JP3071700U - Audio signal output circuit - Google Patents

Abstract

(57) [Summary] In an audio signal output circuit, even if the power supply voltage fluctuates, the output of the operational amplifier can be used without being clipped and the audio characteristics are excellent, and even when the operational amplifier is changed, the reference power supply is changed. Make it easy to respond to changes at the design stage. SOLUTION: Since the power supply 3 of the operational amplifier 1 and the power supply 3 of the reference voltage generation circuit 2 are taken from a single system of power supply, even if the power supply voltage fluctuates, the reference voltage also fluctuates. Can be used as long as the output of the operational amplifier is not clipped. In addition, since the reference voltage is generated by dividing the resistance, it is easy to bring the reference voltage to the center of the maximum amplitude of the operational amplifier, and even if the operational amplifier is changed, it can easily cope with the change of the reference power supply. it can.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to an audio signal output circuit that is used in a DVD player, a DVD-ROM drive, or the like and includes an operational amplifier that amplifies a reproduced audio signal.

[0002]

[Prior art]

 2. Description of the Related Art Conventionally, in an audio signal output circuit, a reproduced audio signal is amplified using an operational amplifier with reference to a predetermined reference voltage and output. In the operational amplifier, the amplitude level of a signal that can be output varies according to the power supply voltage (for example, 9 V) (the maximum voltage varies in proportion to a change in the power supply voltage of the operational amplifier). In this type of conventional audio signal amplifier circuit, when the power supply voltage decreases, the waveform of the output signal is greatly distorted. Therefore, in order to solve such a problem, it is known that a generation circuit for generating a control current corresponding to the power supply voltage and the reference voltage (reference voltage) is provided, and a control current is applied to the feedback-side input terminal of the operational amplifier. (See, for example, JP-A-6-125227).

[0003]

[Problems to be solved by the invention]

 In conventional audio equipment, a power supply system of a relatively high voltage (for example, 9 V) is usually used as a power supply for a motor drive or an operational amplifier, and a lower voltage (for example, 9 V) is used as a power supply for a circuit for processing a digital reproduction signal. For example, a power supply system of 5 V) is used. Since the latter power supply system has less noise components than the former power supply system, the latter power supply system is used to generate the reference voltage, and the op amp requires power because it requires power. Power supply is not appropriate.

However, when the reference voltage is generated from a power supply (for example, 5 V) different from the power supply of the operational amplifier, the variation in the voltage of the other power supply greatly affects the output of the operational amplifier. And the maximum voltage of the output is clipped, deteriorating the audio characteristics. Also, when the operational amplifier used was changed, the reference power supply had to be changed, but the response was troublesome. Note that the amplifier circuit disclosed in the above publication does not know how to generate the power supply for the operational amplifier and the power supply for generating the reference voltage.

The present invention has been made in view of the above-mentioned conventional problems, and can be used without clipping the output of the operational amplifier even when the power supply voltage fluctuates, and has excellent audio characteristics. An object of the present invention is to provide an audio signal output circuit that can easily cope with a change in the reference power supply at the design stage.

[0006]

[Means for Solving the Problems]

 To achieve the above object, a first aspect of the present invention is to provide an audio signal output circuit having an operational amplifier for amplifying an audio signal with a predetermined reference voltage as a reference, wherein the reference voltage is generated by resistance division. A power supply voltage for the operational amplifier and a power supply voltage for the reference voltage generation circuit from a single power supply.

In the above configuration, the output level of the operational amplifier changes depending on its power supply voltage. Therefore, if the amplitude required for the output of the operational amplifier is close to the maximum level amplitude, the reference voltage (amplitude of the amplitude) at that time is assumed. The center voltage) must be selected appropriately. Here, since the power supply of the operational amplifier and the power supply of the reference voltage generation circuit are taken from a single system power supply, even if the power supply voltage varies and fluctuates, the reference voltage also fluctuates, and accordingly, the output of the operational amplifier of the audio signal is reduced. It can be used as long as it is not clipped. In addition, since the reference voltage is generated by dividing the resistance, it is easy to transfer the reference voltage to the center of the operational amplifier with the maximum amplitude as much as possible. can do.

According to a second aspect of the present invention, in the first aspect, the reference voltage generating circuit includes a noise removing circuit. As a result, even a power supply to which a motor or the like is connected and noise is likely to be applied can be used as a power supply for the reference voltage generation circuit.

According to a third aspect of the present invention, in the second aspect, a high-voltage power supply for driving a motor of an audio device and a low-voltage power supply for processing an audio signal lower than the voltage are provided. The high-voltage power supply is used as a power supply for the system. As a result, of the 9 V power supply and the 5 V power supply generally provided in digital audio equipment, the 9 V power supply may be used as a single system power supply, and the power required for driving the operational amplifier can be obtained.

[0010]

[Embodiment of the invention]

 Hereinafter, an embodiment of the device according to the present invention will be described with reference to the drawings. FIG. 1 shows an audio signal output circuit. The circuit includes an operational amplifier 1 composed of an IC for amplifying an audio signal based on a predetermined reference voltage, and a reference voltage generating circuit 2 for generating a reference voltage Vref by resistance division. The power supply voltage of the reference voltage generation circuit 2 is taken from one power supply 3 (9 V in this example; AUDIO + 9). The power supply 3 is a high-voltage power supply for driving a motor, which is usually provided in a digital audio device such as a DVD player. Note that the digital audio device is also provided with a low-voltage power supply for processing audio signals lower than this voltage.

The reference voltage generating circuit 2 includes voltage dividing resistors R1 and R2 connected between the power supply 3 (AUDIO + 9) and GND, and further includes a noise removing circuit in parallel with the resistor R2. The capacitor C1 (for high frequency) and the capacitor C2 (for low frequency) are connected. Input / output 5 (AUDIO-L, AUDIO-R) of this circuit receives left / right audio signals reproduced and decoded by a DVD player or the like and converted into digital / analog, and output 6 (AUDIO-L). Lch, AUDIO-Rch) outputs the amplified left and right audio signals. The audio signal input to the input terminal 5 swings with reference to the reference voltage Vref.

The operational amplifier 1 uses a positive-feedback differential amplifier here. An audio signal swinging with reference to the reference voltage Vref is input to a non-inverting input (+), and a resistor R11 and a capacitor C11 are input to an inverting input (−). As a result, a DC (direct current) component obtained by cutting an AC (alternating current) component is input as a reference voltage.

Next, the operation of the audio signal output circuit configured as described above will be described. Since the amplitude level that can be output by the operational amplifier 1 is limited by the power supply voltage of the operational amplifier 1, it is desirable to bring the reference voltage Vref to the center of the maximum amplitude of the operational amplifier 1 as shown in FIG. . This reference voltage Vref can be easily obtained by setting the voltage dividing resistors R1 and R2 of the reference voltage generation circuit 2. Here, since the power supply of the operational amplifier 1 and the power supply of the reference voltage generation circuit 2 are obtained from one power supply 3 (AUDIO + 9), even if the power supply voltage varies and fluctuates, the reference voltage Vref also fluctuates. Therefore, the peak portion of the audio signal output of the operational amplifier 1 is not clipped.

Further, since the reference voltage Vref is generated by dividing the voltages of the resistors R1 and R2, it is easy to bring the reference voltage Vref to the center of the power supply voltage of the operational amplifier 1, and the operational amplifier 1 is changed. However, it is possible to easily respond to the change of the reference power supply at the systematic stage.

As the power supply 3 (AUDIO + 9), a 9 V power supply out of a 9 V power supply and a 5 V power supply generally provided in digital audio equipment may be used, and the power required for driving the operational amplifier 1 may be used. Can take enough. Further, even if the power supply 3 (AUDIO + 9) of the reference voltage generation circuit 2 is a power supply such as a motor in which noise is likely to be applied, the reference voltage generation circuit 2 has a noise elimination circuit including the capacitors C1 and C2. Since it is provided, it can be used as a reference voltage without being affected by noise.

The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. For example, in the above description, a positive feedback differential amplifier is shown as the operational amplifier 1, but a negative feedback differential amplifier is used. Is similarly applicable.

[0017]

[Effect of the invention]

 As described above, according to the invention of claim 1, since the power supply of the operational amplifier and the power supply of the reference voltage generation circuit are obtained from the power supply of one system, even if the power supply voltage of the one system varies and fluctuates. It can be used as long as the output of the operational amplifier is not clipped, and the sound quality does not deteriorate. Also, even if the operational amplifier is changed, the reference voltage is generated by dividing the resistance, so that it is possible to easily cope with the change of the reference power supply.

According to the second aspect of the present invention, in addition to the above-described effects, it is possible to use a power supply to which a motor or the like is connected and noise is likely to be applied as a power supply for the reference voltage generation circuit.

Further, according to the invention of claim 3, a high-voltage power supply (for example, a 9V power supply) for driving a motor of an audio device and a low-voltage power supply (for example, for processing a digital audio signal lower than this voltage) are provided. (5 V power supply), the power required for driving the operational amplifier can be obtained by using a high voltage power supply as the power supply for the operational amplifier and the power supply for the reference voltage generation circuit.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an audio signal output circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a power supply voltage of an operational amplifier and a reference voltage in the same circuit.

[Explanation of symbols]

 Reference Signs List 1 operational amplifier 2 reference voltage generating circuit 3 power supply Vref reference voltage R1, R2 voltage dividing resistor C1, C2 capacitor (noise removing circuit)

Claims (3)

[Utility model registration claims] 1. An audio signal output circuit comprising an operational amplifier for amplifying an audio signal on the basis of a predetermined reference voltage, comprising: a reference voltage generation circuit for generating the reference voltage by resistance division; An audio signal output circuit, wherein the power supply voltage of the reference voltage generation circuit is taken from a single system of power supply. 2. The audio signal output circuit according to claim 1, wherein the reference voltage generation circuit includes a noise removal circuit. 3. A high-voltage power supply for driving a motor of an audio device and a low-voltage power supply for processing an audio signal lower than this voltage, wherein the high-voltage power supply is used as the one-system power supply. 3. The audio signal output circuit according to claim 2, wherein: