrical signal (transmission signal),
This microphone has a built-in amplifier that amplifies the converted electrical signal to a predetermined level. Reference numeral 4 denotes a hybrid transformer for impedance matching that is connected to the microphone 1 via a cable 2 and a coupling capacitor 3 for removing direct current components, and is used to match the impedance between the microphone 1 and the subsequent transmitter circuit. It is for. A differential amplifier 5 amplifies the transmission signal output from the hybrid transformer 4, and is capable of removing common mode noise during amplification. 6 is a low-pass filter, and 7 is a bypass filter, and these filters 6.7 limit the frequency band of the transmission signal output from the differential amplifier 5 to 300 Hz to 340011 z. Reference numeral 8 denotes a buffer amplifier that amplifies the transmitted speech signal sent through the filter 6.7 to a predetermined level, 9 a hybrid transformer for 2-wire-4-I conversion, and 10 a hybrid transformer 9 and a direct current superimposition converter. An impedance isolation amplifier (engineering/engineering) is inserted and connected between the 2'1IIA type communication lines L□ and L2, and its input/output impedance is 600 ohms DC. In addition, the communication line L□T Lz is approximately 6
It has an impedance of 00Ω. 11 is a balancing circuit (B-N) connected to the hybrid transformer 9, and its nominal impedance (hereinafter simply referred to as impedance) is 600 ohms. Reference numeral 12 denotes a differential amplifier that amplifies the reception signal output from the hybrid transformer 9, and is capable of removing common-mode noise components during amplification. 13 is a low pass filter, 14 is an Ihachi pass filter, and 15 is 3001 for both the above filters.
A frequency range of 1 z to 3400 Hz; an amplifier for amplifying the reception signal limited to the F range; 16 a hybrid transformer connected to the amplifier 15 via a buffer amplifier 17 for impedance matching; 20 the output side of the hybrid transformer 17; A speaker connected via a coupling capacitor 18 for DC component removal and a cable 1 converts an input reception signal into audio and outputs it.

Further, FIG. 2 is a circuit diagram showing a specific example of the configuration of the impedance isolation amplifier 10. As shown in FIG. As shown in the figure, impedance isolation amplifiers (hereinafter referred to as operational amplifiers) oP□, OF2 in this embodiment
and a pair of T-shaped terminal networks T, , T2 consisting of DC impedance elements Za, Zb, and Zc. The output side of the operational amplifier oP1 is connected to the non-inverting input terminal of the operational amplifier oP2 through one T-shaped terminal RT, and the output side of the operational amplifier oP2 is connected through the other T-type four-terminal network T2. and is connected to the non-inverting input terminal of the operational amplifier OP1. Moreover, here, the T-type four-terminal network 2. ．． Za, Zb, and Zc are set so that each short circuit impedance of 22 becomes 600 ohms.

FIG. 3 is a circuit diagram showing the configuration of the balancing circuit 11.

This balancing circuit 11 sets the variable resistor VR and the capacitor C to the calculated values by substituting known values depending on the line length into the calculation formula.

Note that the other party's telephone set connected to the communication line L, L has a similar configuration.

Based on the above configuration, the operation will be explained next.

The voice input to the transmitter 1 is converted into an electrical signal (transmission signal), amplified by the built-in amplifier, and then
Only the alternating current component is taken out via the capacitor 3 and input to the differential amplifier 5 via the hybrid transformer 4.

Furthermore, the transmission signal amplified by this differential amplifier 5 passes through a low-pass filter 6 and a bypass filter 7 to 300H.
z becomes a signal within the 3400 ratio frequency band, which is input to the hybrid transformer 9 via the buffer amplifier 8, and from there to the communication line L via ■/IIO.

Sent to L2.

Further, a reception signal sent in the same manner from the other party's telephone is inputted to the hybrid transformer 9 via the IIO, and outputted from there to the differential amplifier 12. The reception signal amplified by the differential amplifier 12 passes through the low-pass filter 13 and the bypass filter 14 to become a signal within 3001 (z to 3400) (z), and is further amplified to a predetermined level by the amplifier 15, and then sent to the buffer amplifier. 16 to the hybrid transformer 17.The receiving signal output from the hybrid transformer 17 has its direct current component removed by the coupling capacitor 18, and is input to the speaker 20, where it is converted into audio. Output.

However, in this embodiment, the input impedance of ■IIO is the same as that of communication line L1. Since it is always set to a constant value (600 ohms) without being affected by the impedance of L2, and matches the impedance of 600 ohms of the balancing circuit 11, it prevents the transmitting signal from going around to the receiving system, i.e. Side sounds are prevented from occurring.

In other words, in the work shown in Figure 2, the operational amplifier ○
Since the output impedance of P, is around 10'' ohm, it can be considered as 0, and the op amp OP2
The input impedance of is about 106 ohms and can be ignored. The input impedance of the IIO is fixed to the short-circuit impedance (600 ohms) of the T-type four-terminal network Z, and is completely unaffected by the impedance of the communication line.

Therefore, the matching state with the balance circuit 11 is always maintained, and the generation of sidetone can be prevented.

In addition, since the input impedance of .IIO can be fixed as described above, the balancing circuit 10 can have an extremely simple configuration as shown in FIG. 3, and costs can be reduced. In reality, the communication line L1.
Fluctuations in the capacitance reactance of L, etc. may affect the input impedance of I/IIO, but in this case, it can be easily dealt with by replacing the capacitor C of the balancing circuit 11.

Further, in the above embodiment, a so-called hands-free type interphone using the speaker 20 and the microphone 1 was explained as an example, but the present invention is not limited to the above embodiment, but can be applied to interphons other than the hands-free type. This is possible, and furthermore, it is applicable not only to an interphone, but also to a telephone line that uses a direct current superimposed internal telephone line.

〔Effect of the invention〕

As explained above, according to the telephone according to the present invention,
Since it is not affected by impedance fluctuations in the communication line, it is possible to sufficiently suppress the generation of sidetone using an inexpensive balancing circuit with a minimal configuration, resulting in excellent communication quality. be.

[Brief explanation of the drawing]

1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of the impedance isolation amplifier shown in FIG. 1, and FIG. 3 is a block diagram showing the configuration of the impedance isolation amplifier shown in FIG. It is a circuit diagram showing a workpiece. L□, L2...Communication line 9...Hybrid transformer 10...Impedance isolation amplifier 11...Balancing circuit VRl, VR2...Variable resistor C...Capacitor

Claims (1)

[Scope of Claims] A communication device configured to perform two-way direct communication via a two-wire communication line without DC superposition, comprising: a hybrid transformer connected to the communication line; and a hybrid transformer connected to the hybrid transformer. an isolation amplifier inserted and connected between the hybrid transformer and the communication line; and an isolation amplifier connected to the hybrid transformer and having a predetermined nominal impedance approximating the nominal input impedance of the communication line. A telephone set characterized in that it is equipped with a reverse circuit network.