JPS59132271A - Loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To improve the service by superposing a DC bias on a transmission and receiving level respectively capable of switching and fixing the state to the transmission stand-by, receiving stand-by and receiving fixing so as to simplify the operation. CONSTITUTION:A DC bias generating circuit 11 is connected to any one of positions A-C via a switch SW, and a DC voltage is superposed on an addition means 12 of the transmission level input side or an addition means 13 of a receiving level input side of a comparator 6. When the switch SW is connected to the position A, the DC bias nearly equal to the transmission switching threshold value is superposed on the receiving side input of the comparator 6, the receiving stand-by state is attained and when connected to the position B, the DC bias nearly equal to the receiving switching threshold value is superposed on the transmission side of the comparator 6 and the transmission stand-by state is attained, and further, when the SW is connected to the position C, the DC bias increasing he transmission switching threshold value is superposed on the receiving input side so as to attain the receiving fixing state. The three state are selected by one switch SW so as to simplify the operation and to improve the service.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a loudspeaker telephone having an audio switch circuit.

(2) Background of the technology There are known loudspeaker telephones that use a speaker instead of a receiver and a microphone instead of a transmitter in ordinary telephones. An audio switch circuit is provided as a means. Figure 1 is a configuration diagram including the audio switch circuit of a conventional public address telephone, where 1 is a side sound protection circuit such as a high print coil, 2゜4.7.9 is an amplifier, and 3 and 8 are variable for receiving and sending calls. Loss circuit, 5 is a speaker, 10 is a microphone.

6 is a comparator.

The transmission signal from the microphone 10 is amplified by the amplifier 9 and input to the amplifier 7 via the variable loss circuit 8, and the amplified output is sent to the line via the side sound protection circuit 1, and is then sent to the line via an exchange or the like. and transmitted to the other party's phone. A reception signal received from the other party's telephone via the line is amplified by an amplifier 2, and inputted to an amplifier 4 via a variable loss circuit 3, which drives an amplification output speaker 5.

In a public address telephone, the sound from speaker 5 is transmitted to microphone 1.
If it is input as 0 and the near-end to loop gain and far-end to loop gain are 1 or more, howling will occur.

Note that the near end loop gain is the gain of the loop in which the speaker 5 and the microphone 10 are coupled via the side sound protection circuit 1 of the own telephone, and the far end loop gain is as follows.

This is the gain of the loop that includes the coupling between the speaker and microphone of the other party's phone.

In order to make the aforementioned near-end to loop gain and far-end to loop gain 1 or less, a variable loss circuit 8 is provided in the transmitting circuit. A variable loss circuit 3 is provided in the receiver circuit, and a comparator 6 compares the transmitting level and the receiving level.
The loss of the variable loss circuit 8 is controlled to be small and the loss of the variable loss circuit 3 is large. When receiving a call, the loss of the variable loss circuit 8 is large and the loss of the variable loss circuit 3 is large. It is controlled so that it becomes smaller.

Further, a part of the transmitting signal at the time of transmitting a voice goes around from the side sound protection circuit 1 to the amplifier 2 and is amplified, and the receiving level input to the comparator 6 becomes higher than the transmitting level input.

The control state of variable loss circuit 8.3 may be reversed. That is, transmission blocking may occur. Conversely, when receiving a call, the received sound from speaker 5 is transmitted to microphone 1.
, the transmitting level input becomes higher than the receiving level input of the comparator 6.

Call blocking may occur.

In order to prevent the aforementioned blocking of sending and receiving, the loss of the variable loss circuit 8 is made small and the loss of the variable loss circuit 3 is made large during sending.

The transmitting level input to the comparator 6 is set to be relatively higher than the receiving level input, and control is performed so that the above-mentioned relationship is reversed during receiving.

Further, in this type of loudspeaker telephone device, the variable loss circuit 8 is set to a high loss state in a non-call state in which neither the transmitting level signal nor the receiving level signal is input.

When setting the variable loss circuit 3 to a standby state for maintaining a low loss, and when setting the variable loss circuit 3 to a high loss state.

Three types are considered: a case where the variable loss circuit 8 is set to a transmitting standby state in which the loss is maintained at a low level, and a case where the variable loss circuit 8 is set in a standby state in the previous call state.

(3) Prior art and problems Therefore, the inventors of the present invention focused on the fact that the transmitting standby state and the receiving standby state are selected depending on the purpose of use, the installation location, etc., and reduced unnecessary operations of the voice switch. Therefore, we have proposed installing a changeover switch that switches between the transmitting standby state and the receiving standby state according to the time ratio of sending and receiving calls and the difference in noise level between the two call points (Japanese Patent Application No. 57-1613).
No. 07.

Application dated September 16, 1982).

However, even in the standby state, if there is a lot of noise in the surrounding area, the voice switch is reversed to the transmitting state, causing a problem in that the user cannot receive calls.

For this reason, conventionally, a separate switch has been installed to disconnect the microphone circuit in order to stop transmitting and enter the complete listening state. Providing a switch for switching to the receiving state is uneconomical and operation is complicated.

(4) Purpose of the Invention In order to solve the above-mentioned problems, the present invention provides a loudspeaker telephone device equipped with a three-stage changeover switch that allows the user to always be in the receiving state in addition to the transmitting/receiving standby state. is intended to provide.

(5) Structure of the Invention In order to achieve the above object, the present invention inputs the transmitting level and the receiving level to a comparator, and based on the comparison results, a variable loss circuit inserted in the transmitting side and a variable loss circuit inserted in the receiving side. A public address telephone device equipped with an audio switch controlling a variable loss circuit, comprising means for switchably superimposing a direct current bias on a transmitting level and a receiving level input to the comparator, the means are respective predetermined switch notching darkness values from the transmitting standby state to the receiving state and from the receiving standby state to the sending state, and a switch notching darkness value greater than the predetermined switching darkness value to the receiving level input side. The present invention is characterized in that the switch has a three-stage DC bias that provides the following characteristics, and the voice switch can be set to a transmitting standby state, a receiving standby state, and a receiving fixed state.

(6) Examples of the Invention The present invention will now be explained in detail with reference to Examples. FIG. 2 is a block diagram of the loudspeaker telephone device of the present invention. In the figure, the same numbers as in Figure 1 indicate the same objects, 11 is a DC bias generation circuit, 12.13 is an addition means, R,, R7 are attenuators using resistors, and SW are (a) and (b). , (c).

The DC bias generation circuit 11 is connected to any one of (a) to (c) via a switch SW, and applies a direct current to the adding means 12 on the sending level input side of the comparator 6 or the adding means 13 on the receiving level input side. The voltages are superimposed. When the 3-stage switching switch is connected to (A), the receiving side input of the comparator 6 has a transmitting power level that should switch from the receiving state to the transmitting state, that is, approximately equal to the transmitting switching value. A DC bias is superimposed and the device enters a standby state. Also,
When the three-stage changeover switch SW is connected to (b), when there is no transmitting signal input to the transmitting side of the comparator 6, the receiver's power level at which to switch from the transmitting state to the receiving state, that is, the receiving switching dark value, is set. Approximately equal DC bias is superimposed, and a transmitting standby state is established.

On the other hand, when the three-stage changeover switch SW is connected to (c), a large DC bias that makes the transmitting switching value extremely large is superimposed on the receiver's power side, making it impossible to reverse the audio switching, and always keeping the receiving level at the level. is superior to the transmitting level.

It will be the same as when the microphone is disconnected. That is.

(c) The connection is in a fixed receiving state.

FIG. 3 is a diagram illustrating state transitions of the audio switch corresponding to each connection state of the three-stage changeover switch. Third
Figures (a) to (c) correspond to (a) to (c) in Figure 2,
FIG. 3(A) shows the receiving standby state, FIG. 3(B) shows the transmitting standby state, and FIG. 3(C) shows the receiving fixed state.

In Figure 3, Rin is the human power of the receiver, Tin is the human power of the transmitter,
R is the receiving state, T is the transmitting state, a and b are the DC bias values for receiving and transmitting standby determined by resistor attenuators R, R2, respectively, and C is the DC bias value for fixed receiving. shows.

Therefore, as shown in FIGS. 3(a) and 3(b), in the standby state for receiving and transmitting calls, the dark value of voice switching is in the receiving direction,
It is displaced in the sending direction, depending on the environment in which the telephone etc. are placed.
In addition to being able to select an appropriate audio switching value,
When only the voice is to be heard by the other party, a large DC bias value can be set as shown in FIG. 3(C), and the receiver can be fixed (microphone turned off).

(7) Detailed Description of the Invention According to the present invention, it is possible to select among the three states of the receiving standby state, the transmitting standby state, and the fixed receiving state with a single switch, thereby achieving economy. At the same time, it can also simplify operations and improve serviceability.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional general public address telephone, FIG. 2 is a block diagram of a public address telephone according to the present invention, and FIG. ), and is a diagram illustrating the fixed state (c). 1; Side sound protection circuit 2.4, 7, 9; Amplifier 3.8; Variable loss circuit 5; Speaker 6; Comparator 10; Microphone 11; DC bias circuit 12.13; Adding means

Claims (1)

[Claims] This loudspeaker telephone device is equipped with an audio switch that inputs a transmitting level and a receiving level into a comparator, and uses the comparison results to control a variable loss circuit inserted on the transmitting side and a variable loss circuit inserted on the receiving side. and means for switchably superimposing a DC bias on the transmitting level and the receiving level input to the comparator, and the means switches from the transmitting standby state to the receiving state and from the receiving standby state to the transmitting state. The switch is a three-stage switching DC bias that provides a predetermined switching value and a switching value that is larger than the predetermined switching threshold value to the receiving level input side, respectively, and the voice switch is in a transmitting standby state and a receiving standby state. , a loudspeaker telephone device characterized in that it can be set to a fixed reception state.