JPH0533579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a public address telephone device, which is one form of telephone set, in which a conventional transmitter and receiver are replaced with a speaker and a microphone.

BACKGROUND TECHNOLOGY In recent years, loudspeaker telephone devices have become widely used because they have features such as allowing users to talk while their hands are free, as well as allowing small group conference calls to be held around a microphone. Ta. but,
If you simply replace the transmitter with a speaker and the receiver with a microphone, the acoustic coupling between the speaker and microphone and the loop created by the side sound protection circuit inside the phone may cause howling, making it impossible to make a call. .

As a prior art, for example, there is "S-1P type loudspeaker telephone" in Tsuken Jitsuho, Vol. 28, No. 3, pages 451 to 516.

Hereinafter, the conventional loudspeaker telephone as described above will be explained with reference to the drawings. In FIG. 9, reference numeral 90 is a variable gain circuit inserted into the communication circuit through which the reception signal is transmitted, and whose gain is changed by the control signal, and 91 is inserted into the communication circuit through which the transmission signal is transmitted, and whose gain is changed by the control signal. A variable gain circuit 92 compares the level of the received signal and the level of the transmitted signal and provides a control signal to the variable gain circuits 90 and 91. 93 is a side sound prevention circuit that performs 2-wire and 4-wire conversion. , 94 is a speaker for amplifying the reception signal, 95 is a microphone for inputting the transmission signal, 96, 97, 98, 99 are amplifiers, and 100 is a subscriber line.

The operation of the loudspeaker telephone device configured as described above will be described below.

First, subscriber line 100 and side sound protection circuit 93
When a reception signal is input via the comparator circuit 9
Since the level of the reception signal input to the receiver increases, the variable gain circuit 90 on the receiver side provides a gain of 1, and the variable gain circuit 91 on the transmitter side provides a gain of L (|L|<1). The comparison circuit 92 outputs the control signal. This circuit state is called the receiving state. In the receiving state, the received signal is not attenuated, but the transmitted signal is attenuated.

Next, when a voice is transmitted from the microphone 95, the level of the transmitted voice signal input to the comparison circuit 92 increases, so that the variable gain circuit 90 on the receiving side has a gain of L, and the variable gain circuit 91 on the transmitting side has a gain of L. Comparison circuit 92 outputs a control signal that provides a gain of 1.
This circuit state is called the transmitting state. In the transmitting state, the transmitting signal is not attenuated, but the receiving signal is attenuated. In addition, when a receiving signal and a sending signal are input at the same time, that is, a so-called simultaneous call, the comparison circuit 9
Both the level of the received signal and the level of the transmitted signal inputted to 2 become large, but when comparing the two, when the level of the received signal is higher than the level of the transmitted signal, the receiving state is entered, and the transmitted signal When the level of the signal is higher than the level of the receiving signal, the transmitting state is entered. Furthermore, when there is no signal in which neither a receive signal nor a transmit signal is input, the state is either a receive state or a transmit state, but in this example, priority is given to receive calls, so the description will be made assuming that the receive state is set. By attenuating the received signal or the transmitted signal in this way, the loop gain is lowered and howling is prevented.

Problems to be Solved by the Invention However, in the above method, during simultaneous calls, the signal with a higher level is not attenuated, and the signal with a lower level is attenuated. Priority is given to the other communication circuit, and the gain of the received signal and the transmitted signal is switched depending on the level change, resulting in intermittent conversation.Furthermore, when there is no signal, the conversation is in the receiving state, so There is no problem in inputting the signal, but it is difficult to input the transmitting signal, and there are problems in that the topic is easily disconnected.

In view of the above-mentioned problems, the present invention provides a loudspeaker telephone device that operates without interrupting the conversation during simultaneous calls, and has fewer disconnections at the beginning of the conversation when transitioning from a no-signal state to a receiving state or a transmitting state.

Means for Solving the Problems In order to achieve this object, the loudspeaker telephone device of the present invention includes a first variable gain circuit inserted into a speech circuit through which a reception signal is transmitted, and a first variable gain circuit through which a transmission signal is transmitted. A second variable gain circuit inserted into the speech circuit compares the levels of the receiving signal and the transmitting signal, and when the receiving signal level is higher than the transmitting signal level, outputs a receiving signal ON signal, and otherwise turns the receiving signal OFF. A receiving signal detection circuit that sends out a signal compares the levels of the receiving signal and the transmitting signal, and when the transmitting signal level is higher than the receiving signal level, it outputs a transmitting signal ON signal, and when it is not, it outputs a transmitting signal OFF signal. Based on the sending signal detection circuit to send, the receiving signal on signal or the receiving signal OFF signal, and the sending signal ON signal or the sending signal OFF signal,
It determines whether the receiving state is a transmitting state, a simultaneous call state, or a no signal state, and if it is determined that the receiving state is in the receiving state, a receiving state on signal is sent, and if it is determined that the calling state is in the sending state, a transmitting state on signal is sent simultaneously. comprising a gate circuit that sends a simultaneous call state/no signal state ON signal to the first variable gain circuit and the second variable gain circuit when it is determined that the call state is a call state or a no signal state;
When the gate circuit sends out a listening state ON signal, the gain of the first variable gain circuit is set to 1, and the gain of the second variable gain circuit is set to L (where |L|<
1), and when the gate circuit sends out a transmitting state ON signal, the gain of the first variable gain circuit is L and the gain of the second variable gain circuit is 1,
When the gate circuit sends out a simultaneous call state/no signal state ON signal, the gain of the first variable gain circuit and the second variable gain circuit are each set to L ^1/2 .

Effect With this configuration, during simultaneous calls, a gain of L ^1/2 is given to the received signal and the transmitted signal regardless of the levels of the received signal and the transmitted signal, and since they are attenuated by the same amount, Conversation will no longer be intermittent, and even when there is no signal, the received and transmitted signals are given a gain of L ^1/2 , and are attenuated by the same amount. Although speech-initial truncations occur when changing states, the amount is small. Further, in all states, the product of the gains of the two variable gain circuits is L, the loop gain is constant, and the howling prevention effect remains unchanged.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of a loudspeaker telephone system according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a variable gain circuit which is inserted into a communication circuit through which a reception signal is transmitted, and whose gain changes according to a control signal;
2 is inserted into the communication circuit through which the transmission signal is transmitted,
A variable gain circuit whose gain changes depending on the control signal; 3 a control circuit that provides a control signal to the variable gain circuits 1 and 2 based on the level of the received signal and the level of the transmitted signal; 4 a control circuit that performs 2-wire/4-wire conversion; A sidetone circuit, 5 is a speaker for amplifying the reception signal, 6 is a microphone for inputting the transmission signal, 7, 8, 9, and 10 are amplifiers, 11 is a subscriber line, and 12 is an output from the control circuit 3 in the reception state. 13 is a transmitting state control signal that is output from the control circuit 3 in the transmitting state and controls the variable gain circuits 1 and 2; 14 is a transmitting state control signal that controls the variable gain circuits 1 and 2; A simultaneous call state no signal state control signal is outputted from the control circuit 1 when there is a simultaneous call state or no signal state, and controls the variable gain circuits 1 and 2. 15 is a reception signal before gain control by the variable gain circuit 1, and is output from the control circuit. 3
Receiving side variable gain circuit input signal input to 16
17 is a receiving signal that has undergone gain control by the variable gain circuit 1, which is an output signal of the receiving side variable gain circuit that is input to the control circuit 3; 17 is a transmitting signal that has not been gain controlled by the variable gain circuit 2; 3 is a transmitting side variable gain circuit input signal, and 18 is a transmitting signal subjected to gain control by the variable gain circuit 2, and is a transmitting side variable gain circuit output signal inputted to the control circuit 3.

FIG. 2 shows a block diagram of a control circuit for a loudspeaker telephone system according to an embodiment of the present invention. In FIG. 2, 20 is a received signal detection circuit, 21 is a transmitted signal detection circuit, and 22 is a logic circuit that receives the outputs of the received signal detection circuit 20 and the transmitted signal detection circuit 21 and outputs a control signal. 23 is a reception state control signal that is output from the gate circuit 22 and indicates the reception state; 24 is a transmission state control signal that is output from the gate circuit 22 and indicates the transmission state; 25 is an output from the gate circuit 22; 26 is a receiving side variable gain circuit input signal, 27 is a receiving side variable gain circuit output signal, and 28 is a transmitting side variable gain circuit input signal. ,2
Reference numeral 9 indicates the output signal of the variable gain circuit on the transmitting side.

FIG. 3 shows a block diagram of the reception signal detection circuit 20 of this embodiment. In FIG. 3, 30 is a rectifying and smoothing circuit, 31 is a rectifying and smoothing circuit, 32 is a differential amplifier for determining the difference between the outputs of the rectifying and smoothing circuits 30 and 31, and 3 is a rectifying and smoothing circuit.
3 is a comparator that compares the output of the differential amplifier 32 with a certain threshold value; 34 is a receiving side variable gain circuit input signal;
35 is a variable gain circuit output signal on the transmitting side, 36 is a variable resistor that multiplies the output of the rectifying and smoothing circuit 31 by the rate at which the transmitting signal leaks to the receiving side, and 37 is a differential amplifier 32.
This is a variable resistor that creates a voltage to be compared with the output of the .

FIG. 4 shows a block diagram of the transmission signal detection circuit 21 of the loudspeaker telephone device in this embodiment. In FIG. 4, 40 is a rectifying and smoothing circuit, 41 is a rectifying and smoothing circuit, 42 is a differential amplifier for determining the difference between the outputs of the rectifying and smoothing circuits 40 and 41, and 43 is for comparing the output of the differential amplifier 42 with a certain threshold value. a comparator; 44 is a variable gain circuit input signal on the transmitting side; 45 is an output signal from the variable gain circuit on the receiving side; 46 is a variable resistor that multiplies the output of the rectifying and smoothing circuit 41 by the rate at which the receiving signal leaks to the transmitting side;
47 is a variable resistor that creates a voltage to be compared with the output of the differential amplifier 42.

FIG. 5 is a circuit diagram of the gate circuit of this embodiment. In FIG. 5, 50 is a received signal detection circuit output signal which is the output of the received signal detection circuit, 51 is a transmitting signal detection circuit output signal which is the output of the transmitting signal detection circuit, 52 is a receiving state control signal, and 53 is a receiving state control signal. 54 is a simultaneous call state control signal; 54, 57, 58 are NOT circuits; 55, 5 are
9 is an AND circuit, and 56 is an EXCLUSIVE-OR circuit.

FIG. 6 shows a circuit diagram of the variable gain circuit on the receiver side of this embodiment. In Fig. 6, 60 is an operational amplifier (hereinafter abbreviated as OP amplifier), 61
a, 61b, 61c are MOS field effect transistors (hereinafter abbreviated as MOSFET), 62, 63a,
63b, 63c, 64a, 64b, 64c are resistors, 65a, 65b, 65c are capacitors, 66
67 is a receiving state control signal, 67 is a transmitting state control signal,
Reference numeral 68 is a simultaneous call state no signal state control signal.

FIG. 7 shows a circuit diagram of the variable gain circuit on the transmitting side of this embodiment. In Figure 7, 70 is an OP amplifier,
71a, 71b, 71c are MOSFETs, 72, 7
3a, 73b, 73c, 74a, 74b, 74c
is a resistor, 75a, 75b, 75c are capacitors,
76 is a transmitting state control signal, 77 is a receiving state control signal, and 78 is a simultaneous talking state and no signal state control signal.

The operation of the loudspeaker telephone device configured as described above will be described below.

First, when a receiving signal is input via the subscriber line 11 and the side sound protection circuit 4, the level of the receiving side variable gain circuit input signal 15 inputted to the control circuit 3 increases, so that the control circuit 3 It is determined that the call is in the receiving state, and "1" is set as the receiving state control signal 12.
"0" is output as the transmitting state control signal 13, and "0" is output as the simultaneous call state no signal state control signal 14. As a result, the gain of the variable gain circuit 1 on the receiver side is 1, and the gain of the variable gain circuit 1 on the transmitter side is L (|L|
<1), the received signal is not attenuated, but the transmitted signal is attenuated.

Next, when a transmitting signal is input from the microphone 6, the level of the transmitting-side variable gain circuit input signal 17 input to the control circuit 3 increases, so the control circuit 3 determines that the transmitting state is established. "0" as the receiving state control signal 12, "1" as the transmitting state control signal 13, simultaneous talking state no signal state control signal 1
Outputs "0" as 4. As a result, the gain of the variable gain circuit 1 on the receiver side becomes L, and the gain of the variable gain circuit on the transmitter side becomes 1, so that the transmitting signal is not attenuated, but the receiving signal is attenuated.

In addition, when a receiving signal is input via the subscriber line 11 and the side sound protection circuit 4, and a transmitting signal is further input from the microphone 6, that is, a so-called simultaneous call, the receiving side variable gain is input to the control circuit 3. Since the levels of the circuit input signal 15 and the transmitting side variable gain circuit input signal 17 increase, the control circuit 3
is judged to be a simultaneous call state, and the receive state control signal 1 is sent.
2, “0” is set as the transmitting state control signal 13, “0” is set as the transmitting state control signal 13, and “0” is set as the transmitting state control signal 13.
outputs "1" as As a result, the gain of the variable gain circuit 1 on the receiving side becomes L ^1/2 and the gain of the variable gain circuit 2 on the sending side becomes L ^1/2 , and both the received signal and the transmitted signal are attenuated by the same amount.

Furthermore, neither the receiving signal nor the sending signal is input.
In the so-called no-signal state, the levels of the input signals to the control circuit 3 are all low, so the control circuit 3 determines that there is no signal and outputs "0" as the receiving state control signal 12 and transmitting state control signal 13. “0” as
"1" is output as the simultaneous call state no signal state control signal 14. As a result, the gain of the variable gain circuit 1 on the receiving side becomes L ^1/2 and the gain of the variable gain circuit 2 on the sending side becomes L ^1/2 , and both the received signal and the transmitted signal are attenuated by the same amount.

The timing chart for these series of operations is shown in
As shown in the figure.

In the control circuit 3, as shown in FIG.
Based on the level of the variable gain circuit output signal 29 on the transmitting side, it is determined whether there is a received signal. If it is determined that the received signal is present, it outputs "1" to the gate circuit 22, and if the received signal is not present, it outputs "1" to the gate circuit 22. If it is determined, “0” is output to the gate circuit 22. The transmitting signal detection circuit 21 determines whether or not there is a transmitting signal based on the levels of the transmitting side variable gain circuit input signal 28 and the receiving side variable gain circuit output signal 27, and when it is determined that the transmitting signal exists, Gate circuit 2
2 and outputs "0" to the gate circuit 22 if it is determined that there is no transmitting signal. The gate circuit 22 outputs a receive state control signal 23, a transmit state control signal 24, and a simultaneous talk state no signal state control signal 25 based on the outputs of the receive signal detection circuit 20 and the send signal detection circuit 21.

In the receiving signal detection circuit 20, as shown in FIG.
side input, and transmitting side variable gain circuit output signal 35
is smoothed by a rectifying and smoothing circuit 31 and then connected to a variable resistor 36.
After being multiplied by the rate at which the transmitting signal leaks to the receiving side, the signal is input to one side input of the differential amplifier 32.
This is to cancel the transmitting signal that has leaked to the receiving side via the side sound protection circuit 4, and the output of the differential amplifier 32 outputs a value close to the true receiving signal level. When the output of the differential amplifier 32 is at a higher level than the voltage determined by the variable resistor 37, the comparison circuit 33 assumes that a reception signal exists and outputs "1"; otherwise, the reception signal does not exist. It is assumed that this is not the case and outputs “0”.

In the transmitting signal detection circuit 21, as shown in FIG.
The receiving side variable gain circuit output signal 45 is smoothed by the rectifying and smoothing circuit 41, multiplied by the rate of leakage of the receiving signal to the transmitting side by the variable resistor 46, and then sent to the one side input of the differential amplifier 42. is input. This is to cancel the received signal that has leaked to the transmitting side via the speaker 5 and microphone 6, and the output of the differential amplifier 42 outputs a value close to the true transmitting signal level. Comparison circuit 43
When the output of the differential amplifier 42 is at a level higher than the voltage determined by the variable resistor 47, it is assumed that a transmission signal exists and outputs "1", and otherwise it is determined that there is no transmission signal. and outputs “0”.

As shown in FIG. 5, the gate circuit 22 outputs "1" as the receiving state control signal 52 when the receiving signal detecting circuit output signal 50 is "1" and the transmitting signal detecting circuit output signal 51 is "0". It outputs "0" as the transmitting state control signal 53 and "0" as the simultaneous call state control signal 54. When the receive signal detection circuit output signal 50 is "0" and the transmit signal detection circuit output signal 51 is "1", the receive state control signal 52 is "0" and the transmit state control signal 53 is "1".
"0" is output as the simultaneous call state no signal state control signal 54. Receiving signal detection circuit output signal 5
When 0 is "1" and the output signal 51 of the transmitting signal detection circuit is "1", or when the output signal 50 of the receiving signal detecting circuit is "0" and the output signal 51 of the transmitting signal detecting circuit is "0", the receiving signal is “0” as the state control signal 52
, "0" as the transmitting state control signal 53, and "1" as the simultaneous calling state wireless signal state control signal 54.
Output.

As shown in FIG. 6, the receiving side variable gain circuit 1
When the receiving state control signal 66 is “1”, the gain is 1.
When the transmitting state control signal 67 is "1", the gain is L, and when the simultaneous talking state control signal 68 is "1", the gain is L ^1/2 .
So that the resistance value is 62:63a:63b:
63c is 1:1:L ^-1 :L ^-1/2 . The receiving state control signal 66, the transmitting state control signal 67, and the simultaneous talking state no signal state control signal 68 are connected to the resistors 64a and 64.
b, 64c and capacitors 65a, 65b, 65c
smoothed by an integrator circuit composed of
Since it is added to the gates of MOSFETs 61a, 61b, and 61c, the gain changes smoothly.

As shown in FIG. 7, the transmitting side variable gain circuit 2
When the transmitting state control signal 76 is “1”, the gain is 1.
When the receiving state control signal 77 is "1", the gain is L, and when the simultaneous talking state no signal state control signal 78 is "1", the gain is L ^1/2.
The resistance values 72:73a:73b:
73c is 1:1:L ^-1 :L ^-1/2 . The transmitting state control signal 76, the receiving state control signal 77, and the simultaneous talking state no signal state control signal 78 are connected to the resistors 74a and 74.
b, 74c and capacitors 75a, 75b, 75c
smoothed by an integrator circuit composed of
Since it is added to the gates of MOSFETs 71a, 71b, and 71c, the gain changes smoothly.

As described above, according to this embodiment, the gains of the variable gain circuits 1 and 2 are set to L ^1/2 in the simultaneous call state.
Therefore, the gain on the receiving side and the gain on the transmitting side will not change due to changes in the level of the receiving signal and the transmitting signal, so there will be no interruptions in mutual conversation, and the conversation with the higher level will not change. There is no priority given to the circuit. In addition, in the no-signal state, the gains of variable gain circuits 1 and 2 are set to L ^1/2 , respectively.
Therefore, when changing from a no-signal state to a receiving state or a transmitting state, the gain of the variable gain circuit of the active communication circuit changes from L ^1/2 to 1, so
There is less truncation at the beginning of the speech than when changing from L to 1. Furthermore, the received signal detection circuit 20 cancels the leakage of the transmitted signal to the receiving side, and the transmitted signal detection circuit 21 cancels the leakage of the received signal to the transmitting side. can be detected with high accuracy. In the variable gain circuits 1 and 2, the receiving state control signal 12, the transmitting state control signal 13, and the simultaneous talking state no signal state control signal 14 are connected to resistors 64a, 64b, 64c, 74a, 74b,
74c and capacitors 65a, 65b, 65c, 7
5a, 75b, 75c, and MOSFETs 61a, 61b, 61c, 71
a, 71b, and 71c, gain control can be performed smoothly.

Effects of the Invention The present invention has a steady gain of 1 on the receiver side and the transmitter side.
A variable gain circuit that can be selected from three types, L ^1/2 and L (|L|<1), is provided, and the gain of the gain control circuit on the receiver side and the gain of the gain control circuit on the transmitter side are set. 1 and L for listening state, L and 1 for sending state, L ^1/2 and L ^1/2 for simultaneous call state, and L ^1/2 and L ^1/2 for no signal state, respectively. By providing a gate circuit that performs control, during simultaneous calls, the attenuation amount on the receiving side and the sending side is constant, so the calling circuit with the higher level is given priority, and the conversation is interrupted due to changes in the level of the receiving and sending calls. There is no intermittent interruption, and when there is no signal, the amount of attenuation can be divided by L ^1/2 between the receiving side and the sending side, so when a signal is input, the amount of attenuation at the beginning of the line is reduced, and Since the loop gain is constant in all states, the howling margin can be obtained equally, etc.
It is possible to realize a loudspeaker telephone device that can obtain a number of excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a loudspeaker telephone device according to an embodiment of the present invention, FIG. 2 is a block diagram of a control circuit of the same loudspeaker telephone device, FIG. 3 is a block diagram of the received signal detection circuit, and FIG. Figure 5 is a block diagram of the transmission signal detection circuit, and Figure 6 is a circuit diagram of the gate circuit.
The figure is a circuit diagram of a variable gain circuit on the receiving side of the same loudspeaker telephone device, FIG. 7 is a circuit diagram of a variable gain circuit on the transmitting side of the same loudspeaker telephone device, and FIG. 8 is the timing of gain control of the same loudspeaker telephone device. FIG. 9 is a block diagram of a conventional loudspeaker telephone system. 1... Variable gain circuit, 2... Variable gain circuit, 3
... Control circuit, 4 ... Side sound protection circuit, 20 ... Receiving signal detection circuit, 21 ... Transmission signal detection circuit, 22
... Gate circuit, 30, 31, 40, 41 ... Rectification and smoothing circuit, 32, 42 ... Differential amplifier, 33,
43... Comparator.

Claims (1)

[Claims] 1. A first variable gain circuit inserted into a speech circuit through which a reception signal is transmitted, a second variable gain circuit inserted into a transmission circuit through which a transmission signal is transmitted, and a level of the reception signal and transmission signal. and a receiving signal detecting circuit which sends a receiving signal ON signal when the receiving signal level is higher than the transmitting signal level, and otherwise sends a receiving signal OFF signal, and comparing the levels of the receiving signal and the transmitting signal, a transmitting signal detection circuit that transmits a transmitting signal on signal when the transmitting signal level is higher than the receiving signal level, and transmitting a transmitting signal off signal when the transmitting signal level is higher than the receiving signal level; Based on the transmitting signal on signal or the transmitting signal off signal, it is determined whether the receiving state is the receiving state, the transmitting state, the simultaneous speaking state, or the no signal state, and when it is determined that the receiving state is the receiving state, the receiving state signal is transmitted. When it is determined that the talking state is present, a transmitting state ON signal is sent to the first variable gain circuit and the second variable gain circuit. and a gate circuit that sends a signal to a variable gain circuit, and when the gate circuit sends out a listening state ON signal, the gain of the first variable gain circuit is set to 1, and the gain of the second variable gain circuit is set to L. (However, |L|<
1), and when the gate circuit sends out a transmitting state ON signal, the gain of the first variable gain circuit is L and the gain of the second variable gain circuit is 1,
A loudspeaker telephone characterized in that when the gate circuit sends out a simultaneous call state/no signal state ON signal, the gains of the first variable gain circuit and the second variable gain circuit are each set to L ^1/2 . Device.