JPS61118052A - Side tone preventing circuit - Google Patents

Abstract

PURPOSE:To miniaturize the titled circuit by inputting an output of a transmitter to a differential amplifier and inputting an output of the differential amplifier to a receiver so as not to decrease the function of side tone-proof even without use of a hybrid coil. CONSTITUTION:A sound caused by the transmitter 21 is fed to the differential amplifier 29 through a resistor 25, a DC blocking capacitor 26, a resistor 27 and a DC blocking capacitor 28 and also transmitted to a line 23. The resistance value of the resistors 25, 27, the capacitance of the capacitors 26, 28 and the impedance of the line 23 and a balanced circuit network 24 are made equal respectively to avoid a voice signal in the output of the differential amplifier 22. On the other hand, the voice signal from the line 23 is fed to two input terminals of the differential amplifier 29 and the amplified voice signal is given to the receiver 22.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a side sound protection circuit in a two-wire voice communication device.

[Conventional technology]

Figure 4 shows the conventional side sound protection circuit shown in, for example, Electronic Communication Handbook (IEICE) Volume 17, Section 1, 2.3 Circuit Network, and in the figure (1) fl transmitter. (2) is a receiver, (3) is a line, (4) is a balanced circuit network, (5) is a hybrid coil, and (6) is a DC blocking capacitor. Figure 61c5 shows the direction of sound current when transmitting a voice, and Figure 6 shows the direction of voice current when receiving a voice.

Next, the operation will be explained. Figure 5.
The audio signal generated by 1) is sent out to the line (3) in the direction of the arrow shown by the solid line, and is also sent to the receiver (2) through the hybrid coil (5) in the direction of the arrow shown by the solid line. Audio signal flows. The hybrid coil (5) is installed so that when an audio signal flows along one of the arrows on the line (3), the audio signal is generated in the direction of the arrow shown by the dotted line.
), the audio signal also flows to the handset (2) in the direction of the arrow shown by the dotted line, and cancels out the audio signal flowing directly from the handset (11) in the direction of the arrow shown by the solid line.
A side sound protection circuit is formed. By forming a balanced circuit network +4)ri with an in-heater equivalent to the line (3), the bridge circuit is reversed and the effect of the side noise prevention circuit described by nσ is increased. Next, in Fig. 6, when an audio signal is applied from the CC circuit 3) in the direction of the arrow shown by the solid line, the audio signal is applied to the handset (2) through the hybrid coil (5) ft in the direction of the arrow shown by the solid line. flows. At this time, since the hybrid coil is configured as described above, the audio signal flows to the hybrid coil (5) in the direction of the arrow shown by the dotted line, and the audio signal also flows to the receiver (2) in the direction of the arrow shown by the dotted line. , is added to the direction of the arrow shown by the solid line. Therefore, the sidetone is small, and the track (
The audio signal applied from 3) is formed with a side sound protection circuit that can be heard from the receiver (2).

[Problem that the invention seeks to solve]

Since the conventional side sound prevention circuit is configured as described above, it is necessary to use a high print coil.
It has the disadvantage that it cannot be miniaturized and is expensive.

This invention was made in order to solve the above-mentioned problems.It is a side sound prevention circuit that can be constructed in a small size and at low cost without reducing the function of the side sound prevention. The purpose is to obtain.

Means for Solving Problem C] The side sound prevention circuit according to the present invention uses a differential amplifier in place of the conventional hybrid coil, and is provided with a transmitter and a receiver on the input and output sides, respectively.

[For production]

Due to its differential amplification function V, the differential amplifier according to the present invention acts to reduce the sidetone when transmitting a voice and to increase the received voice when receiving a voice.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained with reference to the drawings.
In the figure, @ is the transmitter, 4 is the receiver, Q3 is the line, and 2
4 is a balanced circuit network, @ is a resistor, @ is a DC blocking capacitor,
@ is a resistor, @ is a DC blocking capacitor, and (2) is a differential amplifier. Figure 2 shows the direction of the audio current when transmitting a voice;
The figure shows the direction of voice IIL flow when receiving a call.

Next, the operation will be explained. In FIG. 2, the audio signal generated by the mouthpiece is transmitted along the line fZ in the direction of the solid arrow.
31c is sent out, and resistance 4 and 'r! Two audio signals are applied to the differential amplifier in the direction of the solid arrow through the L flow blocking capacitor (to) and the resistors i, *m to stop capacitor (to). At this time, R1=R.

If Cr = C2 and ZL = ZM are selected, the two audio signals applied to the differential amplifier will have the same phase and the same tL flow, and no audio signal will be generated at the output of the differential amplifier. A side sound protection circuit is formed. Next, when an audio signal is applied in the direction of the arrow shown by the solid line from the line in Figure 3, the DC blocking capacitor (E), resistor □□□, resistor (goods) and DC blocking capacitor ■ Two audio signals are applied to the dynamic amplifier in the directions of solid and dotted arrows. At this time, the two audio signals are not in phase and in the same flow, but the differential amplifier functions as an amplifier, and the audio signals flow to the receiver in the direction of the arrow shown by the solid line. Therefore, side noise is small, and a side noise prevention circuit is formed in which the audio signal applied from the line can be heard from the receiver.

〔Effect of the invention〕

As described above, according to the present invention, since the configuration uses a differential amplifier instead of a pipe print coil, it is possible to obtain an apparatus that is small and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a side sound protection circuit according to an embodiment of the present invention, FIG. FIG. 3 is a circuit diagram showing the direction of the audio signal during reception of a side sound protection circuit according to an embodiment of the present invention, FIG. 4 is a circuit diagram showing a conventional side sound protection circuit, and FIG. 5 is a circuit diagram showing the conventional side sound protection circuit. A circuit diagram showing the direction of the audio signal when the sidetone circuit transmits a call, and FIG. 6 shows the direction of the audio signal when the conventional sidetone protection circuit receives a call. The circuit diagram shown is Ruru. In the figure, C211 is the transmitter, of course the receiver, Q3 is the line, ■
is a balanced circuit, ni), (b) is a resistor, (to), @ is a capacitor length, and 4 is a differential amplifier. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A differential amplifier between the transmitter and the receiver is provided in a sound protection circuit of a two-wire voice communication device in which a transmitter and a receiver are connected to a line terminal, and the output of the transmitter is connected to the differential amplifier. A side sound protection circuit characterized in that the output of the differential amplifier is input to both input terminals, respectively, and the output of the differential amplifier is input to the receiver.