JPS58162157A - Loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To expand the operation range of an automatic loss control type voice switch circuit and to minimize insertion loss, by preventing the hysteresis width of the voice switching circuit from being negative in accordance with the degree of volume control of a receiving circuit. CONSTITUTION:In receiving status, a transmitted voice is once inputted to a control circuit 10, then returned to a receiving input by the revolution of a protective side voice circuit and inputted to the control circuit 10 again through a betaALS circuit 5. By two input signals, the control circuit 10 increases the gain of the betaALS circuit 5 up to the minimum value required for the prevension of howling. Since an output from a speaker 19 is generated in a microphone terminal input 1 also in the receiving status, the control circuit 10 can use the gain of an alphaALS circuit 3 for the prevension of howling and, therefore, increases the gain up to the necessary minimum value. In this case, the control circuit 10 limits the maximum value of the alphaALS circuit 3 so that the generation of negative hysteresis can be prevented at the time of large volume.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a public address telephone for making calls using a microphone and a speaker.

Because loudspeaker telephones have microphones and speakers placed relatively close together, this creates acoustic coupling.

Also, sidetone coupling occurs due to the two-wire and four-wire conversion circuit. Therefore, it is necessary to take some kind of preventive measures. Conventionally, an audio switch circuit is generally used for this purpose. This audio switch circuit compares the level of the transmitting signal coming in from the microphone with the level of the receiving signal coming in from the line, and reduces the loss on either the transmitting side or the receiving side of the communication circuit. This prevents howling. In order to make simultaneous calls as natural as possible using this voice switch circuit, the loss of the voice switch circuit must be minimized. However, in the case of a loudspeaker telephone, the operating conditions of the loudspeaker telephone that determine the large loss in the voice switching circuit vary widely, so it is not possible to determine the minimum necessary large loss.

To solve this problem, an automatic loss control type voice switch circuit that automatically controls the loss of the voice switch circuit according to the usage conditions of the loudspeaker telephone and operates with the minimum amount of loss necessary to always prevent howling. (hereinafter referred to as "rALS circuit") is known.

Here, FIG. 1 shows the control characteristics of the audio switch circuit.

The control characteristics of an audio switch circuit are generally represented by static characteristics (switching characteristics) as shown in FIG. In Figure 1, α
indicates a transmitting area, which represents an area where a loss is caused to the receiving side, and a transmitting signal is transmitted. β indicates a receiving area, which represents an area where loss is caused to the transmitting side, and the receiving signal is transmitted to the speaker. In addition, γ indicates the hysteresis region, and in the case of a circuit with a positive hysteresis width, a so-called hysteresis operation is performed to maintain the state before entering this region, and in the case of a circuit with a negative hysteresis width, the circuit enters the transmitting state. Performs unstable operation that periodically repeats the receiving state.

Therefore, if there is a negative hysteresis region, the speech becomes unnatural when the voice switch circuit is switched.

That is, the microphone picks up the sound emitted from the speaker in the state of the receiving area β (receiving state), the control circuit determines that a transmitting signal has been input, and switches to the state of the transmitting area α. A blocking phenomenon occurs in which the receiver becomes unable to remain in the receiving state, and a blocking phenomenon occurs in which the transmitting state is switched to the receiving state due to a receiver's input signal due to sidetone coupling. In order to prevent this, it is necessary to move the switching line of the control circuit's switching characteristics to the side where it is difficult to switch to the transmitting state when in the receiving state, and to the direction where it is difficult to switch to the receiving state when in the transmitting state. In other words, it is necessary to widen the hysteresis width.

However, if you widen the hysteresis width in this way, it will change from the receiving state (or transmitting state) to the transmitting signal (or receiving signal).
Even if the caller joins to interrupt, it is difficult to switch to the transmitting state (or the receiving state) at high speed. Even if it were possible to switch, the beginning of the interrupted signal would be cut off, making the conversation unnatural.

Therefore, it is desirable to have switching characteristics that do not cause blocking and have the minimum hysteresis width.

In this way, the circuit can be simplified by making the hysteresis width the same as the large loss in the communication path, and the margin against blocking can be controlled in a variable manner depending on the state. In this way, when the ALS circuit operates, the hysteresis width decreases, so in order to prevent a negative hysteresis region, the maximum amount of the ALS circuit can be adjusted up to the dashed line as shown in the switching characteristics in Figure 1. must be limited to. If a sound volume control circuit is installed in a wave phone, the loss will increase as the volume increases, and the hysteresis width will increase accordingly.

For this reason, the line that switches from receiving to transmitting changes depending on the volume.

FIG. 2 shows a case where the maximum amount of the ALS circuit is limited to prevent negative hysteresis when the volume is low. In this case, when the volume is increased, even if the ALS circuit operates, the range where negative hysteresis is likely to occur remains as a positive hysteresis region, and such a large loss is the minimum amount necessary to prevent howling. The loss increases by p, and the extra hysteresis width deteriorates the interrupt characteristics. Therefore, there is a drawback that the conversation at the time of switching becomes unnatural when the tone 1-adjustment becomes louder.

FIG. 3 shows a case where the maximum amount of the ALS circuit is limited so that negative hysteresis cannot occur when the volume is high. In this case, when the volume is reduced, a negative hysteresis region as shown by diagonal lines in FIG. 3 occurs, resulting in unstable operation in which the transmitting state and the receiving state are periodically repeated. Therefore, this case has the disadvantage that when the volume is low, the conversation during switching becomes unnatural.

The present invention improves this point, and the A
The TJS circuit allows the maximum amount of loss reduction or the input to the control circuit to be controlled, and even when the volume is changed, negative hysteresis is achieved with the minimum loss necessary to prevent nodding. It is an object of the present invention to provide a public address telephone that does not cause interference.

The present invention provides a public address telephone including an automatic loss control type voice switch circuit in a transmitting path and/or a receiving path, in which the hysteresis width of the voice switching circuit does not become negative at least in accordance with the volume adjustment of the receiving circuit. It is characterized by being configured as follows.

Further, it is preferable that the path of the signal that controls the audio switch circuit includes a circuit that limits the maximum value of the control signal that reduces loss by varying the magnitude of acoustic coupling in accordance with the magnitude of volume adjustment.

Further, it is preferable that the input of the control circuit of the audio switch circuit includes a gain change circuit that makes the hysteresis width variable depending on the magnitude of the volume adjustment.

An embodiment of the present invention will be described based on the drawings.

FIG. 4 is a block diagram of main parts of the first embodiment of the present invention. The loudspeaker circuit shown in Fig. 4 is equipped with a transmitting system, a receiving system, and communication paths for transmitting and receiving, respectively, and by switching the two communication paths according to the transmitting state and the receiving state, It is constructed to always reduce the necessary loss in the communication path in order to prevent howling.

That is, the microphone end input 1 is connected to the transmitting system transmitting amplifier 2 and also to the aALS circuit 3. The output of this αAL13 circuit 3 is led to a reciprocal volume adjustment circuit 4. The output of this reciprocal volume adjustment circuit 4 is led to the βALE1 circuit 5. The output of this βALS circuit 5 is led to a transmission system attenuator 6. The output of the transmitting system attenuator 6 and the output of the transmitting system transmitting amplifier 2 are led to a communication path changeover switch 7, respectively. A transmission output (a) is sent from this communication path changeover switch 7. Further, in FIG. 4, reference numeral 9 denotes a control input/transmission system changeover switch. The output of a control circuit 10 is led to this control input transmission system changeover switch 9. The other output of this control circuit IO is led to a limiting circuit 11. The output of this limiting circuit 11 is the αAL8
The noise is guided by circuit 3. Another output of this control circuit 10 is a switching control signal (C). Here, the αA18 circuit is
It is a circuit that reduces loss by the amount of reduction in acoustic coupling, and βAL
The s-circuit is a circuit that reduces loss by the amount of reduction in coupling caused by the side sound protection circuit.

Further, in FIG. 4, (b) is a reception input, and this reception input (b) is led to the reception system attenuator 13. The output of this receiver system attenuator 13 is led to the βALE circuit 5'.

The output of this βALS circuit 5' is led to an αALS circuit 3'. Further, the receiving input (b) is led to a receiving amplifier 16 of the receiving system. The output of the receiver amplifier 16 is led to a volume control circuit 17. The outputs of this volume control circuit 17 and the αALS circuit 3' are led to a receiving system communication path changeover switch 18, respectively. A speaker 19 is connected to this receiving system communication path changeover switch 18 . 2.degree. is a control input receiving system selector switch, to which the output of the control circuit 10 is led.

In addition, the volume adjustment circuit 17 is a circuit that changes the receiving volume according to volume adjustment by manual control, and the reciprocal volume adjustment circuit 4 is configured to provide reciprocal losses in conjunction with this volume adjustment circuit 17. The limiting circuit 11 is configured to change in conjunction with this volume adjustment, and when the volume of the received voice output is adjusted to a high level, the αALS circuit 3' operates at a high level, and when the volume is adjusted to a low level, the αALS circuit 3' operates at a low level as well. It is configured as follows. This is a feature of the present invention.

FIG. 5 is a diagram showing the switching characteristics of the circuit shown in FIG. 4. The horizontal axis shows the human power level of the receiver [dB], and the vertical axis shows the human power level of the speaker [dB].

In addition, the input switch (9, 20) to the control circuit 10 and the communication path changeover switch (7, 18) are interlocked.
It is operated by a switching control signal.

In this configuration, first in the transmitting state, each switch is connected to the T side shown in FIG. 4, and a loss is introduced into the receiving system. In this state, the transmitted voice is once input to the control circuit 10, and then returned to the receiver's power through the side sound protection circuit and inputted to the control circuit 10 through the βALS circuit 5. These two input signals cause the control circuit 1° to increase the gain of the βALS circuit 5 by the minimum value necessary to prevent howling.

The switching characteristic at this time is that the switching line from transmitting to receiving (T-+R) is moved to the left as far as the dashed-dotted line, as shown in FIG. When the control of βAL8 exceeds this line, the control circuit 10 stops proceeding with the control.

In the receiving state, each switch is connected to the R side shown in FIG. 4, and there is a loss in the transmitting system. In this state, the receiver's power (b) from the receiver system to the control circuit 10 is
) is input through the volume control circuit 17, so depending on the volume, the switching line (VOL large R-+
T, VOL small R-+ T) moves. Also speaker 1
A reception signal generated from the speaker 19 is generated at the microphone end input 1 by acoustic coupling between the speaker 19 and the microphone, and is inputted to the control circuit 10 through the αALS circuit 3. These two input signals cause the control circuit 19 to increase the gain of the αALE1 circuit 3 to the minimum value necessary to prevent howling. If only this were done, the switching characteristics would be similar to those of the conventional example shown in FIG. 2 or 3. Therefore, control circuit 1
0, as shown in Fig. 3, the maximum amount of the αALS circuit 3 is limited so that negative hysteresis does not occur when the volume is high, and even when the volume ratio is reached in the next limiting circuit 11, as shown in Fig. 3. The control signal to the αALs circuit 3 is controlled in accordance with the volume adjustment signal (,i) so as not to advance the control to the negative hysteresis region control.

Therefore, as shown in the switching characteristics of FIG. 5, the maximum amount of αALEI is limited by the same dot-dashed line in the switching line from receiving to transmitting, regardless of whether the volume is high or low. For this reason, negative hysteresis occurs when the volume is changed, and positive hysteresis width occurs even when ALE control is sufficiently advanced, causing a loss greater than the minimum loss necessary to prevent howling. I don't see many people on the street.

By preventing negative hysteresis in this way, A
Since the operating range of Ls can be widened and large losses can be reduced correspondingly, a loudspeaker telephone with good simultaneous conversation performance can be constructed.

FIG. 6 is a block diagram of main parts of a second embodiment of the present invention. This second embodiment is implemented under conditions of use where acoustic coupling is weak. Compared to the first embodiment shown in FIG. 4, the aAL circuits 3 and 3' are omitted, and the variable gain circuit 21 is connected to the circuit that inputs the signal to the control circuit from the communication path during reception of the reception system. The feature is that a volume control signal (d) is guided to this variable gain circuit 21, and the gain of this variable gain circuit 21 is controlled by changing the volume.

Other points are the same as those of the first embodiment shown in FIG. 4, so repeated explanation will be omitted.

In other words, since the acoustic coupling is weak, the aAL circuit is not used, and the loss is reduced accordingly. Therefore, the maximum amount of αALS circuits cannot be limited as in the first embodiment. For this reason, one possible method is to limit the maximum amount of the pALS circuit 5.5', but with this method, the switching line when the βALS circuit is fully activated may shift due to changes in volume. Interruptions when receiving calls or interrupts when sending calls become better or worse. Therefore, the control circuit 10
A variable gain circuit 21 that changes the gain according to changes in volume is provided on the input line to the input line. The relationship between the gain of this circuit and the switching diagram is such that when the volume is high or medium, the gain is OdB, and when the volume is low, the gain of the variable gain circuit 21 is increased to maintain the medium level.

FIG. 7 is a diagram showing switching characteristics according to the second embodiment.

With such a circuit configuration, negative hysteresis will not occur even if the volume becomes low when βAL8 is activated and the control has progressed to the point where the switching line from transmitting to receiving is indicated by the dashed line in FIG. In addition, the maximum gain of the variable gain circuit 21 is suppressed to prevent malfunctions caused by sound to the control circuit 10 due to input from the human power of the transmitter when receiving a call, so that when the volume is high, the switching line from receiving to transmitting moves. Therefore, even with a simplified circuit of αAL8, negative hysteresis can be prevented by controlling the input to the control circuit 10 according to the volume, widening the operating range of ALE, and providing a loudspeaker telephone with stable interrupt characteristics and good simultaneous talk performance. Can be configured.

As explained above, according to the present invention, in the ALS circuit, the maximum value of the control amount is limited depending on the magnitude of the volume adjustment. Furthermore, the input signal to the control circuit that performs the switching operation of the audio switch is limited depending on the magnitude of the volume adjustment.

Therefore, the maximum amount of the ALS circuit or the input to the control circuit can be controlled according to the volume adjustment, and even when the volume is changed, a negative hysteresis region is generated with the minimum loss necessary to prevent howling. Never. Therefore, the call quality at the time of switching can be improved regardless of changes in volume.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing switching characteristics of a conventional example without a sound adjustment circuit. FIGS. 2 and 3 are diagrams showing switching characteristics of a conventional example when a volume control circuit is provided. FIG. 4 is a block diagram of main parts of the first embodiment of the present invention. FIG. 5 is a diagram showing the switching characteristics of the above embodiment. FIG. 6 is a block diagram of main parts of a second embodiment of the present invention. FIG. 7 is a diagram showing the switching characteristics of the above embodiment. ■...Microphone end input, 2...Talking system transmitting amplifier, 3
．． 3'... αALS circuit, 4... Reciprocal volume adjustment circuit, 5.5'... βALS circuit, 6... Transmission system attenuator, 7... Call path selection switch, 9... Control input transmitting system changeover switch, 10... Control circuit, 11... Limiting circuit, 13... Receiving system attenuator, 16... Receiving system receiving amplifier, 17... Volume adjustment circuit, 18. ...Reception system communication path changeover switch, 20...Control input reception system changeover switch. Patent applicant representative patent attorney Takami Ide 1 VO 2 people, VOL + h Listener's power [dB] (Speaker power level [:dB] -304- Product humiliation [9p] 1/, (1clV? g.

Claims (3)

[Claims] (1) In a public address telephone that includes an automatic loss control type voice switch circuit in the transmitting path and/or the receiving path, the hysteresis width of the voice switch circuit should not become negative at least in accordance with the magnitude of the volume adjustment of the receiving circuit. A public address telephone set up in (2) Claim (1) includes a circuit for limiting the maximum value of the control signal that reduces loss by varying the magnitude of acoustic coupling in accordance with the magnitude of volume adjustment in the path of the signal that controls the audio switch circuit. public address telephone. (3) A loudspeaker telephone according to claim (1), which includes a gain change circuit that makes the hysteresis width variable depending on the magnitude of the volume adjustment, at the input of the control circuit of the audio switch circuit.