JP2003304133A - Pop noise reducing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce package costs, mounting area, and mounting costs or the like without increasing the number of components, and to reduce a, so called, pop noise. <P>SOLUTION: An effect on/off control signal inputted from the outside is applied through a current switch 5 to an integrated circuit 9, and an effect value control signal inputted from the outside is applied through an AND circuit 6 and a digital/analog converter 8 to the integrated circuit 9 in the direction opposite to the direction of the output currents of the current switch 5. Thus, it is possible to prevent the mutual interference of the two signals, and to smooth each signal change. The effect on/off control signal is applied through a comparator 7 to the prescribed input terminal of a switch 4 for opening and closing the switch 4, and the effect value control signal is current/voltage converted by an operating amplifier 10, and applied to the prescribed input terminal of an effect adjusting unit 3 for controlling the effect value of the effect adjusting unit 3 for adjusting the value of effects to the input signal. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio circuit, and more particularly to an audio circuit for reducing unpleasant sound.

[0002]

2. Description of the Related Art Conventionally, in an audio circuit, in consideration of human hearing, an effect is applied to an input signal such as boosting a high frequency band and a low frequency band of the input signal to output the signal. Is being done. FIG. 3 shows a configuration example of a conventional circuit having such a function,
The conventional circuit will be described below with reference to FIG. This conventional circuit is configured so that a predetermined effect, for example, whether or not low-frequency boost is applied to an input signal, can be selected from the outside by a control signal, and the magnitude of the low-frequency boost can be controlled. is there. That is, in this conventional circuit, first, the input signal is applied to the adder 31 and is also input to the effect generator 32 that applies a predetermined effect to the input signal. Effect generator 3
The output signal 2 is applied to the adder 31 via the effect adjuster 33 and the switch 34 for adjusting the effect amount. Here, the adjustment amount of the effect adjuster 33 is controlled by an effect amount control signal input from the outside. This effect size control signal is
A digital signal is applied to the effect amount control input terminal 35 and then analog-converted by the digital-analog converter 36. Further, the opening and closing of the switch 34 is controlled by an effect on / off control signal externally input via the effect on / off control signal input terminal 37.

By the way, when the above-mentioned effect amount control signal is changed in order to change the effect amount, and when the presence / absence of an effect (in other words, on / off of the switch 34) is selected by the effect on / off control signal, When the effect amount control signal and the effect on / off control signal are directly applied to the effect adjuster 33 and the switch 34, when the effect amount control signal changes or the effect on / off control signal It is known that an abnormal sound such as "clicking", that is, a sound generally called "clicking" is output from a speaker or the like when is changed. For this reason, in the conventional circuit, the effect amount control signal and the effect on / off control signal are smoothed by the respective signal changes through the integrating circuits 41 and 42 each including the resistor and the capacitor, and the effect adjuster 33 is provided. By applying the signal to the switch or the switch 34, the occurrence of so-called "click noise" is reduced.

[0004]

However, in the above-mentioned conventional circuit, the integrating circuit 41 for the effect amount control signal and the integrating circuit 42 for the effect on / off control signal are separately provided. Moreover, there is a problem in that a resistor and a capacitor are required for each, and the number of parts is increased. Further, in particular, in the case where the above-mentioned conventional circuit is made into a semiconductor integrated circuit, the capacitors are externally attached, so that it is necessary to provide connection terminals corresponding to the number of capacitors in the semiconductor integrated circuit, which reduces package cost. There is a problem that the mounting area and the mounting cost increase with the increase.

The present invention has been made in view of the above situation, and provides a click noise reduction circuit capable of reducing the so-called click noise without increasing the number of parts as much as possible. Another object of the present invention is to reduce the clicking noise as much as possible, thereby reducing the package cost, the mounting area, and the mounting cost as compared with the conventional capacitors. To provide.

[0006]

In order to achieve the object of the invention described above, a click noise reduction circuit according to the present invention provides a predetermined effect to an input signal in accordance with an effect amount control signal input from the outside. It is designed to be applied in quantity,
In an audio circuit configured such that whether or not to apply the predetermined effect can be selected by an effect on / off control signal input from the outside, an integrating circuit is provided, and the effect amount control signal and the effect on / off signal are provided. An OFF control signal is applied to the integrator circuit such that the current directions thereof are opposite to each other, and the effect amount control signal and the effect ON / OFF control signal that have passed through the integrator circuit are respectively input at predetermined input points. Is configured to be applied to.

In such a configuration, the effect amount control signal and the effect on / off control signal are applied to the integrating circuit in opposite directions so that they can be shared by the integrating circuit. The number of parts can be reduced as compared with the conventional one, and the change of each signal can be made smooth by the integrating circuit, so that the generation of so-called pop noise can be reduced. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. The members, arrangements, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention. First, the configuration of the clicking noise reduction circuit according to the embodiment of the present invention will be described with reference to FIG. The clicking noise reduction circuit according to the embodiment of the present invention is applied to an audio circuit, and is configured as described below. That is, this pop noise reduction circuit is configured to be roughly divided into the main effect adding section 101 and the effect control section 102. Main effect addition part 1
01, first, between the input terminal 12 and the output terminal 13,
An adder 1 is provided, and an input stage of an effect generator (denoted as “K” in FIG. 1) 2 is connected to an input terminal 12. The effect generator 2 applies a desired effect (for example, low-frequency boost, etc.) to the input audio signal, and what kind of effect should be selected should be arbitrarily selected. It need not be limited. The output stage of the effect generator 2 has an effect adjuster 3
Is connected to the input stage of the switch 4 and the output stage of the effect regulator 3 is connected to one terminal 4a of the switch 4. The terminal 4b at the other end of the switch 4 is connected to the other input terminal of the previous adder 1. Here, the switch 4 is configured so that its on / off (opening / closing) is controlled by an external control signal. For example, a semiconductor switch or the like having a known / known configuration is used. It is preferably used. In the embodiment of the present invention, the opening and closing of the switch 4 is controlled by an effect ON / OFF control signal input from the outside.

The effect adjuster 3 is constructed so that the amount of the effect applied to the input signal by the effect generator 2 can be varied according to the effect amount control signal input from the outside. . Therefore, when the effect on / off control signal reaches a level at which the switch 4 is closed, the signal input to the effect adjuster 3 has a predetermined effect with an effect amount corresponding to the effect amount control signal. The signal is input to the adder 1 via the switch 4, added to the signal directly input to the adder 1 via the input terminal 12, and output from the output terminal 13. On the other hand, when the effect on / off control signal reaches a level that opens the switch 4, the input signal is output to the output terminal 13 via the adder 1 without being subjected to a predetermined effect. It is like this.

On the other hand, the effect control section 102 shapes the waveform for reducing so-called pop noise with respect to the effect on / off control signal and the effect amount control signal input from the outside.
The signal is amplified and the corresponding signals are applied to the effect adjuster 3 and the switch 4 as described above, which is configured as described below. That is, first, an effect on / off control signal input terminal 14 to which an effect on / off control signal is applied from the outside,
An effect amount control signal input terminal 15 to which an effect amount control signal is applied from outside is provided respectively. Here, in the embodiment of the present invention, it is premised that both the effect on / off control signal and the effect amount control signal are input as digital signals. The effect on / off control signal is, for example, at the level corresponding to the logical value High when the switch 4 is in the open state, and at the level corresponding to the logical value Low when the switch 4 is in the close state. , Which are input respectively. On the other hand, the effect amount control signal is input as serial or parallel digital data having a predetermined number of bits according to a desired adjustment amount in the effect adjuster 3. In FIG. 1, for convenience, the basic configuration is shown without distinguishing serial or parallel.

The effect on / off control signal input terminal 14 is connected to one input terminal of the AND circuit 6 together with the input stage of the current switch 5. The current switch 5 has a known / well-known configuration configured to output a predetermined current when an input signal of a predetermined level or higher is made. The output stage of the current switch 5 is connected to the input stage of the comparator 7, and
It is connected to an integrating circuit 9 described later. The comparator 7 outputs a predetermined output signal (for example, a logical value High) when a voltage higher than a predetermined voltage is applied to its input stage.
Is connected to a control signal input terminal (not shown).

On the other hand, the effect amount control signal input terminal 1
The other input terminal of the AND circuit 6 is connected to 5, and the output terminal of the AND circuit 6 is connected to the input stage of the digital-analog converter (D / A converter) 8. There is. Therefore, the effect amount control signal is output from the AND circuit 6 and input to the digital-analog converter 8 only when the effect on / off control signal has the logical value High. The digital-analog converter 8 has a publicly known and well-known configuration, and the input effect amount control signal is output as an effect amount control signal having an analog value according to its digital value. Has become. An integrating circuit 9 is connected to the output stage of the digital-analog converter 8. That is, the integrating circuit 9 according to the embodiment of the present invention is composed of the resistor 9a and the capacitor 9b.

One ends of the resistor 9a and the capacitor 9b are connected to each other, and this connection point also serves as the input terminal of the integrating circuit 9, and together with the output stage of the digital-analog converter 8. As described above, the output stage of the current switch 5 and the input stage of the comparator 7 are connected. The other end of the resistor 9a is connected to the input stage of the operational amplifier 10 as the output terminal of the integrating circuit 9, while the other end of the capacitor 9b is connected to the ground. The operational amplifier 10 has a feedback resistor 11 connected between its input and output, converts the input current from the integrating circuit 9 into a voltage with a predetermined amplification degree, and outputs the voltage. The output stage has an effect regulator. 3 is connected to a control signal input terminal (not shown).

In the above structure, the integrating circuit 9 is shared by the current switch 5 and the digital-analog converter 8, so that it is necessary to prevent mutual interference of the respective output signals. Therefore, the current switch 5
The direction of the output current of and the direction of the output current of the digital-analog converter 8 are set to be opposite.
For example, when the effect on / off control signal is switched from the logic value Low to the logic value High and an appropriate effect amount control signal is input, the output current of the current switch 5 flows into the current switch 5 side, that is, so-called suction. If it is set to
The output current of the analog converter 8 needs to be set so as to flow into the capacitor 9b. Of course, the opposite setting may be possible. The circuit in the above configuration may be either a so-called discrete configuration for connecting individual electronic components or a so-called semiconductor integrated circuit.

Next, the operation of the above configuration will be described with reference to FIG. FIG. 2 is an explanatory diagram for explaining the operation of the clicking noise reduction circuit in the embodiment of the present invention. In particular, the comparator 7 for the input state of the effect on / off control signal and the effect amount control signal 6 is an explanatory diagram illustrating an operating state of the operational amplifier 10. FIG. In the figure, the horizontal axis represents the change in the effect on / off control signal, and the vertical axis represents the change in the terminal voltage of the capacitor 41.
They are shown respectively. First, as a premise, it is assumed that the reference voltage of the comparator 7 is set lower than the reference voltage of the current / voltage conversion (I / V conversion) by the feedback resistor 11 and the operational amplifier 10. Under this assumption,
First, when the effect on / off signal is set to the logic value Low state, the logic value Low state is applied to the switch 4 via the current switch 5 and the comparator 7, and the switch 4 is in the open state. Therefore, in this case, the signal applied to the input terminal 12 is output from the output terminal 13 via the adder 1 without any predetermined effect. Next, when the effect on / off control signal is switched from the state of the logic value Low to the logic value High and the effect amount control signal is applied to the effect amount control signal input terminal 15, first, the effect on / off control is performed. The output current of the current switch 5 rises from zero to a predetermined value as the signal changes from the logical value Low to the logical value High. Further, in the AND circuit 6, the effect on / off control signal becomes the logical value High, so that the effect amount control signal is output from the AND circuit 6, and the analog signal is output via the digital-analog converter 8. It will be output as a signal.

The current switch 5 and the digital switch
The respective outputs of the analog converters 8 are both integrated circuits 9
However, as described above, since the directions of the respective output currents are preset to be opposite to each other, in the integrating circuit 9, the output current from the current switch 5 and the digital The level change becomes a smooth change without mutual interference with the output current from the analog converter 8. That is, the terminal voltage of the capacitor 9b gradually rises and first exceeds the reference voltage of the comparator 7 (see FIG. 2), whereby the switch 4 is closed from the comparator 7 to the switch 4. Will be output. As a result, the switch 4 is closed. After that, the terminal voltage of the capacitor 9b continues to rise and exceeds the reference voltage of the operational amplifier 10 (see FIG. 2). As a result, the output change of the digital-analog converter 8 is applied to the operational amplifier 10 via the integrating circuit 9, and the current
The voltage is converted and applied to a control signal input terminal (not shown) of the effect adjuster 3. In this case, the rising of the effect amount control signal applied to the control signal input terminal is slowly changed by the integrating circuit 9.

Then, even if the effect amount control signal is increased in value in order to increase the effect amount in the effect adjuster 3, the change is smoothed by the integrating circuit 9, and the operational amplifier 10 operates in the same manner as described above. Will be applied to a control signal input terminal (not shown). On the other hand, when the effect on / off control signal is changed from the state of the logic value High to the state of the logic value Low in order to stop applying the predetermined effect to the input signal, the current switch 5
The direction of the output current of the integration circuit 9 is opposite to that when the effect on / off control signal becomes the logical value High.
Therefore, the terminal voltage of the capacitor 9b gradually decreases. This, contrary to the case above, first
Below the reference voltage at the op amp 10, then
Below the reference voltage of the comparator 7, a signal for opening the switch 4 is output from the comparator 7 to the switch 4, and the switch 4 is opened.

As described above, by the integrating circuit 9,
As a result of the change of the effect on / off control signal or the change of the effect amount control signal being made slow by the integrating circuit 9 and input to the circuit of the next stage, the effect on / off control signal or the effect is different from the conventional case. When a change in the quantity control signal occurs, the occurrence of so-called pop noise is reduced.

[0019]

As described above, according to the present invention,
Since the integration circuit is made common, there is an effect that it is possible to provide a pop noise reduction circuit in which the number of parts is reduced as compared with the related art. In particular, since the number of capacitors required can be reduced by making the integrating circuit common, the number of external connection terminals can be reduced in the case of making an integrated circuit. In addition, it is possible to reduce the mounting cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration example of a clicking noise reduction circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an operation of the clicking noise reduction circuit in the embodiment of the present invention.

FIG. 3 is a configuration diagram showing a configuration example of a conventional circuit.

[Explanation of symbols]

1 ... Adder 2 ... Effect generator 3 ... Effect adjuster 4 ... switch 5… Current switch 6 AND circuit 7 ... Comparator 8 ... Digital / analog converter 9 ... Integrator circuit 10 ... Operational amplifier 14 ... Effect on / off control signal input terminal 15: Effect amount control signal input terminal

Claims (3)

[Claims] 1. An input signal is provided with a predetermined effect in an amount according to an effect amount control signal input from the outside, and whether or not the predetermined effect is applied is externally determined. In an audio circuit configured to be selectable according to an input effect on / off control signal, an integrator circuit is provided, and the effect amount control signal and the effect on / off control signal are supplied to the integrator circuit by a current thereof. The effect amount control signal and the effect on / off control signal, which have been applied so that the directions thereof are opposite to each other and which have passed through the integrating circuit, are respectively applied to predetermined input locations. Click noise reduction circuit. 2. An effect adjuster configured to apply a predetermined effect to an input signal in an amount according to an effect amount control signal externally input in a digital signal format, and an output of the effect adjuster. An audio circuit comprising a switch configured to select whether or not to output a signal to the outside by an effect on / off control signal input from the outside in a digital signal format. A current switch configured to output a current in response to a signal; an AND circuit that outputs a logical product of the effect on / off control signal and the effect amount control signal; and a digital output signal of the AND circuit. Digital / analog converter for analog conversion, commonly connected to the output stage of the current switch and the digital / analog converter And an effect integration control circuit, and the effect on / off control signal and the effect amount control signal that have passed through the integrator circuit are respectively applied to the switch and the effect adjuster. A pop noise reduction circuit. 3. The pop noise reduction circuit according to claim 2, wherein the output current of the current switch and the output current of the digital-analog converter are set in directions opposite to each other.