JP2009081641A - Unbalance-balance conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a deterioration in sound quality by removing a difference in quality between balance-converted audio signals of a positive phase and an opposite phase in an imbalance-balance conversion circuit. <P>SOLUTION: The imbalance-balance conversion circuit comprises: a volume control circuit for controlling the volume of audio signals; an amplifier circuit for amplifying the audio signals for which volume is controlled by the volume control circuit; and a phase inversion circuit 3 which inverts the phase of the audio signals amplified by the amplifier circuit and feeds them back to the amplifier circuit. The output of the amplifier circuit is outputted as a positive-phase component of the audio signals and the output of the phase conversion circuit is outputted as an opposite-phase component of the audio signals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an unbalance-balance conversion circuit used for an audio amplifier or the like.

In order to handle an unbalanced signal transmitted from an audio playback device such as a CD player as a balanced signal inside the audio amplifier, an unbalanced-balance converting circuit for converting the unbalanced signal into a balanced signal inside the audio amplifier. Need.
Conventional unbalance-balance conversion circuits include a circuit combining a constant current source and a differential amplifier circuit (see Patent Document 1), and a circuit using a phase inversion circuit (see Patent Document 2).

Japanese Patent Laid-Open No. 10-209813 JP 2005-218003 A

Since the conventional unbalance-balance conversion circuit was intended only for unbalance-balance conversion, it was necessary to provide a separate volume control circuit as the next-stage amplifier in order to adjust the volume required for the audio preamplifier. .
FIG. 3 is a circuit diagram showing an example of the configuration of the volume control circuit. By using a volume adjustment IC (Integrated Circuit) 16 having variable resistors R17 and R18 in the feedback circuit of the high gain amplifier 17, a volume adjustment function is realized. Since this volume control circuit is an inverting amplifier circuit, the audio signal output from the output terminal OUT is in reverse phase to the audio signal input from the input terminal IN.

FIG. 2 is a circuit diagram showing an example of the configuration of a conventional unbalance-balance conversion circuit, in which a phase inversion circuit and a volume control circuit are combined to perform unbalance-balance conversion and volume control. The phase inverting circuit 11 is an inverting amplifier circuit including a high gain amplifier 11a and resistors R11 and R12 of the feedback circuit and having a voltage amplification factor of -1.
The audio signal input from the input terminal IN is branched into two systems, and one is passed through a volume control circuit including a high gain amplifier 13 and a volume control IC 12 including variable resistors R13 and R14. The adjusted anti-phase audio signal is output to the output terminal COLD, and the other is supplied to the volume control circuit configured by the volume control IC 14 including the phase inverting circuit 11, the high gain amplifier 15, and the variable resistors R15 and R16. The normal phase audio signal whose volume is adjusted by passing the signal is output to the output terminal HOT.

In the circuit of FIG. 2, there is a difference between the circuit that outputs the audio signal of the normal phase and the circuit that outputs the audio signal of the reverse phase, and the presence or absence of the phase inversion circuit 11 and the volume control circuit are different. There is a problem that the quality of the reproduced sound is deteriorated because the quality of the frequency characteristics, phase characteristics, distortion rate, etc. of the phase signal and the reverse phase signal are not uniform.
The circuit of FIG. 2 has a configuration in which the volume control IC is provided in a circuit that outputs a normal-phase audio signal and a circuit that outputs a reverse-phase audio signal, respectively, but a high-accuracy volume control IC is expensive. Therefore, the cost for that was needed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a circuit capable of eliminating a quality difference between a balanced-phased normal phase audio signal and a reversed-phase audio signal and preventing deterioration in sound quality in an unbalance-balance conversion circuit. There is.

An unbalance-balance conversion circuit according to the present invention includes a volume adjustment circuit that adjusts the volume of an audio signal, an amplification circuit that amplifies an audio signal whose volume is adjusted by the volume adjustment circuit, and an audio signal that is amplified by the amplification circuit. A phase inversion circuit that inverts the phase of the signal and feeds back to the amplifier circuit, outputs the output of the amplifier circuit as a normal phase component of the audio signal, and outputs the output of the phase inverter circuit as a negative phase component of the audio signal To do.

According to the unbalance-balance conversion circuit of the present invention, since a normal phase audio signal and a reverse phase audio signal which have been balance-converted are extracted from the same feedback circuit, the difference in signal quality between them is eliminated, and the sound quality is improved. Deterioration can be prevented.

FIG. 1 is a block diagram showing the configuration of an embodiment of the unbalance-balance conversion circuit of the present invention. The input signal input from the input terminal IN is output to the next stage through the volume adjustment IC 1 for adjusting the volume. The volume control IC 1 includes variable resistors R1 and R2, and is controlled by a microcomputer (not shown).

The high gain amplifier 2 amplifies the audio signal input to the non-inverting input terminal via the variable resistor R1. The audio signal output from the high gain amplifier 2 is branched into two systems, one is output to the output terminal HOT as the positive phase component of the balanced-converted audio signal, and the other is output to the phase inverting circuit 3 described later of the feedback circuit. Entered. As the high gain amplifier 2, an operational amplifier may be used as in the present embodiment, or a differential amplifier circuit configured using discrete components may be used.

The phase inversion circuit 3 includes a high gain amplifier 3 a and inverts the phase of the audio signal output from the high gain amplifier 2. If the resistance values of the two constant resistors R3 and R4 used as the feedback circuit of the high gain amplifier 3a are set to the same value, the voltage amplification factor of this circuit is -1 and only the phase is inverted.
The output of the phase inversion circuit 3 is branched into two systems, one is output to the output terminal COLD as the reverse phase component of the balanced-converted audio signal, and the other is a high gain via the variable resistor R2 of the volume control IC1. Feedback is made to the non-inverting input terminal of the amplifier 2. Since the phase of this feedback signal is inverted by the phase inverting circuit 3, the feedback destination input terminal is a non-inverting input terminal, but can be regarded as negative feedback.

In this way, according to the unbalance-balance conversion circuit of the present embodiment, it is possible to simultaneously extract a normal phase audio signal and a reverse phase audio signal which have been balance-converted from within one feedback circuit, and a volume level. It can also have an adjustment function. Therefore, the difference in signal quality between each other can be eliminated, and deterioration of sound quality can be prevented.

In actual measurement, the S / N of the output signal is improved by 1 dB in the circuit of this embodiment shown in FIG. 1 as compared with the conventional circuit shown in FIG. As the S / N ratio of the output signal is improved, the audible S / N feeling is improved, that is, the noise feeling is reduced. In particular, the quietness and sound spread when playing small sounds has been improved, and the performance of the reproduced sound field has been enhanced.

Further, according to the unbalance-balance conversion circuit of the present embodiment, by changing the volume control circuit from two systems to one system, there is no volume difference between the normal phase component and the reverse phase component, and the cost can be reduced. .
The embodiment described above is an example of the embodiment of the present invention, and the present invention can be implemented without being limited thereto.

It is a block diagram which shows the structure of one Example of the unbalance-balance conversion circuit of this invention. It is a figure which shows an example of a structure of the conventional unbalance-balance conversion circuit. It is a figure which shows an example of a structure of a volume control circuit.

Explanation of symbols

1, 12, 14, 16: Volume control IC
2, 13, 15, 17: High gain amplifier 3, 11: Phase inversion circuit

Claims (1)

A volume control circuit for adjusting the volume of the audio signal;
An amplifying circuit for amplifying the audio signal whose volume is adjusted by the volume adjusting circuit;
A phase inverting circuit for inverting the phase of the audio signal amplified by the amplifier circuit and feeding back to the amplifier circuit;
Output the output of the amplifier circuit as a positive phase component of the audio signal,
An unbalance-balance conversion circuit, wherein the output of the phase inversion circuit is output as an antiphase component of an audio signal.

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