JPH0242266B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a loudspeaker telephone device for making calls over a central office line using loudspeaker technology.

Configuration of conventional example and its problems Figure 1 shows a conventional loudspeaker telephone system. In Figure 1, 1 is a central office line, 2 is a hybrid circuit, and hybrid circuit 2 separates transmitting and receiving signals. It is something. 3 is a handset, which has a built-in handset R and a transmitter T. Reference numeral 4 denotes a loudspeaker for reception, 5 a power amplifier for reception, 6 a microphone for loudspeak transmission, and 7 an amplifier for transmission. 8 is a switch for switching between a handset and a loudspeaker. Reference numeral 9 denotes an audio level switching circuit which prevents howling during a loudspeaker call by switching to a transmitting mode or a receiving mode based on a comparison of the transmitting and receiving levels during a loudspeaker call. In the audio level switching circuit 9, 10 is a receiving amplifier, 11 is a transmitting amplifier, 12 is a transmitting and receiving level comparing circuit, 13 is a receiving signal attenuation circuit, and 14 is a transmitting signal attenuation circuit.

When the switch 8 is on the side of the handset 3, calls can be made using the handset 3 in the same way as with general telephone equipment. When the changeover switch 8 is switched to the audio level switching circuit 9 side, the transmitting audio level coming from the loudspeaker transmitting microphone 6 and the receiving audio level coming from the office line 1 are detected by the transmitting/receiving level comparison circuit 12,
By controlling the amount of attenuation by the receiving signal attenuation circuit 13 and the transmitting signal attenuation circuit 14, the transmitting and receiving signals are switched to realize a pseudo simultaneous loudspeaker call.

However, if the transmission loss of the central office line is very large, the received signal from the other party is small, or the ambient noise is large, the beginning of the voice call may be cut off or the audio level switching may malfunction. The call is being made by switching to the handset/receiver 3 side. Even in the case of telephone calls using the handset 3, under the above environment, the voice level of the telephone calls was low, making it difficult to use.

OBJECTS OF THE INVENTION It is an object of the present invention to improve the drawbacks of the conventional loudspeaker telephone equipment described above and to improve the quality of speech using a handset in a bad environment.

Structure of the Invention In order to achieve the above object, the present invention uses an audio level switching circuit that operates during a loudspeaker call also when talking with a handset, and
A switching circuit with an attenuation of about 30 to 50 dB prevents the housing, and when talking with the handset, the
By setting the amount of attenuation to about 10 dB, the transmitting/receiving level is increased while ensuring natural-looking call quality.

DESCRIPTION OF EMBODIMENTS The present invention will be described below with reference to FIG. 2 showing one embodiment thereof. In FIG. 2, 1 is a central office line, 2 is a hybrid circuit, and hybrid circuit 2 separates transmitting and receiving signals. Reference numeral 3 denotes a handset, which has a built-in receiver R and a transmitter T. Reference numeral 4 denotes a loudspeaker for reception, 5 a power amplifier for reception, 6 a microphone for loudspeak transmission, and 7 an amplifier for transmission. 8
is a switch for switching between a handset and a loudspeaker. Reference numeral 9 denotes an audio level switching circuit, which switches to a transmitting mode or a receiving mode by comparing the transmitting and receiving voice levels. In the audio level switching circuit 9, 10 is a receiving amplifier;
Reference numeral 11 designates a transmitting amplifier, 12 a transmitting and receiving level comparison circuit, 13 a receiving signal attenuation circuit, and 14 a transmitting signal attenuation circuit. Reference numeral 15 denotes a transmitting/receiving attenuation amount control circuit, and when a call is made by the handset/receiver 3, the receiving signal attenuation circuit 1
3 and the attenuation amount of the transmitting signal attenuation circuit 14 by 6 to 10 dB.
and set the attenuation amount to 30 to 50 dB during loudspeaker calls.

If the changeover switch 8 is currently switched to the loudspeaker side, the transmitting/receiving attenuation control circuit 15 sends a signal to the transmitting/receiving level comparison circuit 12 to set the attenuation to 30 to 50 dB. At this time, the transmitting voice level coming from the loudspeaker transmitting microphone 6 and the receiving voice level coming from the central office line 1 are detected by the transmitting/receiving level comparison circuit 12.
By controlling the amount of attenuation in step 4, transmitting and receiving can be switched to realize a pseudo simultaneous loudspeaker call.

On the other hand, when the changeover switch 8 is switched to the handset 3 side, the transmitting/receiving attenuation amount control circuit 15 sends a signal to the transmitting/receiving level comparison circuit 12 to set the attenuation amount to 6 to 10 dB. At this time, when the telephone is in the receiving state, the receiving signal from the office line 1 is amplified by the receiving amplifier 10 and reaches the handset 3 via the receiving signal attenuation circuit 13, while the transmitting signal is transmitted through the transmitting signal attenuation circuit. 1
Since the sound is attenuated by 4, sufficient sidetone characteristics can be ensured. When a transmitting signal is input from the handset 3, the transmitting/receiving level comparison circuit 12 becomes the transmitting mode, the attenuation amount of the transmitting signal attenuation circuit 14 becomes 0, and the central office line 1
A sufficient transmit signal can be sent to the

As mentioned above, by inserting the audio level switching circuit used in loudspeaker calls into the call circuit using a handset under the setting conditions that reduce the attenuation amount, it is possible to use the voice level switching circuit used in loudspeaker calls under the environment where loudspeaker calls are generally not possible, that is, the central office line. By switching to a handset when the transmission loss is large or when there is a lot of noise, higher quality calls can be made than with a conventional handset.

Effects of the Invention As is clear from the above embodiments, according to the loudspeaker telephone device of the present invention, it is possible to improve the call quality in cases where the transmission loss of the central office line is large or in a noisy environment. In particular, according to the present invention, an audio level switching circuit that compares a transmitted signal and a received signal with each other and reciprocally changes the attenuation amounts of the transmitted signal attenuation circuit and the received signal attenuation circuit in accordance with the difference. , and the audio level switching circuit is installed before the switch that switches between the handset side and the loudspeaker side,
The above-mentioned audio level switching circuit is configured to be used both when using a handset and when making a loudspeaker call.Therefore, in either case, switching between transmission and reception is performed well, resulting in extremely good calls. It has the advantage of According to the present invention, the attenuation amount of each of the attenuation circuits on the transmitting side and the receiving side constituting the audio level switching circuit is configured to be switched depending on when the handset is used or when making a loudspeaker call. It has the advantage that it does not require any attenuators or the like and the overall structure can be simplified.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional loudspeaker telephone device, and FIG. 2 is a circuit diagram of a loudspeaker telephone device showing an embodiment of the present invention. 1...Station line, 2...Hybrid circuit, 3...
Handset/receiver, 4... Loudspeaker receiver, 6... Loudspeaker transmitting microphone, 8... Changeover switch, 9... Audio level switching circuit, 12... Transmitting/receiving level comparison circuit,
13... Receiving signal attenuation circuit, 14... Transmitting signal attenuation circuit, 15... Transmitting/receiving attenuation amount control circuit.

Claims (1)

[Claims] 1. A transmitting/receiving level comparison circuit that compares the respective levels of a transmitting signal and a receiving signal, and a transmitting signal attenuation circuit and a receiving signal attenuation circuit whose attenuation amounts are switched reciprocally based on the output of this comparison circuit. An audio level switching circuit equipped with the above-mentioned audio level switching circuit is connected between the switch for switching between the handset side and the loudspeaker side and the central office line, and attenuation of the transmitting signal attenuation circuit and the receiving signal attenuation circuit that constitute the audio level switching circuit. A loudspeaker telephone device configured to switch the volume to different values depending on when a handset is used or when making a loudspeaker call.