JP6235182B1 - Audio playback device - Google Patents

Abstract

Provided is a new sound reproducing apparatus capable of preventing deterioration in sound quality due to distortion of a pulse waveform. The drive pulse processor 20 divides each pulse P of a PWM drive pulse signal into a plurality of equal-width pulses p and outputs the divided pulses. Thereby, it is possible to prevent the amplifier output portion from being instantaneously short-circuited at the timing of switching of the pulse P. In addition, even if distortion occurs, the equal-width pulses p constituting each pulse P all have the same shape, so that energy proportional to the number of equal-width pulses p can be output stably, resulting in sound quality degradation. It can be surely prevented. [Selection] Figure 6

Description

  The present invention relates to an audio reproduction device for driving an acoustic speaker by a PWM drive pulse signal and a ΔΣ drive pulse signal.

  Conventionally, pulse width modulation (PWM) and pulse density are used to convert PCM (Pulse Code Modulation) input signals recorded on music media such as CDs and DVDs into 1-bit digital signals. A modulation method (PDM: Pulse Density Modulation) is known. Of these two methods, PWM is generally used at present, but in order to achieve a high signal-to-noise ratio (SNR), a ΔΣ modulator having noise shaping characteristics is used. Used.

  The PWM drive pulse is ideally a rectangular wave that changes regularly and instantaneously between two levels as shown in FIG. 8A, but actually, as shown in FIG. There is a characteristic that it slowly delays at the rising edge of the pulse. This is because even if the analog drive element (transistor) that generates the pulse is turned on, it takes time until the output reaches the maximum current and the maximum voltage. Similarly, when the output is switched from on to off, it gradually changes. . As a result, the waveform is disturbed as shown in FIG.

  That is, when the output is first switched between plus and minus, both drive circuits are instantaneously turned on and the current is short-circuited in the circuit as shown in FIG. As a result, the power during the short circuit does not reach the speaker and may cause the transistor to generate heat. Next, as shown in the shaded area in FIG. 5B, the energy output due to the lack of distortion of the pulse angle is not exactly proportional to the length of the on / off control signal of the transistor, and the energy loss ratio increases. There is. For this reason, for example, in Patent Document 1 below, these problems are solved by providing a pause time (dead time) at the on / off switching timing of the pulse as shown in FIG. Trying to solve.

Japanese Patent Application Laid-Open No. 2004-128639

  By the way, since the PWM drive pulse has different pulse lengths, when energy loss occurs due to the distortion of the pulse angle due to the influence of the drive element as described above, the ratio of the energy loss is different for each pulse. Therefore, the energy transmitted to the speaker is not proportional to the width of the pulse, which may adversely affect the sound quality.

  That is, as shown in FIG. 8D, the energy loss due to the influence of the driving element is almost equal each time for each pulse, and thus is not so much affected when the pulse width is large, but as the pulse width becomes smaller. In other words, as the volume decreases, the energy loss ratio increases, and the energy transmitted to the speaker is not proportional to the pulse width. In particular, this problem is greatly affected by a pulse having a short pulse width (for example, pulse P2 in FIG. 8D) even if a pause time is provided at the on / off switching timing of the pulse as in Patent Document 1.

  Accordingly, the present invention has been devised to solve these problems, and a main object thereof is to provide a novel audio reproducing apparatus capable of preventing deterioration in sound quality due to distortion of a pulse waveform.

  In order to solve the above problems, a first invention includes a pulse processor that processes an input PWM drive pulse signal, and an amplifier that amplifies the PWM drive pulse signal processed by the pulse processor and drives a speaker. And the pulse processor divides each pulse of the PWM drive pulse signal into a plurality of equal width pulses and outputs the divided pulses.

  Thus, by dividing each pulse of the PWM drive pulse signal into a plurality of equal-width pulses and outputting them, it is possible to prevent the amplifier output portion from being instantaneously short-circuited at the pulse switching timing. In addition, even if distortion occurs, all the equal width pulses constituting each pulse have the same shape, so that energy proportional to the number of equal width pulses can be stably output. As a result, it is possible to prevent deterioration in sound quality due to distortion of the PWM drive pulse waveform, and excellent high sound quality can be exhibited even when the volume is reduced.

  The second invention includes a pulse processor that processes an input ΔΣ drive pulse signal and an amplifier that amplifies the ΔΣ drive pulse signal processed by the pulse processor and drives a speaker, Is an audio reproduction device characterized in that the pulse width of the ΔΣ drive pulse signal is made smaller than the original pulse width and a pause time is provided between adjacent pulses.

  According to such a configuration, it is possible to prevent the amplifier output portion from being instantaneously short-circuited at the pulse switching timing, and all outputs that are output every time even if distortion occurs as in the first invention. Since the pulses have the same shape, energy proportional to the number of pulses can be stably output. As a result, it is possible to prevent deterioration in sound quality due to distortion of the ΔΣ drive pulse waveform, and excellent high sound quality can be exhibited even when the volume is reduced.

  According to a third invention, in the first or second invention, the pulse processor and the amplifier are accommodated in an electromagnetically shielded case, and the case is incorporated in a speaker box. Device. According to such a configuration, high-frequency noise generated by a pulse processor or an amplifier can be reliably shielded in an electromagnetically shielded case and speaker box. Can be reliably prevented.

  According to a fourth invention, in the second invention, a ΔΣ modulator for generating the ΔΣ drive pulse signal from a PCM signal is provided, and the ΔΣ modulator is housed in an electromagnetically shielded case together with the pulse processor and an amplifier. And the audio reproducing apparatus is characterized in that the case is incorporated in a speaker box. Since high-frequency noise is also generated in a ΔΣ modulator that generates a ΔΣ drive pulse signal from a PCM signal, this ΔΣ modulator is electromagnetically shielded together with a pulse processor and an amplifier, as in the third invention, and a speaker box. If it is housed inside, it is possible to reliably prevent deterioration of sound quality due to high frequency noise and adverse effects on surrounding home appliances.

  According to the present invention, it is possible to prevent the amplifier output portion from being instantaneously short-circuited at the pulse switching timing, and even if distortion occurs, all the pulses have the same shape, and therefore proportional to the number of pulses. The output energy can be output stably. As a result, it is possible to prevent deterioration in sound quality due to distortion of the pulse waveform, and excellent high sound quality can be exhibited even when the volume is reduced.

It is a block diagram which shows 1st Embodiment of the audio | voice reproduction apparatus 100 which concerns on this invention. It is a block diagram showing pulse processor 20 concerning a 1st embodiment. It is a wave form diagram which shows the PWM drive pulse which shows the example of the pulse process by the pulse processor. It is a block diagram which shows 2nd Embodiment of the audio | voice reproduction apparatus 100 which concerns on this invention. It is a block diagram which shows the pulse processor 20 which concerns on 2nd Embodiment. FIG. 6 is a waveform diagram showing a ΔΣ drive pulse showing an example of pulse processing by the pulse processor 20. It is a block diagram which shows 3rd Embodiment of the audio | voice reproduction apparatus 100 which concerns on this invention. It is a wave form diagram which shows the conventional PWM drive pulse.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a first embodiment of an audio playback apparatus 100 according to the present invention. As shown in the figure, the audio reproduction device 100 includes a PWM modulator 10, a pulse processor 20, an amplifier 30, and an acoustic speaker 40. The PWM modulator 10 is one of known 1-bit digital modulators, and a PWM signal composed of an on / off signal sequence from a PCM signal (44.1 KHz, 16 bits) recorded on a medium such as a CD or a DVD. A (pulse width modulation signal) is generated and output to the pulse processor 20.

  The amplifier 30 is a known class D amplifier combining four transistors called, for example, a full bridge, and can apply both positive and negative voltages to the acoustic speaker 40 with only one positive power source. The acoustic speaker 40 is a known dynamic speaker composed of an electromagnetic coil, a magnet, and a cone, and converts positive and negative digital signals output from the amplifier 30 into audible sound and outputs the sound.

  The pulse processor 20 has a circuit configuration as shown in FIG. 2, and includes a clock generator 21 that generates a clock signal of 1 MHz or more, a flip-flop circuit 22, and first and second AND circuits 23 and 24. It consists of and. As shown in the figure, this pulse processor 20 inputs each pulse of the PWM signal sent from the PWM modulator 10 to the flip-flop circuit 22, where it is several times the PWM signal generated by the clock generator 21 ( It is divided into a plurality of equal-width pulses p as shown in FIG. 3 by a clock signal having a frequency of 1 MHz or more.

  When the input pulse is positive, the pulse processor 20 outputs it as a positive (+) drive voltage as it is via the first AND circuit 23, and when the input pulse is switched to negative, It is output as a minus (−) drive voltage via the AND circuit 24. Each of these equal-width pulses p is slightly distorted due to the influence of the driving element, but all are generated in the same shape and at a constant interval (rest time).

  In the example of FIG. 3, the first plus-side pulse P1 is divided into five equal-width pulses p1 to p5 and output as a plus (+) drive voltage, and the second minus-side pulse P2 is given as three equal-width pulses p6. Is divided into .about.p8 and outputted as a minus (-) drive voltage. Further, the third plus-side pulse P3 is divided into four equal-width pulses p9 to p12 and output as a plus (+) drive voltage, and the fourth minus-side pulse P4 is divided into four equal-width pulses p13 to p16. And output as a minus (−) drive voltage. Each equal-width pulse p is amplified by the amplifier 30, then sent to the acoustic speaker 40, converted into an audible sound, and output.

  As described above, the audio reproduction device 100 of the present invention is configured to divide each pulse P of the PWM drive pulse signal into a plurality of equal-width pulses p and output by the pulse processor 20 provided at the subsequent stage of the PWM modulator 10. As a result, a certain pause time is formed between adjacent pulses, so that it is possible to prevent the amplifier output portion from being instantaneously short-circuited at the switching timing of the pulses.

  In addition, even if distortion occurs in the pulse P due to the influence of the driving element, a plurality of equal width pulses p constituting each pulse P have the same shape, so that energy proportional to the number of equal width pulses p is stabilized. Can be output. As a result, it is possible to prevent deterioration in sound quality due to distortion of the PWM drive pulse waveform, and a voltage corresponding to the sound can be reliably output even when the volume is reduced, so that excellent high sound quality can be exhibited.

  Next, FIG. 4 to FIG. 6 show a second embodiment of the audio reproducing apparatus 100 according to the present invention. First, as shown in FIG. 4, the sound reproducing device 100 includes a ΔΣ modulator 11, a pulse processor 20, an amplifier 30, and an acoustic speaker 40, and the configuration other than the ΔΣ modulator 11 is as described above. The configuration is almost the same as in the first embodiment. As shown in FIG. 5, the pulse processor 20 according to the present embodiment has the same configuration as that according to the first embodiment except that the clock generator 21 is not provided.

Like the PWM modulator 10, the ΔΣ modulator 11 is one of known 1-bit digital modulators, and has an equal width composed of an on / off signal sequence from a PCM signal recorded on a medium such as a CD or a DVD. A ΔΣ drive pulse (pulse train) signal is generated and output to the pulse processor 20. FIG. 6A shows an example of the waveform of the ΔΣ drive pulse, and a signal is output according to the number of equal-width plus or minus ΔΣ drive pulses P.

  As shown in FIG. 5, each pulse of the ΔΣ signal output from the ΔΣ modulator 11 is input to the flip-flop circuit 22, and a clock signal input accompanying the ΔΣ signal is used as shown in FIG. The width is transformed into a short pulse p whose width is about half. When the modified short pulse p is positive, it is output as a plus (+) drive voltage as it is through the first AND circuit 23, and when the short pulse p is switched to negative, the second AND circuit is output. 24 is output as a minus (−) drive voltage. Each of these short-width pulses p is generated with the same shape and at a constant interval as long as it is shortened to half.

  In the example of FIG. 6, by suspending half of one cycle, each ΔΣ drive pulse P1 to P8 is transformed into a short pulse p1 to P8 that is approximately half of the original pulse width, and is constant between adjacent pulses. By being generated at an interval, this interval becomes a pause time. Even in the case of this short-width pulse p, some distortion occurs due to the influence of the driving element, but both are generated in the same shape and at a constant interval (rest time).

  As described above, the audio reproduction device 100 according to the present embodiment is configured to output the pulse P of the ΔΣ drive pulse signal with the width of each pulse P shortened by the pulse processor 20 provided at the subsequent stage of the ΔΣ modulator 11. Since a pause time is formed between adjacent pulses, it is possible to prevent the amplifier output portion from being instantaneously short-circuited at the pulse switching timing.

  Further, even if distortion occurs in the pulse P due to the influence of the driving element, the plurality of short width pulses p constituting each pulse P all have the same shape, so that the energy proportional to the number of the short width pulses p is stabilized. Can be output. As a result, it is possible to prevent deterioration in sound quality due to distortion of the ΔΣ drive pulse waveform, and even if the volume is reduced, a voltage corresponding to that can be reliably output, so that excellent high sound quality can be exhibited.

  In the present embodiment, an example in which the width of each pulse P of the ΔΣ drive pulse signal is approximately halved by pausing half of one cycle is shown. However, this clock frequency is increased or decreased as appropriate, for example, 3 times or 4 times. Or by setting it to 1.5 times, the pause time between the pulses can be appropriately adjusted. Also, in the case of a medium in which audio information is recorded with a 1-bit ΔΣ drive pulse signal from the beginning, such as SACD (Super Audio CD), ΔΣ modulation processing is not necessary, so that ΔΣ modulation is performed as shown in FIG. The selector switch 12 may be provided at the subsequent stage of the device 11 and the ΔΣ drive pulse signal may be directly input to the pulse processor 20.

  Next, FIG. 7 shows a third embodiment of the sound reproducing apparatus 100 according to the present invention. As shown in the figure, this audio reproducing device 100 is a device that generates electromagnetic waves such as the PWM modulator 10, the ΔΣ modulator 11, the pulse processor 20, and the amplifier 30 described above using an electromagnetic shielding material such as a metal plate or a metal net. The case 50 is housed in a formed case 50, and the case 50 is integrally incorporated in a speaker box 60 to which the acoustic speaker 40 is attached.

  That is, when power transmission of 1 W to 100 W is performed with a signal in the order of MHz such as a PWM drive pulse signal or a ΔΣ drive pulse signal, the amount of radiated radio waves also increases, which may adversely affect sound quality and surrounding electrical appliances. It is done. Therefore, in the present embodiment, these devices are accommodated in a case 50 that is electromagnetically shielded, and further, this case 50 is integrally incorporated in the speaker box 60, which eliminates the need for these devices. Therefore, it is possible to reliably shield the high-frequency radiation and suppress adverse effects on sound quality and surrounding electrical appliances.

  In addition, with this configuration, a space for installing the pulse processor 20 and the amplifier 30 is unnecessary, and the indoor space can be used effectively, and a cable connected to the acoustic speaker 40 is unnecessary or can be greatly shortened. Reduction in sound quality due to cost reduction and signal degradation during transmission can be avoided at the same time.

DESCRIPTION OF SYMBOLS 100 ... Audio | voice reproduction apparatus 10 ... PWM modulator 11 ... Delta-sigma modulator 12 ... Changeover switch 20 ... Pulse processor 21 ... Clock generator 22 ... Flip-flop circuit 23 ... 1st AND circuit 24 ... 2nd AND circuit 30 ... Amplifier 40 ... Acoustic speaker 50 ... Case (electromagnetic shield)
60 ... Speaker box P ... PWM drive pulse, ΔΣ drive pulse p ... Equal width PWM drive pulse, Short width ΔΣ drive pulse

Claims (4)

A pulse processor that processes an input PWM drive pulse signal; and an amplifier that amplifies the PWM drive pulse signal processed by the pulse processor and drives a speaker;
The audio processor according to claim 1, wherein the pulse processor divides each pulse of the PWM drive pulse signal into a plurality of equal width pulses and outputs the divided pulses. A pulse processor that processes an input ΔΣ drive pulse signal, and an amplifier that amplifies the ΔΣ drive pulse signal processed by the pulse processor and drives a speaker;
The ΔΣ drive pulse signal, the pulse processor with positive or negative ΔΣ drive pulse of equal width is from 1 to pulse train multiple continuous, the all of the original pulse width of the ΔΣ drive pulse ΔΣ drive pulse signal An audio reproduction apparatus characterized in that a pause time is provided between adjacent pulses by making the pulse width shorter than the pulse width. The sound reproducing device according to claim 1 or 2,
An audio reproducing apparatus comprising: the pulse processor and the amplifier housed in an electromagnetically shielded case, and the case is incorporated in a speaker box. The sound reproducing device according to claim 2,
A ΔΣ modulator for generating the ΔΣ drive pulse signal from the PCM signal, the ΔΣ modulator together with the pulse processor and the amplifier being housed in an electromagnetically shielded case, and the case being incorporated in a speaker box; An audio reproducing apparatus characterized by the above.

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