WO2019008627A1 - Amplifying device, acoustic processing device and method for controlling class-d amplifier circuit - Google Patents

Abstract

This amplifying device is provided with: a self-excited class-D amplifier circuit including a modulation circuit in which pulse modulation by self-excited oscillation is performed on an acoustic signal; and an operation control unit that supplies, to the modulation circuit, a synchronous signal synchronized with the self-excited oscillation when an index related to the volume of the acoustic signal is lower than a threshold value, and stops supplying the synchronous signal to the modulation circuit when the index is higher than the threshold value.

Description

Amplification apparatus, acoustic processing apparatus, and control method for class D amplification circuit

The present invention relates to a technology for amplifying an acoustic signal.

A self-excited class D amplifier circuit includes a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal. If there is an oscillation source operating at a frequency close to the frequency of the self-oscillation, beat noise may occur in the output signal due to the difference between the frequency of the self-oscillation and the operating frequency of the oscillation source. For example, in an acoustic system in which a plurality of self-excitation class D amplifier circuits are juxtaposed, a beat noise caused by a difference in oscillation frequency among the plurality of class D amplifier circuits becomes a problem.

With the background described above, for example, Patent Document 1 discloses a configuration in which a synchronization signal of a predetermined frequency is supplied to modulation circuits of a plurality of class D amplifier circuits. The self-oscillations of the plurality of class D amplifier circuits (specifically, the modulation circuits) are synchronized with the synchronization signal. At this time, the oscillation frequencies of the plurality of class D amplifier circuits become the same, and beat noise due to the difference in oscillation frequency does not occur.

JP 2005-269580 A

By the way, for example, in the state where the volume of the sound signal is large, the frequency of the self-oscillation is autonomously determined without being influenced by the synchronization signal. That is, the synchronization signal does not contribute to the adjustment of the oscillation frequency but only causes distortion in the waveform of the acoustic signal (and hence deterioration of the sound quality). In consideration of the above circumstances, a preferred aspect of the present invention aims to suppress beat noise while suppressing deterioration in sound quality caused by a synchronization signal.

In order to solve the above problems, an amplification apparatus according to a preferred aspect of the present invention is a self-excited class D amplification circuit including a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal; When an index relating to the volume of the signal falls below a threshold, a synchronization signal synchronized with the self-oscillation is supplied to the modulation circuit, and when the index exceeds the threshold, supply of the synchronization signal to the modulation circuit And an operation control unit for stopping the
The acoustic processing device according to a preferred aspect of the present invention comprises a plurality of amplification devices to which acoustic signals of a plurality of channels are respectively supplied, and each of the plurality of amplification devices is an acoustic signal supplied to the amplification device. And a self-excited class D amplifier circuit including a modulation circuit that performs pulse modulation by self-oscillation, and a synchronization signal synchronized with the self-oscillation when the index related to the volume of the acoustic signal falls below a threshold. And an operation control unit for supplying the modulation circuit and stopping the supply of the synchronization signal to the modulation circuit when the index exceeds the threshold.
A control method according to a preferred aspect of the present invention is a control method of a self-excitation class D amplifier circuit including a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal, and relates to the volume of the acoustic signal. When the index falls below a threshold, a synchronization signal synchronized with the self-oscillation is supplied to the modulation circuit, and when the index exceeds the threshold, the supply of the synchronization signal to the modulation circuit is stopped.

It is a block diagram showing composition of an amplification device concerning a 1st embodiment of the present invention. It is a block diagram showing composition of an acoustic system concerning a 1st embodiment of the present invention. It is a circuit diagram of an amplification device. It is a flowchart which shows operation | movement of an operation control part. It is a circuit diagram of the amplification device in a 2nd embodiment. It is a graph which shows the frequency response of a band rejection filter. It is a block diagram which shows the structure of the sound processing apparatus in 3rd Embodiment. It is a block diagram of the drive part in a modification.

First Embodiment
FIG. 1 is a block diagram showing the configuration of an amplification device A according to a first embodiment of the present invention. The amplification device A according to the first embodiment generates an acoustic signal Z by amplifying an analog acoustic signal Y1 representing various sounds such as voices or musical tones. As illustrated in FIG. 1, the amplification device A includes a self-excited class D amplification circuit 30 and an operation control unit 40. The class D amplifier circuit 30 generates an acoustic signal Z by amplifying the acoustic signal Y1. The operation control unit 40 switches whether to supply the synchronization signal S to the class D amplifier circuit 30. Details of the synchronization signal S will be described later.

FIG. 2 is a block diagram showing the configuration of an acoustic system 100 using the amplification device A illustrated in FIG. As illustrated in FIG. 2, the sound system 100 according to the first embodiment is a system for reproducing various sounds such as musical tones or sounds, and includes a signal supply unit 11, a sound processing unit 12 and a sound output unit 13. Do. Note that any two or more elements of the acoustic system 100 may be integrated. For example, the signal supply device 11 may be mounted on the sound processing device 12.

The signal supply device 11 is a signal source for supplying the sound processing device 12 with a digital or analog sound signal X representing various sounds such as voices or musical tones. For example, a reproduction apparatus for reading the acoustic signal X from a portable or built-in recording medium is a preferred example of the signal supply apparatus 11. In addition, a sound collection device that collects the surrounding sound to generate the sound signal X, or a communication device that receives the sound signal X from another device via the communication network may be used as the signal supply device 11. .

The sound processing device 12 generates the sound signal Z by processing the sound signal X supplied from the signal supply device 11. The sound emitting device 13 is, for example, a speaker or a headphone, and reproduces the sound represented by the sound signal Z generated by the sound processing device 12.

As illustrated in FIG. 2, the sound processing device 12 includes a control unit 21, a signal processing circuit 22, a D / A converter 23, a power supply device 24, a signal generation circuit 25, and the above-described amplification device A. The acoustic signal X output from the signal supply device 11 is supplied to the signal processing circuit 22. When an analog acoustic signal X is output from the signal supply device 11, the acoustic signal X is converted from analog to digital by an A / D converter (not shown) and then supplied to the signal processing circuit 22. Be done.

The control unit 21 is a controller that controls each element of the sound processing device 12 and includes a control device 211 and a storage device 212. The control device 211 is an arithmetic processing circuit such as a CPU (Central Processing Unit), for example, and controls each element of the sound processing device 12 by executing a program stored in the storage device 212. The storage device 212 stores a program executed by the control device 211 and various data used by the control device 211. For example, a known recording medium such as a semiconductor recording medium or a magnetic recording medium, or a combination of plural kinds of recording mediums is a preferred example of the storage device 212.

The signal processing circuit 22 is formed of, for example, a DSP (Digital Signal Processor) for audio processing, and generates an acoustic signal Y0 by performing signal processing on the acoustic signal X supplied from the signal supply device 11. For example, crossover processing that divides the acoustic signal X into a plurality of bands, delay processing that delays the acoustic signal X, equalizer processing that adjusts the frequency characteristics of the acoustic signal X, limiter processing that limits the voltage range of the acoustic signal X, or Howling suppression processing for suppressing howling is exemplified as signal processing by the signal processing circuit 22. Note that part or all of the functions of the signal processing circuit 22 may be realized by the control device 211.

The D / A converter 23 of FIG. 2 converts the digital acoustic signal Y0 generated by the signal processing circuit 22 into an analog acoustic signal Y1. The class D amplifier circuit 30 generates the acoustic signal Z by amplifying the acoustic signal Y1 supplied from the D / A converter 23. The acoustic signal Z amplified by the class D amplifier circuit 30 is supplied to the sound emitting device 13 (load). The power supply 24 generates a power supply voltage and supplies it to each element of the acoustic system 100. The power supply device 24 of the first embodiment is a switching power supply that generates a DC power supply voltage by switching operation of a predetermined frequency.

The signal generation circuit 25 is an oscillation circuit that generates the synchronization signal S. The synchronization signal S is a clock signal that fluctuates at a predetermined frequency Fs. The frequency Fs is set to a predetermined value (e.g., 200 kHz) outside the audible band. When beat noise caused by the frequency difference between the frequency (hereinafter referred to as "switching frequency") Fp of the switching operation of the power supply 24 and the oscillation frequency Fo of self-oscillation of the class D amplifier circuit 30 can be a problem, the first embodiment It is desirable to make the frequency Fs of the synchronization signal S at the same frequency as the switching frequency Fp. However, if the beat noise caused by the frequency difference between the oscillation frequency Fo of the self-oscillation and the switching frequency Fp is not particularly problematic (for example, the frequency at which the frequency difference is outside the audible range), the synchronization signal The frequency Fs of S does not have to match the switching frequency Fp. The signal processing circuit 22 may realize the signal generation circuit 25.

FIG. 3 is a circuit diagram of the amplification device A. As illustrated in FIG. 3, the class D amplifier circuit 30 according to the first embodiment includes the modulation circuit 31, the switch circuit 32, the low pass filter 33, the first feedback circuit 34, and the second feedback circuit 35. The modulation circuit 31 generates a modulation signal Y2 by performing pulse modulation (pulse width modulation or pulse density modulation) by self-oscillation on the acoustic signal Y1. The modulation signal Y2 is a binary signal that fluctuates at a duty ratio corresponding to the signal level of the acoustic signal Y1.

The switch circuit 32 generates the amplified signal Y3 by amplifying the modulation signal Y2 generated by the modulation circuit 31 by a switching operation. The switch circuit 32 of the first embodiment includes a drive circuit 320, a first switch 321, and a second switch 322. Each of the first switch 321 and the second switch 322 is configured of a switching element such as, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The first switch 321 is interposed between the positive power supply (power supply voltage Vp) and the output point O, and the second switch 322 is interposed between the negative power supply (power supply voltage Vm) and the output point O. The drive circuit 320 controls any one of the first switch 321 and the second switch 322 to be in the on state in accordance with the modulation signal Y2 generated by the modulation circuit 31. Specifically, the drive circuit 320 controls the first switch 321 to be in the on state if the modulation signal Y2 is high level, and controls the second switch 322 to be in on state if the modulation signal Y2 is low level. When the first switch 321 is controlled to be on, the power supply voltage Vp is applied to the output point O, and when the second switch 322 is controlled to be on, the power supply voltage Vm is applied to the output point O. That is, the amplification signal Y3 generated at the output point O is a rectangular wave which fluctuates from one of the power supply voltage Vp and the power supply voltage Vm to the other with the same duty ratio as that of the modulation signal Y2.

The low-pass filter (LPF: Low-Pass Filter) 33 reduces the high-frequency component (for example, the band component including the oscillation frequency of the modulation circuit 31) of the amplified signal Y3 output from the switch circuit 32. Output. That is, the low frequency component including the audible band in the amplified signal Y3 is extracted as the acoustic signal Z. As illustrated in FIG. 3, the low pass filter 33 includes, for example, a capacitor Ca and an inductor La.

The acoustic signal Z output from the low pass filter 33 is fed back to the modulation circuit 31 through each of the first feedback circuit 34 and the second feedback circuit 35. Specifically, the path B is to be fed back to the modulation circuit 31 from the output end of the low pass filter 33 via the first feedback circuit 34 and the modulation from the output end of the low pass filter 33 via the second feedback circuit 35 A path for feedback to the circuit 31 is established. The first feedback circuit 34 is a delay circuit that delays the acoustic signal Z, and includes, for example, a plurality of resistive elements Rb (Rb1, Rb2 and Rb3) and a capacitor Cb. The second feedback circuit 35 is a voltage dividing circuit including a plurality of resistive elements Rc (Rc1 and Rc2).

As illustrated in FIG. 3, the modulation circuit 31 of the first embodiment includes an integration circuit 311 and a comparison circuit 312. Integration circuit 311 includes an operational amplifier 315 and a capacitor 316. The acoustic signal Y1 output from the D / A converter 23 is supplied to the positive input terminal of the operational amplifier 315. Further, a voltage obtained by dividing the acoustic signal Z by the resistance element Rc1 and the resistance element Rc2 of the second feedback circuit 35 is supplied to the negative input terminal of the operational amplifier 315. The second feedback circuit 35 functions as negative feedback to make the voltage of the acoustic signal Z supplied to the sound emitting device 13 proportional to the voltage of the acoustic signal Y1. The overall gain and frequency response of the class D amplifier circuit 30 is determined by the second feedback circuit 35.

As illustrated in FIG. 3, the output signal D 1 of the integration circuit 311 is supplied to the positive input terminal of the comparison circuit 312. Further, a feedback signal D 2 obtained by delaying the acoustic signal Z by the first feedback circuit 34 is supplied to the negative input terminal of the comparison circuit 312. The comparison circuit 312 compares the output signal D1 of the integration circuit 311 with the feedback signal D2, and generates a modulation signal Y2 according to the comparison result. That is, comparison circuit 312 sets modulation signal Y2 to a high level in a period in which the voltage of output signal D1 exceeds the voltage of feedback signal D2, and in a period in which the voltage of output signal D1 falls below the voltage of feedback signal D2. Set to low level. As understood from the above description, the first feedback circuit 34 functions as negative feedback for the comparator circuit 312 to perform pulse modulation by self-oscillation.

The frequency (hereinafter referred to as “oscillation frequency”) Fo of the self-oscillation in the modulation circuit 31 (comparison circuit 312) is negative feedback from the output end of the low pass filter 33 to the comparison circuit 312 via the first feedback circuit 34. It depends on the amount of delay in the path B. For example, the delay amount in the negative feedback path B is set such that the autonomous oscillation frequency Fo coincides with the frequency Fs of the synchronization signal S. However, the amount of delay in the path B fluctuates according to the error of the electrical characteristic (the resistance value of each resistance element Rb or the capacitance value of the capacitor Ca) of the first feedback circuit 34 or the impedance of the sound emitting device 13. Therefore, a difference may occur between the oscillation frequency Fo and the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency Fo. For example, when the switching frequency Fp of the power supply 24 and the oscillation frequency Fo are close to each other, the frequency difference between the two becomes a problem. Specifically, beat noise may occur due to the difference between the switching frequency Fp and the oscillation frequency Fo. The above problem may occur similarly in a configuration in which an oscillation source operating at a frequency close to the oscillation frequency Fo of self-oscillation is close to the class D amplifier circuit 30. The power supply device 24 is an example of the oscillation source described above. In the first embodiment, the synchronization signal S generated by the signal generation circuit 25 is used to adjust the oscillation frequency Fo to the frequency Fs of the synchronization signal S under a small volume where beat noise is a problem. .

As illustrated in FIG. 3, the amplification device A of the first embodiment includes an operation control unit 40. The operation control unit 40 switches whether to supply the synchronization signal S generated by the signal generation circuit 25 to the modulation circuit 31 (specifically, the comparison circuit 312). As illustrated in FIG. 1, an amplification device A is configured by the class D amplification circuit 30 and the operation control unit 40.

As illustrated in FIG. 3, the operation control unit 40 of the first embodiment includes a switch 41 and a drive unit 42. The switch 41 is configured of, for example, a MOSFET. The drive unit 42 is realized, for example, by the control device 211 executing a program stored in the storage device 212. The drive unit 42 may be realized by the signal processing circuit 22.

As illustrated in FIG. 3, the switch 41 is disposed between the signal generation circuit 25 and the modulation circuit 31 to control the connection state between the two. The switch 41 according to the first embodiment supplies the synchronization signal S generated by the signal generation circuit 25 to the modulation circuit 31 in the first state (on state), and the second state in which the supply of the synchronization signal S to the modulation circuit 31 is stopped. (Off state) changes from one to the other. The drive unit 42 switches the switch 41 to the first state (on state) or the second state (off state).

The synchronization signal S is supplied to the modulation circuit 31 via the switch 41 in the first state and the resistance element R. Specifically, the synchronization signal S is supplied to the negative input terminal of the comparison circuit 312 together with the feedback signal D2 output from the first feedback circuit 34. In a state where the synchronization signal S is supplied to the modulation circuit 31, the comparison circuit 312 generates the modulation signal Y2 by self-oscillation synchronized with the synchronization signal S. That is, the oscillation frequency Fo of the self-oscillation is forcibly adjusted to the frequency Fs of the synchronization signal S. In other words, pulse modulation by the modulation circuit 31 is synchronized with the synchronization signal S. As understood from the above description, the synchronization signal S is a signal with which the self-oscillation of the modulation circuit 31 is synchronized. The synchronization signal S is set to a relatively high signal level as compared to the level of the acoustic signal Z that has passed through the first feedback circuit 34. Specifically, the synchronization signal S is set to a signal level at which the influence of the synchronization signal S on the operation of the comparison circuit 312 becomes dominant in a state where the signal level of the acoustic signal X is low enough to cause beat noise. . At this time, the influence of the acoustic signal Z supplied via the first feedback circuit 34 can be substantially ignored. On the other hand, in a state where the supply of the synchronization signal S to the modulation circuit 31 is stopped, the comparison circuit 312 self-oscillates due to the negative feedback. The oscillation frequency Fo of the comparison circuit 312 is autonomously set to a frequency according to the delay amount in the negative feedback path B as described above. As understood from the above description, the self-excited class D amplifier circuit 30 is autonomous in a state where the periodic signal is not supplied from the external circuit (second state) or in a state where the influence of the synchronization signal S is not dominant. It is configured as a class D amplifier circuit that self oscillates.

The beat noise caused by the difference from the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency Fo is manifested when the volume of the acoustic signal X (or the acoustic signal Z) is small, and the volume of the acoustic signal X is large Have a tendency to be difficult to hear by human hearing. In consideration of the above tendency, the drive unit 42 according to the first embodiment controls the switch 41 to the first state when the sound volume of the sound signal X is small (typically in the silent state), and the sound volume of the sound signal X Is large, the switch 41 is controlled to the second state. Specifically, the drive unit 42 controls the switch 41 in accordance with an index (hereinafter referred to as an “evaluation index”) Q relating to the volume of the acoustic signal X (or the acoustic signal Z). In the first embodiment, in consideration of the fact that the voltage value of the acoustic signal Z depends on the volume of the acoustic signal X, the voltage value of the acoustic signal Z after amplification by the class D amplifier circuit 30 relates to the volume of the acoustic signal X. It is illustrated as an evaluation index Q.

FIG. 4 is a flowchart illustrating the operation of the drive unit 42 (hereinafter referred to as “synchronous control”). For example, the synchronous control of FIG. 4 is started in response to an interrupt occurring at a predetermined cycle.

When synchronous control is started, the drive unit 42 generates an evaluation index Q (S1). Specifically, the drive unit 42 detects the voltage value of the acoustic signal Z as the evaluation index Q. The driving unit 42 compares the evaluation index Q with a predetermined threshold value Qth, and determines whether the evaluation index Q exceeds the threshold value Qth (S2). The threshold value Qth is set to, for example, an appropriate numerical value within the range of 1/20 or more and 1/10 or less of the voltage value of the peak of the acoustic signal Z. If the evaluation index Q exceeds the threshold Qth (S2: YES), that is, if the sound signal X has a large volume, the drive unit 42 controls the switch 41 to the second state (S3). That is, the supply of the synchronization signal S to the modulation circuit 31 is stopped. Therefore, the comparison circuit 312 generates the modulation signal Y2 by self-oscillation of the oscillation frequency Fo according to the delay amount in the negative feedback path B.

On the other hand, if the evaluation index Q is less than the threshold Qth (S2: NO), that is, if the volume of the sound signal X is small, the drive unit 42 controls the switch 41 to the first state (S4). That is, the synchronization signal S is supplied to the modulation circuit 31. Therefore, the comparison circuit 312 generates the modulation signal Y2 by self-oscillation of the oscillation frequency Fo equal to the frequency Fs of the synchronization signal S. As understood from the above description, the operation control unit 40 of the first embodiment supplies the synchronization signal S to the modulation circuit 31 when the evaluation index Q falls below the threshold Qth, and the evaluation index Q exceeds the threshold Qth. In this case, the supply of the synchronization signal S to the modulation circuit 31 is stopped.

As understood from the above description, in the first embodiment, when the evaluation index Q falls below the threshold value Qth, the self-oscillation of the modulation circuit 31 is synchronized with the synchronization signal S by the supply of the synchronization signal S. That is, the oscillation frequency Fo is adjusted to the frequency Fs of the synchronization signal S. Therefore, it is possible to suppress (ideally not generate) the beat noise due to the difference with the operating frequency (here, switching frequency Fp = Fs) of the oscillation source operating at a frequency close to the oscillation frequency Fo. On the other hand, when the evaluation index Q exceeds the threshold Qth, the supply of the synchronization signal S to the modulation circuit 31 is stopped. Therefore, the deterioration of the sound quality (for example, the decrease of the SN ratio or the increase of the total harmonic distortion) due to the supply of the synchronization signal S is reduced. As exemplified above, according to the first embodiment, the beat noise caused by the difference from the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency Fo while suppressing the deterioration of the sound quality caused by the synchronization signal S It is possible to suppress

Second Embodiment
A second embodiment of the present invention will be described. In addition, about the element which an operation | movement or a function is the same as 1st Embodiment in each structure illustrated below, the code | symbol used by description of 1st Embodiment is diverted and detailed description of each is abbreviate | omitted suitably.

FIG. 5 is a circuit diagram of an amplification device A in the second embodiment. As illustrated in FIG. 5, the amplification device A of the second embodiment has a configuration in which a band rejection filter 36 is added to the class D amplification circuit 30 and the operation control unit 40 similar to those of the first embodiment. The operation control unit 40 of the second embodiment operates in the same manner as the first embodiment. That is, the synchronization signal S is supplied to the modulation circuit 31 when the evaluation index Q falls below the threshold Qth, and the supply of the synchronization signal S to the modulation circuit 31 is stopped when the evaluation index Q exceeds the threshold Qth. Therefore, also in the second embodiment, the same effect as that of the first embodiment is realized.

As illustrated in FIG. 5, a band elimination filter (BEF: Band Elimination Filter) 36 is connected to the rear stage of the low pass filter 33. That is, the band rejection filter 36 intervenes between the low pass filter 33 and the sound emitting device 13. Each of the first feedback circuit 34 and the second feedback circuit 35 is connected between the low pass filter 33 and the band rejection filter 36. That is, a negative feedback path from the input side of the band rejection filter 36 to the modulation circuit 31 is formed. Although the configuration of the band rejection filter 36 is arbitrary, for example, as shown in the example of FIG. 5, the capacitor Cd1 and the inductor Ld connected in parallel to each other, the capacitor Cd2 and the resistive element connected to the subsequent stage of the capacitor Cd1 and the inductor Ld A parallel resonant notch filter including Rd and is suitable as the band rejection filter 36. However, the configuration of the band rejection filter 36 is not limited to the example of FIG.

The band rejection filter 36 attenuates the signal component of the very narrow frequency band among the acoustic signal Z output from the low pass filter 33 as illustrated in FIG. As illustrated in FIG. 6, the frequency band to which the band rejection filter 36 attenuates is a frequency band including the frequency Fs of the synchronization signal S generated by the signal generation circuit 25. An acoustic signal output from the band rejection filter 36 is supplied to the sound emitting device 13.

Also in the second embodiment, as in the first embodiment, in the first state, the oscillation frequency Fo of the modulation circuit 31 is adjusted to the frequency Fs of the synchronization signal S by supplying the synchronization signal S to the modulation circuit 31. . The band rejection filter 36 attenuates the component of the frequency Fs of the synchronization signal S in the output signal from the class D amplifier circuit 30. In the above configuration, for the oscillation frequency Fo (= Fs) defined by the synchronization signal S, the impedance of the sound emitting device 13 viewed from the output side of the class D amplifier circuit 30 becomes maximum (ideally infinite). . Therefore, for the stop band of the band rejection filter 36, the delay amount in the negative feedback path B is less likely to be affected by the impedance of the noise output device 13 (load). Therefore, the autonomous oscillation frequency Fo in a state in which the control of the synchronization signal S is weak (the signal level of the acoustic signal X is large) is set to a frequency (within the stop band of the band rejection filter 36) substantially equal to the frequency Fs of the synchronization signal S. When designed, the oscillation frequency Fo does not significantly fluctuate from the frequency Fs of the synchronization signal S due to the fluctuation of the load impedance. That is, the second embodiment is advantageous in that the oscillation frequency Fo does not easily change even when the impedance of the sound emitting device 13 changes (for example, when the sound emitting device 13 is replaced).

In a configuration in which the frequency difference between the oscillation frequency Fo and the frequency Fs of the synchronization signal S is large, it is difficult to forcibly synchronize (pull in) the self-oscillation by the synchronization signal S. Therefore, in order to synchronize the self-oscillation of the modulation circuit 31, it is necessary to set the signal level of the synchronization signal S sufficiently high as compared with the configuration in which the frequency difference is small. According to the configuration in which the oscillation frequency Fo does not easily fluctuate as in the second embodiment, the expansion of the frequency difference between the oscillation frequency Fo and the frequency Fs of the synchronization signal S is suppressed. Therefore, the self-oscillation of the modulation circuit 31 can be properly synchronized even with the synchronization signal S having a small signal level. Then, by suppressing the signal level of the synchronization signal S, there is an advantage that the deterioration of the sound quality (for example, the decrease of the SN ratio or the increase of the total harmonic distortion) caused by the synchronization signal S is reduced. As understood from the above description, according to the second embodiment, the deterioration of the sound quality is reduced by suppressing the signal level of the synchronization signal S while suppressing the beat noise by stabilizing the oscillation frequency Fo. Can.

Third Embodiment
FIG. 7 is a block diagram showing the configuration of the sound processing apparatus 12 in the third embodiment. The sound processing device 12 of the third embodiment is a multi-channel audio system of N channels. As illustrated in FIG. 7, the sound processing device 12 includes N amplification devices A_1 to A_N corresponding to different channels (N is a natural number of 2 or more). The acoustic signal Y1_n of the n-th channel after being processed by the signal processing circuit 22 and the D / A converter 23 is supplied to any one amplification device A_n (n = 1 to N).

Each amplification device A_n includes the D-class amplification circuit 30 and the operation control unit 40 similar to those of the first embodiment. A sound emitting device 13 is connected to the class D amplifier circuit 30. The class D amplification circuit 30 of the amplification device A_n generates the acoustic signal Z_n by amplifying the acoustic signal Y1_n, and supplies the acoustic signal Z_n to the sound emission device 13. As illustrated in FIG. 7, the synchronization signal S generated by the signal generation circuit 25 (exemplary signal generation unit) is commonly supplied to the operation control unit 40 of each of the N amplification devices A_1 to A_N. The operation control unit 40 of the amplification device A_n supplies the synchronization signal S to the modulation circuit 31 when the evaluation index Q corresponding to the acoustic signal Y1_n (or the acoustic signal Z_n) falls below the threshold Qth, as in the first embodiment. If the evaluation index Q exceeds the threshold Qth, the supply of the synchronization signal S to the modulation circuit 31 is stopped. That is, supply and stop of the synchronization signal S to the modulation circuit 31 are individually controlled for each amplification device A_n.

Also in the third embodiment, the same effect as that of the first embodiment is realized. Further, in the configuration including N amplification devices A_1 to A_N as illustrated in FIG. 7, beat noise may occur due to the difference in oscillation frequency Fo between the respective amplification devices A_n (that is, between channels). . According to the third embodiment, since the individual difference of the oscillation frequency Fo is reduced (ideally eliminated) by the supply of the synchronization signal S, the beat noise caused by the difference of the oscillation frequency Fo between the channels is suppressed. Is possible. The configuration of the second embodiment in which the band rejection filter 36 is disposed downstream of the low pass filter 33 may be applied to the third embodiment. That is, a band rejection filter 36 is provided at a stage subsequent to the class D amplifier circuit 30 in each of the N amplification devices A_1 to A_N.

In addition, in the structure using separate synchronizing signal S for every amplifier A, the beat noise resulting from the frequency difference between synchronizing signals S may generate | occur | produce. In the configuration illustrated in FIG. 7, since the common synchronization signal S is supplied to the N amplification devices A_1 to A_N, there is also an advantage that such a problem does not occur.

<Modification>
The embodiments illustrated above can be variously modified. The aspect of a specific deformation | transformation is illustrated below. Two or more aspects arbitrarily selected from the following examples may be merged.

(1) In each embodiment described above, the voltage value of the acoustic signal Z is illustrated as the evaluation index Q, but the evaluation index Q is not limited to the above examples. For example, the voltage value of the acoustic signal X may be used as the evaluation index Q. Further, assuming that the duty ratio of the modulation signal Y2 is higher as the volume of the sound signal X is larger, a configuration using the duty ratio (modulation degree) of the modulation signal Y2 as the evaluation index Q is also assumed. Also, the sound volume itself of the sound signal X or the sound signal Z may be used as the evaluation index Q. In the configuration in which the sound volume of the acoustic signal X or the acoustic signal Z is calculated as the evaluation index Q, 60 dB close to silence is suitable as the threshold Qth. As understood from the above description, the evaluation index Q regarding the voltage value of the audio signal X or the audio signal Z, the evaluation index Q regarding the volume of the audio signal X or the audio signal Z, and the evaluation according to the duty ratio of the modulation signal Y2. The index Q is positioned as a specific example of the “index related to the sound volume of the acoustic signal”.

(2) In each embodiment described above, the synchronization signal S is supplied to the negative input terminal of the comparison circuit 312 in the modulation circuit 31. However, the position to which the synchronization signal S is supplied in the modulation circuit 31 is not limited to the above illustration. For example, the synchronization signal S may be supplied to the positive input terminal of the comparison circuit 312 together with the output signal D1 of the integration circuit 311.

(3) In the third embodiment, the common synchronization signal S is supplied to the operation control unit 40 of each of the N amplification devices A_1 to A_N, but the signal generation circuit 25 is separately installed for each amplification device A_n, A separate synchronization signal S may be used in each amplification device A. However, according to the above-described embodiments in which the common synchronization signal S is supplied to the N amplification devices A_1 to A_N, the sound processing device is compared with a configuration that generates and supplies separate synchronization signals S for each amplification device A_n. There is an advantage that the 12 configurations are simplified.

(4) In each embodiment described above, the drive unit 42 in the operation control unit 40 is realized by the control device 211 or the signal processing circuit 22. However, the drive unit 42 may be configured by an analog circuit. For example, a drive unit 42a having a configuration illustrated in FIG. 8 is employed.

The drive unit 42 a of FIG. 8 includes a voltage detection unit 45, a reference voltage generation unit 46, and a voltage comparison unit 47. The voltage detection unit 45 generates a detection voltage Vd according to the signal level of the acoustic signal Z. Specifically, the voltage detection unit 45 includes a diode 451 that rectifies the acoustic signal Z (full wave rectification or half wave rectification), and a smoothing circuit 452 that smoothes the rectified voltage. The reference voltage generation unit 46 generates a predetermined reference voltage Vr. Specifically, the reference voltage generation unit 46 includes, for example, a Zener diode 461 and a resistance element 462.

The voltage comparison unit 47 compares the detection voltage Vd supplied from the voltage detection unit 45 with the reference voltage Vr generated by the reference voltage generation unit 46, and controls the switch 41 according to the comparison result. Specifically, when the detection voltage Vd exceeds the reference voltage Vr (that is, when the volume of the acoustic signal X is large), the voltage comparison unit 47 controls the switch 41 to the second state (off state). That is, the supply of the synchronization signal S to the modulation circuit 31 is stopped. On the other hand, when the detection voltage Vd is lower than the reference voltage Vr (that is, when the volume of the acoustic signal X is small), the voltage comparison unit 47 controls the switch 41 to the first state (on state). That is, the synchronization signal S is supplied to the modulation circuit 31. Also in the above configuration, the same effects as those of the above-described embodiments can be realized. The switch 41 is configured of, for example, a MOSFET, an analog switch or a relay.

(5) For example, the following configuration can be grasped from the embodiments exemplified above.
<Aspect 1>
An amplification apparatus according to a preferred aspect (Aspect 1) of the present invention is a self-excited class D amplification circuit including a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal; Operation control to supply a synchronization signal synchronized with the self-oscillation to the modulation circuit when the value is below the threshold, and to stop the supply of the synchronization signal to the modulation circuit when the index exceeds the threshold Have a department. In the above aspect, when the index related to the volume of the acoustic signal is lower than the threshold, the self-oscillation of the modulation circuit is synchronized with the synchronization signal by the supply of the synchronization signal. That is, the oscillation frequency is adjusted to the frequency of the synchronization signal. Therefore, it is possible to suppress the beat noise due to the difference from the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency. On the other hand, when the index related to the sound volume of the acoustic signal exceeds the threshold, the supply of the synchronization signal to the modulation circuit is stopped. Therefore, the deterioration of the sound quality (for example, the decrease of the SN ratio or the increase of the total harmonic distortion) due to the supply of the synchronization signal is reduced. In the state where the index related to the volume of the acoustic signal exceeds the threshold, it is difficult to hear the beat noise due to the difference from the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency.
<Aspect 2>
In the preferable example (aspect 2) of aspect 1, the operation control unit controls whether to supply the synchronization signal to the modulation circuit, using the voltage value of the output signal from the class D amplifier circuit as the index. . The above aspect has an advantage that supply or stop of the synchronization signal to the modulation circuit can be easily controlled by using the voltage value of the output signal from the class D amplifier circuit as an index.
<Aspect 3>
The amplification device according to the preferred embodiment (embodiment 3) of aspect 1 or aspect 2 includes a band elimination filter for attenuating a component of a frequency band including the frequency of the synchronization signal among output signals from the class D amplification circuit. In the above aspect, with regard to the oscillation frequency defined by the synchronization signal, the impedance of the load viewed from the class D amplifier circuit becomes maximum (ideally infinite). Therefore, there is an advantage that the oscillation frequency does not easily fluctuate even when the impedance of the load fluctuates.
<Aspect 4>
A sound processing apparatus according to a preferred aspect (aspect 4) of the present invention comprises a plurality of amplification devices to which sound signals of a plurality of channels are respectively supplied, and each of the plurality of amplification devices is supplied to the amplification device. A self-oscillation class D amplifier circuit including a modulation circuit that performs pulse modulation by self-oscillation on the acoustic signal to be synchronized, and the self-oscillation is synchronized if the index related to the volume of the acoustic signal falls below a threshold And an operation control unit for stopping the supply of the synchronization signal to the modulation circuit when the index exceeds the threshold. In the above aspect, when the index related to the volume of the acoustic signal is lower than the threshold, the self-oscillation of the modulation circuit is synchronized with the synchronization signal by the supply of the synchronization signal. That is, the oscillation frequency is adjusted to the frequency of the synchronization signal. Therefore, it is possible to suppress the beat noise caused by the difference in oscillation frequency among the plurality of amplification devices (between channels). On the other hand, when the index related to the sound volume of the acoustic signal exceeds the threshold, the supply of the synchronization signal to the modulation circuit is stopped. Therefore, the deterioration of the sound quality (for example, the decrease of the SN ratio or the increase of the total harmonic distortion) due to the supply of the synchronization signal is reduced. In the state where the index related to the volume of the acoustic signal exceeds the threshold, it is difficult to hear the beat noise due to the difference from the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency.
<Aspect 5>
A sound processing apparatus according to a preferred example of the fourth aspect (Aspect 5) includes a signal generation unit that supplies a common synchronization signal to the plurality of amplification devices. In the above aspect, since the synchronization signal is commonly supplied to a plurality of amplification devices, the advantage is that the configuration of the sound processing device is simplified as compared to the configuration in which separate synchronization signals are generated and supplied for each amplification device. There is.
<Aspect 6>
A control method according to a preferred aspect (Aspect 6) of the present invention is a control method of a self-excited class D amplifier circuit including a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal, When an index relating to the volume of the signal falls below a threshold, a synchronization signal synchronized with the self oscillation is supplied to the modulation circuit, and when the index exceeds the threshold, the synchronization signal is supplied to the modulation circuit. Stop. In the above aspect, when the index related to the volume of the acoustic signal is lower than the threshold, the self-oscillation of the modulation circuit is synchronized with the synchronization signal by the supply of the synchronization signal. That is, the oscillation frequency is adjusted to the frequency of the synchronization signal. Therefore, it is possible to suppress the beat noise due to the difference from the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency. On the other hand, when the index related to the sound volume of the acoustic signal exceeds the threshold, the supply of the synchronization signal to the modulation circuit is stopped. Therefore, the deterioration of the sound quality (for example, the decrease of the SN ratio or the increase of the total harmonic distortion) due to the supply of the synchronization signal is reduced. In the state where the index related to the volume of the acoustic signal exceeds the threshold, it is difficult to hear the beat noise due to the difference from the operating frequency of the oscillation source operating at a frequency close to the oscillation frequency.

DESCRIPTION OF SYMBOLS 100 ... Acoustic system, 11 ... Signal supply apparatus, 12 ... Sound processing apparatus, 13 ... Sound emission apparatus, 21 ... Control unit, 211 ... Control apparatus, 212 ... Storage apparatus, 22 ... Signal processing circuit, 23 ... D / A conversion 24: Power supply device 25: Signal generation circuit 30: Class D amplifier circuit 31: Modulation circuit 311: Integration circuit 312: Comparison circuit 32: Switch circuit 320: Drive circuit 321: First switch , 322: second switch, 33: low pass filter, 34: first feedback circuit, 35: second feedback circuit, 36: band rejection filter, 40: operation control unit, 41: switch, 42, 42a: drive unit , A, A_1 to A_N: amplification devices.

Claims (6)

A self-excited class D amplifier circuit including a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal;
When an index relating to the volume of the acoustic signal falls below a threshold, a synchronization signal synchronized with the self-oscillation is supplied to the modulation circuit, and when the index exceeds the threshold, the synchronization signal to the modulation circuit And an operation control unit for stopping supply of the amplification device. The amplification device according to claim 1, wherein the operation control unit controls whether the synchronization signal is supplied to the modulation circuit, using the voltage value of the output signal from the class D amplifier circuit as the index. The amplification device according to claim 1 or 2, further comprising a band elimination filter for attenuating a component of a frequency band including the frequency of the synchronization signal among output signals from the class D amplifier circuit. A plurality of amplification devices to which acoustic signals of a plurality of channels are respectively supplied;
Each of the plurality of amplification devices is
A self-excited class D amplifier circuit including a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal supplied to the amplification device;
When an index relating to the volume of the acoustic signal falls below a threshold, a synchronization signal synchronized with the self-oscillation is supplied to the modulation circuit, and when the index exceeds the threshold, the synchronization signal to the modulation circuit And an operation control unit for stopping the supply of the sound. The sound processing device according to claim 4, further comprising: a signal generation unit that supplies a common synchronization signal to the plurality of amplification devices. A control method of a self-excited class D amplifier circuit including a modulation circuit that performs pulse modulation by self-oscillation on an acoustic signal, comprising:
When an index relating to the volume of the acoustic signal falls below a threshold, a synchronization signal synchronized with the self-oscillation is supplied to the modulation circuit, and when the index exceeds the threshold, the synchronization signal to the modulation circuit How to control the supply of Class D amplifier circuit.

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