JPS63208342A - Loudspeaker simultaneous telephonic communication equipment - Google Patents

Abstract

PURPOSE:To attain the reception during transmission and to prevent howling completely by using an output of a differential amplifier applying positive feedback of a received output with a gain of nearly '1', taking its synthesized signal as one input and taking only the reception output as the other input as a transmission output. CONSTITUTION:If other party is busy, a reception signal passes through a talking circuit network CL, amplified by an amplifier A1, and drives a microphone in common use for speaker MS via an amplifier A2 whose gain is the unity. The reception output is inputted also to an input terminal (b) of the differential amplifier DA at the same time and since its signal is the same as the output of the amplifier A1 inputted to an input terminal (a) of the amplifier DA, the output of the amplifier DA is zero. If its own station starts talking while the opposite party is busy, although the synthesis signal between the transmission input and the reception output is inputted to the terminal (b), since only the received output is cancelled by a signal from the terminal (a), only the transmission input is amplified and outputted at the output terminal (c) of the amplifier DA and it is sent to a line L via the circuit network CL.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a telephone loudspeaker simultaneous call device that allows calls to be completed using a microphone and a speaker without using a handset.

[Background Art] Typically, this type of loudspeaker telephone set uses a voice switch circuit that automatically switches between sending and receiving calls based on voice, as shown in FIG. In the figure, the output of the microphone Me is amplified by an amplifier A1, and its transmitting level is input to the non-inverting side of the comparator CP via a rectifying and smoothing circuit DS, and the receiving input from the line L2 is After being amplified by the amplifier A, the signal is input to the inverting side of the comparator CP via the rectifying and smoothing circuit DS2. Now, when the transmitting level increases, the output of the comparator CP becomes H level, and the potential at point X rises with a short time constant set by the resistor R1 and capacitor C1. .

is turned on, and analog switch AS2 on the receiver side is turned off via an inverter. Next, when the transmitter input disappears, the potential at point X decreases with a relatively long time constant set by capacitor C1 and resistor R2, and analog switch A
The open/closed states of S , , A S 2 are reversed. Naori 1
is the backflow blocking diode at this time. In this way, microphone MC → amplifier AI → analog switch AS,
→ Amplifier A2 → Telephone network CL → Amplifier A → Analog switch AS2 → Amplifier A3 → Speaker SP → Microphone MC The loop gain of the closed circuit of the microphone MC is always kept below 1 throughout transmitting and receiving calls, and thereby the microphone is connected from the speaker to the microphone. This is designed to prevent howling caused by looping around.

However, with this conventional loudspeaker system, when both parties are talking, the other party's voice can hardly be heard, so it is not possible to have a completely simultaneous conversation, and when the own party starts talking, the other party's voice is interrupted. There was a drawback that the other party's voice would become incoherent, or the other party's voice would be cut off immediately after the player's own station had finished speaking.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and its purpose is to enable a speaker to listen to the voice of the other party while speaking, and to completely eliminate howling. The purpose of the present invention is to provide a public address simultaneous communication device that prevents the use of multiple telephone calls.

[Disclosure of the Invention] However, the simultaneous loudspeaker communication device according to the present invention positively feeds the receiving output to the transmitting input with a gain of approximately 1, uses the synthesized signal as one input, and uses only the receiving output as the other input. This device is characterized in that the output of the amplifier is used as the transmitting output, and in order to prevent howling due to feedback from the speaker to the microphone, the receiving output is positively fed back to the transmitting input with a gain of 1. , a differential amplifier is used to cancel out only the receiving output with other inputs.

Embodiment FIG. 1 shows an embodiment of the present invention, in which a reception signal inputted from a line via a telephone communication network CL is amplified by a first amplifier AI, a first amplifier A, The output of is gain 1
is inputted to the microphone/speaker MS via the second amplifier A2, and the output of the differential amplifier DA which takes the output of the first amplifier AI as one input and the microphone/speaker MS as the other input. It is configured to be sent to the line via the communication network CL.

In Fig. 1, when the other party is speaking, the received signal passes through the communication circuit CL, is amplified by the first amplifier A1, and then passes through the second amplifier A2, that is, a buffer amplifier with a gain of 1, and is sent to the microphone. Drive speaker MS. This reception output is also input to one input terminal a of the differential amplifier DA at the same time, but the signal is the same as the output of the first amplifier A1 which is input to the other input terminal a of the differential amplifier DA. Therefore, the output of the differential amplifier DA becomes zero. Next, when the local station starts talking while the other party is talking, a composite signal of the transmitting input and the receiving output is input to the input terminal of the differential amplifier DA, but only the receiving output is input to the input terminal. Since it is canceled by the signal from a, only the transmitting input signal is amplified and outputted to the output terminal C of the differential amplifier DA, and this is sent to the line through the communication network CL.

According to the above configuration, even if the local station and the other station are talking at the same time, there is no discomfort because the receiving signal is not blocked as in the conventional case, and the transmitting output does not leak from the communication circuit network CL to the receiving circuit side. However, since the positive feedback to the transmitting circuit is canceled by the differential amplifier DA, a closed loop is not formed for the leakage signal, and the occurrence of howling is prevented.

FIG. 2(,) shows another embodiment in which the receiving signal input from the line via the telephone communication network CL is transmitted to the amplifier A,
This amplified output drives a speaker SP, and in front and behind this speaker SP, as shown in FIG. MC2 is placed and both microphones MC,,MC2
The output of is the splitting input of the differential amplifier DA. The output of the differential amplifier DA is output to the line via the transmitting side amplifier A3 and the communication circuit [CL.

Now, in FIG. 2(a), when only the other station is talking, the reception signal input through the communication circuit #4cL is amplified by the amplifier A and output from the speaker SP, and this is transmitted to both microphones MC, MC2. Since the two signals are inputted equally to each other, they cancel each other out by the differential amplifier DA, and the transmitting output becomes zero. Next time when only your own station is talking, the microphone MC
Since the microphone MC2 is located on the back side of the speaker SP, almost no output is output, so the differential amplifier DA
Only the signal from the microphone MC is outputted from the microphone MC, and sent to the line via the telephone communication network CL. Furthermore, when both stations are talking at the same time, a composite signal of the transmitting input and the receiving output is input to the front microphone MC, and the same audio signal of the receiving output is also input to the rear microphone MC2. Therefore, the signal from the microphone MC is canceled by the differential amplifier DA, and only the signal from the microphone MC is output from the differential amplifier DA.

Next, the embodiment shown in Fig. 3 is an improved version of the circuit shown in Fig. 2, and the level and phase of the audio input may not necessarily be the same for both microphones MC, MC2 depending on the installation location and other conditions. Therefore, the level adjustment circuit LC and the phase control circuit PC can be used to make adjustments.

[Effect of the invention 1] As described above, the device of the present invention positively feeds the receiving output to the transmitting input with a gain of approximately 1, uses the combined signal as one input, and uses only the receiving output as the other input, and uses a differential The output of the amplifier is used as the transmitting output, and in order to prevent oscillation due to looping from the speaker to the microphone, the receiving output is positively fed back to the transmitting input, and a differential amplifier is used to output only the transmitting voice. Since this is designed to offset the input value of , even if the own station and the other station are talking at the same time, there is no risk of the other party's conversation cutting off or cutting off the beginning, and there is no need to worry about sending a message. Even if the speech output leaks from the communication circuit network to the receiving circuit side, there is an advantage that there is no possibility of howling occurring because a closed loop is not formed for the leakage signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the device of the present invention, and FIG.
Figure (a) is a block diagram of another embodiment, (b) is a cross-sectional view of the same essential parts as above, Figure 3 is a block diagram of still another embodiment, and Figure 4 is a block diagram of another embodiment.
The figure is a block diagram of a conventional example. L...Line, MC,, MC2...Microphone, SP...
・Speaker, MS...Speaker that also serves as microphone, A +
v A 21 A 3...Amplifier, DA...Differential amplifier, CL...Telephone circuit network. Agent Patent Attorney Ishi 1) Long 78P...Speaker Figure 1 DA...Differential Amplifier 2c/) '1 Quantity ■ Summer 1;:511. :1:Σ

Claims (3)

[Claims] (1) A simultaneous loudspeaker communication system consisting of a differential amplifier whose output is positive feedback to the transmitting input with a gain of approximately 1, the composite signal being used as one input, and only the receiving output being used as the transmitting output. . (2) The received signal input from the line via the communication circuit network is amplified by the first amplifier, and the output of the first amplifier is
Connect to the microphone/speaker via the second amplifier of
A simultaneous sound amplification system according to claim 1, wherein the output of a differential amplifier having the output of the first amplifier as one input and the microphone-cum-speaker as the other input is sent to the line via the communication circuit network. Telephone device. (3) The reception signal that is input from the line via the communication circuit network is output to the speaker via the amplifier, and the two microphones placed in front and behind the speaker are used as both inputs of the differential amplifier. 2. The simultaneous loudspeaker telephone call apparatus according to claim 1, wherein the output is sent to a line via the telephone call network.