JPS62147851A - Hand free circuit with singing protection circuit - Google Patents

Abstract

PURPOSE:To stop a singing while a gain is decreased to a proper valve by providing a means decreasing the gain and a means decreasing the gain further while using a pulse signal to an automatic gain adjusting circuit. CONSTITUTION:A singing detector 13 detects a singing in a transmission output T to start an automatic gain adjusting circuit 14 with pulse generator. The automatic gain adjusting circuit 14 decreases the closed gain to bring the state that a singing continues at a prescribed level. Then a pulse signal outputted from a pulse generator in the automatic gain adjusting circuit 14 is superimposed on an input signal to a gain adjusting transistor 38 provided in the automatic gain adjusting circuit 14 to decrease the gain further thereby stopping the continuing singing as well.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hands-free communication circuit for a car telephone device.

(Prior Art) A conventional device of this type has been disclosed in Japanese Patent Application Laid-open No. 117463/1983 (public address telephone device). This device appropriately controls the amount of loss in the variable loss circuits of the transmitting system and the receiving system, prevents the occurrence of ringing, and realizes hands-free calling. FIG. 2 is a block diagram showing an example of the configuration of a conventional hands-free telephone device. In the figure, 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 an hybrid transformer, 9 is a volume variable circuit, and 10 is an AGC It is a circuit. In this configuration, variable loss circuits 3 and 6 are inserted in order to prevent ringing caused by the closed loop formed from the speaker 4 via the microphone 1 and the nozzle 8. In this circuit, if the loss of the variable loss circuit 3 is large, the loss of the variable loss circuit 6 is controlled to be small.

In this state, a fixed amount of loss is provided that does not cause noise. Similarly, if the loss of the variable loss circuit 3 is small, the loss of the variable loss circuit 6 is large, and this loss amount is also a fixed loss amount that does not cause noise.

(Problem to be Solved by the Invention) However, the device with the above configuration is not effective if the amount of acoustic coupling between the microphone 1 and the speaker 4 or the amount of return loss of the hybrid transformer 8 is within the designed range. However, it has been found that when applied to a car telephone system, an abnormal amount of acoustic coupling or return loss exceeding the design range occurs. In this case, generation of noise cannot be avoided. If the amount of loss in the variable loss circuit 3 or 6 is sufficiently reduced in order to avoid ringing, a satisfactory communication state cannot be obtained. This is because simultaneous communication, which is essential for smooth conversation, is impaired.

SUMMARY OF THE INVENTION In order to avoid the above-mentioned drawbacks, it is an object of the present invention to provide a noise-free communication device that is provided with a means for activating a protection circuit and exiting the ringing state when an IS sound occurs.

(Means for solving the problem) The present invention consists of a means for detecting the ringing state of the noise-free communication device Tδ, and an automatic gain adjustment circuit inserted into the receiving system circuit or the transmitting system circuit using the output signal thereof. However, the automatic gain adjustment circuit has a means for reducing the gain, and a means for reducing the gain further than the gain that should be adjusted by the automatic gain adjustment circuit by using the signal of the signal generator. This is a hands-free circuit with a sound protection circuit that uses the above two means to reduce the gain to an appropriate amount and stop the sound.

(Function) The frequency component, trust level, and duration are detected by the sound detector, and it is detected whether the signal of the transmitting/receiving circuit (hereinafter referred to as the communication channel) is in the state of sound generation.

If a sound is generated, a start signal is output and the automatic gain adjustment circuit is started.

If the communication channel is in a normal communication state, the automatic gain adjustment circuit outputs the input signal for the first time, but if a noise is generated as described above, the first control is to output the input signal from the communication channel. When it becomes larger, the bias potential of the gain adjusting transistor is increased to turn on the transistor and control the input signal to be attenuated.

Furthermore, as a second control, d provided in the automatic gain adjustment circuit
The output signal of the pulse generator is superimposed on the bias potential of the transistor, and the bias potential is increased to attenuate the signal to a level slightly lower than the noise generation level.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 11 is an amplifier, 12 is a variable loss circuit, 13 is a sound detector, 14 is an automatic gain adjustment circuit with a pulse generator, I5 is a power amplifier, 16 is a variable loss circuit, and Noah is an audio switch control. circuit, 18 is the volume variable circuit, 19 is A
In the GC circuit, T is the transmitting output and R is the receiver's power. When the sound is generated as described above, the transmitter output T is connected to a radio (not shown) or a hybrid; Detecting this, the automatic gain adjustment circuit 14 with a pulse generator is activated. The automatic gain adjustment circuit 14 lowers the loop gain so that the sound continues at a certain level, and also lowers the gain in the automatic gain adjustment circuit 4.
(shown in FIG. 5), the gain adjustment transistor 3 is provided in the automatic gain adjustment circuit 14 to receive the signal output from the
8 (shown in FIG. 5) and further lowers the gain to stop the above-mentioned continuous sound.

FIG. 3 is a block diagram showing a second embodiment of the invention. Similar to the first embodiment, when the sound state occurs, the receiver's power R
is connected to the output of a radio (not shown) or a hybrid, and the sound detector 13 detects the sound state of the input signal and starts the automatic gain adjustment circuit 14. The automatic gain adjustment circuit 14 lowers the loop gain so that the sound continues at a certain level, and the output signal is output from the signal generator 48 (shown in FIG. 5) in the automatic gain adjustment circuit 14. The automatic gain adjustment circuit 14
This signal is superimposed on the input signal of the gain adjustment transistor 38 (shown in FIG. 5) provided inside the circuit, and the gain is further lowered to stop the above-mentioned continuous sound.

FIG. 11 shows a detailed circuit diagram of the sound detector. In the figure, reference numeral 20 denotes an input terminal for manually inputting the signal of the transmitting output T. 2
1a to 21d are operational amplifiers, and the operational amplifier 21a
, resistors 24a and 24b constitute a Schmitt circuit 45. The operational amplifier 21a outputs a single frequency signal in a sounding state,
Utilizing the fact that the output waveform is different from a random frequency signal such as voice, it is determined whether or not a sound is being generated. It is even more effective if a bandpass filter that covers the vicinity of the sound frequency is inserted after the operational amplifier 21a. 22a
~22e is a capacitor, 23a~23d are diodes,
24a to 24m are resistors. Capacitors 22a, 22
b, diode 23a.

23b and resistor 24c constitute a rectifier circuit 46 to perform DC conversion, and an operational amplifier 21b performs impedance conversion. Further, a time constant circuit 44 is constituted by the resistors 24d and 24e and the capacitor 22c, and the duration of the input terminal 200 angstrom force signal is determined to determine the sounding state. diode 23c
This speeds up the discharge of the capacitor 22c, which also helps in determining whether a sound is a sound or a voice.

On the other hand, the signal at the input terminal 2θ is amplified by the operational amplifier 2Jc, converted to direct current by the rectifier circuit 43, and level determined by the operational amplifier 21d. If the level is above a certain level, the transistor 25 is turned off, the level of the output of the time constant circuit 44 is determined by the operational amplifier 21e, a start signal is sent to the output terminal 26, and the automatic gain adjustment circuit 14 with a pulse generator is started. do. As explained above, the sound state is determined by detecting a certain frequency component that is at a certain level or higher and continues for a certain period of time.

In Figure 5! 1 shows an example of an automatic gain adjustment circuit with a pulse generation circuit. In the figure, 30 is the input terminal of the variable loss circuit 1.
Connect with 6. 34a to 34i are resistors, 35a, 35b
is an amplifier, which is passed through a resistor 34a, the impedance is converted by an amplifier 35a, and the output terminal 33 is connected to a power amplifier 5.
Connect to. At this time, the gain adjustment transistor (FET
) 387jZOFF, the signal is transmitted from the input terminal 30 to the output terminal 33 without change. The second input terminal 31 is connected to the transmitter output T, and the input signal is amplified by resistors 34b, 34c and an amplifier 35b. 36a to 36d are capacitors, 37a to 37c are diodes, and capacitor 36a,
36b, diodes 37m and 37b, and a resistor 34d. When the input signal at the input terminal 31 increases, the bias potential of the transistor 38 increases, and the transistor 38 turns from OFF to ON. At this time, the input signal at the input terminal 30 is the resistance 34a, =
The input signal at the input terminal 3 is attenuated by the p-silano star 38, and as a result, the input signal at the input terminal 3 is attenuated by the loop, so that the output signal at the output terminal 33 and the human input signal at the input terminal 31 reach a certain level.

On the other hand, the third input terminal 32 is connected to the sound detector 13, and when the detector 13 detects a sound state, the automatic gain adjustment circuit 14
Generates a no-irepel signal, which is the activation signal. The automatic gain adjustment circuit 14 holds the high level signal in a clip-flop circuit 40, and a level conversion circuit 47 using a PNP transistor 4 and an NPN transistor 42.
Then, the bias potential of the gain adjustment transistor 38 is controlled.

If the input signal at the input terminal 32 is at level 7, the NPN transistor 42 is turned off, and the transistor 38
The bias potential of increases. Otherwise, the NPN transistor 42 is in the ON state and the transistor 38
The bias potential of is connected to the negative overshoot source, and the transistor 38 becomes OFF'F. As a result, the input signal at the input end 30 is transmitted to the output end 33 without change.

As mentioned above, when the signal at the input terminal 32 is at a high level (sound detection signal) and the bias potential of the gain adjustment transistor 38 is controlled by the input signal at the input terminal 31 and reaches a certain level for the sound state, the above-mentioned The bias potential of transistor 38 is controlled by the output signal of signal generator 48. The signal is connected to capacitors 36c, 36d and resistor 34e.
, 34f and a Schmitt circuit amplifier 39.
c and resistor 34g, transistor 38
is superimposed on the bias potential signal of , and the bias potential is slightly increased every pulse generation period. As a result, as described above, the output signal of the output terminal 33 and the input signal of the input terminal 3 are attenuated to a level slightly lower than the level of the sound state, and the sound can be stopped.

(Effects of the Invention) As explained in detail above, the hands-free circuit having the circuit of the present invention generates a ringing sound that is unavoidable in current car phone systems when providing a hands-free calling function to a car phone device. It serves as a powerful protection against the dangers of

When we conducted experiments in a certain area, we found that the loss of the hybrid transformer shown in Figure 1 was 15 to 20 dB compared to the normal 15-20 dB.
Although the probability is small, it is known that OdB lines also exist.

A normal hands-free device can withstand only about 6 dB of this loss, so the user has to manually adjust the volume each time it generates a ringing sound, but this is done automatically according to the present invention. be able to.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a communication device according to the present invention, FIG. 2 is a block diagram of a conventional communication device, FIG. 3 is a block diagram of a second embodiment of the invention, and FIG. 4 is a ringing detection Figure 5 shows an automatic gain adjustment circuit. l...Microphone, 2.11...Amplifier, 3,6
゜12.16...Variable loss circuit, 4...Speaker,
5゜15...Power amplifier, 7...Audio switch control circuit, 8...Hybrid transformer, 9,18...
Sound maximum variable circuit, lθ, 19...AGC circuit, 13...
・Sound detector, 14... Automatic gain adjustment circuit, 44...
Time constant circuit, 45...Nyuminote circuit, 46...f
Rectifier circuit, 47... Level conversion circuit, 48... Noculus generator, 49... Rectifier circuit.

Claims (1)

[Claims] In a communication circuit used in a mobile telephone device, a ring detection means for detecting whether or not a communication channel is in a ringing state; and a control signal and pulse generation according to the degree of coupling between the communication channels. automatic gain adjustment means for controlling the gain of the communication channel by a control signal from the device, and the automatic gain adjustment means is activated by an output signal indicating that the sound detection means is in a sound state. Hands-free circuit with noise protection circuit.