JPS62159924A - Hand free circuit with singing protection circuit - Google Patents

Abstract

PURPOSE:To stop the singing in a telephone set such as an automobile telephone set by providing a singing detector and a phase shift circuit to a talking device, using the phase shift circuit to change the phase of the signal and decreasing the closed loop gain to the singing component. CONSTITUTION:The hand free talking device is provided with the singing detector 11 and the phase shift circuit 12. Then the singing detector 11 detects the singing by utilizing that the singing has a single frequency and is consecutive for a prescribed time and outputs the signal to start the phase shift circuit 12 when the singing reaches a prescribed level or over. Thus, the phase shift circuit 12 changes the phase of the signal from a variable loss circuit 6 and gives an output to a power amplifier 5. Since the phase of the singing component is changed, the gain of the singing component in the closed loop comprising a path of speaker 4 - microphone 1 - transmission system circuit (amplifier 2 - transmission terminal T) - hybrid or the like (not shown in figure) - reception system circuit (reception terminal R - power amplifier 5) - speaker 4 is decreased to stop the singing.

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 variable volume circuit, 10 is an AGC It is a circuit. In FIG. 2, in order to prevent noise caused by the closed loop consisting of the speaker 4, the space, the microphone 1, and the hybrid transformer 8 and the speaker 4, variable loss sections 3 and 6 are included in the closed loop.
is inserted. Based on the outputs of the amplifier 2 and the variable loss circuit 6, the audio switch control circuit 7 reduces the loss of the variable loss circuit 6 when the loss of the variable loss circuit 3 is taken as a dog, and conversely reduces the loss of the variable loss circuit 3. When variable loss circuit 6
A fixed amount of loss that does not cause noise is given to the closed loop.

(Problems 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 no-brid transformer 8 becomes an abnormal value. This often exceeds the design range, resulting in noise.

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

It is an object of the present invention to provide a hands-free circuit with a noise protection circuit that eliminates the above-mentioned problems and does not generate noise even if the acoustic coupling amount or return loss changes significantly, and does not impair simultaneous conversation performance. purpose.

(Means for Solving the Problems) The present invention provides a sound detection system that detects that a signal in a transmitting system circuit or a receiving system circuit has a single frequency component that continues at a predetermined level or higher for a predetermined period of time or more. The vessel and
The hands-free circuit with a sound protection circuit is characterized in that it includes a phase shift circuit that changes the phase of a signal in the transmitting system circuit or the receiving system circuit based on the output of the sound detector.

(Function) The sound detection circuit detects the sound generated in the closed loop formed by the microphone - transmitting system circuit - hybrid, etc. - receiving system circuit - speaker - microphone, and outputs it to the transmitting system circuit or the receiving system circuit. By activating the inserted phase shift circuit and changing the phase of the signal, the gain of the sound in the closed loop is reduced and the sound is stopped.

(Embodiment) FIG. 1 is a block diagram showing a first embodiment of the present invention.
1 and a phase shift circuit 12, and a transmitting terminal T,
The receiver terminal R is connected to a wireless device or a hybrid (not shown). When the sound detector 11 detects a sound state, it activates the phase shift circuit 12, and the activated phase shift circuit 12 changes the phase of the signal from the variable loss circuit 6 and outputs it to the power amplifier 5. Since the phase of the sound component also changes, the speaker 4~
Microphone 1 - Transmission system circuit (Amplifier 2 - Transmission terminal T)
The gain of the sound component in the closed loop that goes through ~hybrid etc. (not shown) ~reception system circuit (reception terminal R~power amplifier 5) ~speaker 4 decreases, and the sound stops.

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

In FIG. 3, 21h to 21d are operational amplifiers, and 22h to 21d are operational amplifiers.
22e is a capacitor, 23h 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, resistance 24a.

Multi-waveform shaping is performed by a Schmitt circuit consisting of 24b, diodes 23a, 23b, and capacitors 221L to 22b.
, and is converted into direct current by a rectifier circuit consisting of a resistor 24c. The output waveform of the Schmitt circuit is different when the input to the terminal 20 is a single frequency sound and when the input is a random frequency sound, 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. By inserting a bandpass filter covering the vicinity of the sound frequency on the output side of the seamit circuit, the effectiveness of the determination can be further improved. 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 consisting of a diode 23c and a resistor 24de24e. 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 judgment by the Schmitt 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, a part of the input from the terminal 20 is amplified by an amplifier consisting of an operational amplifier 21c, resistors 24f and 24g, capacitors 22d and 22e, and a diode 23d.

23e, and a rectifier circuit consisting of a resistor 24h converts it into direct current. The direct current is connected to the operational amplifier 21d and the resistors 241 and 243.
The level is judged by a threshold circuit consisting of the following, and when the level is above a certain level, the citransistor 25 is turned off by the output of the threshold circuit. Transistor 25 is OFF
In this case, if the output of the time-fixing circuit is equal to or higher than a certain level determined by a threshold circuit including an operational amplifier 21e and a resistor 241.24m, a signal is output 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 the sound by utilizing the fact that the sound has a single frequency and lasts for a certain period of time, whereas the sound has a random frequency. When the sound level exceeds a certain level, it outputs a signal to start the phase shift circuit.

FIG. 4 shows an embodiment of the phase shift circuit 12 shown in FIG. In Fig. 4, 31a to 31g are resistors, 32 is a capacitor, 33 is an operational amplifier, 34°35 is an FET, J6 is a flip-flop circuit, 37°38 is a transistor,
The terminals 30, 31 and 32 are connected to the output side of the variable loss circuit 6, the output side of the sound detector 11, and the input side of the power amplifier 5 shown in FIG. 1, respectively. When there is no input to the terminal 31, the flip-flop 36 is in a reset state, so the transistor 37 is turned on, the FET 3.5 is turned off, the transistor 38 is turned off, and the FET'34 is turned on. Therefore, the input signal from terminal 30 is FET3
It is output from the terminal 32 through ``4''. the first to terminal 31
When the signal from the sound detector 11 shown in the figure is input, the flip-flop 36 is set, so the transistor 37 is turned off, the FET 35 is turned on, and the transistor 38 is turned on.

FET 34 is turned off. Therefore, the input signal from the terminal 30 passes through a primary phase shift circuit consisting of resistors 31a to 31d, a capacitor 32, and an operational amplifier 33, changes the phase characteristics, passes through the FET 35, and is output from the terminal 32.

FIG. 5 is a block diagram showing a second embodiment of the present invention, in which a ringing detector 11 is connected to the receiving terminal R, and the output of the ringing detector 11 is transmitted to the variable loss circuit 3. The ringing state is stopped by activating the phase shift circuit 12 inserted between the terminal T and the talking terminal T, and has the same sounding state stopping effect as in the first embodiment described above. .

An experiment in a certain area revealed that the loss amount of the hybrid transformer 8 shown in FIG. 2 is normally 15 to 20 dB, but it has been found that there are lines of O dB, although the probability is small. In a normal hands-free device, this amount of loss is 6
Since it can withstand only about dB, the user must manually adjust the volume each time it generates a noise.

However, according to the first or second embodiment described above, the noise can be sufficiently prevented even under this condition, and moreover, it can be done automatically. (Effects of the Invention) As explained above, according to the present invention, the phase of the signal is changed by the phase shift circuit inserted in the receiving circuit or the transmitting circuit to reduce the closed loop gain for the sound component. This is to stop the beeping sound. Therefore, when a car telephone device is provided with a hands-free calling function, it becomes an effective protection function against the risk of ringing, which is inevitable in current car phone systems.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of a hands-free circuit according to the present invention, and FIG. 2 is a block diagram of a conventional hands-free communication device,
FIG. 3 is a block diagram of a second embodiment of a sound detector, FIG. 4 is a phase shift circuit, and FIG. 5 is a second embodiment of a hands-free circuit according to the present invention. 1... Microphone, 2... Amplifier, 3, 6...
Variable loss circuit, 4... Speaker, 5... Power amplifier, ? ... Audio switch control circuit, 9 ... Volume variable circuit, 1° ... AGC circuit, 11 ... Sound detection circuit,
12...Phase shift circuit. Patent applicant Oki Electric Industry Co., Ltd. Procedural amendment (Mutsu) Showa, 62/23B

Claims (1)

[Claims] (1) A sound detector that detects that a signal in a transmitting system circuit or a receiving system circuit has a single frequency component that persists at a predetermined level or higher for a predetermined period of time or more; and the transmitting system circuit or the receiving system circuit. A hands-free circuit with a noise protection circuit, characterized in that the hands-free circuit has a phase shift circuit inserted into the circuit and changes the phase of a signal in the inserted circuit based on the output of the noise detector.