JP2007096507A - Audio signal amplifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an audio signal amplifying apparatus mounted with a class D amplifier and capable of preventing deterioration in the linearity due to switching noise of the class D amplifier when an audio signal is reproduced in a small sound volume and to provide an audio signal amplification method. <P>SOLUTION: A switching section 113 by way of SW circuits A, B, C selects and activates an analog amplifier 105 in the case of a sound volume position < a threshold value N1 on one hand, and selects and activates the class D amplifier 106 in the case of the sound volume position ≥ the threshold value N1 on the other hand. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an audio signal amplifying device, and more particularly to an audio signal amplifying device equipped with a class D amplifier and an analog amplifier.

  Recently, audio devices equipped with high power efficiency class D (class D) amplifiers have become widespread. In such an audio apparatus, an FM radio demodulated signal, a CD reproduction signal, a DVD reproduction signal, an MD reproduction signal, or the like is amplified by a class D amplifier and output from a speaker.

  As an audio apparatus using a class D amplifier, for example, Patent Document 1 is known. In the audio signal amplifying apparatus of the same document, when AM radio is amplified by a class D amplifier, the class D amplifier generates a high frequency signal in the middle wave band in accordance with its operation, and the high frequency signal is mixed into the AM tuner. In order to prevent the occurrence of noise, the reception level is detected when receiving AM radio, and when the detected reception level is lower than a predetermined reference level, it is amplified and detected by a class AB amplifier. When the received level is higher than a predetermined reference level, it is amplified by a class D amplifier, and when receiving FM radio, in the case of a CD playback signal, DVD playback signal, and MD playback signal, class D Amplification is performed by an amplifier.

  However, in an audio apparatus equipped with a conventional class D amplifier, when reproducing an audio signal at a low volume, especially in an amplifier having a high power supply voltage such as a high power amplifier, the linearity deteriorates due to switching noise of the class D amplifier. There is a problem of making it.

JP 2005-080114 A

  The present invention has been made in view of the above, and, in an audio signal amplifying apparatus equipped with a class D amplifier, prevents deterioration of linearity due to switching noise of the class D amplifier when reproducing an audio signal at a low volume. One of the objects is to provide an audio signal amplifying device capable of performing the above.

  In order to solve the above-mentioned problems and achieve the object, the present invention provides a class D amplification means for amplifying and outputting an audio signal in class D, an analog amplification means for amplifying and outputting the audio signal, and a volume. Detection means for detecting a level, and selection means for selecting and operating the class D amplification means or the analog amplification means according to the volume level detected by the detection means.

  Exemplary embodiments of an audio signal amplifying device according to the present invention will be explained below in detail with reference to the accompanying drawings. Note that the present invention is not limited to this embodiment, and not all combinations of features described in the embodiment are necessary for the solving means of the invention. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or that are substantially the same.

  The audio signal amplifying apparatus according to the present embodiment includes a class D amplifying unit, an analog amplifying unit, a detecting unit, and a selecting unit. The class D amplification means amplifies the audio signal by class D and outputs it. The analog amplifying means amplifies the audio signal class A, class B or class AB and outputs the amplified signal. The detecting means detects the volume level. The selection unit selects and operates the class D amplification unit or the analog amplification unit according to the detected volume level. Specifically, when the volume level is low, the selection unit selects and operates the analog amplification unit. In other cases, the class D amplification means is selected and operated. Here, analog amplification refers to class A, class B, and class AB amplification. When selecting and operating the analog amplification means, it is desirable to stop the operation of the class D amplification means. As a result, when reproducing an audio signal at a low volume, the use of an analog amplifier instead of the class D amplifier can prevent deterioration of linearity due to switching noise of the class D amplifier.

  Here, the output stage of the class D amplification means and the analog amplification means may be mounted on a common circuit. Thereby, the circuit scale can be made small and low-cost.

  Further, the detection means and the selection means can be configured as follows, for example.

  The detection means detects the volume volume of the volume volume device, and the selection means selects and operates the class D amplification means when the volume volume is greater than or equal to a first threshold value, while the volume volume is less than the first threshold value. In this case, the analog amplification means may be selected and operated.

  The detecting means detects the input level to the analog amplifying means, and the selecting means selects and operates the class D amplifying means when the input level to the analog amplifying means is equal to or higher than the second threshold, while the input level If is less than the second threshold value, the analog amplification means may be selected and operated.

  The detecting means detects the input level to the class D amplifying means, and the selecting means selects and operates the class D amplifying means when the input level to the class D amplifying means is greater than or equal to the third threshold value. If the input level is less than the third threshold value, the analog amplification means may be selected and operated.

  The detecting means detects an output level from at least one of the analog amplifying means and the class D amplifying means, and the selecting means selects and operates the class D amplifying means when the output level is equal to or higher than the fourth threshold value. On the other hand, when the output level is less than the fourth threshold value, the analog amplification means may be selected and operated.

  The detecting means detects the distortion of the output amplitude of the analog amplifying means, and the selecting means selects and operates the class D amplifying means when the distortion of the output amplitude is not less than the fifth threshold, while the distortion of the output amplitude is detected. If the value is less than the fifth threshold value, the analog amplification means may be selected and operated.

  Further, when selecting the class D amplification means or the analog amplification means, the selection means selects the class D amplification means or the analog amplification means according to the external control signal for selecting the class D amplification means or the analog amplification means. Then, it may be operated. The user can select the class D amplification means or the analog amplification means with the operation unit or the remote controller.

  FIG. 1 is a block diagram illustrating a configuration example of an audio signal amplifying apparatus 100 according to the first embodiment. As shown in FIG. 1, the audio signal amplifying apparatus 100 according to the first embodiment includes an A / D converter 101, a D / A converter 102, a PWM modulation unit 103, a variable resistor 104, an analog amplifier 105, and the like. , Class D amplifier 106, SW circuits 107A, B, C, speaker 108, audio volume device 109, output level instruction unit 110, VOL position detection unit 111, digital / analog discrimination unit 112, and switching unit 113.

  An analog audio signal is input from the analog input terminal and output to the A / D converter 101 and the variable resistor 104. Here, the source of the analog audio signal is, for example, an AM / FM tuner. A digital audio signal is input from the digital input terminal and output to the D / A converter 102 and the PWM modulation unit 103. Here, the source of the digital audio signal is, for example, CD, MD, DAT, DVD or the like.

  The A / D converter 101 A / D converts the analog audio signal input from the analog signal input terminal and outputs the analog audio signal to the PWM modulation unit 103 as a digital audio signal. The D / A converter 102 D / A converts the digital audio signal input from the digital signal input terminal and outputs the analog audio signal to the variable resistor 104. The PWM modulation unit 103 performs PWM modulation on the input digital audio signal and outputs it. The variable resistor 104 adjusts the amplitude of the input analog audio signal according to the instruction signal input from the output level instruction unit 110 and outputs the analog audio signal.

  The SW circuit 107A switches the input between the analog audio signal and the ground in accordance with the switching signal input from the switching unit 113. Further, the SW circuit 107B switches the input between the digital audio signal and the ground in accordance with the switching signal input from the switching unit 113.

  The analog amplifier 105 performs analog amplification (Class A, Class B, or Class AB amplification) on the input analog audio signal and outputs the result. The class D amplifier 106 amplifies the input digital audio signal by class D and outputs it. The SW circuit 107 </ b> C switches the input between the output of the analog amplifier 105 and the output of the class D amplifier 106 in accordance with the switching signal input from the switching unit 113. The speaker 108 emits the input output of the analog amplifier 105 or the output of the class D amplifier 106.

  The audio volume device 109 outputs a volume volume signal corresponding to the volume volume position. The output level instruction unit 110 outputs an instruction signal to the variable resistor 104 or the PWM modulation unit 103 in accordance with the volume volume signal input from the audio volume device 109. Specifically, the output level instruction unit 110 outputs the instruction signal to the PWM modulation unit 103 when the volume volume signal input from the audio volume device 109 is equal to or greater than a predetermined threshold value, and the PWM modulation pulse width. To change. Further, when the volume level signal is less than a predetermined threshold, the output level instruction unit 110 outputs the instruction signal to the variable resistor 104 and adjusts the resistance value. The instruction signal may be output not only to one of the variable resistor 104 and the PWM modulation unit 103 but also to both.

  The VOL position detection unit 111 detects the volume volume position of the audio volume device 109 and outputs it to the digital / analog determination unit 112.

  The digital / analog discriminating unit 112 determines the discriminating signal indicating the analog amplifier 105 or the class D amplifier 106 according to the volume volume position detection result input from the VOL position detecting unit 111 (for example, “0”: analog amplifier, “1”). ": Class D amplifier)" is output to the switching unit 113. Specifically, the digital / analog discriminating unit 112 outputs a discrimination signal indicating the class D amplifier 106 when the volume level position ≧ the threshold value N1, and indicates the analog amplifier 105 when the volume level position <the threshold value N1. A discrimination signal is output.

  The switching unit 113 outputs a switching signal to the SW circuits 107A, B, and C in accordance with the determination signal input from the digital / analog determination unit 112. Specifically, the switching unit 113 converts the input to the SW circuit 107A to an analog audio signal when the determination signal input from the digital / analog determination unit 112 indicates an analog amplifier (for example, “0”). A switching signal for switching, a switching signal for switching the input to the ground to the SW circuit 107B, and a switching signal for switching the input to the output of the analog amplifier 105 are output to the SW 107C. On the other hand, when the determination signal input from the digital / analog determination unit 112 indicates a class D amplifier (for example, “1”), the switching unit 113 switches the SW circuit 107A to switch the input to the ground. The switch circuit 107B outputs a switching signal for switching the input to the digital audio signal, and the SW 107C outputs a switching signal for switching the input to the output of the class D amplifier 106.

  The operation of the audio signal amplifying apparatus 100 configured as described above will be described. First, when an analog audio signal is input from the analog input terminal, it is A / D converted by the A / D converter 101 and output to the PWM modulation unit 103 as a digital audio signal, and PWM modulated by the PWM modulation unit 103. The amplitude of the analog audio signal input from the analog input terminal is adjusted by the variable resistor 104. On the other hand, the digital / analog discriminating unit 112 outputs a discrimination signal indicating the analog amplifier 105 or the class D amplifier 106 to the switching unit 113 according to the volume position detection result input from the VOL position detecting unit 111. Switches the SW circuits 107A, B, and C in accordance with the discrimination signal input from the digital / analog discrimination unit 112. In the case of volume volume position <threshold N1, an analog audio signal is input from the SW circuit 107A to the analog amplifier 105, amplified, and then output to the speaker 108 via the SW circuit 107C. On the other hand, when the volume volume position ≧ the threshold value N1, the digital audio signal is input from the SW circuit 107B to the class D amplifier 106 and amplified, and then output to the speaker 108 via the SW circuit 107C.

  When a digital audio signal is input from the digital input terminal, the digital audio signal is output to the PWM modulation unit 103 and PWM modulated by the PWM modulation unit 103. The digital audio signal is D / A converted by the D / A converter 102, and the amplitude of the analog audio signal is adjusted by the variable resistor 104. Similarly to the case where the analog audio signal is input, when the volume position <threshold N1, the analog audio signal is input from the SW circuit 107A to the analog amplifier 105, amplified, and then passed through the SW circuit 107C. It is output to the speaker 108. On the other hand, when volume position ≧ threshold value N1, the digital audio signal is input from the SW circuit 107B to the class D amplifier 106 and amplified, and then output to the speaker 108 via the SW circuit 107C.

  Note that it is desirable that the operation of the class D driver 122 is stopped when the digital / analog determination unit 112 performs analog determination. The stop here may not be a complete stop, for example, a standby state. This prevents the switching noise of the class D amplifier from being mixed during reproduction of the analog amplifier.

  As described above, according to the audio signal amplifying apparatus 100 according to the first embodiment, the switching unit 113 selects and operates the analog amplifier 105 when the volume volume position <the threshold value N1, while the volume volume position ≧ Since the class D amplifier 106 is operated in the case of the threshold value N1, it is possible to prevent deterioration of linearity due to switching noise of the class D amplifier with a simple configuration when reproducing an audio signal at a low volume. .

(Modification 1)
FIG. 2 is a block diagram showing a configuration of the audio signal amplifying apparatus 100 according to the first modification. The audio signal amplifying apparatus 100 according to Modification 1 uses an amplifier output stage circuit (hybrid amplifier) 124 in which the output stages of the analog amplifier 105 and the class D amplifier 106 are shared in the audio signal amplifying apparatus 100 of FIG. Is. 2, parts having the same functions as those in FIG. 1 are denoted by the same reference numerals, description of common parts is omitted, and only different points will be described.

  In FIG. 2, an analog voltage amplification stage 121 amplifies and outputs an input analog audio signal. The class D driver 122 generates and outputs a drive signal corresponding to the input digital audio signal. The switching unit 113 outputs a switching signal to the SW circuit 123 in accordance with the determination signal input from the digital / analog determination unit 112. Specifically, the switching unit 113 inputs the input to the SW circuit 123 when the determination signal input from the digital / analog determination unit 112 indicates an analog amplifier (for example, “0”). When the determination signal indicates a class D amplifier (for example, “1”), a switching signal for switching the input to the class D driver 122 is output to the SW circuit 123. The switch circuit 123 switches inputs between the analog voltage amplification stage 121 and the class D driver 122 in accordance with a switching signal from the switching unit 113. The amplifier output stage circuit 124 performs an analog current amplification / class D amplification operation. When the analog voltage amplification stage 121 is selected by the SW circuit 123, the amplifier output stage circuit 124 performs an analog current amplification operation and outputs the amplified output to the speaker 108. When the class D driver 122 is selected, a class D amplification operation is performed and an amplified output is output to the speaker 108.

  As described above, according to the audio signal amplifying apparatus 100 according to the first modification, the amplifier output stage circuit (hybrid amplifier) 124 in which the output stages of the analog amplifier 105 and the class D amplifier 106 are shared is used. The configuration can be a small-scale and low-cost configuration.

(Modification 2)
FIG. 3 is a block diagram showing a configuration of the audio signal amplifying apparatus 100 according to the second modification. The audio signal amplifying apparatus 100 according to the modified example 2 replaces the D / A converter 102 of the audio signal amplifying apparatus 100 in FIG. Between them. As described above, since the D / A converter 102 is arranged at the subsequent stage of the PWM modulation unit 103 and the digital audio signal after PWM modulation is D / A converted, the configuration of the D / A converter is reduced. Can be made cheaper.

  FIG. 4 is a block diagram illustrating the configuration of the audio signal amplifying apparatus 200 according to the second embodiment. The audio signal amplifying apparatus 100 according to the first embodiment is configured to switch between the analog amplifier 105 and the class D amplifier 106 in accordance with the volume volume position. In contrast, the audio signal amplifying apparatus 200 according to the second embodiment is configured to switch between the analog amplifier 105 and the class D amplifier 106 in accordance with the output level of the analog amplifier 105. 4, parts having the same functions as those in FIG. 1 are denoted by the same reference numerals, description of common parts is omitted, and only different points will be described.

  The output level detection unit 201 detects the output level of the analog amplifier 105 and outputs it to the digital / analog discrimination unit 112. Here, the output level of the analog amplifier 105 corresponds to the volume. The digital / analog discriminating unit 112 switches discrimination signals (for example, “0”: analog amplifier, “1”: class D amplifier) indicating the analog amplifier 105 or the class D amplifier 106 according to the output level of the analog amplifier 105. Output to the unit 113. Specifically, the digital / analog discriminating unit 112 outputs a discrimination signal indicating the class D amplifier 106 when the output level of the analog amplifier 105 ≧ the threshold value N2, and when the output level of the analog amplifier 105 <the threshold value N2. Outputs a discrimination signal indicating the analog amplifier 105. The switching unit 113 outputs a switching signal to the SW circuits 107A, B, and C in accordance with the determination signal input from the digital / analog determination unit 112.

  As described above, according to the audio signal amplifying device 200 according to the second embodiment, the switching unit 113 selects and operates the analog amplifier 105 when the output level of the analog amplifier 105 <the threshold value N2, while When the output level of the amplifier 105 is equal to or greater than the threshold value N2, the class D amplifier 106 is selected and operated. Therefore, when the audio signal is reproduced at a low volume, the configuration is simple and the switching noise of the class D amplifier is used. The deterioration of linearity can be prevented.

  In the second embodiment, the output level of the analog amplifier 105 is detected and the amplifier is selected. However, the present invention is not limited to this, and the input level of the analog amplifier 105 may be detected. Good. Further, the input or output level of the class D amplifier 106 may be detected instead of the analog amplifier 105. That is, one or both of the input / output levels of the analog amplifier 105 and the class D amplifier 106 may be detected, and the amplifier may be selected based on the detection result.

  FIG. 5 is a block diagram illustrating the configuration of the audio signal amplifying apparatus 300 according to the third embodiment. The audio signal amplifying apparatus 300 according to the third embodiment is configured to detect distortion of the output amplitude of the analog amplifier 105 and switch between the analog amplifier 105 and the class D amplifier 106 according to the distortion of the output amplitude. 5, parts having the same functions as those in FIG. 1 are denoted by the same reference numerals, description of common parts is omitted, and only different points will be described.

  The distortion detection unit 301 detects distortion of the output amplitude of the analog amplifier 105 and outputs the distortion to the digital / analog determination unit 112. Here, the distortion of the output amplitude of the analog amplifier 105 corresponds to the volume. The digital / analog discriminator 112 discriminates signals indicating the analog amplifier 105 or the class D amplifier 106 according to the distortion of the output amplitude of the analog amplifier 105 (for example, “0”: analog amplifier, “1”: class D amplifier). Is output to the switching unit 113. Specifically, the digital / analog discriminating unit 112 outputs a discrimination signal indicating the class D amplifier 106 when the distortion of the output amplitude of the analog amplifier 105 ≧ the threshold value N3, and the distortion of the output amplitude of the analog amplifier 105 <the threshold value. In the case of N3, a discrimination signal indicating the analog amplifier 105 is output. The switching unit 113 outputs a switching signal to the SW circuits 107A, B, and C in accordance with the determination signal input from the digital / analog determination unit 112.

  As described above, according to the audio signal amplifying apparatus 300, the switching unit 113 selects and operates the analog amplifier 105 when the distortion of the output amplitude of the analog amplifier 105 <the threshold value N3. Since the class D amplifier 106 is selected and operated when the distortion of the output amplitude ≧ the threshold value N3, the linearity due to the switching noise of the class D amplifier is obtained with a simple configuration when the audio signal is reproduced at a low volume. Can be prevented. In the third embodiment, the configurations of the first modification and the second modification may be adopted.

  FIG. 6 is a block diagram illustrating the configuration of the audio signal amplifying apparatus 400 according to the fourth embodiment. The audio signal amplifying apparatus 400 according to the fourth embodiment includes an analog amplifier according to an external control signal corresponding to an operation of a switch for selecting an analog amplifier 105 or a class D amplifier 106 provided in an operation unit (not shown). 105 and a class D amplifier 106 are switched. 6, parts having the same functions as those in FIG. 1 are denoted by the same reference numerals, description of common parts is omitted, and only different points will be described.

  The operation unit (not shown) is provided with a switch for switching between the analog amplifier 105 and the class D amplifier 106, and an external control signal corresponding to the switch operation is input to the control signal detection unit 401. With this switch, the user selects the analog amplifier 105 when the volume is low, and selects the class D amplifier 106 otherwise.

  The control signal detection unit 401 detects an external control signal and outputs it to the digital / analog discrimination unit 112. The digital / analog discriminating unit 112 sends a discriminating signal (for example, “0”: analog amplifier, “1”: class D amplifier) indicating the analog amplifier 105 or the class D amplifier 106 to the switching unit 113 according to the external control signal. Output. Specifically, the digital / analog discrimination unit 112 outputs a discrimination signal indicating the class D amplifier 106 when the external control signal indicates a class D amplifier, and when the external control signal indicates an analog amplifier, A discrimination signal indicating the analog amplifier 105 is output. The switching unit 113 outputs a switching signal to the SW circuits 107A, B, and C in accordance with the determination signal input from the digital / analog determination unit 112. Although the case where an external control signal corresponding to the operation of the switch is input has been described here, the present invention is not limited to this, and an external control signal may be input from a remote controller or the like.

  As described above, according to the audio signal amplifying apparatus 400 according to the fourth embodiment, the switching unit 113 switches between the analog amplifier 105 and the class D amplifier 106 according to the external control signal. When reproducing an audio signal at a low volume, it is possible to prevent deterioration of linearity due to switching noise of the class D amplifier with a simple configuration. In the fourth embodiment, the configurations of the first modification and the second modification may be adopted.

  As described above, the audio signal amplifying device according to the present invention is widely applicable to audio devices equipped with a class D amplifier.

1 is a block diagram illustrating a configuration example of an audio signal amplifying device according to Embodiment 1. FIG. 10 is a block diagram illustrating a configuration example of an audio signal amplifying device according to Modification 1. FIG. FIG. 12 is a block diagram illustrating a configuration example of an audio signal amplifying device according to Modification 2. FIG. 6 is a block diagram illustrating a configuration example of an audio signal amplifying device according to a second embodiment. FIG. 10 is a block diagram illustrating a configuration example of an audio signal amplifying device according to a third embodiment. FIG. 10 is a block diagram illustrating a configuration example of an audio signal amplifying device according to a fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Audio signal amplifier 101 A / D converter 102 D / A converter 103 PWM modulation part 104 Variable resistance 105 Analog amplifier 106 Class D amplifier 107A, B, C SW circuit 108 Speaker 109 Audio | voice volume apparatus 110 Output level instruction | indication part 111 VOL position detection unit 112 digital / analog discrimination unit 113 switching unit 121 analog voltage amplification stage 122 class D driver 123 SW circuit 124 amplifier output circuit 200 audio signal amplification device 201 output level detection unit 300 audio signal amplification device 301 distortion detection unit 400 audio Signal amplification device 401 Control signal detector

Claims (8)

Class D amplification means for amplifying and outputting an audio signal in Class D;
Analog amplification means for analog amplification and outputting the audio signal;
Detection means for detecting the volume level;
Selection means for selecting and operating the class D amplification means or the analog amplification means according to the volume level detected by the detection means;
An audio signal amplifying apparatus comprising: An A / D converter for A / D converting an analog audio signal input from an analog audio signal input terminal and outputting a digital audio signal;
A D / A converter that D / A converts a digital audio signal input from a digital audio signal input terminal and outputs an analog audio signal;
With
The class D amplification means outputs the digital audio signal after class D amplification,
The audio signal amplifying apparatus according to claim 1, wherein the analog amplifying unit analog-amplifies and outputs the analog audio signal. The detecting means detects a volume of the volume device;
The selection means selects and operates the class D amplification means when the volume is greater than or equal to a first threshold value, and selects analog amplification means when the volume volume is less than the first threshold. The audio signal amplifying apparatus according to claim 1, wherein the audio signal amplifying apparatus is operated. The detection means detects an input level to the analog amplification means,
The selecting means selects and operates the class D amplifying means when the input level to the analog amplifying means is equal to or higher than a second threshold value, while the analog level when the input level is lower than the second threshold value. 3. The audio signal amplifying apparatus according to claim 1, wherein the amplifying unit is selected and operated. The detection means detects an input level to the class D amplification means,
The selecting means selects and operates the class D amplifying means when the input level to the class D amplifying means is greater than or equal to a third threshold value, while the input level is less than the third threshold value when the input level is less than the third threshold value. 3. The audio signal amplifying apparatus according to claim 1, wherein the analog amplifying means is selected and operated. The detection means detects an output level from at least one of the analog amplification means or the class D amplification means,
The selection means selects and operates the class D amplification means when the output level is greater than or equal to a fourth threshold value, and selects the analog amplification means when the output level is less than the fourth threshold value. 3. The audio signal amplifying apparatus according to claim 1, wherein the audio signal amplifying apparatus is operated. The detection means detects distortion of the output amplitude of the analog amplification means,
The selection means selects and operates the class D amplification means when the distortion of the output amplitude is greater than or equal to a fifth threshold value, and performs analog amplification when the distortion of the output amplitude is less than the fifth threshold value. 3. The audio signal amplifying apparatus according to claim 1, wherein the means is selected and operated.   The said selection means stops one operation | movement which was not selected when selecting the said D class amplification means or the said analog amplification means, The Claim 1 characterized by the above-mentioned. Audio signal amplifier.

Images