JPS62168445A - Hand-free circuit with singing protecting circuit - Google Patents

Abstract

PURPOSE:To generate no singing even if a sound coupling quantity or a return loss is varied remarkably, by detecting a singing state, and controlling automatically a sound volume regulator inserted into a receiving system circuit. CONSTITUTION:When it is detected that singing exists in the output of a variable losing circuit 3, a singing detector 1 starts a sound volume regulator 12. The sound volume regulator 12 increases the attenuation quantity to a signal, and lowers a loop gain to singing of a closed loop passing through aloud speaker 4 a microphone 1 a transmitting system circuit a receiving system circuit the loudspeaker 4, to a loop gain or below of the limit of generation of singing. In this way, even if an acoustic coupling quantity or a return loss is varied remarkably, no singing is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hands-free circuit with a ringing protection circuit used in a car telephone device or the like.

(Prior Art) FIG. 2 is a block diagram showing an example of the configuration of a conventional hands-free telephone device (for example, Japanese Patent Laid-Open No. 56-117463
1 is a microphone, 2 is an amplifier, 3 and 6 are variable loss circuits, 4 is a speaker, 5 is a power amplifier, 7 is an audio switch control circuit, 8 is a hybrid transformer, 9 is a volume variable circuit, 10 is an AGO It is a circuit. In FIG. 2, variable loss sections 3 and 6 are inserted into the closed loop to prevent noise caused by the closed loop consisting of the speaker 4, the space, the microphone 1, the hybrid transformer 8, and the speaker 4. Based on the outputs of the amplifier 2 and the variable loss circuit 6, the audio switch control circuit 7 makes the loss variable when the loss of the variable loss circuit 3 is large, makes the loss of the loss circuit 6 small, and conversely makes the loss of the variable loss circuit 3 small. Variable loss circuit 6 when small
The closed loop is given a fixed amount of loss that does not cause noise.

(Problem to be Solved by the Invention) However, when the device with the above configuration is applied to a car phone system, etc., the amount of acoustic coupling between the microphone 1 and the speaker 4, or the amount of return loss of the hybrid transformer 8 becomes an abnormal value, which is not designed Exceeding the range often occurs and generates a ringing sound.

In order to avoid this, if the amount of loss in the variable loss circuits 3 and 6 is set to be sufficiently large, a problem arises in that simultaneous communication, which is essential for smooth conversation, is impaired and a satisfactory conversation condition cannot be obtained.

The present invention eliminates the above-mentioned problems and provides a band circuit with a sound protection circuit that does not generate sound even if the acoustic coupling amount or return loss changes significantly and does not impair simultaneous conversation performance. The purpose is to

(Means for Solving the Problems) The present invention provides a single frequency signal that inputs a signal from either a transmitting system circuit or a receiving system circuit, and maintains a predetermined level or higher for a predetermined period of time. A sound detector is inserted into the other circuit to detect that the sound has a component of This is a hands-free circuit with a noise protection circuit, characterized in that it is equipped with a volume adjuster for setting a predetermined gain.

(Function) The sound detector detects when sound occurs in the closed loop including the transmitting system circuit and the receiving system circuit. The volume adjuster reads the output level of the sound detector at regular intervals, and when the level is low, controls the gain to an externally specified value.

However, when a sound occurs and the output of the sound detector becomes a high level, the volume controller reads it and reduces the gain by a certain amount to lower the closed loop gain. This operation of reducing the gain is repeated until the sound stops.

(Embodiment) Fig. 1 is a block diagram showing an embodiment of the present invention, in which a ringing detector 1 is provided in the noise-free telephone device shown in Fig. 2, and a volume variable circuit 9 shown in Fig. 2 is provided. Instead, a volume adjuster 12 is provided which is controlled by the output of the sound detector 1, and the transmitting terminal T and receiving/receiving terminal are connected to a radio or a vibration nut (not shown). Sound detector 1
1 activates the volume adjuster 12 when it detects that there is a sound in the output of the variable loss circuit 3. The volume adjuster 12 increases the amount of attenuation for the signal, and
- Transmitting system circuit (amplifier 2 - transmitting terminal T) - Vibride etc. (not shown) - Receiving system circuit (receiving terminal R - power amplifier 5
) ~ The sound is stopped by lowering the open loop gain for the closed loop sound generated via the speaker 4 below the open loop gain that is the limit for generating the sound.

FIG. 3 shows an embodiment of the sound detector 11.

In FIG. 3, 21a to 21d are operational amplifiers, and 22a to 21d are operational amplifiers.
22e is a capacitor, 23a to 23e are diodes, 2
4a to 24m are resistors. A part of the output of the variable loss circuit 3 shown in FIG.
a, resistor 24a.

The waveform is shaped by the Cmit circuit consisting of 24b,
Diodes 23a, 23b, capacitors 22a-22b
, and is converted into direct current by a rectifier circuit consisting of a resistor 24c. The output waveform of the seamit circuit is different depending on whether the input to the terminal 20 is a sound having a single frequency or a voice having a random frequency, and the output of the rectifier circuit is larger when the input is a sound. Therefore, it is possible to determine whether the sound is a ringing sound or not. The effectiveness of the determination can be further improved by inserting a bandpass filter that filters out frequencies near the sound frequency on the output side of the seamit circuit. The output of the rectifier circuit is passed through an impedance conversion circuit consisting of an operational amplifier 21b to a capacitor 22c.

The signal is input to a time constant circuit including a diode 23c and resistors 24d and 24e. The time constant circuit determines the duration of the input signal, and if it continues for a predetermined time or more, it is determined to be a sound, and together with the determination by the seamit circuit and the rectifier circuit, the sound state is determined reliably. Make it. Note that the diode 23c quickly discharges the capacitor 22c.

On the other hand, part of the input from the terminal 20 is amplified by an amplifier consisting of an operational amplifier 21c, a resistor 24 (, 24g), capacitors 22d, 22e, and a diode 23d.

23e, and a rectifier circuit consisting of a resistor 24h converts it into direct current. The direct current flows through an operational amplifier 21d, resistors 24i and 24j
The level is judged by a threshold circuit consisting of the following, and when the level is above a certain level, the transistor 25 is turned off by the output of the threshold circuit. Transistor 25 is OFF
In this case, the output of the time constant circuit is the operational amplifier 21e.

When the signal is above a certain level determined by a threshold circuit including resistors 24I and 24m, a signal is outputted from the threshold circuit to the transmitting terminal 26. This output signal activates the phase shift circuit 12 shown in FIG.

As explained above, the sound detector shown in Fig. 3 detects sounds by utilizing the fact that sounds have a single frequency and last for a certain period of time, whereas sounds have random frequencies. However, when the sound reaches a certain level or higher, a signal is output to start the volume adjuster.

FIG. 4 shows an embodiment of the volume adjuster 12 shown in FIG.

In FIG. 4, 30 is an input terminal connected to the output of the AGO circuit 1θ shown in FIG. 33a to 33h are resistor strings, and the signal inputted from the input terminal 30 is transmitted to the input terminals Q0 to QtKM of the switch circuit 340 from the connection point of each resistor while gradually attenuating. The switch circuit 34 connects one of the input terminals Q0 to Q7 to the output terminal CO in response to control signals DA, DB, and DC from the volume setting circuit.
Connect M.

The output terminal 00M is connected to the input side of the variable loss circuit 6 shown in FIG. 1 via the output terminal 3. On the other hand, input terminal 32
is connected to the sound detector 1 shown in FIG. The volume setting circuit 35 reads output data from a controller 36 such as a radio and the output from the sound detector 11, and outputs outputs DA, DB, and DC for setting the switches of the switch circuit 34. That is, the volume setting circuit 35 first sends control signals DA, DB, and D to the switch circuit 34 so as to give an attenuation amount corresponding to the data from the controller 36 to the input signal from the input terminal 3θ.
Send C. Next, the level of the input signal from the input terminal 32 is determined, and if the level is HIGH, the output terminal COM of the switch circuit 34 is connected to the input terminal Q. From Q. +
Control signals DA, DB, and DC are sent to change the connection to 1, and when the level thereof is LOW, no control is performed on the switch circuit 34. The above operation is repeated, for example, every 0.1 seconds as the signal stabilization time. FIG. 5 is a flowchart illustrating the operation of the p IJ neem setting circuit 35. An experiment in a certain area revealed that the loss of the hybrid transformer shown in Fig. 1 is 15 to 20 dB compared to the usual 15 to 20 dB, but that there are lines with O dB, although the probability is small. In a typical hands-free device, this amount of loss is 6 dB.
Since it can withstand only a certain amount of noise, the user must manually adjust the volume each time it makes a noise. According to this embodiment, this can be done automatically.

(Effects of the Invention) As explained above, according to the present invention, the sound state is detected and the volume adjuster inserted into the receiver circuit is automatically controlled. There is no need to adjust.

The present invention provides an effective protection function against the risk of ringing, which is unavoidable in current car telephone systems, when the automatic telephone is equipped with a hands-free calling function.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the hands-free circuit according to the present invention, and FIG.
FIG. 3 is an operation flowchart of a conventional hands-free telephone device, FIG. 3 is a ringing detector, FIG. 4 is a volume adjuster, and FIG. 5 is an operation flowchart of a yl-'IJ,-me setting circuit. 1... Microphone, 2... Amplifier, 3, 6...
Variable loss circuit, 4...Speaker, 5...Power amplifier, 7...Audio switch control circuit, 10...AQC circuit, 1...Sound detector, 2...Volume adjustment Equipment Patent Applicant: Oki Electric Industry Co., Ltd.'-1, +, 6, 6, 1, 1, 1, 1, 1, 1, 1, 2, 3, 5, 5, 1, 1, 1, L) to #II\゛7 people 7 Lee U story 1! Figure 2 Figure 3 Person t! 1llt instrument procedural amendment (Mutsu) 62, 3.23 Showa year month day

Claims (1)

[Claims] (1) A sound that inputs a signal from either the transmitting circuit or the receiving circuit and detects that the signal has a single frequency component that lasts at a predetermined level or higher for a predetermined period of time or more. A sound detector and a volume control device inserted into the other circuit to read the output level of the sound detector at regular intervals and reduce the gain by a certain amount when the level is high, and set the gain to a predetermined gain when the level is low. A hands-free circuit with a noise protection circuit characterized by being equipped with a regulator.