JPS6058724A - Noise control circuit - Google Patents

Abstract

PURPOSE:To prevent interruption of voice and interruption of head of voice due to fading by providing a time constant circuit having a fast charging time and slow discharge time of a noise detection voltage behind a noise detection circuit and superimposing the output on a detection voltage of an intermediate frequency level. CONSTITUTION:An output of a frequency discriminating circuit is inputted to the time constant circuit 14 via a noise detection circuit 12 and an inverse amplifier 13, its output is superimposed on the output of an intermediate frequency level detector 15 via an inverse amplifier 16, inputted to a non-inverting terminal of a comparator 18 via an inverse amplifier 17, a reference voltage is inputted to an inverting terminal via a variable resistor 19, and a noise control voltage is obtained by comparing both the inputs. When an input electric field is increased by the time constant circuit 14, the time constant is decreased and the time constant is increased at a weak electric field. Thus, the rising and falling time of the output of the circuit 14 is changed as shown in figure (a) to the input electric field. Further, when the reference voltage is set to a high value for weak electric field by the variable resistor 19, the interruption of voice output due to the momentary interruption of the electric field is prevented, and when the reference voltage is set to a low voltage for a strong electric field, the interruption of head of speech at rising is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a noise control circuit for use in mobile radio receivers, etc., which eliminates discontinuities in audio output due to fading during weak electric fields.

Configuration of a conventional example and its problems Figure 1 shows a conventional noise control device, in which 1 is a frequency discrimination circuit of a receiver, 2 is an amplifier, 3 is a polygon, and 4 is a band-pass filter ( BPF), s is a detection circuit composed of diodes DI, D2, resistor R1, and capacitor C1, 6 is a switching transistor, 7 is an audio frequency amplifier, 8 is a speaker, and vl is a power supply voltage.

In the above configuration, the output of the frequency discrimination circuit 1 is amplified by the amplifier 2, divided by the volume 3, and supplied to the BPF 4.
Only noise components outside the audio frequency band pass through the detection circuit 5.
The wave is detected by At this time, when the volume 3 is moved in the direction of A to increase the output, the output of the detection circuit 5 becomes approximately 0°7V, which is the threshold voltage of the switching transistor 6.
When the value exceeds , the switching transistor 6 is turned on, so that the audio frequency amplifier 7 is no longer biased, the audio frequency amplifier 7 is turned off, and no sound is output from the speaker 8. Note that if you turn the volume 3 in the direction opposite to A, the sound will come out from the speaker 8.

However, in the configuration described in section 2, if the time constant of the detection circuit 5 is shortened by 3 pages in order to speed up the rise of the sound output, the sound becomes intermittent due to fading in a weak electric field, making it difficult to hear, and conversely, If the constant is made large, there is a drawback that the beginning of the conversation may be cut off during a telephone conversation, making it difficult to hear.

Purpose of the Invention The present invention eliminates the problems of the above-mentioned conventional example,
The purpose is to prevent audio from being cut off intermittently due to fading in a weak electric field, and at the same time to speed up the rise of the audio to prevent audio from cutting off at the beginning.

Structure of the Invention In order to achieve the above object, the present invention provides a time constant circuit which has a fast charging time and a slow discharging time for the noise detection voltage after the noise detection circuit, and converts its output into a detection voltage at an intermediate frequency level. By superimposing it with the above, it is possible to prevent the audio from intermittent due to fading when the electric field is weak, and also to speed up the rise time of the audio when the BreathTalk switch is turned on (when pressed) and the fall time when the electric field is strong. It is.

Description of examples An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 2, 11 is a band pass filter (BPF), 1
3, 16, and 17 are inverting amplifiers composed of operational amplifiers and resistors, and 12 is a diode D3. A noise detection circuit includes D4, a resistor R2, and a capacitor C2. A time constant circuit 14 includes a diode D5, a resistor R3, and a capacitor C3.

16 is an intermediate frequency level detector, 18 is a comparator, 1
9 is a polyurethane for setting a reference voltage, and vl is a power supply voltage.

Next, the operation will be explained in FIG. 2, where the output of a frequency discrimination circuit (not shown) is amplified and then inputted to the BPF 11, and then inputted to the time constant circuit 14 via the noise detection circuit 12 and the inverting amplifier 13. The output of the time constant circuit 14 is superimposed and synthesized with the output of the intermediate frequency level detector 16 via the inverting amplifier 16, and is inputted to one terminal (→) of the comparator 18 via the inverting amplifier 17. The other terminal (C) is inputted with the reference voltage determined by the adjustment of Porium 19, and the noise control voltage is obtained by comparing the two voltages. ) shows the changes in the above-mentioned voltages for each voltage 0. First, as is well known in the noise detection type press-in, it decreases as the input electric field increases and becomes almost 0 above the input 0 dB. Therefore, the inverted voltage B becomes as shown in Fig. 4. On the other hand, the output C of the intermediate frequency level detector 16 decreases linearly as the input electric field increases, as shown in Fig. 5. Therefore, the inverted and amplified output increases linearly in proportion to the input electric field as shown in Fig. 6.The composite voltage 2 of the output B of the time constant circuit 14 and the output of the inverting amplifier 16 is By passing through the first phase, the input electric field changes as shown in Figure 7.On the other hand, C
In the time constant circuit 14 whose basic form is an R integration circuit, a diode D6 is provided in parallel with the resistor R3, and as the input electric field increases, the voltage applied to the diode D6 increases as shown in FIG. The diode D6 becomes conductive, which is equivalent to shorting the resistor R3 with a low resistance, resulting in a small time constant. On the other hand, in a weak electric field, the time constant increases due to non-conduction of the diode D6. As a result, the rise and fall times of the output of the time constant circuit 14 change as shown in FIG. 8 with respect to the input electric field.

Also, the comparator 18 compares the composite voltage E with the reference voltage.
When the noise control voltage decreases, the noise control voltage becomes a low value, and the sound comes out from the speaker 8 as in the case of FIG.

Next, when the reference voltage for noise control is set to a high value for weak electric fields using poly-19, the contribution of the noise detection voltage of B becomes dominant as shown in Figures 4 and 6, and as shown in Figure 8. As a result, the rise is fast and the fall is slow, and it is possible to prevent audio output from being interrupted due to fading due to instantaneous interruption of the electric field. On the other hand, if the reference voltage is set to a low voltage for strong electric fields, the contribution of the intermediate frequency level detector 16 will become dominant, and both the rise and fall will become faster. Even the noise that sometimes occurs can be suppressed in a short time.

Effects of the Invention The present invention has the above-mentioned configuration, and the noise detection signal is transmitted through a time constant circuit whose rise is fast and whose fall is slow.
Noise control output is obtained by combining the output with the intermediate frequency detection output and comparing it with the reference level, so there is no interruption in the voice even in the case of weak electric field input, and on the other hand, it is possible to avoid interruptions in speech even in the case of strong electric field. This has the advantage of eliminating

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional noise control circuit.
FIG. 2 is a block diagram showing the configuration of a noise control circuit according to an embodiment of the present invention, FIGS. FIG. 3 is a characteristic diagram showing changes in the rise and fall times of the circuit with respect to the input electric field. 1...Frequency discrimination circuit, 11...BP
F, 12... Noise detection circuit, 14...
Time constant circuit, 16... intermediate frequency level detector,
18... Comparator 〇 Name of agent Patent attorney Toshio Nakao and 1 other famous cosmetics world @ 4 Figure 5 xjJ Henryo No. Figure 7 Figure 8 Input constant human force seismic field

Claims (1)

[Claims] Arrival from frequency discrimination circuit (sound detection output is input, OR
It has a time constant circuit in which a diode is provided in parallel with the resistance of the integrating circuit, and the output of the intermediate frequency Lebel detector and the output of the time constant circuit are combined and inputted to one terminal of the input of the comparator, Connect the reference potential to the other terminal,
A noise control circuit characterized in that the output of the comparator is a noise control voltage.