JPS60235564A - Loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To attain talking of a proper sound level and to attain smooth switching of transmission/reception by constituting the titled set that a line loss varied with the subscriber line length is detected simply by a line voltage to correct the line loss with the gain of a variable gain characteristic circuit. CONSTITUTION:The sound inputted to a microphone 1 is inputted to a variable amplifier 17 via an amplifier circuit 2 and a variable loss circuit 3, the voice is amplified at the variable amplifier circuit 17 according to a line voltage signal detected by a line voltage detecting circuit 16 with a gain corresponding to the line loss of the subscriber line 14. Then the sound is transmitted to an exchange 15 from a side soundproof circuit 5 via the subscriber line 14. The sound signal of the talking party is inputted to the variable amplifier circuit 18 from the exchange 15 via the subscriber line 14 and the side soundproof circuit 5, it is amplified by a gain corresponding to the line voltage of the subscriber line according to the line voltage signal and outputted from a speaker 10 as a voice via a variable loss circuit 7, a sound volume adjusting circuit 8 and an amplifier circuit 9. Thus, the changeover of transmission/reception by a comparator circuit 12 is executed smoothly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a loudspeaker telephone that uses a microphone and a speaker to make calls.

[Prior art]

A public address telephone is a device that uses a microphone and speaker to make calls instead of the handset of a regular telephone.
A voice switch circuit is provided as a howling prevention means. FIG. 1 is a block diagram of a conventional loudspeaker telephone and subscriber line, where / is a microphone, λ, Hiro, 6 and 9.
is an amplifier circuit, 3 and 7 are variable loss circuits, 3 is a side sound prevention circuit such as a hybrid coil, Z is a volume adjustment circuit that adjusts the amplification volume, IO is a speaker, /l is a rectifying and smoothing circuit on the transmitting side, / 3 is a rectifying and smoothing circuit on the receiver side, 12 is a comparison circuit,
/Hiro is a subscriber line and /S is a switch.

Next, the operation will be explained. The voice input to the microphone is converted into a transmitting voice signal, which is sent via the amplifier circuit, the variable loss circuit 3, and the amplifier circuit from the side sound circuit 5 to the subscriber line through the exchange IS. . At this time, a part of the transmitted audio signal input to the side sound protection circuit j becomes side sound and is sent to the amplifier circuit 6, the variable loss circuit, the volume adjustment circuit t, and the amplifier circuit? The signal is transmitted to the speaker 10 via the speaker 10, and converted into audio by the speaker 10. This voice is again input to the microphone, but if the gain of this closed loop is 1 or more, howling occurs and communication becomes impossible. In a public address telephone, in order to reduce the gain of this closed loop to less than /, the transmitting side,
Rectifying and smoothing circuit on the receiver side／ ／ 、 ／ 、? converts the audio signal into a DC voltage signal, compares the level of the transmitted and received audio signals in the comparison circuit 12, and reduces the amount of loss in the variable loss circuit 3 since the level of the transmitted audio signal is higher at the time of transmission. , the loss amount of the variable loss circuit 7 is increased. Conversely, when receiving a call, the voice signal of the other party is input from the exchange 15 through the subscriber line/hiro to the side sound circuit 15, and then to the amplifier circuit 6. The sound is output from the speaker 10 via the variable loss circuit 7, the volume adjustment circuit for manually adjusting the volume of the loudspeaker, and the amplifier circuit 1, but the comparison circuit 1
2, since the receiving audio signal level is higher than the transmitting audio signal level, the amount of loss in the variable loss circuit is reduced, and the amount of loss in the variable loss circuit 3 is increased to prevent housing.

Therefore, switching between transmitting and receiving in the loudspeaker telephone is performed by the difference in output voltage between the rectifying and smoothing circuit // on the transmitting side and the rectifying and smoothing circuit /3 on the receiving side.

Conventional loudspeaker telephones are configured as described above.
If the line loss changes depending on the length of the subscriber line,
The transmitting/receiving audio signal level changes, which affects the call quality.In particular, when the line loss is large, the receiving audio signal level, that is, the level of the audio signal from the other party, decreases, and the comparison circuit changes the transmitting/receiving audio signal level. There were drawbacks such as difficulty in switching from the state to the receiving state.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional public address telephone as described above, and the line loss of the subscriber's line is simply detected by the line voltage, and the line loss of the subscriber's line is compensated for. The purpose of this invention is to provide a loudspeaker telephone with excellent communication quality by automatically adjusting the level of transmitted and received audio signals.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Second
The figure is a block diagram of a loudspeaker telephone and a subscriber line according to the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same parts. /6 is a line voltage detection circuit that detects the line voltage when the loudspeaker telephone is in a talking state.
is a variable gain characteristic circuit that has a variable gain characteristic that varies logarithmically depending on the line voltage signal of the line voltage detection circuit 16, and amplifies or attenuates the transmitting and receiving voice signals, respectively; here, a variable amplification circuit is used. It is being The variable amplifier circuits /7 and 1g are configured to amplify the transmitting audio input signal and the receiving audio output signal of the side sound protection circuit S, respectively. In addition, FIG. 3 shows the relationship between subscriber line length, line voltage, and line loss, and FIG.
and the gain characteristics for a line voltage of 1 g are shown.In a public address telephone with such a circuit configuration, the voltage supply to the subscriber line/da is performed by the exchange/S. As shown in FIG. 3, the line loss in the subscriber line is proportional to the length of the subscriber line, and the line voltage decreases logarithmically as the length of the subscriber line becomes better or worse.

In the loudspeaker telephone according to the present invention, in order to improve the line loss characteristics shown in FIG. 3, the variable amplifier circuit/7. I gave it to him. Therefore, when transmitting a call, the voice input to the microphone l is first converted into a transmitting voice signal, and then passed through the amplifier circuit λ and the variable loss circuit 3 to the variable amplifier circuit/
7 is input. and.

In this variable amplifier circuit/7, line voltage detection circuit/6
subscriber line/according to the line voltage signal detected by
It is amplified with a gain corresponding to the line voltage, that is, the line loss. Then, it is sent from the side sound circuit S to the exchange 15 via the subscriber line/da. In addition, when receiving a call, the voice signal of one party is input from the exchange 15 to the subscriber line/F and the variable amplifier circuit/l via the side sound protection circuit 5, which corresponds to the line voltage of the subscriber line according to the IT pressure signal. is amplified with a gain of Thereafter, the signal is output as audio from the speaker 10 via the variable loss circuit, the volume adjustment circuit S, and the amplifier circuit 9. For this reason, line loss, which conventionally caused voice signals to be transmitted and received to be attenuated and call quality to deteriorate, can be eliminated by variable amplifier circuits/? .

At the same time, an audio signal of an appropriate voltage level is always inputted to the rectifying and smoothing circuit 13 on the receiver side, so that switching between transmitting and receiving by the comparator circuit 2 is performed smoothly.

In addition, in the above embodiment, a variable amplification circuit is provided as a variable gain characteristic circuit for correcting line loss, but a variable attenuation circuit whose gain changes logarithmically with respect to line voltage is used. The same effect can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, the line loss that changes depending on the subscriber line length of the loudspeaker telephone is simply detected by the line voltage, and the line loss is transmitted and received, so that calls can be made at an appropriate voice level. In addition, it is possible to smoothly switch between sending and receiving calls, which has the effect of providing a loudspeaker telephone with excellent call quality.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional loudspeaker telephone and a subscriber line, Fig. 2 is a block diagram showing an embodiment of a loudspeaker telephone and a subscriber line according to the present invention, and Fig. 3 is a block diagram showing the subscriber circuit length and line loss. Figure 1 is an amplification characteristic diagram of a variable amplification circuit which is a component of the present invention. l・・Microphone, ko, u, 6.9@・amplifier circuit, 3
．． R...variable loss circuit, S...side sound prevention circuit, TLL/volume adjustment circuit, io-/speaker, /I. /3・φ rectifier smoothing circuit, /2・・comparison circuit, 7%・・subscriber line, /j・・exchange, /6・・line voltage detection circuit, /7,1g・・variable gain characteristic circuit (variable amplifier circuit). In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Mei3 figure 77oAJa4? & (km)

Claims (1)

[Scope of Claims] (1) A rectifying and smoothing circuit that rectifies and smoothes the transmitting and receiving voice signals, respectively, and a comparison circuit that compares the magnitude of the outputs of these rectifying and smoothing circuits to switch between the transmitting state and the receiving state. , a line voltage detection circuit that detects the line voltage of the subscriber line in order to eliminate line loss in the subscriber line, and a variable gain characteristic that compensates for the line loss according to the line voltage signal from the line voltage detection circuit. and a variable gain characteristic circuit that amplifies or attenuates the transmitting and receiving audio signals, respectively. (j) A loudspeaker telephone according to claim 1, wherein the variable gain characteristic circuit is a variable amplification circuit. (3) The loudspeaker telephone according to claim 1, wherein the variable gain characteristic circuit is a variable attenuation circuit◇