JPS5894257A - Voice switching circuit - Google Patents

Abstract

PURPOSE:To get rid of a fact that the other calling party becomes entirely silent, and to prevent anxiety for setting a channel, by setting a loss value inserted into a transmitting line, in case when a calling party of a loudspeaker- telephone set is executing a call, to the extent that a room noise, etc. can be transferred to the other calling party. CONSTITUTION:On each of a transmitting line by a microphone 1 and an amplifier 2, and a receiving line by a loudspeaker 12 and an amplifier 13, variable losing circuits 5, 15, and auxiliary variable losing circuits 21, 25 are provided. A difference of the respective output levels of these circuits 5, 15 is derived by a differential amplifier 23, is compared with a reference value by the respective comparators 22, 24, in accordance with which is larger, the transmitting signal level or the receiving signal level, and in accordance with a result of its comparison, the auxiliary variable losing circuits 21, 25, etc. are controlled. In this state, in accordance with an output of the amplifier 23, a level of a high gain amplifier 8' is set, and when a calling party is not calling, a loss value inserted into the transmitting line is set to the extent that a room noise, etc. can be transferred to the other calling party, and anxiety for setting a channel is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an audio switch circuit, in particular, a variable loss circuit provided in each of the sending and receiving paths, and reducing the loss of both constant loss circuits. This invention relates to a voice switch circuit in a loudspeaker telephone that is controlled so that the value is always greater than a predetermined value.

In public address telephones, which use a microphone and a speaker instead of the handset in a normal telephone, a voice switch circuit is provided as a howling prevention means.

FIG. 1 is a diagram showing an example of an amplified IT telephone equipped with a conventional audio switch m't-. In FIG. ! The f signal is amplified by amplifiers 2 and 4 provided in the transmission path, and sent out to the line via a side sound protection circuit 1it-, such as a pipe lid coil, and transmitted to the other party's telephone. Further, a receiving signal received from the other party's telephone via the line is amplified by a variable amplifier 16 and an amplifier 13 provided in the receiving path, and drives the speaker 12. These microphones 1
Also, the distance between the speaker 12 and the caller is much larger than that of a normal handset, so it is difficult to maintain a good communication distance.
requires that amplifier 2.4.13 and variable amplifier 16 have high gain. As a result, unless there is some means tfs in the transmitting and receiving paths, the near-end to rounding gain, including the acoustic coupling between the loudspeaker 12 and the microphone 1 and the sidetone coupling in the side sound protection circuit 11; Or the acoustic coupling;
The far-end loop gain, including the acoustic coupling between the speaker and the microphone at the other party's telephone, becomes greater than 1, causing no-ring. In order to prevent the howling, an audio switch circuit is provided in FIG. 1, the main elements of which are variable loss circuits 3 and 14 inserted into the sending and receiving paths, and a comparator 8. The comparator 8 receives the envelope component (hereinafter referred to as the transmit signal level) of the transmit signal supplied from the variable loss circuit 5 , the amplifier 6 and the rectifier 7 and the envelope component (hereinafter referred to as the transmit signal level) of the transmit signal supplied from the variable loss circuit 15 , the amplifier IO and the rectifier 9 . The received signal level is compared with the envelope component of the received signal (hereinafter referred to as the received signal level). As a result, if it is determined that the transmitting signal level is higher than the receiving signal level, the comparator 8 sets the variable loss circuit 3 in the transmitting path to a low loss (for example, θ decibel),
The variable loss circuit 14 in the receiving path is connected to a high loss circuit (for example, 40
decibels) and puts the voice switch circuit into the transmitting state ◇ Also, when the comparator 8 determines that the receiving signal level is higher than the transmitting signal level, it sets the variable loss circuit 14 to a low loss (for example, θ decibels). Then, the variable loss circuit 1I13 is set to a high loss (for example, 40 decibels), and the voice switch circuit is placed in a receiving state. In addition, in both the transmitting state and the receiving state, the value of the loss # of the variable loss circuits 3 and 14 is set to a predetermined value so that the near-end to loop gain and the far-end to loop gain do not exceed 1. Since the level is maintained at 40 decibels or more (for example, 40 decibels), howling is prevented. Note that since the transmitting signal level and the receiving signal level during a call vary greatly due to room noise, line noise, etc., the comparator 8 is simple. When the variable loss circuits 3 and 14 are controlled based on the result of comparing both signal levels, a phenomenon occurs in which the voice switch circuit frequently switches between the transmitting state and the receiving state, which causes discomfort to the caller. As a countermeasure, the comparator 8 sets the variable loss circuits 5 and 15 as well as the variable loss circuits 3 and 14 to low loss or high loss, so that once the voice switch circuit is in the listening state t or the listening state, It has a so-called hysteresis characteristic that easily reverses the call state and releases the call.Therefore, even if the receive signal level of the loudspeaker telephone set to the receive state drops to the level of no call, the transmit signal remains at a sufficiently high level. The variable loss circuit 3 inserted in the transmission path is maintained at a high loss (for example, 40 decibels) unless the signal arrives.

As is clear from the above explanation, according to a conventional voice switch circuit, even when the other party who is talking to a loudspeaker telephone set to receive a call stops talking, the loudspeaker I
As long as the E-telephone caller does not start transmitting, the high-loss variable loss circuit 3 continues to be inserted into the transmission path, and indoor noise from the loudspeaker telephone side is not transmitted to the other caller, resulting in almost no sound. Otherwise, it will cause the other party to feel anxious about the communication path being cut off, etc.An object of the present invention is to eliminate the drawbacks of the conventional voice switch circuit as described above, and to enable the other party to make a call to the other party who has canceled the call. The goal is to realize a voice switch circuit that does not cause concerns such as road interruptions.

The purpose of this is to provide a loudspeaker telephone that is equipped with variable loss circuits in each of the sending path and the receiving path, and is controlled so that the total loss value of both variable loss circuits is always greater than a predetermined value. means for detecting a level difference between a transmitting signal sent to the receiving channel and a receiving signal inputted to the receiving channel, and a means for comparing the detected level difference with two predetermined reference values, large and small; When the level difference indicates an intermediate value between the two reference values, this is achieved by setting the variable loss circuit of the transmission path to a loss value greater than the loss value in the transmitting state and smaller than the loss value in the receiving state, Further, means is provided for comparing the transmitting signal input to the transmitting channel and the receiving signal input to the receiving channel with predetermined reference levels, and the transmitting signal in the transmitting state and the receiving signal in the receiving state are provided. Time reception 11
This is achieved by setting the variable loss circuit of the sending path to a loss value greater than the loss value when all signals are in the transmitting state and smaller than the loss value during the receiving state when all signals are below the reference level.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. FIGS. 2 and 3 each illustrate a loudspeaker telephone equipped with a voice switch circuit according to one embodiment of the present invention. Note that the same reference numerals indicate the same objects throughout the figures. In FIG. 2, the transmitting signal level supplied from the variable loss circuit 5, amplifier 6, and rectifier 7 and the receiving signal level supplied from the variable loss circuit 15, amplifier 10, and rectifier 9 are the positive and negative signals of the differential amplifier 23, respectively. Input to the phase input terminal and inverting input terminal. The result is differential amplification! 23 outputs a level difference Me between the transmitting signal level and the receiving signal level, and is transmitted to the high gain amplifier 8' and the two ratio IIR units 22 and 24. When the input level difference Me is positive, that is, when the transmitting signal level is higher than the receiving signal level, the high gain amplifier 8' operates on the variable loss circuit ll! 3' and 51 are set to low loss (for example, θ decibels), variable loss circuits 14 and 15 are set to high loss (for example, 40 decibels), and the voice switch circuit is placed in a transmitting state. Furthermore, when the input level difference Vc is negative, that is, when the receiving signal level is larger than the transmitting signal level, the high gain amplifier 8'
5 is set to low loss (for example, 0 decibels), variable loss circuits 3' and 5 are set to high loss (for example, 40 decibels), and the voice switch circuit is placed in a receiving state. On the other hand, the comparator 22 inputs a level difference Vct - upper limit reference level +
Compared with v1 and lower limit reference level 0, condition +V1)V
o) If 0 is established, the variable loss circuit 3' sets the auxiliary variable loss circuit 21 inserted in the transmitting path to a value larger than the low loss value (for example, O decibel) set during the transmitting state, and when the receiving state is in the receiving state. The loss value (for example, 20 decibels) is set smaller than the set high loss (for example, 40 decibels), and unless the condition +Vs > V a ) O is satisfied, the auxiliary variable loss circuit 21 is set to be lossless.

If the upper limit reference level +vI is set to a positive value that is sufficiently lower than the value indicated by the level difference Ve during transmitting, when the voice switch circuit is in the transmitting state and the transmitting signal level decreases, the transmitting path For example, the loss value inserted into
Increase to 0 dB.

Also, the comparator 24 converts the manually input level difference Va into the upper reference level O and the lower reference level -V! compared with condition 0)
If V c) - V is established, the variable loss circuit 3 inserted in the transmitting path must be greater than the low loss (for example, 0 decibel) set during the transmitting state, and the high loss set during the receiving state. The auxiliary variable loss circuit 25, which is set to a loss value (for example, 20 decibels) smaller than the loss (for example, 40 decibels) and inserted in the receiving channel, is set to a high loss value (for example, 20 decibels) that is set when the variable loss circuit 3' is in the receiving state. 40 decibels) and the currently set loss value (for example, 20 decibels) (20 decibels in this example).

On the other hand, if condition 0':)V O > Vt is not established, the comparator 24 sets the variable loss circuit 3' as controlled by the high gain amplifier A 8', and sets the auxiliary variable loss circuit 25 to no loss. do. If the lower limit reference level -v1 is set to a negative value that is sufficiently higher than the value indicated by the level difference ve at the time of receiving a call, the voice switch circuit will be in the receiving state, and if the receiving (No. 1 level) decreases, the transmitting The loss value inserted into the path increases, for example, from 40 decibels to 20 decibels.

As is clear from the above description, according to the present embodiment, when the level difference Vc indicates an intermediate value between the upper limit reference level of the comparator 22 +7 times and the lower limit reference level -vl of the comparator 24, the The variable loss circuit 3' and the auxiliary variable loss circuit 21q) fjj loss point value inserted into the channel are the variable loss circuit 3'
' is set to a value (for example, 20 decibels) that is larger than the low loss (for example, θ decibel) set during the transmitting state and smaller than the high loss (for example, 40 decibels) set during the receiving state. Therefore, even if the person using the loudspeaker telephone is talking or not, there is no risk that indoor noise, etc. will be transmitted to the other party, and the other party will have concerns about setting up the communication path. In the figure, the comparator 8 operates in the same manner as in FIG. Further, the transmit signal level and the receive signal level are also input to comparators 31 and 34, respectively.

The comparator 31 sets the level of the input transmission signal to the reference level V.
, and when the transmit signal level becomes equal to or lower than the reference level V, the output signal is transmitted to the AND circuit 32. In the AND circuit 32, the comparator 8 converts the variable loss circuit 3' to a low loss (
For example, when the transmitting state is set to θ dB), the comparator 3
When the output signal No. 1 is received, the auxiliary variable loss circuit 21t-variable loss circuit 3' inserted in the transmitting path will be set to a value larger than the low loss value (for example, 0 decibel) set during the transmitting state, and when the receiving state is in the receiving state. A loss value (for example, 20 decibels) K is set smaller than the set high loss value (for example, 40 decibels), and in other cases, the auxiliary variable loss circuit 211 is set to have no loss. If we now set the reference bell v to a positive value sufficiently lower than the transmitting signal level during transmission, the voice switch circuit is in the transmitting state and the transmitting signal level is at the reference level v.
When the loss value decreases below s, the loss value inserted into the transmission channel increases from θ decibels to 20 decibels, for example. Further, the comparator 34 converts the input reception signal level to a reference level v4.
When the receiving signal level becomes equal to or lower than the reference level v4, the output signal is transmitted to the AND circuit 33. When the comparator 8 receives the output signal of the comparator 34 in a receiving state in which the variable loss circuit 14 is set to low loss (for example, 0 decibels), the AND circuit 33 connects the variable loss circuit inserted in the transmission path. 3' is a loss value (for example, 0 dB) that is larger than the low loss (for example, 0 dB) set during the transmitting state and smaller than the high loss (for example, 40 dB) that is set during the high-talk state.
For example, 20 decibels), and the auxiliary variable loss circuit 25 inserted in the receiving path is set to a high loss value (for example, 40 decibels) set when the variable loss circuit 3' is in the listening state, and the currently set loss value ( Set it equal to the loss difference (for example, 20 decibels) from the current reference level V4, which is set equal to the loss difference (for example, 20 decibels). , the voice switch circuit is in the receiving state, and the giant receiving signal 1 novel is at the reference level V.

For a reduced c fit below, the loss value inserted into the transmission path is reduced from, say, 40 dB, and the reduced loss value (
20 dB), which increases the loss value inserted into the receiving channel.

As is clear from the above description, according to the present embodiment, when the voice switch circuit is in the receiving state and the yaw code level falls below the reference level v4, or when the voice switch circuit is in the transmitting state. In addition, when the transmitting signal level drops below the reference level V, the total loss value of the variable loss circuit 3' and the auxiliary variable loss circuit 21 inserted into the transmitting channel is determined by the variable loss circuit 3' 0, which is set to a value (for example, 20 decibels) that is larger than the low loss (for example, θ decibel) that is set during the receiving state and smaller than the high loss (for example, 40 decibels) that is set during the receiving state. Even when a call is not being made, there is no risk that indoor noise, etc. will be transmitted to the other party, making the other party anxious about setting up the communication route. This is only one example, and the loss values set for the variable loss circuits 3' and 14 and the auxiliary variable loss circuits 21 and 25 are not limited to those shown in the figure, and may be any other loss value. It is also possible to increase the value by setting , but the effect of the present invention does not change in either case.

Furthermore, the reference level +v, , -v, ,v, ,v,
is not limited to being set according to the level of indoor noise, line noise, etc., and many variations may be considered.
In any case, the effect of the present invention remains the same.According to the present invention, the loss value inserted into the transmission path when the caller of the single loudspeaker is not making a call is equal to Since the setting is set to an extreme level that can be transmitted to the other party, and the other party is prevented from being completely silent, it is possible to prevent the other party from feeling anxious about the setting of the communication path.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a public address telephone equipped with a conventional voice switch circuit, and FIG. 2 is a diagram showing a public address telephone equipped with a voice switch circuit according to an embodiment of the present invention.
FIG. 3 is a diagram showing a loudspeaker telephone equipped with a voice switching circuit according to another embodiment of the present invention. , 23 is a differential amplifier, 8' is a high gain amplifier, 3.3', 5.14 and 15
is a variable loss circuit, 21 and 25 are auxiliary variable loss circuits,
8.22.24.31 and 34 are comparators, 7 and 9
is a flow device, 11 is a side sound prevention circuit, 12 is a speaker, 32 and 33 are AND -; fr, Vc are level differences, +V is an upper limit reference level, -V is a lower limit reference level, vs and v4 are Indicates the standard level! 1 zuzu 7 zuen 3 zu

Claims (1)

[Claims] (1) In a loudspeaker telephone that is equipped with variable loss circuits in each of the sending and receiving paths, and is controlled so that the total loss of both variable loss circuits is always greater than a predetermined value, an input signal is input to the front delivery route. means for detecting a level difference between a transmitting signal sent to the receiving channel and a receiving signal manually inputted to the receiving channel, and a means for comparing the detected level difference with predetermined nine large and small two reference values, When the level difference indicates an intermediate value between the two reference values, the variable loss circuit of the transmitting channel is set to a loss value greater than a loss value in a transmitting state and smaller than a loss value in a receiving state. Audio switch circuit. (匈) In an audio switch circuit that is equipped with a variable loss circuit in each of the sending path and the receiving path, and is controlled so that the total loss value of both constant loss circuits is always equal to or higher than a predetermined value, Means is provided for comparing the receiving signal inputted to the receiving channel with nine predetermined standard levels, and the transmitting signal in the transmitting state and the receiving signal in the receiving state are respectively compared with the standard level. Audio switch circuit 0, characterized in that when the signal level is below the level, the variable loss circuit of the transmission path is set to be larger than the loss value in the transmitting state and smaller than the loss value in the receiving state.