JP2006121425A - Class d amplifier device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a class D amplifier device which amplifies a modulated signal obtained by modulating a sound signal based on, for example, a PWM system, and can reduce phase rotation influencing reproduction. <P>SOLUTION: The amplifier device includes amplification units 30, 32 respectively provided with modulation circuits 38, 44 each modulating a sound signal to generate a modulated signal; amplifier circuits 40, 46 each amplifying the modulated signal to generate an amplified signal; and low-pass filtering circuits 42, 48 each allowing a low-pass component of the amplified signal to pass. The outputs from the amplification units 30, 32 are outputted to speakers 35H, 35L. In this class D amplifier device, the modulating circuits 38, 44 included in the amplification units 30, 32 modulate a sound signal by carrier frequencies corresponding to the frequency characteristic of each of the plurality of speakers 35H, 35L. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present application belongs to the technical field of a class D amplifier, and more specifically, to the technical field of a class D amplifier that amplifies a modulation signal obtained by modulating a sound signal by, for example, a PWM (Pulse Width Modulation) method. Belongs.

  2. Description of the Related Art Conventionally, amplifying devices for audio products (hereinafter referred to as amplifiers as appropriate) include types such as a class A amplifier, a class B amplifier, and a class C amplifier, depending on a method for setting a bias voltage in a transistor constituting the amplifying device. . In addition to these, development of an amplifier called a class D amplifier (in general, it may be called a “switching amplifier” or a “PWM amplifier”) focusing on its high efficiency. Has been actively conducted. At this time, as the efficiency, for example, it is known that the analog amplifier is about 40%, whereas the class D amplifier has an efficiency of about 90%.

  Here, the class D amplifier performs modulation processing on a sound signal, for example, a digital sound signal, by a PWM method, amplifies the modulation signal obtained by the modulation processing as a rectangular wave, and then LPF (Low Pass Filter) It is an amplifier which outputs to a speaker via.

  FIG. 1 shows a block circuit of a conventional class D amplifier.

  In FIG. 1, reference numeral 10 indicates an amplification unit of a class D amplifier, and reference numeral 12 indicates a speaker unit. In the amplification unit 10, the sound signal 100 that is a digital signal (for example, a PCM signal) from the input terminal 14 is supplied to the modulation circuit 16, and the modulation circuit 16 modulates the sound signal 100 to generate a modulation signal (for example, PWM signal) 102 is supplied to the amplifier circuit 18. The amplifier circuit 18 amplifies the modulated signal 102 and supplies the amplified signal 104 to the low-pass filter circuit (LPF) 20, which passes the low-frequency component of the amplified signal 104 and outputs the output signal. 106 is supplied to the speaker unit 12. In the speaker unit 12, the output signal 106 is supplied to a high-frequency speaker (tweeter) 24 via a high-pass filter circuit (HPF) 22 and also low-pass through a low-pass filter circuit (LPF) 26. Is supplied to a loudspeaker (woofer) 28.

  In the amplification unit 10, the carrier frequency of the modulation circuit 16 is set to 384 KHz or 768 KHz, the cut-off frequency fc of the low-pass filter circuit 20 is set to 30 KHz to 80 KHz, and the carrier frequency is the cut-off frequency. It is desirable to set it to 10 times or more of fc.

  In the class D amplifier shown in FIG. 1, the case where the carrier frequency of the modulation circuit 16 is set to 768 KHz and the cutoff frequency fc of the low-pass filter circuit 20 is set to 30 KHz will be taken as an example. In this case, the above condition that the carrier frequency is set to 10 times or more of the cutoff frequency fc is satisfied.

  The characteristics of the class D amplifier in which the carrier frequency and the cut-off frequency fc are set to 768 KHz and 30 KHz as described above are shown in the graphs of FIGS. 2A shows the relationship between frequency and output level, and the graph in FIG. 2B shows the relationship between frequency, gain, and phase rotation angle.

  In the graph of FIG. 2A, if the fundamental frequency is 1 KHz, the characteristics of the low-pass filter circuit 20 change as indicated by the symbol L with respect to the frequency. Here, an unnecessary output M is generated in a region of ± 2 KHz with a carrier frequency of 768 KHz, and an unnecessary output N is generated in a region of ± 2 KHz of 1536 KHz, which is twice the carrier frequency of 768 KHz. These unnecessary outputs M and N are not completely removed by the low-pass filter circuit 20. That is, the cut-off frequency fc of the low-pass filter circuit 20 is set to 30 KHz, but the output of the low-pass filter circuit 20 does not suddenly become zero when the frequency reaches 30 KHz, and the frequency increases from 30 KHz. Therefore, unnecessary outputs M and N having a frequency higher than 30 KHz cannot be completely removed. From the graph of FIG. 2A, it is understood that it is desirable to set the cut-off frequency lower than 30 KHz in order to increase the removal amount of unnecessary outputs M and N by the low-pass filter circuit 20. .

  On the other hand, in the graph of FIG. 2B, since the cut-off frequency fc is set to 30 KHz, the gain decreases as shown by the solid line P as the frequency increases from 30 KHz. By the way, as the frequency increases from around 3 KHz, which is 1/10 of the cutoff frequency fc, as shown by the broken line Q, when phase rotation starts and the frequency becomes the cutoff frequency fc (= 30 KHz), the phase rotation angle becomes Reaching 90 °. Therefore, if the cutoff frequency fc is set lower than 30 KHz, there is a problem that the frequency at which phase rotation starts is lower than the vicinity of 3 KHz.

  As can be understood from the above description, from the viewpoint of increasing the amount of unnecessary output M and N removed by the low-pass filter circuit 20, it is desirable to set the cut-off frequency lower than 30 KHz, while the cut-off frequency fc Is set lower than 30 KHz, there is a problem that the frequency at which phase rotation starts becomes lower than around 3 KHz.

  The present application has been made in view of the above-described problems, and an example of the purpose is to provide a class D amplifier that can reduce phase rotation that affects reproduction.

  In order to solve the above problem, the invention according to claim 1 is a modulation circuit that modulates a sound signal to generate a modulation signal, an amplification circuit that amplifies the modulation signal to generate an amplification signal, and the amplification In a class D amplifier that includes a plurality of amplification units each including a low-pass filtering circuit that passes a low-frequency component of a signal, and that outputs the output from each amplification unit to a speaker corresponding to each amplification unit, The modulation circuit included in each amplification unit modulates the sound signal with a carrier frequency corresponding to a frequency characteristic of each of the plurality of speakers.

  Next, the best mode for carrying out the present application will be described with reference to FIGS. The embodiment described below is an embodiment in the case where the present application is applied to a class D amplifier that amplifies a sound signal, which is a digital signal, for example, after being modulated by a PWM method, for example.

  FIG. 3 shows a block circuit of a class D amplifier according to an embodiment of the present application.

  In FIG. 3, reference numeral 30 indicates a high-frequency amplification unit, reference numeral 32 indicates a low-frequency amplification unit, and reference numeral 34 indicates a speaker unit. Here, the high-frequency amplification unit 30 is for a high-frequency speaker (tweeter) 35H in the speaker unit 34, and the low-frequency amplification unit 32 is for a low-frequency speaker (woofer) 35L in the speaker unit 34. It is.

  In the high frequency amplifying unit 30, a sound signal 108 that is, for example, a digital signal (PCM signal or the like) from the input terminal 36 is supplied to a modulation circuit 38, and the modulation circuit 38 modulates and modulates the sound signal 108. A signal (for example, PWM signal) 110 is supplied to the amplifier circuit 40. As the modulation circuit 38 in the high-frequency amplification unit 30, not only a modulation circuit that modulates a PCM signal into a PWM signal but also a circuit that modulates a PCM signal into a 1-bit ΔΣ signal can be used. The amplifier circuit 40 amplifies the modulation signal 110 and supplies the amplified signal 112 to a low-pass filter (LPF) 42. The low-pass filter circuit 42 passes the low-frequency component of the amplified signal 112 and outputs it. A signal 114 is supplied to the speaker unit 34.

  Similarly, in the low frequency amplifying unit 32, the sound signal 108 that is a digital signal (for example, a PCM signal) from the input terminal 36 is supplied to the modulation circuit 44, and the modulation circuit 44 modulates the sound signal 108. Then, a modulation signal (for example, PWM signal) 116 is supplied to the amplifier circuit 46. The amplifier circuit 46 amplifies the modulated signal 116 and supplies the amplified signal 118 to a low-pass filter (LPF) 48. The low-pass filter circuit 48 passes the low-frequency component of the amplified signal 118 and outputs an output signal. 120 is supplied to the speaker unit 34.

  In the speaker unit 34, the output signal 114 from the high frequency amplifying unit 30 is supplied to a high frequency speaker (tweeter) 35H via a high frequency filter circuit (HPF) 50. An output signal 120 from the amplification unit 32 is supplied to a low-frequency speaker (woofer) 35L via a low-frequency filter circuit (LPF) 52.

  The carrier frequency of the modulation circuit 38 in the high frequency amplification unit 30 is set high, for example, set to 5.6 MHz, and the carrier frequency of the modulation circuit 44 in the low frequency amplification unit 32 is set low, For example, it is set to 768 KHz. The cut-off frequency fc of the low-pass filter circuit 42 in the high-frequency amplification unit 30 is set to 400 KHz, for example, and the cut-off frequency fc of the low-pass filter circuit 42 in the low-frequency amplification unit 32 is 50 KHz. Is set to

  As described above, in the high frequency amplification unit 30, the carrier frequency of the modulation circuit 38 is set to 5.6 MHz, and the cut-off frequency fc of the low frequency filter circuit 42 is set to 400 KHz. In the unit 32, the carrier frequency of the modulation circuit 44 is set to 768 KHz, and the cut-off frequency fc of the low-pass filter circuit 48 is set to 50 KHz. Accordingly, the condition that the carrier frequency of the modulation circuits 38 and 44 is set to 10 times or more the cut-off frequency fc of the low-pass filter circuits 42 and 48 is satisfied.

  In the class D amplifier configured as described above, the cutoff frequency fc of the low-pass filter circuit 42 is 400 KHz in the high-frequency amplification unit 30, and therefore phase rotation starts from around 40 KHz which is 1/10 of the frequency. Arise. However, since the vicinity of 40 KHz or higher is larger than the audible band (˜20 KHz), the phase rotation that affects the reproduction can be reduced, and the sound quality from the high frequency speaker 35H is not hindered.

  Further, in the low frequency amplifying unit 32, the cutoff frequency fc of the low frequency filter circuit 48 is 50 KHz, so that phase rotation occurs from around 5 KHz which is 1/10 of the frequency. However, since the output signal 120 from the low-frequency amplification unit 32 is supplied to the low-frequency speaker 35L, the phase rotation that affects the reproduction can be reduced, that is, the phase rotation is reduced. The generated component of the vicinity of 5 KHz or higher does not cause a problem in the sound quality from the low-frequency speaker 35L.

  As described above, according to the class D amplifier according to the embodiment of the present application, it is possible to reduce the phase rotation that affects the reproduction, and thus the sound quality from the high frequency speaker 35H and the low frequency speaker 35L is hindered. It does not occur, and deterioration of sound quality can be prevented.

  FIG. 4 shows the characteristics of the high-frequency amplification unit of the class D amplifier according to the embodiment of the present application.

  In FIG. 4, even if the frequency is increased, no phase rotation occurs in the audible band (up to 20 KHz), that is, the phase rotation angle is 0 °, and the frequency is higher than the audible band (up to 20 KHz). Accordingly, phase rotation occurs. However, even if phase rotation occurs in a region higher than the audible band (up to 20 KHz), the sound quality from the speaker is not hindered. As described above, in the low frequency amplification unit, phase rotation occurs from around 5 KHz, which is 1/10 of the cutoff frequency fc = 50 KHz of the low frequency filter circuit. Since the output signal is supplied to the low-frequency speaker, the sound quality from the low-frequency speaker is not hindered by a component of about 5 KHz or more that causes phase rotation. As described above, according to the class D amplifier according to the embodiment of the present application, it is possible to reduce phase rotation that affects reproduction.

  In the class D amplifier according to the embodiment of the present application shown in FIG. 3, a high frequency amplification unit is provided corresponding to the high frequency speaker, and a low frequency amplification unit is provided corresponding to the low frequency speaker. Although a total of two amplification units are provided, the number of amplification units is not limited to two, and three or more amplification units may be provided corresponding to the frequency characteristics of a plurality of speakers. For example, when a mid-range speaker (skoker) is provided in addition to a high-frequency speaker and a low-frequency speaker, a mid-range amplification unit can be provided. In this case, the relationship of the carrier frequency in each of the modulation circuits included in each of the three amplification units is as follows: high frequency amplification unit> middle frequency amplification unit> low frequency amplification unit.

This is a block circuit of a conventional class D amplifier. It is a graph which shows the characteristic of the conventional class D amplifier, the graph of (A) shows the relationship between a frequency and an output level, and the graph of (B) shows the relationship between a frequency, a gain, and a phase rotation angle. 3 is a block circuit of a class D amplifier according to an embodiment of the present application. It is a graph which shows the characteristic of the amplification unit for high regions of the class D amplifier by the embodiment of this application.

Explanation of symbols

30 High-frequency amplifier unit 32 Low-frequency amplifier unit 34 Speaker unit 35H High-frequency speaker 35L Low-frequency speaker 38, 44 Modulation circuit 40, 46 Amplifying circuit 42, 48 Low-frequency filter circuit 50 High-frequency filter circuit 52 Low frequency Filtration circuit

Claims (3)

A modulation circuit that modulates a sound signal to generate a modulation signal, an amplification circuit that amplifies the modulation signal to generate an amplification signal, and a low-pass filtering circuit that passes a low-frequency component of the amplification signal, respectively In a class D amplifier that includes a plurality of amplification units and outputs the output from each of the amplification units to a speaker corresponding to each of the amplification units,
The class D amplification device, wherein the modulation circuit included in each amplification unit modulates the sound signal with a carrier frequency corresponding to a frequency characteristic of each of the plurality of speakers. In the class D amplification device according to claim 1,
Corresponding to each of the high-frequency speaker and the low-frequency speaker, the high-frequency amplification unit and the low-frequency amplification unit are respectively provided.
The class D amplifier according to claim 1, wherein a carrier frequency of the modulation circuit in the high frequency amplification unit is set higher than a carrier frequency of the modulation circuit in the low frequency amplification unit. The class D amplifier according to claim 2,
In the low-pass filter circuit, a cutoff frequency is set,
In the amplification unit, the carrier frequency of the modulation circuit is set to 10 times or more the cut-off frequency of the low-pass filter circuit.

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