JPH0260268A - Hand-free circuit for vehicle telephone - Google Patents

Abstract

PURPOSE:To prevent the meaningless switching of a path at the time of the silence of both sides by controlling the path so as to give always attenuation to a receiver side path at the time of the silence of both a transmitter side and a receiver side by impressing very small bias voltage to a transmitter side path before being inputted to a comparator. CONSTITUTION:The voltage VC of a fixed voltage source 13 in a circuit is used as the bias voltage VB to be impressed to a signal VT outputted from a transmitter side sound level detection circuit 5. Thus, even at the time of the silence of both the transmitter side and the receiver side, i.e., even when (VT, VR)=(0, 0), since VB is inputted to the comparator 11 through R1 as a transmitter side sound level, the comparator 11 decides that the transmitter side path is large in its sound level, and a switch 9 is controlled so that the signal to be inputted to the receiver side path passes through an attenuator 8 always.

Description

[Detailed description of the invention] [Table of contents] (Existing industrial fields of application, prior art (Fig. 5) Means for solving the problem to be solved by the invention (Fig. 1) Working examples (1) ) First embodiment (FIGS. 2 and 3) (2) Second embodiment (FIG. 4) Effects of the invention [Summary] The present invention relates to a hands-free circuit for a car phone, and in particular, In a hands-free circuit that performs path control to attenuate the audio path on the transmitting side or the receiving side of a hands-free car phone with the aim of fixing the path to prevent meaningless path switching when both sides are silent. , a transmitting side switching means to which an attenuated signal and a non-attenuated signal of the transmitted signal are input, a receiving side switching means provided with a signal output terminal for attenuating the received signal and a non-attenuated signal output terminal, and controlling these switching means. A comparison means for outputting a control signal to control the transmission, and a biasing means for selecting the transmission side signal path preferentially when no transmission signal or reception signal is input to the signal input to the comparison means, When there is silence on the receiving side, the transmitting side path is given priority and the receiving side path is attenuated.

[Industrial Field of Application] The present invention relates to a hands-free path control system for a hands-free mobile phone, and more particularly to a path control system when both the transmitting and receiving sides are in a silent state.

[Conventional technology]

In conventional hands-free telephones for vehicles, a hands-free circuit for preventing howling is usually used in order to suppress howling caused by the sound from a speaker being picked up by a microphone. Although there are various types of howling prevention circuits, a common method is a path control method that applies attenuation to the transmitting side path or the receiving side path depending on the volume relationship between the paths on the transmitting side and the receiving side.

For example, if a caller turns off the receiving signal path of the other party while they are talking, it will result in a one-way conversation.
It attenuates the signal received by the other party to the extent that howling does not occur, and on the other hand, when the other party is speaking, the signal transmitted from the microphone side of the caller is attenuated.

FIG. 5 shows a conventional hands-free circuit for a car phone.

In FIG. 5, 1 is a microphone, 2 is an amplifier on the transmitting side, 3 is an attenuator on the transmitting side, 4 is a switch on the transmitting side, 5 is an audio level detection circuit on the transmitting side, 6 is a speaker, and 7 is an amplifier on the receiving side. , 8 is a receiving side attenuator, 9 is a receiving side switch, 10 is a receiving side audio level detection circuit, and 11 is a comparator.

In the hands-free circuit shown in FIG.
Path control is performed to prevent howling by attenuating signals with low audio levels.

For example, when a caller speaks, a transmitting signal input from the microphone 1 is output via the transmitting side audio level detection circuit 5 and outputs V.
T is input to the comparator 11 and is compared with the reception signal output VR which is simultaneously input to the comparator 11 via the reception side audio level detection circuit 10.

In this case, since the transmitting signal output (7) is large, the transmitting signal is not attenuated and is directly transmitted to the transmitting output circuit through the switch 4.

On the other hand, the received signal whose audio level is determined to be low is transmitted from the switch 9 via the attenuator 8, attenuated, and then sent to the speaker side.

[Problem to be solved by the invention]

However, in a hands-free phone for use in a vehicle, there is generally a lot of engine noise, running noise, etc. inside the vehicle, so path switching malfunctions are more likely to occur than in a hands-free phone for indoor use. This is when a path is switched during a call due to running noise such as a horn from the vehicle, causing the call to be interrupted or the volume to suddenly decrease.

Furthermore, due to the surrounding noise of the vehicle, the switching noise at the time of path switching can be clearly recognized as the voice of a land-side telephone, such as an indoor one.

In particular, when there is no call, that is, when both parties are silent, the relationship between the audio levels on the sending and receiving sides is unstable, so even when the telephone is not in use, the path between the sending side and the receiving side is In the meantime, meaningless path switching occurs, causing switching noise.

Furthermore, due to variations in the manufacturing process of telephones, a specific bus may be selected when both parties are silent, and as a result, paths are switched every time there is a change in ambient noise such as driving noise. Such meaningless path switching can be heard as intermittent changes in the ambient noise, increasing or decreasing, which causes discomfort to the user.

Therefore, an object of the present invention is to fix the path of the hands-free circuit in a hands-free phone for a car phone so that pointless path switching is not performed when both parties are silent, and in this case, the hands-free circuit on the vehicle side is fixed. This system prioritizes the calling path and attenuates the receiving signal, enabling smooth hands-free calls.

[Means to solve the problem]

In order to achieve the above object, the present invention applies a minute bias voltage to the transmitting side path before inputting it to the comparator.
Path control is performed so that attenuation is always applied to the receiving side path when both sides of the receiving side are silent.

FIG. 1 is an explanatory diagram of the principle of the hands-free circuit of the present invention.

In Fig. 1, 1 is a microphone, 2 is an amplifier on the transmitting side, 3 is an attenuator on the transmitting side, 4 is a switch on the transmitting side, 5 is an audio level detection circuit on the transmitting side, 6 is a speaker, and 7 is an amplifier on the receiving side. , 8 is a receiving side attenuator, 9 is a receiving side switch, 10 is a receiving side audio level detection circuit, 11 is a comparator, and 12 is a bias voltage source.

In the present invention, the transmitting signal output V via the transmitting side audio level detection circuit 5 which converts the audio level into a DC level.
For example, a bias voltage (V) corresponding to the output of the audio level detection circuit on the transmitting side, which is always very small, is applied to V, +V.
, and is input to the comparator 11.

Therefore, when both parties are silent, the output of the comparator 11 always becomes the transmitting signal>the receiving signal.

[Effect]

As a result, the transmitting side path is controlled so that it directly passes through the switch 4 without going through the attenuator 3 and is output to the transmitting output, while the receiving side bus is always received via the attenuator 8. It is controlled to attenuate the signal and output it to the speaker side.

〔Example〕

(1) First Embodiment As an embodiment of the present invention, an example in which the bias voltage (2) is obtained from the in-circuit power supply (2) will be described.

FIG. 2 is a hands-free circuit of the present invention. In FIG. 2, the same symbols as in FIG. 1 indicate the same parts, 13 is a fixed voltage source, 21 is a diode for detecting the audio level on the transmitting side,
22 indicates a diode for detecting the audio level on the receiver side, and C
1. C2 is a smoothing capacitor, and R1% and R4 are resistors.

In this embodiment, the voltage (2) of the fixed voltage source 13 in the circuit is used as the bias voltage V to be applied to the signal (7) output from the transmitting side audio level detection circuit 5. That is, VIl obtained by dividing voltage VC by resistors R3 and R4 is divided by resistor R
1 to the input end of the transmitting path to the comparator 11.

By configuring as in this embodiment, even when there is no sound on both the transmitting side and the receiving side, that is, (Va, VR) = (0, 0), V is compared as the transmitting side audio level through R1 on the transmitting side path. Since the signal is input to the receiver 11, the comparator 11 determines that the audio level of the transmitting side path is high, and the switch 9 is controlled so that the signal inputted to the receiving side path always passes through the attenuator 8.

Of course, if there is input from a phone call etc. to the receiving bus, V,
>V, +V, and the output of the comparator 11 is determined to be the receiving side audio level > the sending side audio level, and the bus passing through the attenuator 3 is selected as the sending side path, and the receiving side bus is given priority. .

Note that the capacitors C1 and C2, together with the impedance and resistors R1 to R4 in each audio level detection circuit, obtain the time constant (attack time) of the rise response at the time of audio input and the time constant of the discharge response at the end. .22 makes the rising response faster and the resistance R1+
R4 and resistor R2 delay the end of the process.

FIG. 3 is an operational explanatory diagram showing the relationship between the audio level when the transmitting side bus and the receiving side bus are each prioritized.

In the region ■ where the audio level of the transmitting side is dominant, the signal passing through the receiving path is attenuated, and in the region ■ where the audio level of the receiving side is dominant, the signal passing through the transmitting path is attenuated, and the line (a)
b) shows the demarcation line for switching between the two buses.

The demarcation line (a) is a demarcation line when a conventional hands-free circuit is used. The audio level on the sending and receiving sides is (0,0
) is on the demarcation line (a), the bus selection becomes uncertain and meaningless switching occurs.

On the other hand, in the present invention, by applying the bias voltage VB to the signal 1 outputted from the transmitting side audio level detection circuit 5,
The demarcation line (b) for bus switching is shifted to the receiving side. Therefore, in order to switch to the receiving side path, the receiving human power voltage ERG is required, so that when both parties are silent, priority is always given to the transmitting side path.

Note that E Ro = V a−K Dwryr −
−−−−−(1) (KDtt*: detection coefficient of the receiving side audio level detection circuit) When expressed as
) --------... (2) From equation (2), the bus is always fixed on the transmitting side while the transmitting signal 7 input to the comparator 11 satisfies the above relationship.

In this embodiment, an example was explained in which a bias voltage was applied to the output of the transmitting side signal, but the receiving side audio level detection circuit 1
A similar effect can be obtained by adding a minute voltage (V or -V) with a polarity that reduces the voltage to the zero output.

(2) Second Embodiment As a second embodiment of the present invention, when each of the audio level detection circuits has a constant DC bias voltage, the bias voltage V for the transmitting side bus priority control is obtained. An example will be explained with reference to FIG.

In FIG. 4, the same symbols as in FIG. 1 indicate the same parts.
Reference numeral 14 indicates a voice level detection circuit on the transmitting side, and 15 indicates an audio level detection circuit on the receiving side.

In this embodiment, each of the audio level detection circuits 14 and 15 has a DC bias voltage, so even when there is no sound on both the transmitting side and the receiving side, the output bias voltages of D7o and VDRO exist, respectively, and in the transmitting side path, the resistor Rs , R6, and input it to the comparator 11 as VDT.

On the other hand, on the receiving side path, the voltage is divided by resistors R7 and R8. ,
is input to the comparator 11 as .

Therefore, if the micro bias voltage for which the comparator 11 always determines that the transmitting side path is dominant is ■, then Voyo-
Rs/(Rs +Rs)=V+++(Vollo'Rs
/(R7+Ra))・−・−(3) Each resistance value R5, R6, R7, R
8 should be set.

By configuring as shown in Fig. 4, the bias voltage (V DTOLV
o*o) are the same (e.g. V DTO= V IIRQ
= 10v), the comparator 11 always determines that the transmitting side path is superior, and performs control to attenuate the signal (for example, noise) input to the receiving side path.

In this case, the detection voltage VDT is generated by resistors R5 and R8. Attenuation of and detection voltage ■ by resistors R7 and R8. .

There will be a difference in the attenuation of 0, and there is a concern that it will affect each audio level detection circuit at the time of input. There is no problem if you correct it.

It goes without saying that this object can be achieved by making the DC bias of each audio level detection circuit have a predetermined DC potential difference in some way.

〔Effect of the invention〕

According to the present invention, in a hands-free circuit for a car phone, bus control when both the transmitting and receiving sides are silent can be fixed by simply adding a very simple circuit. It is possible to prevent meaningless path switching.

Moreover, by using the prioritized bus as the transmission path for the on-board phone, land-side users can always hear the on-board voice and surrounding sounds when they are not speaking, allowing them to make hands-free calls. You can talk on the phone without being disturbed by the switching noise caused by the unique bus switching.

[Brief explanation of the drawing]

Fig. 1 is an illustration of the inventive principle of the hands-free circuit of the present invention, Fig. 2 is an illustration of the first embodiment of the invention, Fig. 3 is an illustration of the operation of the invention, and Fig. 4 is a diagram of the second embodiment of the invention. FIG. 5 is an explanatory diagram of a conventional hands-free circuit. 3.-Sending side attenuator, 4-Sending side switch, 5-Sending side audio level detection circuit, 6-.-Speaker, 7-Receiving side amplifier, 8-.
- Receiving side attenuator, 9-.- Receiving side switch, 10-.
- receiving side audio level detection circuit, 11... comparator,
12--Bias voltage, 13--Fixed power supply voltage. Patent Applicant Fujitsu Ltd. Representative Patent Attorney Akira Yamatani 1-Microphone, 2-Sending side amplifier, invention! Detour Figure 1 This invention, 1st history Shii J, l#AT; ZJ Figure 2 wj Kui Mo Ming times Figure 3

Claims (3)

[Claims] (1) In a hands-free circuit that performs path control to attenuate the audio path on the transmitting or receiving side of a hands-free car phone, a transmitting-side switching means (4 ), receiving side switching means (9) provided with a signal output terminal for attenuating the received signal and a non-attenuating signal output terminal, and comparison means (9) for outputting a control signal for controlling these switching means (
11), and a bias applying means (12) is provided for the signal input to the comparing means (11) so that the transmitting side signal path is selected preferentially when no transmitting signal or receiving signal is input. A hands-free circuit for a car telephone, characterized in that when the receiving side is silent, the transmitting side path is given priority and the receiving side path is attenuated. (2) The hands-free circuit for a car telephone according to claim 1, characterized in that a fixed voltage source V_B is used as the bias applying means. (3) The hands-free circuit for a car telephone according to claim 1, wherein level detection means (14) and (15) having different sensitivities on the transmitting side and the receiving side are used as the bias applying means.