JP2007116262A - Digital amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital amplifier equipped with a step-up function in the digital amplifier circuit without providing an extra switching means such as a DC/DC converter. <P>SOLUTION: The digital amplifier comprises a pulse modulation circuit 120 modulating a voice signal, and a step-up or step-up/down switching circuit 130 driven with the output from the modulation circuit. An output having a peak value higher than a power supply voltage VDD from a battery 610 can be outputted by the switching circuit equipped with the step-up or step-up/down function, and a voice amplification signal where deterioration of voice is prevented is outputted even when a high output is requested. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital amplifier, and more particularly to a digital amplifier that is effective in preventing deterioration of sound quality due to a power supply circuit being stopped.

  In recent years, with the progress of multi-function and high integration of AV equipment, digitalization of composite AV machines has been attracting attention. As this type of composite AV machine, an AV component in which a CD player, an AM / FM radio tuner, an audio amplifier, and the like are configured in the same casing is known.

  Furthermore, recently, switching from an analog amplifier to a digital amplifier has been studied as an audio amplifier incorporated in a composite AV machine as described above. By using a digital amplifier, it is smaller and lower in size than a conventional analog amplifier. Since heat generation, high sound quality, etc. can be expected, digital amplifiers are becoming the mainstream of audio amplifiers for composite AV machines.

  As this type of digital amplifier, for example, the technique disclosed in Patent Document 1 is known.

  As shown in FIG. 1 of the document, the digital amplifier described in Patent Document 1 includes a pulse width modulation unit 30, a switching unit 50, and a DC power source unit 17 that supplies a DC signal to the switching unit 50. The pulse width modulation means 30 converts the audio frequency band input signal into a pulse width modulation signal, the switching means 50 is switched by the pulse width modulation signal, and the DC signal is used as the pulse width modulation signal. A signal in the audio frequency band is extracted from the width modulation signal, and a signal obtained by amplifying the audio frequency band input signal is obtained.

  In this digital amplifier, the AC audio signal input from the terminal 3 is converted into a pulse waveform by the pulse width modulation means 30, and the peak value of this pulse waveform is amplified to the power supply voltage Vcc by the switching means 50. By passing the waveform through the high-cut filter sections 60 and 80, an audio signal is extracted and the speaker is driven.

  Here, since the peak voltage of the audio signal extracted from the filter unit is determined by the pulse width and the power supply voltage Vcc, the digital amplifier disclosed in Patent Document 1 requires a peak voltage of Vcc or more due to the demand for large output amplification. Even in this case, since the maximum value of the audio signal is limited to Vcc, the audio signal waveform is distorted, and as a result, the audio characteristics are deteriorated.

  In particular, when battery driving is assumed, since the upper limit value of Vcc is determined by the output voltage of the battery, this sound distortion is likely to occur.

As a technique for increasing the upper limit value of Vcc, a configuration in which the voltage of the battery is boosted by using a DCDC converter and used as the power supply voltage of the switching means is also considered. In addition, since it is necessary to provide switching means for the DCDC converter, there is a problem that the circuit scale increases.
JP-A-11-168326

  Therefore, the present invention provides a digital amplifier having a boosting function in a digital amplifier circuit without separately providing a switching means such as a DCDC converter.

  In order to achieve the above object, the invention described in claim 1 is a digital amplifier that performs switching amplification of an audio signal and outputs the analog signal, and uses the audio signal for generating a pulse waveform for driving a step-up switching circuit. Features.

  As described above, by using the audio signal to generate the pulse waveform for driving the boosting type switching circuit, it is possible to perform the amplification of the audio signal and the boosting of the power supply voltage by the same switching circuit.

  Here, as the step-up switching circuit, a well-known step-up switching circuit used in a step-up DCDC converter or the like can be used, and a pulse waveform for driving the switching circuit is generated using an audio signal as a reference. Thus, the amplification of the audio signal and the boosting of the power supply voltage can be performed by the same switching circuit.

  As a result, the switching element and the driver for driving the switching element can be shared as compared with the configuration in which the step-up DCDC converter is used as the power supply voltage supply means of the digital amplifier circuit. Improvements can be made.

  The invention according to claim 2 is a digital amplifier for switching and amplifying an audio signal to output an analog signal, the error amplifier detecting a difference between the analog output and the audio signal, and an output of the error amplifier. A pulse modulation circuit for generating a pulse waveform, a switching element driven by the output of the pulse modulation circuit, a coil arranged in series with a power supply line of the switching element, and a parallel arrangement on the output line of the switching element And a capacitor.

  As described above, the pulse waveform is generated based on the difference between the analog output and the audio signal, and the coil is arranged on the power supply line of the switching element, thereby amplifying the audio signal and boosting the power supply voltage. It becomes possible to do in.

  According to a third aspect of the present invention, there is provided a digital amplifier for switching and amplifying an audio signal and outputting the analog signal, wherein the audio signal is used for generating a pulse waveform for driving the step-up / step-down switching circuit.

  As described above, by using the audio signal to generate the pulse waveform for driving the step-up / step-down switching element, it is possible to perform the amplification of the audio signal and the step-up / step-down of the power supply voltage with the same switching element.

  According to a fourth aspect of the present invention, there is provided a digital amplifier for switching and amplifying an audio signal for analog output, an error amplifier for detecting a difference between the analog output and the audio signal, and an output of the error amplifier. A pulse modulation circuit for generating a pulse waveform, a first switching element driven by an output of the pulse modulation circuit, a first coil arranged in series on a power line of the first switching element, and the first A second coil arranged in parallel behind the first switching element, a second switching element or rectifying element arranged in series behind the second coil, and a stage after the second switching element or rectifying element. And a capacitor arranged in parallel.

  In this way, the pulse waveform is generated based on the difference between the analog output and the audio signal, and the coil is arranged in the power supply line and the output line of the switching element, thereby amplifying the audio signal and increasing / decreasing the power supply voltage. The same switching element can be used.

  Note that an FET is preferably used as the switching element, and a diode is preferably used as the rectifying element.

  The invention according to claim 5 is a digital amplifier that performs switching amplification of an audio signal and outputs the analog signal, and is based on an error amplifier that detects a difference between the analog output and the audio signal, and an output of the error amplifier. A pulse modulation circuit for generating a pulse waveform, a first and a second switching element driven by an output of the pulse modulation circuit, and a series arrangement between the first switching element and the second switching element. And a capacitor arranged in parallel downstream of the second switching element.

  As described above, the pulse waveform is generated based on the difference between the analog output and the audio signal, and the coil is arranged between the first switching element and the second switching element, thereby amplifying the audio signal and the power source. It is possible to perform voltage step-up / step-down with the same switching element.

  In each of the above inventions, the pulse modulation circuit may include a PWM conversion circuit, a ΔΣ conversion circuit, or the like, and may include a function of performing a predetermined arithmetic process on the audio signal. As a modulation method used in the digital amplifier circuit, there are a pulse width modulation method PWM (Pulse Width Modulation) and a pulse density modulation method PDM (Pulse Density Modulation), and the data format input to the digital amplifier circuit is as follows. PCM (Pulse Code Modulation) used in music CDs.

  Here, the audio signal input to the pulse modulation circuit may be an analog signal or a digital signal. When an analog signal is input, the analog signal is directly input to the pulse modulation circuit. Any of the configurations that are converted into a pulse signal, or once converted into a digital signal via an A / D converter and then input into the pulse modulation circuit may be used.

  On the other hand, when a digital signal is input, the digital signal is directly input to the pulse modulation circuit and converted into a pulse signal or once converted into an analog signal through a D / A converter. Any configuration that is input to the pulse modulation circuit later may be used.

  As an embodiment of the pulse modulation circuit, an analog input PWM modulation circuit or an analog input ΔΣ circuit is used for an analog signal input, and a digital input PWM modulation circuit or a digital input ΔΣ circuit is used for a digital signal input. Use it.

  The digital amplifier according to the present invention includes any of a switching amplifier, a digital amplifier, and a class D amplifier.

  As described above, according to the present invention, it is possible to provide a digital amplifier having a boosting function in a digital amplifier circuit without separately providing a switching means such as a DCDC converter. As a result, even if the battery is driven, it is possible to suitably prevent the distortion of the sound output caused by the shortage of the power supply voltage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments described below, and can be modified as appropriate.

  FIG. 1 is a block diagram showing an internal configuration of an audio component in which a digital amplifier according to the first embodiment of the present invention is incorporated. As shown in the figure, the audio component includes an AM / FM radio receiving unit 510, an audio tape reproducing unit 520, a CD / DVD player 530, and a digital amplifier circuit 100 configured as a circuit module. .

  Then, an AM / FM radio reception unit 510 that outputs an audio signal in an analog format and an audio tape reproduction unit 520 are connected to the switch SW1, and a signal selected by the switch SW1 is input to the A / D converter 540.

  The analog audio signal output from the AM / FM radio receiving unit 510 or the audio tape reproducing unit 520 is converted into a digital signal by the A / D converter 540, and the pulse in the digital amplifier circuit 100 is passed through the attenuator 112. Input to the modulator 120.

  On the other hand, a CD / DVD player 530 that outputs an audio signal in a digital format and a port P3 for inputting an external digital signal are connected to a switch SW2, and the signal selected by this switch SW2 passes through an attenuator 112. And input to the pulse modulator 120 in the digital amplifier circuit 100.

  The digital amplifier circuit 100 includes a pulse modulator 120 and a switching circuit 130, and amplifies an audio signal input from the AM / FM radio receiving unit 510, the audio tape reproducing unit, the CD / DVD player 530, or the external port P3. Then, an analog output is made to the speaker 620 provided outside the audio component 500 via the port P2.

  Here, the switching circuit 130 is configured by a boosting or step-up / stepping switching circuit, and is driven by a power supply voltage VDD supplied from a battery 610 provided outside the audio component 500. The battery 610 is connected to the port P1 and supplies power to the AM / FM radio reception unit 510, the audio tape playback unit, and the CD / DVD player 530.

  FIG. 2 is a circuit block diagram showing a configuration of a digital amplifier according to the second embodiment of the present invention. The configuration shown in the figure is an example in which a boosting function is provided by using an analog audio signal as a reference voltage of an error amplifier provided in a boosting switching circuit.

  The switching circuit 130 includes a high-side switching element FET1 and a low-side switching element FET2, and the power supply voltage VDD of these switching elements is supplied from the battery 610 via a coil L arranged in series with the power supply line. . The boosting function is provided by the energy storage action of the coil L. A diode may be used instead of the high-side switching element FET1.

  Further, an output capacitor Cout is arranged in parallel at the subsequent stage of the switching element FET1, the signal output from the switching element FET1 is smoothed by this output capacitor, and the audio signal is output to the speaker 620 via the coupling capacitor Cc. The The coupling capacitor Cc may be arranged inside the digital amplifier circuit 100.

  The error amplifier 140 detects the difference between the output feedback signal of the switching circuit 130 obtained by the voltage division of the resistors R11 and R12 and the analog audio signal input superimposed on the reference voltage Vref, and uses this difference as a predetermined gain ratio. And outputs to the PWM circuit 122.

  The PWM circuit 122 generates a pulse waveform subjected to pulse width modulation based on the difference signal output from the error amplifier 140, and outputs the pulse waveform to the switching elements FET1 and FET2 via the drive elements Amp1 and Amp2. . The switching operation of the switching elements FET1 and FET2 is performed according to the pulse waveform output from the PWM circuit 122.

  FIG. 3 is a circuit block diagram showing a configuration of a digital amplifier according to the third embodiment of the present invention. The configuration shown in the figure is an example in which a step-up / step-down function is provided by using an analog audio signal as a reference voltage of an error amplifier provided in a step-up / step-down switching circuit.

  The switching circuit 130 of the digital amplifier according to the present embodiment includes a high-side switching element FET1 and a low-side switching element FET2, and the power supply voltage VDD of these switching elements is an input capacitor Cin arranged in parallel with the power supply line. Is supplied from the battery 610 via a coil L arranged in series. A diode may be used instead of the switching element FET1 on the high side.

  Further, a capacitor C1 arranged in series and a coil L2 arranged in parallel are provided between the switching elements FET1 and FET2, and an output capacitor Cout is arranged in parallel downstream of the switching element FET1.

  The step-up / step-down switching circuit 130 configured as described above performs step-up / step-down of the power supply voltage and switching amplification of the audio signal. The other configuration is the same as in FIG.

  FIG. 4 is a circuit block diagram showing a configuration of a digital amplifier according to the fourth embodiment of the present invention. The configuration shown in the figure is an example in which a step-up / step-down function is provided by using an analog audio signal as a reference voltage of an error amplifier provided in the step-up / step-down switching circuit.

  The switching circuit 130 of the digital amplifier according to the present embodiment includes an input-side switching element pair including a high-side switching element FET1 and a low-side switching element FET2, and a high-side switching element FET3 and a low-side switching. And an output-side switching element pair including the element FET4.

  Between these switching element pairs, a coil L is arranged in series, the power supply voltage VDD is supplied from the battery 610 to the input side switching element pair, and the output capacitor Cout is provided in the subsequent stage of the output side switching element pair. Are arranged in parallel.

  The switching operation of the switching elements FET1 to FET4 is performed according to the pulse waveform output from the PWM circuit 122 via the drive elements Amp1 to Amp4.

  The step-up / step-down switching circuit 130 configured as described above performs step-up / step-down of the power supply voltage and switching amplification of the audio signal. The other configuration is the same as in FIG.

  FIG. 5 is a circuit block diagram showing a configuration example when the speaker 620 is differentially driven using two digital amplifier circuits shown in FIGS. As shown in the figure, by connecting the digital amplifier circuits 100-1 and 100-2 to the speaker 620 to form a bridge, the dynamic range width is expanded and the speaker in the example of FIGS. The coupling capacitor Cc arranged in front of 620 becomes unnecessary.

  According to the present invention, a digital amplifier having a boosting function can be configured without separately providing a switching means such as a DCDC converter, so that it can be applied to a composite AV machine that requires battery-driven amplification with a large volume. Be expected.

1 is a block diagram showing an internal configuration of an audio component in which a digital amplifier according to a first embodiment of the present invention is incorporated. It is a circuit block diagram which shows the structure of the digital amplifier which concerns on the 2nd Embodiment of this invention. It is a circuit block diagram which shows the structure of the digital amplifier which concerns on the 3rd Embodiment of this invention. It is a circuit block diagram which shows the structure of the digital amplifier which concerns on the 4th Embodiment of this invention. FIG. 5 is a circuit block diagram illustrating a configuration example in the case of differentially driving a speaker 620 using two digital amplifier circuits illustrated in FIGS. 2 to 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Digital amplifier circuit, 120 ... Pulse modulation circuit, 122 ... PWM circuit, 130 ... Switching circuit, 140 ... Error amplifier, 500 ... Audio component, 510 ... AM / FM radio receiving part, 520 ... Audio tape reproducing part, 530 ... CD / DVD player, 540, A / D converter, 610, battery, 620, speaker

Claims (5)

A digital amplifier that amplifies an audio signal by switching and amplifying it,
A digital amplifier using an audio signal for generating a pulse waveform for driving a step-up switching circuit. A digital amplifier that amplifies an audio signal by switching and amplifying it,
An error amplifier for detecting a difference between the analog output and the audio signal;
A pulse modulation circuit that generates a pulse waveform based on the output of the error amplifier;
A switching element driven by the output of the pulse modulation circuit;
A coil arranged in series with the power line of the switching element;
And a capacitor arranged in parallel with the output line of the switching element. A digital amplifier that amplifies an audio signal by switching and amplifying it,
A digital amplifier using an audio signal for generating a pulse waveform for driving a step-up / step-down switching circuit. A digital amplifier that amplifies an audio signal by switching and amplifying it,
An error amplifier for detecting a difference between the analog output and the audio signal;
A pulse modulation circuit that generates a pulse waveform based on the output of the error amplifier;
A first switching element driven by the output of the pulse modulation circuit;
A first coil arranged in series with the power line of the first switching element;
A second coil arranged in parallel at a subsequent stage of the first switching element; a second switching element or a rectifying element arranged in series at a subsequent stage of the second coil;
A digital amplifier comprising: a capacitor arranged in parallel at a subsequent stage of the second switching element or rectifying element. A digital amplifier that amplifies an audio signal by switching and amplifying it,
An error amplifier for detecting a difference between the analog output and the audio signal;
A pulse modulation circuit that generates a pulse waveform based on the output of the error amplifier;
First and second switching elements driven by the output of the pulse modulation circuit;
A coil disposed in series between the first switching element and the second switching element;
A digital amplifier comprising: a capacitor arranged in parallel at a subsequent stage of the second switching element.

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