JPH04180330A - Telephone set - Google Patents

Abstract

PURPOSE:To prevent the occurrence of howling by providing two microphones incorporated in a handset and a differential amplifier, and cancelling sounds inputted uniformly to both the microphones by each other by inputting them to the inverting input terminal and the non-inverting input terminal of the differential amplifier, and differential-amplifying them. CONSTITUTION:The handset 1 is provided with the built-in microphone M2 in addition to a transmitting microphone M1, and the output signal S1 of the microphone M1 is inputted to the non-inverting input terminal of the differential amplifier 6, and the output signal S2 of the microphone M2 is inputted to the inverting input terminal. The microphone M2 is installed at a position where a sound B from a talker is scarcely inputted. Here, the component of the sound A contained in the sound signal S1 is cancelled by the component of the sound A contained in the sound signal S2, and the sound signal SDA of only the component of the sound B from the talker is obtained. Accordingly, a positive feedback loop having been the cause of the howling is disconnected, and the occurrence of the howling is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a telephone set with a monitor speaker that can monitor voice signals (calls) on a telephone line, and more specifically relates to such a telephone set. This invention relates to the prevention of howling caused by the monitor function of the system.

A telephone with a monitor speaker can listen to what the other party is saying without holding the receiver, and an unspecified number of people can listen at the same time, but on the other hand, it causes so-called howling due to the operation of the monitor function. Sometimes. That is, since the voice signal on the monitored telephone line also includes a transmitting signal, when the voice output from the monitor speaker enters the transmitter, it is amplified and output from the monitor speaker again, and further, By repeating the vicious cycle in which the output voice enters the speaker, oscillation occurs and howling occurs.

In contrast, conventionally, when monitoring with a speaker, the transmitter circuit is deactivated, and when speaking, that is, when voice is input to the transmitter, the transmitter circuit is activated and the monitor circuit is deactivated. This method was used to prevent howling from occurring.

However, the above method has the trouble of having to switch the 0N10FF of the transmitter circuit and monitor circuit when starting to speak into the transmitter.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve such problems and provide a telephone that allows a telephone call to be made in a normal state using a handset without causing howling even when the telephone is being monitored using a monitor speaker. shall be.

In order to achieve the above object, the present invention provides a telephone that is provided with a monitor speaker and has a function of monitoring an audio signal on a telephone line and outputting it as audio from the monitor speaker. A handset is equipped with two built-in microphones, one of which is located a predetermined distance away from the other microphone, and one of the two audio signals output from the two microphones is input to the inverting input terminal, and the other one is input to the inverting input terminal. The configuration includes a differential amplifier that performs differential amplification by inputting an audio signal to a non-inverting input terminal.

With this configuration, the sound equally input to the two microphones (hereinafter referred to as "microphones") in the handset is transmitted as an audio signal to the inverting input terminal and non-inverting input terminal of the differential amplifier, respectively. Since they are input and amplified differentially, they cancel each other out.

On the other hand, the voice input only to the transmitting microphone is transmitted to the telephone line without being canceled by the differential amplification.

By the way, the distance between the monitor beaker and the handset (two microphones) is usually long enough compared to the distance between the two microphones in the handset, so the audio output from the monitor speaker is equally input to the two microphones. It can be assumed that On the other hand, during a call, the speaker speaks into the transmitting microphone, so the speaker's voice is input to the transmitting microphone, but is hardly input to the other microphone in the handset. Or even if it is input, there will be a large level difference between the speaker's voice level input to the other microphone and the speaker's voice level input to the transmitting microphone.

Therefore, the sound from the monitor speaker is canceled by the differential amplifier, and an audio signal containing only the speaker's voice is extracted from the differential amplifier and sent to the telephone line. As a result, even if the audio output from the monitor speaker enters the microphone, the audio will not be output from the monitor speaker again.

1 case of “Remains” Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the main part configuration of a telephone with a monitor speaker that embodies the present invention. As shown in this figure,
This embodiment differs from conventional telephones with monitor speakers because it has two microphones inside the handset (1).
A differential amplifier (6) outputs the audio signals output from these microphones.
The point is that differential amplification is performed. That is, the handset (1) has a built-in microphone (M2) in addition to the transmitting microphone (Ml), and the output signal (Sl) of the microphone (Ml) is input to the non-inverting input terminal of the differential amplifier (6). Mike (M
The output signal (S2) of 2) is input to the inverting input terminal.

In the differential amplifier (6), these signals (S+) (S2)
Differential amplification is performed on the signals, and the audio signal (SIA) obtained by the differential amplification is input to the speech network (2). The configuration other than the above is the same as the conventional one, and the speech network (2) includes, in addition to the signal line from the differential amplifier (6), a signal line to the receiving speaker (R3P) in the handset (1). , and signal lines connected to the telephone line are connected, and 2-wire to 4-wire conversion is performed between the two signal lines on the telephone line side and the four signal lines on the handset side. The monitor function is realized by amplifying the voice signal on the telephone line with a power amplifier (3) and outputting it as voice from a monitor speaker (4).

Hereinafter, the operation of the above-configured telephone will be explained when talking while monitoring the audio signal on the telephone line with the monitor speaker (4).

As shown in Figure 2, the voice (
B) is input from the transmitting microphone (Ml), and this microphone (
The audio signal (Sl) output from the differential amplifier (6) is input to the non-inverting input terminal of the differential amplifier (6). Handset (
1) also has a built-in microphone (N2), but the microphone (
A microphone (N2) is provided at a position a predetermined distance away from the transmitting microphone (Ml) so that almost no voice (B) from the speaker enters the microphone (N2). On the other hand, the monitor speaker (4) outputs audio (A) obtained by monitoring audio signals on the telephone line (audio signals for both receiving and transmitting calls).
is output, and this voice (A) may also be input to the microphone in the handset. Therefore, the voice (A) from the monitor speaker (4) and the voice (B) from the speaker are both input to the transmitting microphone (Ml), and the waveform of the voice (A) is
If the waveform is as shown in Figure (a) and the waveform of voice (B) is as shown in Figure (b), then the transmitting microphone (Ml
) is inputted with a waveform of audio (A+B), which is a mixture of audio (A) and audio (B), as shown in FIG. Therefore, the waveform of the audio signal (Sl) output from the transmitting microphone (Ml) has a waveform similar to the waveform shown in FIG. On the other hand, since almost no voice (B) from the speaker enters the microphone (N2), the waveform of the voice (A) (
A sound having a waveform substantially the same as that in FIG. 2(a)) is input, and the waveform of the sound signal (S2) output from the microphone (N2) also has a waveform substantially similar to the waveform of the sound (A).

The audio signals (S, ) and (S2
) is differentially amplified by a differential amplifier (6) to produce an audio signal (S
Dll) is obtained. This audio signal (SIl,l) is
Since it is a signal obtained by amplifying the difference between the audio signals (S+) and (S2), its waveform is similar to the audio (A+B) waveform (Figure 2 (C)) and the audio (A) waveform ( Figure (a)
) is the difference waveform from a similar waveform. By the way, usually
The distance between the monitor beaker (4) and the handset (1) (two microphones) is sufficiently long compared to the distance between the two microphones in the handset (1), so the monitor speaker (4)
It can be considered that the audio (A) from the two microphones (Ml) (N2) is input evenly. therefore,
The waveform of the output signal (SDl, l) of the differential amplifier (6) is
The waveform is almost similar to the waveform of the speaker's voice (B) (FIG. 2(b)).

That is, due to the differential amplification, the voice (A) component included in the voice signal (S,) is canceled out by the voice (A) component included in the voice signal (S2), and the voice (B) from the speaker is An audio signal (SDll) containing only the components is obtained.

This audio signal (Sn2) is then sent to the telephone line after being converted from 2-wire to 4-wire in the speech network (2), but the audio signal on the telephone line does not include the audio (A) component. Therefore, there is no audio (A) component in the signal input to the monitor speaker (4) via the power amplifier (3). Therefore, the audio output from the monitor speaker (4) is ), the sound will not be output from the monitor speaker (4) again. In other words, the positive feedback loop (monitor speaker -> microphone -> circuit inside the telephone -> monitor speaker) that caused howling is cut off, and howling is prevented from occurring.

As explained above, according to the present invention, even if the sound output from the monitor speaker enters the microphone, that sound will not be output from the monitor speaker again, so the monitor speaker can transmit the sound over the telephone line. Even when monitoring the voice signal (call) of the handset, it is possible to make a call using the handset without causing howling. Moreover, at this time, the ON10F of the transmitter circuit and monitor circuit inside the telephone
There is no need to perform an operation to prevent howling such as switching F. Therefore, you can hang up the handset and talk, or
A call can be listened to by an unspecified number of people at the same time.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the main structure of a telephone with a monitor speaker according to the present invention, and FIG. 2 is an audio waveform diagram for explaining the operation of preventing howling from occurring in the telephone. (1)...Handset. (4)...Monitor speaker. (Ml)...Talking microphone. (M2)...Mike. (S,)...Audio signal output from the transmitting microphone (Ml). (S2)...Audio signal output from the microphone (M2). (6)...Differential amplifier. (A) ...Audio from the monitor speaker. (B) ...Voice from the speaker. (SDll)...Audio signal output from the differential amplifier.

Claims (1)

[Claims] (1) In a telephone that is equipped with a monitor speaker and has the function of monitoring audio signals on a telephone line and outputting them as audio from the monitor speaker, a transmitting microphone and another microphone located a predetermined distance from the transmitting microphone are provided. A handset with two built-in microphones, one of the two audio signals output from the two microphones is input to the inverting input terminal, and the other audio signal is input to the non-inverting input terminal. A telephone set comprising: a differential amplifier that performs differential amplification;