JPH0311983Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a hands-free control circuit for a telephone with a hands-free calling function. The present invention relates to a hands-free control circuit that can prevent radio waves from being emitted from a speaker.

(Prior Art) A hands-free circuit using a so-called voice switching method is known, which performs a loudspeaker call by comparing the levels of a transmitting voice and a receiving voice and giving priority to the voice with a higher level.

Such a hands-free circuit has a transmitting/receiving level comparison circuit that compares the levels of the transmitting voice and the receiving voice, and the switching operation between transmitting and receiving is performed by the signal from the transmitting/receiving level comparing circuit. In general, the above-mentioned transmitting/receiving level comparison circuit operates even in states other than hands-free calling, and in this state, the transmitting and receiving levels are unstable around zero, so the transmitting and receiving levels are unstable. The switching is repeated irregularly, resulting in switching noise, which is emitted from the phone's speaker.

In order to prevent the emission of this switching noise, conventionally,
When making hands-free calls, the amplifier on the speaker side of the phone was disconnected using a switch.

(Problems to be Solved by the Invention) According to the above-mentioned conventional hands-free circuit, a switch means is required to connect and control the amplifier on the speaker side of the telephone. In addition to installing a hands-free additional device, it is necessary to modify the speaker to install a switch means for connecting and controlling the speaker side amplifier.

The present invention is proposed to solve these problems, and is a hands-free control that does not require a switch to connect and control the amplifier on the speaker side of the telephone, and therefore allows the addition of a hands-free function easily. The purpose is to obtain a circuit.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides
A switch means is provided at the receiving level input terminal or the transmitting level input terminal of the receiving level comparison circuit, and the switching means fixes the receiving level input terminal or the transmitting level input terminal to a high level or a low level when not making a hands-free call. By doing so, the transmission/reception switching operation is not performed, thereby preventing switching noise from occurring.

(Configuration of Example) The drawing is a circuit diagram showing an embodiment of the present invention.

As shown in the drawings, the hands-free control circuit according to the embodiment includes a receiving amplifier circuit 1 that amplifies received voice, a transmitting amplifier circuit 2 that amplifies transmitted voice,
A diode 3 for rectifying the output signal (alternating current) of the receiver amplifier circuit 1, a capacitor 4 and a low resistor 5 for smoothing the signal rectified by the diode 3 into a receiver level signal (direct current) corresponding to the output signal, and a transmitter. Regarding speech audio, it has the same function as the diode 3, capacitor 4, and resistor 5, and the speech amplifier circuit 2
A diode 6 and a capacitor 7 that generate a transmission level signal (DC) corresponding to the output signal (AC) of the
and a resistor 8, a transmitting/receiving level comparison circuit 9 for comparing the levels of the receiving level signal and the transmitting level signal,
It is turned on or off by the state identification signal input to the control terminal 10, and when it is turned on, the level of one of the inputs of the transmitting/receiving level comparison circuit 9 (in the case of the embodiment, the transmitting level input terminal 9A) is fixed. Transistor 1 functioning as a switching means (fixed at ground level (low level) in the case of the embodiment)
It is made up of 1st class.

This hands-free control circuit consists of transistor 1
The parts other than the level fixing circuit No. 1 are the same as the conventional hands-free control circuit.

Further, the level fixing circuit using the transistor 11 may be connected to the receiving level input terminal 9B of the transmitting/receiving level comparison circuit 9, and the level to be fixed may be set to high level (that is, a PNP type transistor may be used as the transistor 11). and connect that emitter to the positive level).

(Operation of the Embodiment) The signal input to the control terminal 10 is a status identification signal that identifies whether the call that has occurred is a normal call (a call made using a handset) or a hands-free call. For example, a signal can be used to control the on/off of a microphone.

During a hands-free call, the state identification signal input to the control terminal 10 is a low level signal. Therefore, transistor 11 is off, and the hands-free control circuit performs the same hands-free control operation as in the prior art.

When not in a hands-free call (during a normal call or when no call is occurring), the state identification signal input to the control terminal 10 is at a high level and the transistor 11 is turned on. As a result, the input terminal 9A of the transmitting/receiving level comparison circuit 9 is fixed at a low level (earth), and the output signal of the transmitting/receiving level comparing circuit 9 is fixed to the receiving control signal side. As a result, irregularly repeated switching operations in the transmitting/receiving switching circuit (not shown) of the hands-free control circuit are suppressed, and switching noise is eliminated.

(Effects of the invention) As is clear from the above explanation, the present invention allows the hands-free control circuit to set the level of one input of the sending/receiving level comparison circuit to a low level or a high level when the hands-free call is not being made. By fixing it to For example, when adding a hands-free function, there is no need to modify other parts of the phone (for example, the amplifier circuit on the speaker side), making it extremely easy to add the function. It will be done.

[Brief explanation of the drawing]

The drawing is a circuit diagram of an embodiment of the present invention. Main symbols, 9...Sending/receiving level comparison circuit, 1
0... Control terminal, 11... Switch means (transistor).

Claims (1)

[Scope of utility model registration request] A hands-free control circuit using a voice switching method, which has a transmitting/receiving level comparison circuit that compares the transmitting voice level and the receiving voice level, and switches between transmitting and receiving based on the output of the transmitting/receiving level comparing circuit. is connected to either the receiving level input terminal or the transmitting level input terminal of the transmitting/receiving level comparison circuit, and is activated by the input of a signal that distinguishes between a hands-free call state and other states, A hands-free control circuit comprising a switch means for fixing the level of the receive level input terminal or the transmit level input terminal in a state other than a hands-free call.