JPH0439258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a loudspeaker telephone device that enables simultaneous two-way communication by loudspeaker.

[Prior Art] Telephones with a loudspeaker calling function are a means of calling that has many advantages, such as allowing a large number of people to participate in a call without having to hold their hands.

However, to date, this type of telephone (speaker phone) has been put into practical use with an alternate call system.

This is because when a speaker and a microphone that are close to each other are driven at the same time, the sound from the speaker goes around to the microphone, causing an acoustic difference between the speaker that emits received information and the microphone that receives transmitted information. This is because a strong coupling occurs and so-called howling occurs.

For example, there is a technique disclosed in Japanese Patent Application Laid-open No. 42345/1983 to prevent such howling phenomenon.

However, in the conventional technology described above, in order to prevent howling caused by the mixing of the received signal from the speaker with the original transmitted signal from the microphone, it is necessary to cancel the received signal (cancellation processing). , the level of the canceling signal is adjusted using the training signal, paying attention only to the level of that signal. Therefore, the problem remains that the configuration of the device becomes extremely complicated and the cost increases.

[Means for Solving the Problem] The present invention includes a speaker that outputs a received signal from a telephone line as audio, a microphone that inputs audio including the sound generated from the speaker, and inverts the phase of the input to the microphone. In a loudspeaker telephone device comprising an inverting circuit and an output circuit that simultaneously outputs the inverted input and the received signal to a telephone line, the voltage level of the received signal between the telephone line and the speaker is within a predetermined range. In other words, there is a discrimination circuit that determines whether the voltage level is within a range that does not cause distortion in the speaker sound, and if it is within a predetermined range, it supplies that voltage level to the speaker, and if it exceeds the predetermined range, it attenuates the voltage of the received signal. The present invention attempts to solve the above-mentioned conventional problems with a simple configuration of providing a speaker operating circuit for supplying a signal to the speaker.

[Function] In this invention, when the voltage level of the reception signal between the telephone line and the speaker is within a predetermined range,
The phase of the audio signal input to the microphone is alternated by an inverting circuit, and outputted to the telephone line by an output circuit, where a receiving signal from the other party and a transmitting signal input at the same time as the inverted receiving signal are transmitted on the line. As a result, the received signal is canceled out and howling is prevented.

Further, if the discrimination circuit determines that the voltage level of the reception signal exceeds the above range, the voltage level is attenuated to an appropriate value by the speaker operating circuit to perform appropriate cancellation.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to FIGS. 1 to 5.
This will be explained based on the diagram.

FIG. 1 is a diagram showing the overall configuration of this embodiment. In the figure, 1 performs 2-4 wire exchange,
In the speech network as an output circuit that separates the received signal and the transmitted signal, resistors R1, R2, R
3, a balancing network BN, a sending amplifier A1 consisting of transistors, etc. Reference numeral 2 denotes a reception system circuit that outputs the reception signal sent from the telephone lines L1 and L2 via the diode bridge DB and the speech network 1 from the speaker SP, and includes an audio adjustment volume.
VR, voltage dividing resistors R21, R22, receiver amplifier A
21 and an AGC circuit that maintains the level of the input signal to the receiver amplifier A21 at a constant level.
Further, 3 is a transmission system circuit. Of these, the ECM is a microphone, and its output is capacitor C13.
and a resistor R31. A31 and A32 are inverting preamplifiers made of transistor circuits, and the output signal from the phase advance circuit 31 is amplified to a predetermined level by these two stages of inverting preamplifiers A31 and A32. It is now entered into .

Figure 2 shows a discrimination circuit that determines whether the voltage level of the received signal between the telephone line and the speaker is within a predetermined range, and an attenuation circuit that attenuates the voltage level of the received signal when it exceeds the predetermined range. FIG. 2 is a circuit diagram showing a specific configuration of the AGC circuit 21 having the function of FIG. In the figure, Q1 is a switching transistor,
The collector side is connected via a capacitor 21 to a time constant circuit consisting of a voltage dividing resistor 23 and a capacitor C22, and a resistor R2 for determining the bias level.
4. Diodes D21, D22, and D23 are connected. Furthermore, the output of the receiver amplifier A21 is connected to a diode D22 via a capacitor C24.
It is fed back to the connection point between and D23.

FIG. 3 is a perspective view showing the appearance of the housing H that houses the microphone ECM, speaker SP, etc.

In the figure, H1 is a speaker chamber, on the upper surface of which a speaker SP is fixed, and the volume VR
An adjustment knob VR1 is attached so as to be movable along the guide hole H1a. In addition, H2 is a microphone room, and speaker room H1 is a shielding plate HB.
It is completely acoustically shielded by the front opening HB1, and the microphone is transmitted through the air through the front opening HB1.
Input to ECM. As mentioned earlier, this
This is a cause of howling that degrades call performance, but as long as the Microphone ECM is attached to the phone, it is unavoidable that audio signals will be input from the speaker SP to the Microphone ECM due to air propagation. Therefore, in this embodiment, howling is prevented as follows.

That is, if the reception signals input from the telephone lines L1 and L2 are now X (see Fig. 4, a),
When this is output from the speaker SP and input to the microphone ECM by air propagation,
This signal is outputted again to the telephone lines L1 and L2 as a signal with a slightly delayed phase as shown by Y in the figure. This signal is passed to the fourth stage by the phase lead circuit 31.
The phase returns to the original state again as shown by Y' in Figure b.
However, since the level of this signal is significantly attenuated by passing through the phase lead circuit 31 consisting of a CR circuit, the two-stage inverting amplifier A31, A
32 to a sufficient level. At this point, the signal Y' output from the inverting amplifier A32
is exactly the same as the receiving signal X on the line. Thereafter, this signal Y' is input to the transmitting input section of the speech network, and its phase is inverted by 180 degrees in the transmitting amplifier A1 and the 2-wire to 4-wire converter, and the signal Y' is inverted and received as shown in Fig. 4, c. telephone line L1 as signal Y'',
Output to L2. At this time, on the line, a reception signal X' from the other party, which was sent several milliseconds after the reception signal X described above, and an inverted reception signal Y'', which is an inversion of the reception signal As a result, X' and Y'' of the received signal components are canceled out, preventing howling, and only the transmitting signal is output to the telephone line. , good call performance can be obtained.

By the way, as mentioned above, the reception signals X and X'
There is a very small time difference (for example, several milliseconds), but this time difference is extremely small compared to the time it takes for humans to recognize speech (several tens to hundreds of milliseconds), and the audio signal itself Within this amount of time, there is almost no difference in frequency or level, and they can be considered to be exactly the same signal. Therefore, the signals Y'' and X', which have the phases of X inverted, completely cancel each other out on the line.

However, in order to completely cancel out the inverted reception signal and the reception signal as described above, the sound output from the speaker SP needs to be a proper sound without distortion. In other words, if an excessively large reception signal is input to the reception amplifier A21 and the output signal from the reception amplifier A21 is distorted as shown in FIG. The signal is naturally distorted, so even if this signal is inverted and output on the circuit,
It cannot be expected to have much of a canceling effect with the received signal on a line without distortion.

Therefore, the AGC circuit 21 is provided as a means for preventing distortion of the output signal from the receiver amplifier A21 even when an excessive input is applied.

The following describes an AGC circuit 2 that functions as a circuit for determining the voltage level of a received signal and an attenuation circuit for attenuating the voltage level of the received signal according to the determination.
The structure and operation of 1 will be explained. In addition, AGC circuit 2
1 and the receiving amplifier A21 constitute a speaker operating circuit.

The receiving signal current amplified by the receiving amplifier A21 passes through the capacitor C24 and then passes through the diode D23.
The DC component is taken out and charged to the capacitor C22. At this time, the reception signal is at a level within a predetermined range, that is, the reception amplifier A21
If the level is within the range where distortion does not occur in the output signal from the capacitor C22, the voltage generated at the capacitor C22 is low and the transistor is turned off.
Therefore, the input reception signal is directly input to the reception amplifier A21 via the resistor R21, and after being amplified to a predetermined level, a good sound without distortion is output from the speaker SP. In addition, if an excessive reception signal is input, capacitor C2
2, the transistor Q1 is turned on for a time set by the time constant of the capacitor C22 and the resistor R23. As a result, the reception signal is voltage-divided by the resistors R21 and R22, becomes an excessive signal level, and is input to the reception amplifier A1, and the reception signal is output from the reception amplifier A21 as shown in FIG. Proper signal without distortion to the speaker
It is supplied to the SP and outputs good audio. Also,
When the output signal from the receiving amplifier A21 falls, the transistor Q1 is turned off again, and as described above, the receiving signal is directly output to the receiving amplifier A21 via the resistor, and the same operation is repeated thereafter.

In this way, by providing the AGC circuit 21, even if an excessive reception signal is input, good sound without distortion is output, so even if this sound is input to the microphone ECM, the above-mentioned cancellation Howling can be completely prevented by this action.

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain good sound without distortion from the speaker, and to prevent howling from occurring due to this sound being input to the microphone. This has the effect that it is possible to realize good simultaneous two-way communication.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a circuit diagram showing the specific configuration of the AGC circuit shown in FIG. 1, and FIG. A perspective view of the external appearance, FIG. 4a is a signal waveform diagram of the received signal X from the other party sent out on the line shown in FIG. 2, and the received signal Y re-inputted from the speaker to the microphone, FIG. 4b 4c is a signal waveform diagram showing the received signal X and the re-input received signal Y' outputted from the phase lead circuit, and FIG. Figure 5a and b are signal waveform diagrams showing the reception signal X' existing on the line, Figure 5a and b are output signal waveform diagrams of the reception amplifier at the time of excessive input; indicates the case where an AGC circuit is provided. 1...Speech network (output circuit, inverting circuit), 2...Sending system circuit, 3...Receiving system circuit,
21...AGC circuit (discrimination circuit, attenuation circuit), A2
1... Receiving amplifier, H... Housing, SP...
...Speaker, ECM...Microphone.

Claims (1)

[Scope of Claims] 1. A speaker that outputs a received signal from a telephone line as audio, a microphone that inputs audio including the sound generated from the speaker, an inverting circuit that inverts the phase of input to the microphone, and an inverting circuit that inverts the phase of input to the microphone. In a loudspeaker telephone device comprising an output circuit that simultaneously outputs the received input signal and the received signal to a telephone line, the voltage level of the received signal between the telephone line and the speaker is within a predetermined range. A discriminating circuit is provided, and a speaker operating circuit is provided, which supplies the voltage level to the speaker when the voltage level is within a predetermined range, and attenuates the voltage of the received signal and supplies it to the speaker when it exceeds the predetermined range. A loudspeaker telephone device characterized in that the range is set to be a range that does not cause distortion in speaker sound.