JPS63232668A - Communication equipment - Google Patents

Abstract

PURPOSE:To execute an optimum reception matching with the receiving condition and simultaneously, to reduce the leakage of transmission signals, by setting a bridge circuit to an unbalanced state in corresponding to the transmission signals. CONSTITUTION:When an impedance Zl becomes higher at the time of reception, the voltage Va becomes low in level so as to make an impedance Zb higher and hold the balanced state of a bridge circuit 3. When calling is made to a microphone 9, a current control circuit 11 is controlled by the output signal of an amplifier 10 and the impedance Zb becomes low. Accordingly, the balanced state of the bridge circuit is broken and the level of the transmission signal supplied to an amplifier 5 becomes low and, as a result, the side tone is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a circuit technology suitable for application to communication devices that utilize communication lines, particularly telephones.

[Conventional technology]

Telephones are transitioning from traditional black telephones to electronic telephones. Examples of computerized telephones are given in Nikkei Electronics J (1977% No. 6-27, published by Nikkei McGraw-Hill, pp. 60-70). It is being developed.

The present inventor conducted various technical studies in order to make good calls using the electronic telephone set. Although the following is not a publicly known technique, it is a technique studied by the present inventor, and its outline is as follows.

That is, some electronic telephones operate using DC power supplied via a telephone line. When there is a long distance between the telephone office and the telephone set, the impedance of the communication line becomes large and the voltage supplied to the telephone set, in other words, the terminal voltage decreases.

In this case, the level of the received sound on the telephone decreases, and the audibility becomes K<. Therefore, an automatic gain control circuit is provided in the IC in the telephone set to increase the gain and improve the above phenomenon, but the inventor clearly identified the following problems.

[Problem that the invention seeks to solve]

That is, the packing machine transmits the transmission signal using a telephone line, and also makes it audible through its own speaker. Therefore, when the gain is controlled to be high by automatic gain control, the sound generated from the own speaker, so-called sidetone, becomes louder, making it extremely difficult to hear.

The present inventor has made repeated studies to solve the above problems. Then, in addition to controlling the gain of the telephone according to the receiving condition, if the level of the received signal drops, the gain should be controlled to high for the received signal and low for the transmitted signal. This led me to propose the present invention.

An object of the present invention is to provide a communication device that can perform good communication both during transmission and reception.

Another object of the invention is to improve the sidetone of telephones.

The above and other objects and novel features of the present invention will become apparent from the present specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this Ml/C is as follows.

That is, a bridge circuit whose one side is the impedance of a communication line such as a telephone line, and a receiving state is determined by detecting the level of the received signal transmitted through the communication line and controlling the impedance of the other side of the bridge circuit. In addition, a control circuit is provided for controlling the impedance of the other side by detecting the level of the transmission signal.

[Effect]

According to the above-mentioned method, when receiving, the impedance of the bridge circuit is controlled according to the received signal to ensure good reception, and when transmitting, the impedance of the bridge circuit is controlled by detecting the transmitted signal, so when transmitting , it is possible to achieve the object of the present invention, which is to perform good communication regardless of K at the time of reception.

〔Example〕

Hereinafter, an embodiment of a communication device to which the present invention is applied will be described with reference to FIG.

Note that FIG. 1 shows a one-way diagram of the communication device.

1 indicates the exchange installed at the telephone office,
Capacitors c, c', resistors R, R So communication line! , 1 indicates the impedance z1.

Impedance z1 becomes high impedance when the distance between one communication line A, J is long, and becomes low impedance when the distance is short. □ The telephone 2 corresponds to a communication device according to the present invention,
The resistor R4*R1*the impedance zB and the controllable impedance zb constitute the bridge circuit 3 in the present invention.

Pretend the above y Shi0ro 31t-Z J / Z b-R
Although it is balanced at t/R1, the impedance z1 changes depending on the installation conditions of the telephone 2, and the balanced condition is disrupted.

In this state, Ia (so-called shunt current), which will be described later, becomes large, making it impossible to perform transmission and reception under optimal conditions.

However, in response to the change in impedance z1, zb
The above-mentioned balance can be maintained by varying the value, and the control circuit 21 is provided for this purpose.

Since the control circuit 21 performs different circuit operations during reception and transmission, the circuit operation during reception will be explained first.

At the time of reception, the reception signal is supplied from the exchange 2 as a current signal, and the amount of current IL depends on the impedance ZA.
Changes in response to IIC, low current at high impedance,
High current occurs when impedance is low. In addition, since various load circuits such as a speech network 4 are configured in the IC blocker, the bridge circuit 3 includes an IL-Ice
-Ia current is supplied.

At the time of reception, the current IL is transmitted to the amplifier 5 through paths A and B shown by dotted lines, and a reception sound is generated from the speaker 7 of the handset 6. At the same time, 1 current I.

flows through the resistor R1, the transistor Q, and the resistor R0, generating a voltage Va serving as a control signal. Voltage Va becomes high level when current Ia is large, and becomes low level when current Ia is small. The voltage Va is applied to the inverting input terminal of the differential amplifier 80 via the resistor R11. The collector voltage Vc of the transistor Q1 is connected to the non-inverting input terminal of the differential amplifier 8 through the resistor R42*R+a.
The voltage difference between both terminals drives the transistor Q.

When receiving, a microphone 9° amplifier 10 for transmitting. If the current control circuit 110 circuit is ignored, the voltage Va corresponds to the current Ia, so if the impedance ZB is large, it changes to a low level. impedance z
b is an electronic polynium 22.b connected to a resistor R21. Capacitor C
1 are connected in parallel, and when the voltage level of the voltage Va is high, the resistance of the electronic polynium 21 becomes small. Zl
When becomes large as described above, voltage Va becomes low level and zb becomes large to maintain the above-mentioned equilibrium. As a result, the current Ia becomes approximately 0, and most of the current Ia is supplied to the amplifier 5, making the received sound louder. Then, optimal reception is performed in accordance with the installation conditions of the telephone set 2.

Next, the circuit operation during transmission will be described.

When a call is made into microphone 9.

The current control circuit 11 is controlled by the output signal of the amplifier 10, and the current flowing through the resistor R71 and the resistor RoK is increased. The voltage drop across the resistor R0 becomes large, and the voltage Va becomes high level. In this case, impedance Zb does not change, but impedance Zb is controlled to only one impedance.

Among the equilibrium conditions determined by Z4/Zb -R, /R, impedance zb becomes a low impedance, and the equilibrium state of the bridge circuit 3 is disrupted.

The current Ia' flows again to 5, and the resistances R+ and R
The level of the transmission signal supplied to the amplifier 5 via t becomes low level, and the sidetone is improved.

The telephone shown in the above embodiment has the following effects.

+11 By providing a control circuit that supplies a busy reception signal to a bridge circuit whose side is the impedance of the telephone line and balances the bridge circuit by obtaining a control signal 1 corresponding to the change in impedance, it is possible to adjust the installation conditions of the telephone. The effect of receiving data can be obtained.

(2) By supplying a transmission signal to the bridge circuit and obtaining a control signal corresponding to the transmission signal to make the bridge circuit unbalanced, it is possible to reduce the sidetone of the telephone by %.

(3) 11+ and (2) above improve the degree of freedom in the installation conditions and usage conditions of the telephone.

Although the invention made by the present inventor has been specifically explained above based on examples, the present invention is not limited to the above-mentioned examples, and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, the control circuit 21 may be constituted by a MOS transistor.

In the above description, the invention made by the present inventor was mainly applied to an electronic telephone set, which is the field of application to which the invention is based.

The present invention is not limited thereto, and can be widely used in communication devices that use communication lines, such as intercoms, for example.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, a control signal is obtained from a received signal whose level changes in response to the impedance of the communication line, and the bridge circuit that transmits the signal is balanced, and the control signal unbalances the bridge circuit in response to the transmitted signal. By providing a control circuit, it is possible to perform optimal reception according to reception conditions and reduce leakage of transmitted signals.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a communication device to which the present invention is applied. l...exchange, 2...telephone, 3...bridge circuit. 7...Speaker, 8...Amplifier, 9...Microphone. 11... Current control circuit, 21... Control circuit, 22.
...Electronic polynium, ZJ, Zb...Impedance, IA, Ia, Ia...Current, Va...Voltage serving as a control signal.

Claims (1)

[Claims] 1. A bridge circuit whose one side is the impedance of the communication line, and a received signal whose level changes depending on the impedance of the communication line is detected, and the impedance of the other side of the bridge circuit is controlled to balance the bridge circuit. What is claimed is: 1. A communication device comprising: a control circuit that at least improves reception conditions, detects a transmitted signal, controls impedance on the other side of the bridge circuit, and reduces leakage of the transmitted signal.