JP4137732B2 - Digital amplifier driving method and audio signal reproducing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving method of a digital amplifier (class D amplifier) that performs switching amplification of a digital signal such as an audio signal using a PWM (pulse width modulation) signal, and an audio signal reproducing apparatus using such a driving method. It is about.
[0002]
[Prior art]
With the progress of audio compression technology, it is possible to record a large amount of audio information (audio data) of digital information on an information recording medium such as an MD (Mini Disc: Trademark). An audio compression technique is described in Patent Document 1, for example.
[0003]
In an audio signal reproducing apparatus that reads audio information recorded on such an information recording medium, a digital amplifier that switches and amplifies an audio signal obtained by converting the audio information into a signal has been rapidly used. This is because a high-speed switching element capable of reproducing an audio signal can be obtained relatively easily, and power can be saved due to the original high power efficiency. Among audio signal reproduction apparatuses, power saving is essential for the portable type.
[0004]
In such an audio signal reproduction device, audio information compressed and recorded in the MD is read out by an optical pickup, and the compressed audio signal is expanded (demodulated) in a signal processing circuit unit composed of a system LSI or the like. The audio signal is a multi-bit digital signal, which is further converted into a 1-bit digital signal audio signal using a ΔΣ modulation circuit. The 1-bit digital signal thus obtained is amplified in amplitude by a digital amplifier, then restored to an analog audio signal by a low-pass filter, and electromechanically converted by headphones or the like (see, for example, Patent Document 2). ).
[0005]
Further, an audio signal converted into a 1-bit digital signal is further modulated into a PWM signal by a PWM modulation circuit. By modulating the PWM signal and inputting it to the digital amplifier, the switching frequency of the digital amplifier can be reduced, and further power saving can be achieved (for example, see Patent Document 3).
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-335967 (released on December 17, 1993)
[0007]
[Patent Document 2]
JP 2002-158549 A (published on May 31, 2002)
[0008]
[Patent Document 3]
JP 2003-110376 A (published April 11, 2003)
[0009]
[Problems to be solved by the invention]
However, with further progress in power saving, it cannot be said that the above-described conventional audio signal reproduction device that modulates the PWM signal and then inputs it to the digital amplifier is sufficient. A proposal is awaited.
[0010]
The present invention has been made to meet such a demand, and a digital amplifier driving method capable of further reducing power consumption in a low power consumption audio signal reproducing apparatus of a type that inputs a PWM signal to a digital amplifier. An object of the present invention is to provide an audio signal reproducing apparatus with lower power consumption using the same.
[0011]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the inventor of the present application has a fixed sampling frequency in a PWM modulation circuit in a conventional audio signal reproduction device including a PWM modulation circuit that modulates a PWM signal. Attention was paid to the fact that modulation was performed at the same sampling frequency in any compression form.
[0012]
In other words, the fixed sampling frequency is set to a value that allows sound quality-oriented audio data recorded at a low compression rate to be satisfactorily sounded.For audio data that is recorded at a high compression rate and does not place importance on sound quality, The modulation is performed unnecessarily at a high sampling frequency. Since the power consumed by the gate capacitance of the FET of the digital amplifier is proportional to the sampling frequency of the PWM signal (gate power = PWM sampling frequency × constant (gate capacitance × gate voltage)), the digital amplifier can be reduced by reducing the sampling frequency. The power consumed by itself can be reduced. The inventor of the present application has found room for further power saving, and has come to carry out the present invention.
[0013]
In order to achieve the above object, the digital amplifier driving method of the present invention extends the compressed audio signal that is input, and modulates the expanded audio signal into a PWM signal to drive the digital amplifier. The method is characterized in that the sampling frequency at the time of modulating to the PWM signal is changed corresponding to the compression form of the audio signal.
[0014]
As a result, audio signals (songs and tracks) recorded in a compressed form that the user does not consider the sound quality as important, such as the LP4 mode (1/20 compression) of MD with a high compression ratio and the monaural mode. Correspondingly, the switching frequency of the digital amplifier can be reduced by reducing the sampling frequency at the time of PWM modulation to a low frequency that can obtain a certain sound quality, and the power consumption of the digital amplifier can be reduced. Thus, it is possible to realize power saving in a device including a digital amplifier.
[0015]
Also, in response to audio signals (songs and tracks) recorded in a compression format that the user thinks sound quality is important, such as MD SP mode (1/5 compression), which has a low compression rate By increasing the sampling frequency at the time of PWM modulation, it is possible to ensure sound quality equivalent to that of the prior art.
[0016]
In addition, since the audio signal with a high compression rate can reduce the frequency and save power, the audio signal reproduction apparatus that handles the reproduction of an object (such as an MD) in which the audio signal with a high compression rate is recorded. It is particularly effective.
[0017]
In order to achieve the above object, the audio signal reproduction apparatus of the present invention expands a plurality of audio signals having different compression forms corresponding to the respective compression forms, and the PWM modulation means converts the decompressed audio signals. In an audio signal reproducing apparatus that drives a digital amplifier by PWM modulation, a compression determination unit that determines a compression form of an audio signal, and a frequency that changes a sampling frequency of the PWM modulation unit according to a determination result of the compression determination unit And a variable means.
[0018]
According to this, the compression discrimination means discriminates the compression form of the audio signal, and the frequency variable means changes the sampling frequency of the PWM modulation means according to the discrimination result by the compression discrimination means. As a result, the sampling frequency can be matched to the contents of the audio signal (sound quality emphasis, recording amount emphasis, etc.) shown in the compression form.
[0019]
For example, an audio signal (a song with a high compression ratio) recorded in a compression format that the user does not consider the sound quality important, such as MD LP4 mode (1/20 compression), which is a high compression ratio, or monaural mode. And track), the sampling frequency at the time of PWM modulation is lowered to a low frequency such that a certain sound quality can be obtained, thereby reducing the power consumption by reducing the switching frequency of the digital amplifier, and the audio signal reproducing device Further power saving can be realized.
[0020]
Also, in response to audio signals (songs and tracks with a low compression rate) in a compressed form that the user thinks sound quality is important, such as the MD SP mode (1/5 compression), which is a low compression rate, By increasing the sampling frequency during PWM modulation, it is possible to ensure sound quality equivalent to that of the prior art.
[0021]
Even if the information recording medium is the same, if the compression form differs for each song (track), the sampling frequency is switched to the sampling frequency corresponding to the compression form for each song, which makes the user feel uncomfortable. Therefore, power saving can be achieved.
[0022]
Note that the sampling frequency for the compression mode may be preset (default setting), set by the user (user setting), or may use the default setting and the user setting.
[0023]
Further, according to this, since the audio signal with a high compression rate can reduce the frequency to save power, the reproduction of an object (such as MD) in which the audio signal with a high compression rate is recorded is handled. This is particularly effective in an audio signal reproduction device.
[0024]
In addition to the above configuration, the audio signal reproduction device of the present invention may be characterized in that the frequency variable means sets the sampling frequency using a preset compression form versus frequency table.
[0025]
According to this, it is possible to ensure good sound quality for those that emphasize sound quality, and for those that do not ask for sound quality, the sampling frequency can be lowered to an extent that there is no problem and effective power saving can be achieved. The compression type vs. frequency table in which the relationship between the compression type and the sampling frequency is set is provided in advance, and the frequency variable means uses this table to change the sampling frequency. The above-described effect can be given to all users by changing the sampling frequency uniformly without feeling.
[0026]
In addition to the above-described configuration, the audio signal reproduction device of the present invention has frequency setting means that enables a user to set a sampling frequency for each compression form, and the frequency variable means includes a compression form pair based on a user setting. The sampling frequency may be set using a frequency table.
[0027]
According to this, it becomes possible for the user himself to set the sampling frequency for each compression form using the frequency setting means, and the frequency variable means sets the sampling frequency using the compression form vs. frequency table based on the user setting. To do. Therefore, if the user is accustomed to various settings, for example, the modes other than the SP mode are all used at a low frequency to save power, and the sampling frequency described above can be used with a high degree of freedom in accordance with the specifications of each user. The effect by changing can be acquired.
[0028]
In addition to the above configuration, the audio signal reproduction device of the present invention is provided with a power saving mode, and in the normal mode, the frequency variable means sets the sampling frequency using the compression mode vs. frequency table for the normal mode, In the power saving mode, the sampling frequency may be set using the compression mode vs. frequency table for the power saving mode.
[0029]
By providing a compression mode vs. frequency table for the normal mode and the power saving mode, the power saving effect by changing the sampling frequency is focused on sound quality in the normal mode, and power saving is emphasized in the power saving mode. Thus, it can be obtained with sharpness, and by combining with the user settings of the compression mode vs. frequency table, the degree of freedom is further increased, and further power saving can be achieved.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
One embodiment of the present invention will be described with reference to FIGS. 1 to 3 as follows.
[0031]
The reproduction apparatus of the present embodiment is a magneto-optical disk reproduction apparatus (audio signal reproduction apparatus) that reproduces an audio signal of a digital signal recorded on a magneto-optical disk (audio signal source) such as an MD (mini disk: trademark), for example. ). As shown in FIG. 1, this magneto-optical disk reproducing apparatus includes an optical pickup 2, an RF amplifier 3, a decoder circuit / signal processing circuit / memory controller / audio signal processing circuit (hereinafter referred to as a signal processing circuit unit) 8 A memory 4, a class D amplifier 24, a low-pass filter 9, a slide motor 6, a spindle motor 5, a driver circuit 10, a servo control circuit 7, a control microcomputer 13, a power circuit 11, and an input A device 14 and a display device 12 are provided.
[0032]
The reproducing operation will be described. The optical pickup 2 is a reproducing head that irradiates a magneto-optical disk (hereinafter referred to as disk) 1 as a reproducible recording medium with laser light and takes in reflected light from the disk 1. The optical pickup 2 reads audio information (audio data) of digital information recorded on the disc 1 as an analog RF signal.
[0033]
The disk 1 has a recording area for recording audio information, which is main information, and a writing area (hereinafter referred to as a TOC area) in which various information can be arbitrarily written by a user of the apparatus. Various information is written in the TOC area using the optical pickup 2 and a magnetic head (not shown).
[0034]
The RF amplifier 3 amplifies the audio signal of the RF signal read by the optical pickup 2 and sends it to the signal processing circuit unit 8. Further, the RF amplifier 3 generates servo control signals such as a focus error signal and a tracking error signal from the RF signal and sends them to the servo control circuit 7.
[0035]
The signal processing circuit unit 8 includes a memory controller 21, a signal processing circuit 20, a decoder circuit 22, and an audio signal processing circuit 23. Each of the circuits 20 to 23 constituting the signal processing circuit unit 8 is provided so as to be able to communicate with the control microcomputer 13 in order to perform subcode processing and the like.
[0036]
Among these, the signal processing circuit 20 demodulates the RF signal transmitted from the RF amplifier 3 to convert it into a digital audio signal, and performs predetermined processing such as error correction on the audio signal. Although details will be described later, in the embodiment, the signal processing circuit 20 determines the compression mode (compression form) of the audio signal that is the RF signal to be demodulated, and transmits the determination result to the control microcomputer 13. .
[0037]
The memory controller 21 controls the writing operation and the reading operation of the audio signal of the digital signal to the memory 4 according to the instruction of the control microcomputer 13, and the audio signal subjected to predetermined processing such as error correction is stored in the memory 4. At the same time, the audio signal output from the memory 4 is output to the decoder circuit 22. The decoder circuit 22 decompresses (demodulates) the compressed audio signal of the digital signal into a multibit digital signal and outputs it to the audio signal processing circuit 23.
[0038]
The audio signal processing circuit 23 includes a ΔΣ modulation circuit, a PWM modulation circuit 23a, and the like. The audio signal, which is a multi-bit digital signal that has been decompressed, is ΔΣ-modulated by the ΔΣ modulation circuit into a 1-bit digital signal. Further, this is further subjected to PWM modulation by the PWM modulation circuit 23a to perform signal processing such as an audio signal composed of a PWM signal. Note that a multi-bit digital signal may be directly PWM modulated without being subjected to ΔΣ modulation. It is also possible to convert directly to a PWM signal by ΔΣ modulation. As will be described in detail later, the PWM modulation circuit 23a performs PWM modulation at a sampling frequency instructed from the control microcomputer 13.
[0039]
The memory (storage means) 4 temporarily stores an audio signal of a digital signal. For example, a semiconductor memory such as a 16 Mbit DRAM (Dynamic Random Access Memory) is appropriate. As described above, the memory 4 is controlled by the memory controller 21 in the signal processing circuit unit 8 and is provided for the purpose of protecting the audio signal in order to prevent interruption of reproduction due to disturbance such as vibration. .
[0040]
The class D amplifier unit 24 is a digital amplifier that switches and amplifies the audio signal of the PWM signal output from the signal processing circuit unit 8, and the details of the switching amplifier configured around the class D amplifier unit 24 are shown in FIG. Will be described. The audio signal amplified by the class D amplifier unit 24 is restored to an analog audio signal by a low-pass filter (LPF in the figure) 9 and is electromechanically converted by the headphones 25 or the like to be sonicated. In FIG. 1, the low-pass filter 9 is one system, but the low-pass filter 9 is actually composed of two systems 9a and 9b.
[0041]
The slide motor 6 is a motor for moving the optical pickup 2 in a direction orthogonal to a recording track (not shown) of the disk 1. The spindle motor 5 is a motor for rotating the disk 1. The driver circuit 10 supplies power to the slide motor 6, the spindle motor 5, and a driving device (not shown) that drives an objective lens (not shown) of the optical pickup 2. Yes.
[0042]
The servo control circuit 7 feedback-controls each of the devices driven by the driver circuit 10 so that operations such as causing the light emitted from the optical pickup 2 to follow the target recording track of the disk 1 are accurately performed. Circuit. The servo control circuit 7 determines control amounts such as focus, tracking, seek, and spin based on the servo signal output from the RF amplifier 3 in accordance with an instruction from the control microcomputer 13, and uses the control amount as a control signal as a driver circuit. 10 is sent out. The optical pickup 2, the RF amplifier 3, the servo control circuit 7 and the like constitute a reproducing means.
[0043]
The input device 14 includes a switch and a key (not shown). For example, after the switch is turned on to enable input, a plurality of audio signals (recorded on the disc 1 are recorded by manual input operation using a keyboard or the like). An operation for processing the reproduction order of the digital signal) is input to the control microcomputer 13.
[0044]
The control microcomputer (control means) 13 is a microcomputer that centrally manages the signal processing circuit unit 8, the servo control circuit 7, the power supply circuit 11, the display device 12, and the like. The control microcomputer 13 controls each of the above devices and circuits so that the disk 1 is reproduced based on these processing operations input from the input device 14, and displays various current states on the display device 12. Display data creation and the created data is transmitted. In addition, the control microcomputer 13 determines whether or not the audio signal amount in the memory 4 is equal to or greater than a preset upper limit value, or is equal to or less than a preset lower limit value. .
[0045]
As will be described in detail later, the frequency variable unit 13a in the control microcomputer 13 is based on the compression mode determined by the compression determination unit 20a of the signal processing circuit 20 in the signal processing circuit unit 8, and in the audio signal processing circuit 8d. The sampling frequency of PWM modulation is made variable.
[0046]
The power supply circuit 11 supplies power to the optical pickup 2, the RF amplifier 3, the signal processing circuit unit 8, the class D amplifier unit 24, the driver circuit 10, the control microcomputer 13, the servo control circuit 7, the display device 12, and the like. ing.
[0047]
The display device 12 may be, for example, a disc playback device main body, an external remote control device, or the like, and may be provided not only on one side but also on both sides. The operation state may be displayed by displaying such as color expression of LED.
[0048]
In the above configuration, at the time of reproduction, audio information or the like is read from the disk 1 by the optical pickup 2 as an RF signal. The RF signal is amplified by the RF amplifier 3 and demodulated or predetermined signal processing is performed by the signal processing circuit 20 in the signal processing circuit unit 8 to be restored as a digital audio signal. At this time, the audio signal of the digital signal is data in a time-axis compressed state.
[0049]
The RF signal amplified by the RF amplifier 3 is also sent to the servo control circuit 7 as a servo control signal used for feedback control. The servo control circuit 7 determines a control amount based on an instruction from the control microcomputer 13 based on the servo control signal, and outputs a control signal to the driver circuit 10. In the driver circuit 10, the slide motor 6, the spindle motor 5, and the objective lens driving device of the optical pickup 2 are operated in accordance with the magnitude of the control signal. As a result, the optical pickup 2 is sent to the target recording track, the rotational speed of the disc 1 is controlled to a predetermined value, and the position of an objective lens (not shown) is driven so as to accurately follow the recording track. .
[0050]
The audio signal of the digital signal processed by the signal processing circuit 20 is written and temporarily stored in the memory 4 and is read out to the memory controller 21 of the signal processing circuit unit 8 in the order of writing. The read audio signal of the digital signal is expanded by the decoder circuit 22 in the signal processing circuit unit 8 to be a multi-bit digital signal, which is subjected to ΔΣ modulation and PWM modulation by the audio signal processing circuit 23 and is subjected to PWM signal. Audio signal. The audio signal of the PWM signal is switched and amplified by the class D amplifier unit 24, restored to an analog audio signal by a low-pass filter, and electromechanically converted by the headphones 25 or the like to be sonicated.
[0051]
FIG. 2 shows an example of the electrical configuration of a switching amplifier composed of a typical digital amplifier that constitutes the class D amplifier unit 24. The signal processing circuit 23 includes a ΔΣ modulation circuit and a PWM modulation circuit (not shown). First, a series of binary signals is created from an analog input, a multi-bit digital input, or a 1-bit signal by the ΔΣ modulation circuit. Further, two series of 1-bit signals (normal phase signal and reverse phase signal) are generated based on the generated binary signal, and this is further subjected to PWM modulation by the PWM modulation circuit 23a, and each is output from the output terminals p11 and p12. Output.
[0052]
Between the power line of the high voltage V1 connected to the power supply terminal e1 and the GND line, a series circuit composed of N-channel output transistors q1 and q2 and a series circuit composed of N-channel output transistors q3 and q4 are included. An H bridge circuit is connected. The positive-phase PWM signal output from the positive-phase output terminal p11 of the audio signal processing circuit 23 is supplied to the gate of the output transistor q1 through the buffer b11 and to the gate of the output transistor q4 through the buffer b12. Given. On the other hand, the reverse-phase PWM signal output from the reverse-phase output terminal p12 of the audio signal processing circuit 23 is supplied to the gate of the output transistor q3 through the buffer b21 and the output through the buffer b22. This is applied to the gate of the transistor q2. Thus, the output transistors q1 and q4 and the output transistors q3 and q2 perform switching by a reciprocal operation.
[0053]
The connection point of the output transistors q1 and q2 is a negative phase output terminal, and is connected to a negative phase output terminal p22 via a low-pass filter 9b including a coil l2 and a capacitor c2. The connection point of the output transistors q3 and q4 is It becomes a positive phase output terminal and is connected to a positive phase output terminal p21 via a low pass filter 9a comprising a coil 11 and a capacitor c1. A load 26 such as a speaker is connected between the output terminals p21 and p22.
[0054]
Next, switching of the sampling frequency in the PWM modulation circuit 23a in the audio signal processing circuit 23 will be described.
[0055]
When the disc 1 is an MD, the audio signal is compressed in the monaural mode, the SP mode with a compression ratio of 1/5 to the original data, the LP mode with the compression ratio 1/10, and the LP4 with the compression ratio 1/20. There are four modes. The compression mode of the audio signal is recorded for each song in the track mode portion of the TOC area of the disc 1 described above. In the TOC area, address information and the like of the recording area where the corresponding music is recorded are recorded. When the optical pickup 2 reads out the audio information of the designated song in the recording area as an RF signal, it also reads out the information recorded in the TOC area and sends it to the signal processing circuit 20 of the signal processing circuit unit 8. And forward.
[0056]
The signal processing circuit 20 in the signal processing circuit unit 8 demodulates the RF signal input from the RF amplifier 3 into a digital signal, but has a function as the compression determination unit 20a, and is an audio signal of the RF signal. The compression mode (compression mode) is determined, and the determination result is transmitted to the control microcomputer 13.
[0057]
The control microcomputer 13 has a function as the frequency variable unit 13a, and sets the sampling frequency of the PWM modulation circuit 23a in the audio signal processing circuit 23 based on the compression mode determined by the compression determination unit 20a of the signal processing circuit 20. Decide and instruct the audio signal processing circuit 23.
[0058]
Here, the control myco 13 sets the sampling frequency of PWM modulation for the compression mode using the compression mode versus frequency table (compression mode versus frequency table) shown in FIG. In the compression mode versus frequency table, the sampling frequency for the compression mode is defined on a one-to-one basis.
[0059]
FIG. 3 shows an example. Here, the sampling frequency of 1000 kHz in the SP mode with a low compression rate, which is selected when sound quality is important, is set to the highest frequency, and in the LP2 mode, it is set to 900 kHz which is 10% lower than this. Also, in the LP4 mode with the highest compression rate that does not emphasize sound quality, the frequency is 800 KHz, which is 20% lower. In the monaural mode, although the compression rate is 1/5, since it is considered impossible to record music in the monaural mode, the sampling frequency in this case is set to 700 kHz and is lowered by 30%.
[0060]
In this way, according to the compression mode of the audio signal (song / track), the sampling frequency matches the content of the audio signal indicated by the compression mode (emphasis on sound quality, emphasis on recording volume, etc.). As a result, it is possible to achieve further power saving while obtaining the same level of satisfaction as before.
[0061]
4 shows a procedure in which the audio signal processing circuit 23 varies the sampling frequency of the PWM modulation circuit 23a by the control microcomputer 13.
[0062]
First, when reproduction of audio information is instructed, the sampling frequency of the PWM modulation circuit 23a is changed to a sampling frequency corresponding to the compression mode of the audio signal of the first song (S1). Specifically, the compression determination unit 20a of the signal processing circuit 20 determines the compression mode, and based on this, the frequency variable unit 13a of the control microcomputer 13 selects the sampling frequency of the PWM modulation circuit 23a corresponding to the compression mode, and this Based on the above, the audio signal processing circuit 23 changes the sampling frequency of the PWM modulation circuit 23a.
[0063]
While detecting the change of the music (S2), the audio signal is processed by the PWM modulation with the changed sampling frequency to reproduce the music. When it is detected in S2 that the music has changed, it is subsequently determined whether or not the compression mode has changed (S3). If the compression mode has not changed, the process returns to S2 to change the music. Play songs while detecting. On the other hand, when the compression mode is changed, the sampling frequency is changed to the sampling frequency corresponding to the compression mode of the audio signal of the music. The details of the change are the same as in S1.
[0064]
In the present embodiment, the control microcomputer 13 sets the sampling frequency of the PWM modulation circuit for the compression mode based on the preset compression mode versus frequency table shown in FIG. If a mode is provided, the sampling frequency may be varied based on this predetermined table only when the user selects the power saving mode using the input device 14 or the like.
[0065]
Alternatively, the user himself / herself may set the sampling frequency for the compression mode using the input device (frequency setting means) 14 of FIG. 1 and the like, and may vary the sampling frequency using the compression mode versus frequency table set by the user. . Such user settings are preferred by the user if the compression mode vs. frequency is shown in a table, and the frequency can be selected in the compression mode, and this can be selected and set as appropriate using a set menu or the like. Can be set to street.
[0066]
Also, separate compression mode vs. frequency tables are provided for the normal mode and the power saving mode, the sampling frequency is set using the normal mode table, and in the power saving mode, the power saving mode is set. The sampling frequency may be set using a table.
[0067]
By providing a compression mode vs. frequency table for the normal mode and the power saving mode, the power saving effect by changing the sampling frequency emphasizes the sound quality in the normal mode, and emphasizes the power saving in the power saving mode. It can be obtained with sharpness.
[0068]
Specifically, for example, in the normal mode, a compression mode vs. frequency table in which the monaural mode and the LP4 mode having a high compression rate are set to a low sampling frequency is prepared in advance. In the power saving mode, a mode other than the SP mode having a low compression rate is prepared. By preparing a compression mode vs. frequency table with LP2 mode, LP4 mode, and monaural mode as a low sampling frequency in advance, you can listen to high-quality sound in the normal mode, and in the power saving mode, the power consumption is further reduced than in the normal mode Can be measured.
[0069]
Further, in this case, by combining the compression mode vs. frequency table in the normal mode and the power saving mode with the configuration set by the user himself, the degree of freedom is further increased, and further power saving can be achieved.
[0070]
In the above embodiment, a magneto-optical disk reproducing apparatus that reproduces an audio signal of a digital signal recorded on a magneto-optical disk such as an MD is exemplified. However, the present invention also includes a PWM modulation circuit that modulates a PWM signal even in a semiconductor reproduction device such as a WMA or MP3 player that does not use an optical pickup driving means. As in the case described above, the same effect as described above can be obtained by changing the sampling frequency of the PWM modulation circuit in accordance with the compression mode when reproducing music having a different compression mode. be able to. In the apparatus shown in FIG. 1, the optical pickup driving means includes an optical pickup 2, an RF amplifier 3, a spindle motor 5, a slide motor 6, a servo control circuit 7, and a driver circuit 10.
[0071]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the technical means disclosed in different embodiments can be appropriately combined. Embodiments to be described are also included in the technical means of the present invention.
[0072]
【The invention's effect】
As described above, the driving method of the digital amplifier of the present invention is a method of driving a digital amplifier that expands an input compressed audio signal, modulates the expanded audio signal into a PWM signal, and drives the digital amplifier. It is characterized in that the sampling frequency at the time of modulating to the PWM signal is changed corresponding to the compression form of the audio signal.
[0073]
As a result, for a sound signal (song or track) recorded in a compressed form that the user does not consider the sound quality as important, the sampling frequency at the time of PWM modulation is low enough to obtain an appropriate sound quality. By reducing the frequency, the power consumption of the digital amplifier can be reduced, and consequently, power saving in a device including the digital amplifier can be realized. Also, for audio signals (songs and tracks) recorded in a compressed format that the user thinks the sound quality is important, by increasing the sampling frequency during PWM modulation, Can be secured.
[0074]
In addition, since the audio signal with a high compression rate can reduce the frequency and save power, the audio signal reproduction apparatus that handles the reproduction of an object (such as an MD) in which the audio signal with a high compression rate is recorded. It is particularly effective.
[0075]
As described above, in the audio signal reproduction device of the present invention, the expansion means expands a plurality of audio signals having different compression forms corresponding to the respective compression forms, and the PWM modulation means performs PWM modulation on the expanded sound signals. In the audio signal reproducing apparatus for driving the digital amplifier, compression determination means for determining the compression form of the audio signal, and frequency variable means for changing the sampling frequency of the PWM modulation means in accordance with the determination result of the compression determination means It is characterized by having.
[0076]
According to this, the compression discrimination means discriminates the compression form of the audio signal, and the frequency variable means changes the sampling frequency of the PWM modulation means according to the discrimination result by the compression discrimination means. As a result, the sampling frequency can be matched to the contents of the audio signal (sound quality emphasis, recording amount emphasis, etc.) shown in the compression form.
[0077]
In other words, in response to an audio signal (a song or track with a high compression rate) recorded in a compression format that the user does not consider the sound quality as important, a sound quality equivalent to the sampling frequency at the time of PWM modulation can be obtained. By reducing the frequency to such a low level, it is possible to reduce the switching frequency of the digital amplifier to achieve further power savings, and at the same time, the compressed audio signal (the compression rate is low) (Song or track), the sampling frequency at the time of PWM modulation can be increased to ensure the sound quality equivalent to the conventional one.
[0078]
Even if the information recording medium is the same, if the compression form differs for each song (track), the sampling frequency for each song can be switched to a sampling frequency corresponding to the compression form, which makes the user feel uncomfortable. No power can be saved.
[0079]
Further, according to this, since the audio signal with a high compression rate can reduce the frequency to save power, the reproduction of an object (such as MD) in which the audio signal with a high compression rate is recorded is handled. This is particularly effective in an audio signal reproduction device.
[0080]
In addition to the above configuration, the audio signal reproduction device of the present invention may be characterized in that the frequency variable means sets the sampling frequency using a preset compression form versus frequency table.
[0081]
According to this, it is possible to ensure good sound quality for those that emphasize sound quality, and for those that do not ask for sound quality, the sampling frequency can be lowered to an extent that there is no problem and effective power saving can be achieved. The compression type vs. frequency table in which the relationship between the compression type and the sampling frequency is set is provided in advance, and the frequency variable means uses this table to change the sampling frequency. The above-described effect can be given to all users by changing the sampling frequency uniformly without feeling.
[0082]
In addition to the above-described configuration, the audio signal reproduction device of the present invention has frequency setting means that enables a user to set a sampling frequency for each compression form, and the frequency variable means includes a compression form pair based on a user setting. The sampling frequency may be set using a frequency table.
[0083]
According to this, it becomes possible for the user himself to set the sampling frequency for each compression form using the frequency setting means, and the frequency variable means sets the sampling frequency using the compression form vs. frequency table based on the user setting. To do. Therefore, if the user is accustomed to various settings, for example, the modes other than the SP mode are all used at a low frequency to save power, and the sampling frequency described above can be used with a high degree of freedom in accordance with the specifications of each user. The effect by changing can be acquired.
[0084]
In addition to the above configuration, the audio signal reproduction device of the present invention is provided with a power saving mode, and in the normal mode, the frequency variable means sets the sampling frequency using the compression mode vs. frequency table for the normal mode, In the power saving mode, the sampling frequency may be set using the compression mode vs. frequency table for the power saving mode.
[0085]
By providing a compression mode vs. frequency table for the normal mode and the power saving mode, the power saving effect by changing the sampling frequency is focused on sound quality in the normal mode, and power saving is emphasized in the power saving mode. Thus, it can be obtained with sharpness, and by combining with the user settings of the compression mode vs. frequency table, the degree of freedom is further increased, and further power saving can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of a magneto-optical disk reproducing apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an example of the electrical configuration of a switching amplifier composed of a digital amplifier.
FIG. 3 is an explanatory diagram showing an example of a compression mode versus frequency table used by a control microcomputer.
FIG. 4 is a flowchart showing a procedure in which an audio signal processing circuit varies a sampling frequency of a PWM modulation circuit by a control microcomputer.
[Explanation of symbols]
1 Magneto-optical disk
13 Control microcomputer
13a Frequency variable part
20 Signal processing circuit
20a Compression discriminator
22 Decoder circuit (decompression means)
23 Audio signal processing circuit
23a PWM modulation circuit
24 Class D amplifier (digital amplifier)

Claims (5)

In a digital amplifier driving method of expanding a compressed audio signal and modulating the expanded audio signal into a PWM signal to drive a digital amplifier,
A method of driving a digital amplifier, characterized by changing a sampling frequency when converting into a PWM signal corresponding to a compression form of an audio signal. In an audio signal reproducing apparatus in which a plurality of audio signals having different compression forms are expanded by an expansion unit corresponding to each compression form, and the PWM modulation unit performs PWM modulation on the expanded audio signal to drive a digital amplifier.
Compression determination means for determining the compression form of the audio signal;
An audio signal reproduction apparatus comprising: a frequency variable unit that changes a sampling frequency of the PWM modulation unit according to a determination result of the compression determination unit. 3. The audio signal reproducing apparatus according to claim 2, wherein the frequency variable means sets a sampling frequency using a preset compression form versus frequency table. Having a frequency setting means that allows the user to set the sampling frequency for each compression mode;
3. The audio signal reproducing apparatus according to claim 2, wherein the frequency variable means sets the sampling frequency using a compression mode vs. frequency table based on a user setting. Power saving mode is provided,
In the normal mode, the frequency variable means sets the sampling frequency using the compression mode vs. frequency table for the normal mode, and sets the sampling frequency using the compression mode vs. frequency table for the power saving mode in the power saving mode. The audio signal reproduction device according to claim 3 or 4, wherein

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