JPS596026Y2 - Click prevention circuit for loudspeaker telephones - Google Patents

Description

[Detailed description of the invention] The present invention relates to a loudspeaker telephone that operates by switching a reversible electroacoustic transducer as a speaker or a microphone, and in particular, the present invention relates to a loudspeaker telephone that operates by switching a reversible electroacoustic transducer as a speaker or a microphone, and in particular, a loudspeaker telephone that prevents click noise that occurs when switching from the speaker to the microphone. Regarding the prevention circuit.

Conventionally, loudspeaker telephones using reversible electroacoustic transducers that share the functions of a speaker and a microphone have been constructed as follows.

That is, as shown in FIG. 1, 1 is a reversible electroacoustic transducer;
When this reversible electroacoustic transducer 1 operates as a microphone, the transmission signal obtained from the microphone is transmitted to the amplifier 4 on the transmission path side 3 via the transfer contact 2 of the relay.
The signal is amplified and sent to the telephone line 6 via the side sound protection circuit 5.

Further, when the reversible electroacoustic transducer 1 operates as a speaker, a received signal arriving at the telephone line 6 is reproduced by the speaker via the sound protection circuit 5, the amplifier 8 on the receiving path 7, and the contact 2.

9 is a coil of a relay corresponding to the contact 2.

Reference numeral 10 denotes a control circuit, which basically controls a relay as a switching means according to the presence or absence of a reception signal, and when there is no reception signal, the reversible electroacoustic transducer 1 is placed on the transmission path 3 side, and the reversible electroacoustic transducer 1 is placed on the transmission path 3 side; When the signal is present, the reversible electroacoustic transducer 1 is connected to the receiving path 7 side.

However, due to the imperfection of the side sound protection circuit 6 during voice transmission,
Even if the transmitting signal passes through this side sound protection circuit 6 and goes around to the receiving path 7, the transmitting signal from the transmitting path 3 side is also introduced and detected so that it will not malfunction as if there is a received signal. This signal is used to cancel the signal from the receiving path 7 side.

Note that the output form of the control circuit 10 is such that when switching the reversible electroacoustic transducer to the receiving path side, a predetermined voltage (for example, the power supply voltage of the entire circuit (not shown)) is generated, and on the other hand, when switching the reversible electroacoustic transducer to the transmitting path side, it is in an open state, for example. It shall be.

Next, the operation will be explained. When a reception signal of a predetermined level or higher arrives on the line 6, a part of it is inputted to the control circuit 10 via the amplifier 8.

The control circuit 10 detects this and generates a predetermined voltage.

As a result, the coil 9 of the relay is energized and its contact 2 is switched and connected to the receiving path 7, the reversible electroacoustic transducer 1 operates as a speaker, and the received signal is reproduced.

Further, when the reception signal ends, the output terminal of the control circuit 10 is opened and the relay is restored.

Therefore, the reversible electroacoustic transducer 1 that was operating as a speaker is restored to the transmission path side by the contact 2.

According to the loudspeaker telephone configured in this manner, the reversible electroacoustic transducer 1 is quickly switched when a reception signal arrives or stops, so as not to impair the naturalness of the conversation, and the reversible electroacoustic transducer 1 is quickly switched to function as a speaker and a microphone. must be maintained.

However, even if the reception signal stops arriving and the reversible electroacoustic transducer 1 stops reproducing the reception signal, the reproduction diaphragm of the reversible electroacoustic transducer 1 will vibrate to some extent due to noise mixed in the reception signal. ing.

The vibration amplitude of this reproduction diaphragm is about 10 to 100 times larger than the vibration amplitude of the diaphragm when it normally functions as a microphone.

Therefore, when the reversible electroacoustic transducer 1 is switched from the receiving path side 7 to the transmitting path side 3, the switching is often done before the amplitude of the diaphragm disappears, and a signal with a level corresponding to the amplitude is used as the transmitting signal. It will be sent out via the transmission path 3 for a moment.

This transmission signal becomes a click noise that interferes with the telephone call, and may also cause the control circuit 10 to malfunction.

The present invention has been developed in view of the above-mentioned drawbacks, and when the reversible electroacoustic transducer is restored and connected from the receiving signal reproducing state to the transmitting signal transmitting state, vibrations due to noise mixed in the receiving signal do not disappear. This is to prevent communication interference due to transmission noise caused by the transmission.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, and the same components or parts as those of a conventional loudspeaker telephone will be designated by the same reference numerals, and the description thereof will be omitted.

That is, in FIG. 2, a series circuit of a capacitor 21 and a resistor 22 is connected between the amplifier 4 and a fixed contact on the transmission path side 3 which the transfer contact 2 of the relay contacts.

A transistor 23 is connected to the connection point between this resistor 22 and the amplifier 4.
The collector electrode of this transistor 23 is connected, and the emitter electrode of this transistor 23 is grounded.

Capacitor 21 is for coupling, resistor 22 and transistor 23
and constitute a variable attenuation circuit.

On the other hand, a relay coil 9 is connected between the output end of the control circuit 10 and the earth, and in parallel with this coil 9, a resistor 25 and a capacitor 2 are connected to form a time constant circuit.
6 are connected in series, and the series connection point is connected to the base electrode of the transistor 23 via the base resistor 24.

The operation of the click prevention circuit configured in this manner is similar to that shown in FIG. 1 when, for example, a reception signal arrives from the line 6.

Here, the coil 9 of the relay is excited by the output of the control circuit 10, and the capacitor 26 is energized via the resistor 24.
is charged.

When the charging voltage exceeds a predetermined value, a sufficient base current flows through the transistor 23 via the base resistor 24, and the impedance between the collector and emitter of the transistor 23 decreases significantly.

A variable attenuation circuit having an amount of attenuation determined by this impedance and the resistance 22 is inserted into the transmission path 3.

Next, when the reception signal stops arriving, the control circuit 10
The output end of is opened.

Then, the relay is restored and the reversible electroacoustic transducer 1 is restored to the transmission path side 3.

The charge stored in the capacitor 26 is discharged through the resistor 24, the transistor 23, the resistor 25, and the relay coil 9.

Note that the current flowing through the coil 9 of this relay is less than its holding current value.

Therefore, the transistor 23 is connected to the capacitor 26 and the resistor 24 after the output terminal of the control circuit 10 is opened.
Then, it becomes non-conductive after a discharge time determined by the resistor 25 and the winding resistance value of the coil 9 of the relay.

When the transistor 23 becomes non-conductive, the amount of attenuation of the variable attenuation circuit becomes almost zero, and the output of the reversible electroacoustic transducer 1 becomes:
The signal is applied to the amplifier 4 without attenuation.

According to experiments, it has been confirmed that the time it takes for the vibration amplitude of the diaphragm of the reversible electroacoustic transducer 1 due to noise mixed in the received signal to disappear after being switched to the transmission path side is approximately 10 to 30 mS. .

Therefore, if the predetermined time from conduction to non-conduction of the transistor 23, that is, the discharge time is set to about 50 mS, a variable attenuation circuit having a large attenuation amount until the vibration amplitude of the diaphragm disappears is inserted. It turns out.

Generally, it is desirable that the switching time from the stop of the reception signal until the transmission of the transmission signal is about 200 mS, so the above-mentioned time of 50 mS does not actually impede communication.

That is, the predetermined time of 50 mS for the variable attenuation circuit is 20 mS.
It can be considered to be included in the switching time of 0 mS,
There is no need to reduce the naturalness of the call.

In addition, as is clear from the above explanation of the operation, the presence or absence of the output voltage of the control circuit, that is, the output voltage that changes in a step manner, is integrated, and the attenuation amount of the variable attenuation circuit is controlled by the integrated output, so reversible electroacoustic conversion No new noise is generated on the transmitting path in either case of switching from the receiving path side to the transmitting path side or from the transmitting path side to the receiving path side.

If new noise occurs in the transmission path when the reversible electroacoustic transducer is switched from the transmission path side to the reception path side, it will not only be transmitted to the other party, but will also be transmitted to the other party, and will also be transmitted to the other party through the side noise prevention circuit. Noise is also generated from the speakers, degrading the quality of the call, but the present invention eliminates this problem.

In addition, if the other party's telephone is a similar loudspeaker telephone, the other party will be in the transmitting state at the time when the other party is trying to enter the receiving state, and at that time, the receiving channel of the other party will be disrupted by the noise on the other party's side. The level of communication increases and acts to force the other party to receive the call, causing malfunctions, but according to the present invention, such problems do not occur.

As explained above, according to the click prevention circuit of the loudspeaker telephone of the present invention, the noise generated when the reversible electroacoustic transducer is switched from the receiving state as a speaker to the transmitting state as a microphone can be combined with the received signal. This can be reliably prevented without changing the switching time between transmission signals and without creating new noise, which is highly effective.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing a conventional loudspeaker telephone, and Fig. 2 is a connection diagram showing a conventional loudspeaker telephone.
FIG. 1 is a connection diagram showing a loudspeaker telephone that is an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Reversible electroacoustic transducer, 2...Switcher, 10...Control circuit, 22...Resistor, 23...Transistor .

Claims (1)

[Scope of utility model registration request] a reversible electroacoustic transducer that operates as a speaker or a microphone; a control circuit that generates an output voltage according to a received signal on a receiving path; and a control circuit that operates the reversible electroacoustic transducer on the receiving path or is a loudspeaker telephone having a switching means for switching and connecting to a transmission path, an integrating circuit that integrates the output voltage of the control circuit, and a magnitude of the output voltage of the integrating circuit that is inserted and connected to the transmission path; 1. A click prevention circuit for a loudspeaker telephone, comprising: a variable attenuation circuit whose attenuation amount is controlled according to .