JPS62290251A - Handfree telephone set - Google Patents

Abstract

PURPOSE:To prevent a side tone, and a howling, by generating an offset current having the negative phase of a transmission/reception current based on the latter, and overlapping it on the transmission/reception current, in a telephone set in which a transmission/reception is performed by a microphone, and a speaker provided on a telephone set main body. CONSTITUTION:By inputting a sound from a microphone 10, a sound signal is phase-advanced by a phase advancing circuit 30, and is amplified at a positive inversion amplifier 50, and a positive(continuous line) sound signal is outputted toward a point C, and a negative (dotted line) sound signal, toward a point B. Simultaneously, a phase-advanced sound signal is changed to the one with the negative phase (dotted line) by an inversion amplifier 60, and it is overlapped on, the positive sound signal at a point D, thereby, the side tone is prevented. Prior to the above, the phase-advanced sound signal is level-controlled by the negative sound signal fedback at a point A, and its gain is adjusted so that an offset effect between the positive and the negative phases arrives at a prescribed level. As a result, the sound outputted from a speaker 20 is decreased to a micro level, and the howling can be prevented. Also, the sound signal between the points B and C is sent out onto a line. telephone line.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a hands-free telephone that prevents sidetone and oscillation (howling) with a simple circuit configuration. .

[Conventional technology]

An example of a transmitting/receiving circuit in a conventional telephone is shown in FIG. This transmitting/receiving circuit is a 2-wire to 4-wire conversion circuit using a resistive hybrid system, and the terminals are
, and a transmitter 'J'&1 is provided between points B and D, which is connected via a 24Ω resistor R1 and an amplifier 3, and a balancing net 5 is connected between points B and C.
However, a resistor R3 of 150Ω is provided between points C and D. At the point, capacitor C4, resistor R6 and amplifier 4 are connected.
The receiver 2 is connected via the line, and the point E is at ground potential (via the line). Here, transmitter 1 and receiver 2
is built into the handset and connected to the phone body via a cord.

In the above configuration, when voice is input to the transmitter 1, the point B
, C, and is sent to the line, and the voice signal received from the line is turned on, appears between E, and is output as voice from the receiver 2. Therefore, simultaneous communication between the sender and the receiver becomes possible.

Now, between points BSD, between points DXC, points C, E, and point B
, E is ZBD, Z, and Z. E, and ZIIE, Zllo・ZCE= Znc'
When ZIIE is established, the audio signal between points B and C will no longer appear as a point, resulting in complete sidetone prevention, but in reality, Z
A slight amount of sidetone is generated in the relationship between RD, ZCE, ZDC, and ZBE to approximate an actual dialogue situation.

[Problem that the invention seeks to solve]

However, according to the transmitting/receiving circuit in a conventional telephone, if the handset is eliminated and the telephone is used as a hands-free telephone having a speaker and a microphone, an amplifier with a large amplification factor will be used for both the microphone circuit and the speaker circuit. The sound input from the microphone is transmitted to the speaker circuit due to the sidetone effect.
This is greatly amplified and output as sound from the speaker, which is then input to the microphone again. This is repeated and a slight phase lag occurs between the sounds input to the microphone, resulting in oscillation (howling) and degrading the quality of transmission and reception.

[Means for solving problems]

The present invention has been made in view of the above, and in order to prevent sidetones and the accompanying howling, a canceling current having the opposite phase to the transmitting/receiving current is generated based on the transmitting/receiving current. The present invention provides a hands-free telephone in which this canceling current is superimposed on the current.

Hereinafter, the hands-free telephone according to the present invention will be explained in detail.

〔Example〕

FIG. 1 shows an embodiment of the present invention, in which 10 is a microphone, 20 is a speaker, 30 is a phase advancing circuit that advances the phase of the audio signal of the microphone 10, 40 is an amplifier that amplifies the audio signal input to the speaker 20, 50 amplifies the audio signal phase-advanced by the phase-advancing circuit 30 and outputs it to point C in the same phase;
60 is an inverting amplifier that outputs the phase-advanced audio signal in reverse phase, 70 is a choke coil CH and resistor R, which together with the capacitor CI constitute the negative feedback gain side 2711 circuit. 80 is a current generation source;
Dl is a negative feedback control diode, C2 is a capacitor that is the source of the internal circuit, Rz and R:+ correspond to those in Figure 3, and 90 corresponds to the balancing network 5 in Figure 3. It is.

In the above configuration, when a voice is input from the microphone 10, the phase of the voice signal is advanced by the phase advance circuit 30, amplified by the positive inverting amplifier 50, and the voice signal is in positive phase (solid line) toward point C.
An audio signal of opposite phase (dotted line) is output toward point B. At the same time, the phase-advanced audio signal is made to have an opposite phase (dotted line) by the inverting amplifier 60, and is superimposed on the positive-phase audio signal at the point to prevent sidetone. Prior to this, the level of the forward F-th audio signal is controlled by the negative phase audio signal that is negatively fed back at point A, and its gain is adjusted so that the canceling effect of both positive and negative phases at the point reaches a predetermined level. be done.

As a result, the sound output from the speaker 20 becomes minute and howling is prevented. In addition, audio 1 between points B and C
No. 8 is sent out onto the line in the same manner as in the example of FIG.

On the other hand, as shown in FIG. 2, even if the audio signal received from the line appearing as a dot is input as audio from the speaker 20 to the microphone 10, the opposite signal at point A and point B will be generated as in the case of FIG. Howling is prevented by the superposition of phase currents.

Note that with the above telephones, earphones can be used when making confidential calls.

〔Effect of the invention〕

As explained above, according to the hands-free telephone unit of the present invention, a canceling current having an opposite phase to the transmitting/receiving current is generated based on the transmitting/receiving current, and this canceling current is superimposed on the transmitting/receiving current. It is possible to prevent this and suppress the occurrence of howling associated with this.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are explanatory views showing one embodiment of the present invention. FIG. 3 is an explanatory diagram showing a conventional transmitting/receiving circuit. Explanation of symbols 10---Microphone 20---m=・
-Speaker 30・-・・−phase advance circuit 40−・−
・-Amplifier s o----1・Positive inverting amplifier 60・----Inverting amplifier Patent applicant Nippon Tsuken Co., Ltd. Agent Patent attorney Hei 1) Tadao Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] A telephone that transmits and receives calls using a microphone and a speaker provided on the telephone body, comprising means for generating a current having a phase opposite to a transmitting and receiving current, and generating sidetone in the transmitting and receiving current using the current having the opposite phase. A hands-free telephone characterized by comprising means for overlapping on the side.