JP2016063300A - Audio amplifier, electronic apparatus, and audio signal reproduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an audio amplifier capable of high sound quality reproduction.SOLUTION: An audio amplifier 200 for driving an electroacoustic conversion element 102 is provided. A delay circuit 202 generates a first audio signal S1 by delaying an input audio signal Sin a DSD format. A first class-D amplifier 204, connected to one end of the electroacoustic conversion element 102, performs switching according to the first audio signal S1. A decimation filter 206 converts the input audio signal Sto a second audio signal S2 in a PCM (pulse code modulation) format. A digital volume control circuit 208 generates a third audio signal S3 by multiplying the second audio signal S2 by a coefficient corresponding to a volume setting value VOL. A pulse modulator 212 converts an output S4 of a noise shaper 210 to a fifth audio signal S5 in a pulse modulated format. A second class-D amplifier 214 performs switching according to the fifth audio signal S5.SELECTED DRAWING: Figure 2

Description

  The present invention relates to audio signal processing, and more particularly to a class D amplifier.

  In recent years, high-resolution sound sources have been promoted in the audio field. Under such circumstances, a format called DSD (Direct Stream Digital) is widely used in network distribution of sound sources, and a reproducing apparatus corresponding to the format is required. The DSD method itself has conventionally existed and has been adopted in SACD (Super Audio CD) and the like.

  FIG. 1 is a diagram showing a DSD playback system. The reproduction system 500 includes a decimation filter 502, a DSP (Digital Signal Processor) 506, a noise shaper 508, a pulse width modulator 510, a class D amplifier 512, and a speaker 514.

  The decimation filter 502 thins out the sampling frequency of the bit stream S51 by 1/64 and converts it to PCM (pulse code modulation) data S53. The DSP 506 performs various digital arithmetic processing such as volume control on the PCM data 23. The noise shaper 508 includes a ΔΣ modulator and separates quantization noise of the audio signal S54 outside the audio band. The pulse width modulator 510 performs pulse width modulation on the output data S55 of the noise shaper 508. The class D amplifier 512 amplifies the output pulse S56 of the pulse width modulator 510 and drives the speaker 514. The speaker 514 outputs an analog audio signal S57 obtained by smoothing the output pulse S56.

JP 2002-319238 A

  The DSD method is a kind of PDM (Pulse Density Modulation), in which an audio waveform is recorded as a 1-bit pulse density modulated bit stream, and in principle, it is passed through a low-pass filter to obtain the original audio. Can play waveforms. However, in the conventional reproduction system 500 shown in FIG. 1, since the bit stream is converted into PCM data, the original advantages of the DSD method are impaired, and there is room for improvement in sound quality.

  The present invention has been made in view of such a problem, and one of exemplary purposes of an aspect thereof is to provide an audio amplifier capable of high-quality sound reproduction.

  One embodiment of the present invention relates to an audio amplifier that drives an electroacoustic transducer. The audio amplifier delays the input audio signal in the DSD format and generates a first audio signal, a first class D amplifier connected to one end of the electroacoustic transducer and switching in accordance with the first audio signal; A decimation filter that converts an input audio signal into a second audio signal in PCM (pulse code modulation) format, and a digital volume circuit that generates a third audio signal by multiplying the second audio signal by a coefficient according to a set value of the volume. A noise shaper for noise shaping the third audio signal to generate a fourth audio signal, a pulse modulator for converting the fourth audio signal into a pulse-modulated fifth audio signal, and the other end of the electroacoustic transducer Connected to the second and switching according to the fifth audio signal It includes a grade amplifier, a.

  According to this aspect, an audio signal having an amplitude that does not depend on the set value of the volume is applied to one end of the electroacoustic transducer by the first class D amplifier, and the second class D amplifier is applied to the other end of the electroacoustic transducer. Thus, an audio signal having an amplitude and a polarity according to the set value of the volume is applied. Thereby, the drive voltage applied between the both ends of the electroacoustic transducer changes according to the set value of the volume, and the volume can be changed. In addition, since a part of the drive voltage includes a component of a pure 1-bit audio signal that does not undergo PCM conversion processing, sound quality can be improved.

The coefficient may be determined so that the analog audio waveform at one end and the analog audio waveform at the other end of the electroacoustic transducer have the same amplitude and the same polarity when the set value of the volume is minimum.
Thereby, the drive voltage between the both ends of the electroacoustic transducer becomes substantially zero, and a volume of zero can be realized.

The coefficient may be determined so that the analog audio waveform at one end and the analog audio waveform at the other end of the electroacoustic transducer have the same amplitude and opposite polarity when the set value of the volume is maximum.
Thereby, the maximum volume can be realized in a pair of class D amplifiers to which a certain power supply voltage is applied.

  The delay amount of the delay circuit may be determined to be equal to the signal processing delay and the propagation delay from the decimation filter to the pulse modulator.

The audio amplifier may be integrated on a single semiconductor substrate.
“Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuit on one chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

  Another embodiment of the present invention relates to an electronic device. The electronic apparatus may include an electroacoustic transducer and any one of the above-described audio amplifiers that drives the electroacoustic transducer.

  The electronic device is provided between the one end of the electroacoustic transducer and the first class D amplifier of the audio amplifier, and between the other end of the electroacoustic transducer and the second class D amplifier of the audio amplifier. And a second filter.

  It should be noted that any combination of the above-described constituent elements and the expression of the present invention converted between methods, apparatuses, etc. are also effective as an aspect of the present invention.

  According to an aspect of the present invention, a 1-bit audio signal in DSD format can be reproduced with high sound quality.

1 is a diagram showing a DSD playback system. FIG. 1 is a circuit diagram of an audio amplifier according to an embodiment. It is a figure which shows the relationship between the volume setting value VOL and the coefficient K of a digital volume circuit. It is an operation | movement waveform diagram of an audio amplifier when changing the volume value VOL from the maximum value to the minimum value. 5A to 5C are external views of electronic devices.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are physically directly connected, or the member A and the member B are electrically connected. The case where it is indirectly connected through another member that does not affect the state is also included.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

  FIG. 2 is a circuit diagram of the audio amplifier 200 according to the embodiment. The audio amplifier 200 is built in an electronic device (also referred to as an audio system) 100 together with some external parts. Specifically, the electronic device 100 includes an electroacoustic transducer 102, a first filter 104P, a second filter 104N, and an audio amplifier 200. The audio amplifier 200 is a functional IC integrated on a single semiconductor substrate. The audio amplifier 200 receives a 1-bit audio signal S11 in DSD format at an audio input terminal (AUDIN) and drives the electroacoustic transducer 102. Examples of the electroacoustic transducer 102 include a speaker, headphones, and earphones. The first filter 104P is provided between the P-pole output terminal (OUTP) of the audio amplifier 200 and one end of the electroacoustic transducer 102, and the second filter 104N is electrically connected to the N-pole output terminal (OUTN) of the audio amplifier 200. Provided between the other ends of the acoustic transducer 102.

  The audio amplifier 200 includes a delay circuit 202, a first class D amplifier 204, a decimation filter 206, a digital volume circuit 208, a noise shaper 210, a pulse modulator 212, and a second class D amplifier 214.

The audio input of the audio amplifier 200 (Audin), the input audio signal _{S IN} of the DSD format (1 bit) from the sound source 106 are input. The delay circuit 202 receives the input audio signal _{S IN} of the DSD format, a predetermined time tau, to generate a first audio signal S1 is delayed. The first audio signal S1 is a pure 1-bit audio signal that does not undergo PCM conversion. The first class D amplifier 204 is connected to one end of the electroacoustic transducer 102 via the OUTP terminal and the external filter 104P, and switches according to the first audio signal S1.

Decimation filter 206 converts the input audio signal _{S IN} PCM (pulse code modulation) to the second audio signal S2 format. The digital volume circuit 208 multiplies the second audio signal S2 by a coefficient K corresponding to the volume setting value (command value) VOL to generate a third audio signal S3. For example, the audio amplifier 200 receives the set value VOL from the microcontroller 108 via the bus.

  The noise shaper 210 performs noise shaping on the third audio signal S3 to generate a fourth audio signal S4. The noise shaper 210 is constituted by a ΔΣ modulator or the like. Noise in the audio band is driven out of the audio band of 20 kHz or more by the noise shaper 210 (noise shaping). The pulse modulator 212 converts the fourth audio signal S4 into a pulse-modulated fifth audio signal S5. For example, the pulse modulator 212 may be a pulse width modulator, and the fifth audio signal S5 may be a PWM audio signal. The pulse modulator 212 may be a digital circuit or an analog circuit, and can be configured using a known technique. The pulse modulation method is not particularly limited, and may be a PDM method or PFM (pulse frequency), and its output S5 is a 1-bit digital signal that can be input to the class D amplifier 214. The time average waveform may be data corresponding to the audio waveform. The second class D amplifier 214 is connected to the other end of the electroacoustic transducer 102, and switches according to the fifth audio signal S5.

  The first class D amplifier 204 and the second class D amplifier 214 operate by receiving a common power supply voltage VDD, and therefore the amplitudes (high level voltages) of the output pulses of the first class D amplifier 204 and the second class D amplifier 214 are equal.

FIG. 3 is a diagram showing the relationship between the volume setting value VOL and the coefficient of the digital volume circuit 208. Factor K is, when the set value VOL the volume (the volume minimum level) the minimum MIN, one end of the analog audio waveform _{S OUTP} and the other analog audio waveform _{S OUTN} are the same amplitude of the electroacoustic transducer 102, the same polarity It is determined to have

The coefficient K, when the set value is a maximum (volume maximum level) MAX of volume, one end of the analog audio waveform _{S OUTP} and the other analog audio waveform _{S OUTN} are the same amplitude of the electroacoustic transducer 102, the reverse It is determined to have polarity.

  In the intermediate set value VOL, the coefficient K changes between a minimum value (for example, -1) and a maximum value (for example, +1) continuously or discontinuously depending on the set value VOL.

  The delay amount τ of the delay circuit 202 is determined to be equal to the signal processing delay and the propagation delay from the decimation filter 206 to the pulse modulator 212.

  The above is the configuration of the audio amplifier 200. Next, the operation will be described. FIG. 4 is an operation waveform diagram of the audio amplifier 200 when the volume value VOL is changed from the maximum value to the minimum value.

When the volume setting value VOL is maximum, the coefficient K is negative, and the analog audio waveforms S _OUTP and S _OUTN at both ends of the electroacoustic transducer 102 are in opposite _phases . At this time, the amplitude of the drive waveform S _OUTP -S _OUTN between both ends of the electroacoustic transducer 102 is maximized.

As the set value VOL is decreased, the amplitude of the analog audio waveform S _OUTN is decreased, and the amplitude of the drive waveform S _OUTP -S _OUTN is also decreased.

When the coefficient K becomes zero, the waveform S _{OUTN at} the other end of the electroacoustic transducer 102 becomes zero. The driving waveform at this time is equal to S _OUTP .

Further, when the volume setting value VOL becomes smaller, the coefficient K becomes positive and the waveform S _OUTN is in phase with S _OUTP . As the set value VOL decreases, the amplitude of the waveform S _OUTN increases and the amplitude of the drive waveform S _OUTP -S _OUTN further decreases. When the volume set value VOL eventually becomes the minimum value, the waveforms S _OUTP and S _OUTN completely coincide with each other, the drive waveform becomes zero, and the sound volume also becomes zero.

The above is the operation of the audio amplifier 200. Next, the advantages will be described.
In the audio amplifier 200 according to the embodiment, the audio signal S _OUTP having an amplitude that does not depend on the volume setting value VOL is applied to one end of the electroacoustic transducer 102 by the first class D amplifier 204, An audio signal S _OUTN having an amplitude and a polarity corresponding to the set value VOL of the volume is applied to the other end of 102 by the second class D amplifier 214. As a result, the drive waveform S _OUTP −S _OUTN applied between both ends of the electroacoustic transducer 102 changes according to the volume setting value VOL, and the volume can be changed.

Here, a part of the drive waveform S _OUTP includes a component of a pure 1-bit audio signal that does not undergo PCM conversion processing, so that the sound quality can be improved compared to the audio system of FIG.

  5A to 5C are external views of the electronic device 100. FIG. FIG. 5A illustrates a display device 600 that is an example of the electronic apparatus 100. The display device 600 includes a housing 602 and speakers 102L and 102R. The audio amplifier IC 300 is built in the housing 602 and drives the speakers 102L and 102R.

  FIG. 5B shows an audio component 700 that is an example of the electronic device 100. The audio component 700 includes a housing 702 and speakers 102L and 102R. The audio amplifier IC 300 is built in the housing 702 and drives the speakers 102L and 102R.

  FIG. 5C illustrates a small information terminal 800 that is an example of the electronic device 100. The small information terminal 800 is a mobile phone, PHS (Personal Handy-phone System), PDA (Personal Digital Assistant), tablet PC (Personal Computer), audio player, or the like. The small information terminal 800 includes a housing 802, a speaker 102, and a display 804. The audio amplifier IC 300 is built in the housing 802 and drives the speaker 102.

  By using the audio amplifier IC 300 in an electronic device as shown in FIGS. 5A to 5C, high sound quality can be realized. In addition, the audio amplifier IC 300 can be used for an intercom or the like.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Electronic device, 102 ... Electroacoustic transducer, 104 ... Filter, 106 ... Sound source, 108 ... Microcontroller, 200 ... Audio amplifier, 202 ... Delay circuit, 204 ... First class D amplifier, 206 ... Decimation filter, 208 ... Digital Volume circuit, 210 ... Noise shaper, 212 ... Pulse modulator, 214 ... Second class D amplifier, _SIN ... Input audio signal, S1 ... First audio signal, S2 ... Second audio signal, S3 ... Third audio signal, S4 ... 4th audio signal, S5 ... 5th audio signal.

Claims (12)

An audio amplifier that drives an electroacoustic transducer,
A delay circuit for delaying an input audio signal in DSD format to generate a first audio signal;
A first class D amplifier connected to one end of the electroacoustic transducer and switching in accordance with the first audio signal;
A decimation filter for converting the input audio signal into a second audio signal in PCM (pulse code modulation) format;
A digital volume circuit for generating a third audio signal by multiplying the second audio signal by a coefficient corresponding to a set value of the volume;
A noise shaper for noise shaping the third audio signal to generate a fourth audio signal;
A pulse modulator for converting the fourth audio signal into a pulse-modulated fifth audio signal;
A second class D amplifier connected to the other end of the electroacoustic transducer and switching in accordance with the fifth audio signal;
An audio amplifier comprising:   The coefficient is determined so that the analog audio waveform at the one end and the analog audio waveform at the other end of the electroacoustic transducer have the same amplitude and the same polarity when the set value of the volume is minimum. The audio amplifier according to claim 1.   The coefficient is determined such that when the set value of the volume is maximum, the analog audio waveform at the one end and the analog audio waveform at the other end of the electroacoustic transducer have the same amplitude and opposite polarity. The audio amplifier according to claim 1 or 2.   4. The audio amplifier according to claim 1, wherein a delay amount of the delay circuit is determined to be equal to a signal processing delay and a propagation delay from the decimation filter to the pulse modulator.   5. The audio amplifier according to claim 1, wherein the pulse modulator performs pulse width modulation on the fourth audio signal. 6.   6. The audio amplifier according to claim 1, wherein the audio amplifier is integrated on a single semiconductor substrate. An electroacoustic transducer;
The audio amplifier according to any one of claims 1 to 6, which drives the electroacoustic conversion element;
An electronic device comprising: A first filter provided between one end of the electroacoustic transducer and the first class D amplifier of the audio amplifier;
A second filter provided between the other end of the electroacoustic transducer and the second class D amplifier of the audio amplifier;
The electronic apparatus according to claim 7, further comprising: An audio signal playback method comprising:
Delaying an input audio signal in DSD format to generate a first audio signal;
A step of switching a first class D amplifier connected to one end of the electroacoustic transducer in accordance with the first audio signal;
Converting the input audio signal into a second audio signal in PCM (pulse code modulation) format;
Multiplying the second audio signal by a coefficient corresponding to a set value of the volume to generate a third audio signal;
Noise shaping the third audio signal to generate a fourth audio signal;
Pulse-modulating the fourth audio signal and converting it to a fifth audio signal;
A second class D amplifier connected to the other end of the electroacoustic transducer switches in response to the fifth audio signal;
A playback method comprising:   The coefficient is determined so that analog audio waveforms at the one end and the other end of the electroacoustic transducer have the same amplitude and the same polarity when the set value of the volume is minimum. 10. The reproduction method according to 9.   10. The coefficient is defined such that when the set value of the volume is maximum, the waveform of the one end and the other end of the electroacoustic transducer has the same amplitude and opposite polarity. The reproduction method according to 10.   The reproduction method according to claim 9, wherein the fifth audio signal is a signal obtained by pulse-width modulating the fourth audio signal.

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