JP2011045003A - Ultrasonic audio reproducing method and ultrasonic audio reproducing device - Google Patents

Ultrasonic audio reproducing method and ultrasonic audio reproducing device Download PDF

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JP2011045003A
JP2011045003A JP2009193137A JP2009193137A JP2011045003A JP 2011045003 A JP2011045003 A JP 2011045003A JP 2009193137 A JP2009193137 A JP 2009193137A JP 2009193137 A JP2009193137 A JP 2009193137A JP 2011045003 A JP2011045003 A JP 2011045003A
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signal
ultrasonic
pwm
carrier signal
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JP5479816B2 (en
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Hiroshi Tonegawa
寛 利根川
Hiroshi Sato
宏 佐藤
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Foster Electric Co Ltd
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Foster Electric Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones

Abstract

<P>PROBLEM TO BE SOLVED: To achieve ultrasonic audio reproduction by a simple circuit configuration. <P>SOLUTION: An ultrasonic audio reproducing device includes: an ultrasonic carrier signal generator for generating an ultrasonic carrier signal having a frequency two or more times the upper limit frequency of an audio signal to be reproduced and serving as a carrier for ultrasonic audio reproduction; an adder for adding the audio signal and the ultrasonic carrier signal; a PWM carrier signal generator for generating a triangular-wave or sawtooth-wave PWM carrier signal having a frequency twice the ultrasonic carrier signal and being synchronized with the ultrasonic carrier signal; a comparator for comparing the amplitudes of an output signal of the adder and the PWM carrier signal and generating a PWM signal; and a drive part for generating a drive signal of an ultrasonic vibrator based on the PWM signal generated by the comparator. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は超音波音響再生装置方法と超音波音響再生装置とに関し、特に、簡易な回路構成であって効率の良い超音波再生が可能な技術に関する。   The present invention relates to an ultrasonic acoustic reproduction apparatus method and an ultrasonic acoustic reproduction apparatus, and more particularly to a technique capable of efficient ultrasonic reproduction with a simple circuit configuration.

超音波音響再生装置では、超音波信号（超音波搬送波信号）を音声信号で変調し、変調された超音波信号で超音波振動子を振動させることで、指向性の強い音響再生を実現している。   In an ultrasonic sound reproducing device, an ultrasonic signal (ultrasonic carrier wave signal) is modulated with an audio signal, and an ultrasonic transducer is vibrated with the modulated ultrasonic signal, thereby realizing highly directional sound reproduction. Yes.

たとえば、図６に示すように、周波数ｆｃの超音波搬送波信号を、周波数ａの音声信号で変調することで、周波数ｆｃ±ａの超音波信号が得られる。
なお、この超音波音響再生装置として用いられる変調回路としては、図７に示すように、音声信号源１からの音声信号に直流重畳部２で直流成分を重畳して、搬送波生成部３からの超音波搬送波信号を乗算部４において直流重畳音声信号で変調する。これにより、図６に示す周波数ｆｃ，ｆｃ±ａの振幅変調出力が得られる。 For example, as shown in FIG. 6, by modulating an ultrasonic carrier signal having a frequency fc with an audio signal having a frequency a, an ultrasonic signal having a frequency fc ± a is obtained.
As shown in FIG. 7, the modulation circuit used as the ultrasonic sound reproducing apparatus superimposes a direct current component on the audio signal from the audio signal source 1 by the direct current superimposing unit 2 and outputs from the carrier wave generating unit 3. The ultrasonic carrier signal is modulated by the multiplication unit 4 with the DC superimposed audio signal. Thereby, the amplitude modulation output of the frequencies fc and fc ± a shown in FIG. 6 is obtained.

また、図８に示すように、移相器，乗算器，ＬＰＦを有するリング変調器を用いたＳＳＢ方式（Weaver法）が用いられることもある。この場合、図８のように、４個の乗算器が必要になるため、回路構成が複雑になる。   Further, as shown in FIG. 8, an SSB method (Weaver method) using a phase modulator, a multiplier, and a ring modulator having an LPF may be used. In this case, as shown in FIG. 8, since four multipliers are required, the circuit configuration becomes complicated.

なお、このような超音波音響再生装置としては、たとえば、以下の特許文献１に記載されたものが存在している。   In addition, as such an ultrasonic sound reproducing device, for example, one described in Patent Document 1 below exists.

特開２００３−１５３３７０号公報JP 2003-153370 A

以上のような超音波音響再生装置では、乗算器を用いて変調を行うため、対応できるＤＳＰやアナログ乗算器が必要になり、変調回路の構成が複雑になり、また、コストもかかるという問題があった。   In the ultrasonic sound reproducing apparatus as described above, since modulation is performed using a multiplier, a compatible DSP or analog multiplier is required, the configuration of the modulation circuit becomes complicated, and the cost is high. there were.

本発明は、以上のような課題を解決するためになされたものであって、簡素な回路構成で実現できる超音波音響再生方法および超音波音響再生装置を提供することを目的とする。   The present invention has been made to solve the above-described problems, and an object thereof is to provide an ultrasonic sound reproducing method and an ultrasonic sound reproducing device that can be realized with a simple circuit configuration.

以上の課題を解決する本発明は、以下に記載するようなものである。
（１）請求項１記載の発明は、再生すべき音声信号の上限周波数の２倍以上の周波数であって超音波音響再生の搬送波となる超音波搬送波信号を生成し、前記音声信号と前記超音波搬送波信号とを加算し、前記超音波搬送波信号の２倍の周波数の三角波あるいは鋸波のＰＷＭ搬送波信号を生成し、前記加算部の出力信号と前記ＰＷＭ搬送波信号とを振幅比較して生成したＰＷＭ信号を超音波振動子の駆動信号として出力する、ことを特徴とする超音波音響再生方法である。 The present invention for solving the above problems is as described below.
(1) The invention according to claim 1 generates an ultrasonic carrier signal having a frequency that is at least twice the upper limit frequency of the audio signal to be reproduced and serves as a carrier wave for ultrasonic acoustic reproduction. The sonic carrier wave signal is added to generate a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal, and the output signal of the adding unit and the PWM carrier signal are compared in amplitude. An ultrasonic sound reproduction method characterized by outputting a PWM signal as a drive signal for an ultrasonic transducer.

（２）請求項２記載の発明は、再生すべき音声信号の上限周波数の２倍以上の周波数であって超音波音響再生の搬送波となる超音波搬送波信号を生成する超音波搬送波信号生成部と、前記音声信号と前記超音波搬送波信号とを加算する加算部と、前記超音波搬送波信号の２倍の周波数の三角波あるいは鋸波のＰＷＭ搬送波信号を生成するＰＷＭ搬送波信号生成部と、前記加算部の出力信号と前記ＰＷＭ搬送波信号とを振幅比較してＰＷＭ信号を生成する比較部と、前記比較部で生成されたＰＷＭ信号に基づいて超音波振動子の駆動信号を生成する駆動部と、を備えたことを特徴とする超音波音響再生装置である。   (2) The invention according to claim 2 is an ultrasonic carrier signal generation unit that generates an ultrasonic carrier signal having a frequency that is at least twice the upper limit frequency of the audio signal to be reproduced and that is a carrier wave for ultrasonic acoustic reproduction. An adder that adds the audio signal and the ultrasonic carrier signal; a PWM carrier signal generator that generates a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal; and the adder A comparator that generates a PWM signal by comparing the amplitude of the output signal and the PWM carrier signal, and a drive unit that generates a drive signal for the ultrasonic transducer based on the PWM signal generated by the comparator. It is the ultrasonic sound reproducing device characterized by having provided.

（３）請求項３記載の発明は、再生すべき音声信号の上限周波数の２倍以上の周波数であって超音波音響再生の搬送波となる超音波搬送波信号を生成する超音波搬送波信号生成部と、前記音声信号と前記超音波搬送波信号とを加算する加算部と、前記超音波搬送波信号の２倍の周波数の三角波あるいは鋸波のＰＷＭ搬送波信号を生成するＰＷＭ搬送波信号生成部と、前記加算部の出力信号と前記ＰＷＭ搬送波信号とを振幅比較してＰＷＭ信号を生成する比較部と、前記比較部で生成されたＰＷＭ信号に基づいて超音波振動子の駆動信号を生成する駆動部と、前記駆動部で生成された駆動信号により超音波振動を発生させる超音波振動子と、を備えたことを特徴とする超音波音響再生装置である。   (3) An invention according to claim 3 is an ultrasonic carrier signal generation unit that generates an ultrasonic carrier signal having a frequency that is at least twice the upper limit frequency of an audio signal to be reproduced and that serves as a carrier wave for ultrasonic acoustic reproduction. An adder that adds the audio signal and the ultrasonic carrier signal; a PWM carrier signal generator that generates a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal; and the adder A comparator for generating a PWM signal by comparing the amplitude of the output signal and the PWM carrier wave signal, a drive unit for generating a drive signal for an ultrasonic transducer based on the PWM signal generated by the comparator, and An ultrasonic sound reproducing apparatus comprising: an ultrasonic transducer that generates ultrasonic vibrations based on a drive signal generated by a drive unit.

（４）請求項４記載の発明は、前記超音波搬送波信号の振幅は前記音声信号の最大振幅と等しく、前記ＰＷＭ搬送波信号の振幅は前記超音波搬送波信号の振幅の２倍である、ことを特徴とする請求項２−３記載の超音波音響再生装置である。   (4) In the invention according to claim 4, the amplitude of the ultrasonic carrier signal is equal to the maximum amplitude of the audio signal, and the amplitude of the PWM carrier signal is twice the amplitude of the ultrasonic carrier signal. The ultrasonic sound reproducing apparatus according to claim 2, wherein

（５）請求項５記載の発明は、前記駆動部は、スイッチング回路により構成される、ことを特徴とする請求項２−４のいずれか一項に記載の超音波音響再生装置である。
（６）請求項６記載の発明は、前記ＰＷＭ搬送波信号は、前記超音波搬送波信号に同期した状態である、ことを特徴とする請求項２−５のいずれか一項に記載の超音波音響再生装置である。 (5) The invention according to claim 5 is the ultrasonic sound reproducing device according to any one of claims 2 to 4, wherein the driving unit is configured by a switching circuit.
(6) The ultrasonic acoustic signal according to any one of claims 2 to 5, wherein the PWM carrier wave signal is in a state of being synchronized with the ultrasonic carrier wave signal. It is a playback device.

本発明によれば、以下のような効果が得られる。
この発明では、音声信号の上限周波数の２倍以上の周波数の超音波搬送波信号を生成して音声信号と加算し、超音波搬送波信号の２倍の周波数の三角波あるいは鋸波のＰＷＭ搬送波信号を生成し、加算信号とＰＷＭ搬送波信号とを振幅比較してＰＷＭ信号を出力する。 According to the present invention, the following effects can be obtained.
In this invention, an ultrasonic carrier signal having a frequency twice or more of the upper limit frequency of the audio signal is generated and added to the audio signal to generate a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal. Then, the amplitude of the addition signal and the PWM carrier wave signal is compared, and a PWM signal is output.

これにより、音声信号と超音波搬送波信号とが加算された状態の加算信号がパルス幅変調された状態のＰＷＭ信号として出力される。よって、このＰＷＭ信号を超音波振動子に供給することで、超音波音響再生がなされる。すなわち、乗算器などを用いた変調回路を使用せずに、簡素な回路構成で超音波音響再生が可能になる。また、ＰＷＭ信号はスイッチングによるＤ級増幅が可能であるため、超音波振動子を駆動する駆動回路を簡素化すると共に高効率化することも可能になる。   As a result, the addition signal in a state where the audio signal and the ultrasonic carrier signal are added is output as a PWM signal in a pulse width modulated state. Therefore, ultrasonic sound reproduction is performed by supplying this PWM signal to the ultrasonic transducer. That is, ultrasonic acoustic reproduction can be performed with a simple circuit configuration without using a modulation circuit using a multiplier or the like. In addition, since the PWM signal can be class D amplified by switching, the drive circuit for driving the ultrasonic transducer can be simplified and the efficiency can be increased.

本発明の実施形態の超音波音響再生装置の構成を示す構成図である。It is a block diagram which shows the structure of the ultrasonic sound reproducing apparatus of embodiment of this invention. 本発明の実施形態の超音波音響再生装置の動作を示すフローチャートである。It is a flowchart which shows operation | movement of the ultrasonic sound reproducing apparatus of embodiment of this invention. 本発明の実施形態の超音波音響再生装置の特性を示す特性図である。It is a characteristic view which shows the characteristic of the ultrasonic sound reproducing apparatus of embodiment of this invention. 本発明の実施形態の超音波音響再生装置の特性を示す特性図である。It is a characteristic view which shows the characteristic of the ultrasonic sound reproducing apparatus of embodiment of this invention. 本発明の実施形態の超音波音響再生装置の特性を示す特性図である。It is a characteristic view which shows the characteristic of the ultrasonic sound reproducing apparatus of embodiment of this invention. 超音波音響再生装置の周波数特性を示す特性図である。It is a characteristic view which shows the frequency characteristic of an ultrasonic acoustic reproduction apparatus. 従来の超音波音響再生装置の構成を示す構成図である。It is a block diagram which shows the structure of the conventional ultrasonic sound reproducing | regenerating apparatus. 従来の超音波音響再生装置の構成を示す構成図である。It is a block diagram which shows the structure of the conventional ultrasonic sound reproducing | regenerating apparatus.

以下、図面を参照して本発明を実施するための最良の形態（以下、実施形態）を詳細に説明する。
〈第一実施形態〉
図１は本発明の第一実施形態の超音波音響再生装置１０の主要部の構成を模式的に示す説明図である。なお、この超音波音響再生装置１０により、超音波音響再生方法が実行される。 The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below in detail with reference to the drawings.
<First embodiment>
FIG. 1 is an explanatory view schematically showing the configuration of the main part of the ultrasonic sound reproducing apparatus 10 according to the first embodiment of the present invention. Note that the ultrasonic sound reproducing method is executed by the ultrasonic sound reproducing device 10.

音声信号源１１は、超音波音響再生によって再生すべき音声信号を生成する信号源である。ここで、音声信号とは、可聴信号を意味している。
超音波搬送波信号生成部１２は、再生すべき音声信号の上限周波数の２倍以上の周波数（ｆc_us）であって超音波音響再生の搬送波となる超音波搬送波信号を生成する。 The audio signal source 11 is a signal source that generates an audio signal to be reproduced by ultrasonic acoustic reproduction. Here, the audio signal means an audible signal.
The ultrasonic carrier signal generation unit 12 generates an ultrasonic carrier signal that has a frequency (fc_us) that is at least twice the upper limit frequency of the audio signal to be reproduced and serves as a carrier wave for ultrasonic acoustic reproduction.

加算部１３は、音声信号と超音波搬送波信号とを加算する。
ＰＷＭ搬送波信号生成部１４は、超音波搬送波信号の２倍の周波数（ｆc_pwm＝２・ｆc_us）であって、超音波搬送波信号に同期した三角波あるいは鋸波のＰＷＭ搬送波信号を生成する。ここで、同期しているとは、周波数２倍の関係について、１Ｈｚ未満であってもずれることなく、一致した状態が保たれていることを言う。 The adder 13 adds the audio signal and the ultrasonic carrier signal.
The PWM carrier signal generation unit 14 generates a triangular or sawtooth PWM carrier signal having a frequency (fc_pwm = 2 · fc_us) twice that of the ultrasonic carrier signal and synchronized with the ultrasonic carrier signal. Here, “synchronized” means that the same state is maintained without deviation even when the frequency is less than 1 Hz with respect to the frequency doubled relationship.

なお、超音波搬送波信号の振幅は、音声信号の最大振幅と等しくすることが望ましく、さらに、ＰＷＭ搬送波信号の振幅は超音波搬送波信号の振幅の２倍であることが、歪み無く、効率のよい状態で超音波音響再生を行うために望ましい。   It is desirable that the amplitude of the ultrasonic carrier signal is equal to the maximum amplitude of the audio signal, and that the amplitude of the PWM carrier signal is twice that of the ultrasonic carrier signal, which is efficient without distortion. It is desirable to perform ultrasonic acoustic reproduction in a state.

比較部１５は、加算部１３の出力信号（音声信号と超音波搬送波信号とが加算された信号）と、ＰＷＭ搬送波信号とを振幅比較して、ＰＷＭ信号を生成する。
駆動部１６は、比較部１５で生成されたＰＷＭ信号に基づいてスイッチングなどのＤ級増幅を行って、超音波振動子の駆動信号を生成する。 The comparison unit 15 compares the amplitude of the output signal of the addition unit 13 (a signal obtained by adding the audio signal and the ultrasonic carrier signal) and the PWM carrier signal to generate a PWM signal.
The drive unit 16 performs class D amplification such as switching based on the PWM signal generated by the comparison unit 15 to generate a drive signal for the ultrasonic transducer.

フィルタ部１８は、超音波搬送波周波数近傍の周波数の信号を通過させて、他の周波数成分を減衰させるローパスフィルタあるいはバンドパスフィルタなどにより構成されたフィルタ部である。なお、このフィルタ部１８は、駆動部１６に内蔵させることや、省略することも可能である。   The filter unit 18 is a filter unit configured by a low-pass filter or a band-pass filter that passes a signal having a frequency near the ultrasonic carrier frequency and attenuates other frequency components. The filter unit 18 can be built in the drive unit 16 or omitted.

超音波振動子２０は、駆動部１６で生成された駆動信号により超音波振動を発生させる振動子などの電気音響変換素子である。
すなわち、以上の超音波音響再生装置１０では、まず、音声信号源１１から音声信号ｆa（図３（ａ）参照）が入力される（図２中のステップＳ２０）。この音声信号としては、一般的な可聴信号、すなわち、オーディオ信号であり、たとえば、上限を２０ｋＨｚとする。 The ultrasonic transducer 20 is an electroacoustic transducer such as a transducer that generates ultrasonic vibrations using a drive signal generated by the drive unit 16.
That is, in the ultrasonic acoustic reproduction apparatus 10 described above, first, the audio signal fa (see FIG. 3A) is input from the audio signal source 11 (step S20 in FIG. 2). The audio signal is a general audible signal, that is, an audio signal, and has an upper limit of 20 kHz, for example.

ここで、音声信号の上限周波数の２倍以上の周波数の超音波搬送波信号ｆc_us（図３（ｂ）参照）を超音波搬送波信号生成部１２にて生成する（図２中のステップＳ２０１）。
この超音波搬送波信号としては、音声信号の上限周波数の２倍以上の周波数であり、かつ、超音波振動子２０において効率よく振動できる周波数を選択することが望ましい。たとえば、ここでは、４０ｋＨｚとする。 Here, an ultrasonic carrier signal fc_us (see FIG. 3B) having a frequency twice or more the upper limit frequency of the audio signal is generated by the ultrasonic carrier signal generator 12 (step S201 in FIG. 2).
As this ultrasonic carrier wave signal, it is desirable to select a frequency that is at least twice the upper limit frequency of the audio signal and that can vibrate efficiently in the ultrasonic transducer 20. For example, it is 40 kHz here.

そして、この超音波搬送波信号と音声信号とを加算部１３で加算する（図２中のステップＳ２０２）。ここでは、乗算器を用いた振幅変調などではなく、単純な加算、あるいは、重畳で良い。   Then, the ultrasonic carrier signal and the audio signal are added by the adding unit 13 (step S202 in FIG. 2). Here, simple addition or superposition may be used instead of amplitude modulation using a multiplier.

一方、ＰＷＭ搬送波信号生成部１４では、以上の超音波搬送波信号の２倍の周波数であって、該超音波搬送波信号に同期した三角波あるいは鋸波のＰＷＭ搬送波信号ｆc_pwm（図３（ｃ）参照）を生成する（図２中のステップＳ２０３）。この場合、以上の超音波搬送波信号が４０ｋＨｚであれば、ＰＷＭ搬送波信号は８０ｋＨｚとする。ここで、超音波搬送波信号とＰＷＭ搬送波信号とを同期させるためには、超音波搬送波信号とＰＷＭ搬送波信号とを、共通の発振器の信号から、逓倍や分周などにより生成することが望ましい。このように、共通の発振器からの信号を用いて、逓倍あるいは分周を用いることで、仮に、周波数のずれが生じたとしても、上述した、周波数２倍かつ同期状態の条件が崩れることがなくなる。   On the other hand, the PWM carrier signal generation unit 14 has a frequency twice that of the above ultrasonic carrier signal and a triangular or sawtooth PWM carrier signal fc_pwm synchronized with the ultrasonic carrier signal (see FIG. 3C). Is generated (step S203 in FIG. 2). In this case, if the above ultrasonic carrier signal is 40 kHz, the PWM carrier signal is 80 kHz. Here, in order to synchronize the ultrasonic carrier signal and the PWM carrier signal, it is desirable to generate the ultrasonic carrier signal and the PWM carrier signal from a common oscillator signal by multiplication or division. In this way, by using multiplication or frequency division using a signal from a common oscillator, even if a frequency shift occurs, the above-described double frequency and synchronized condition conditions are not lost. .

また、比較部１５は、加算部１３の出力信号（音声信号と超音波搬送波信号とが加算された信号）と、ＰＷＭ搬送波信号とを振幅比較して、ＰＷＭ信号を生成する。このＰＷＭ信号は、ＰＷＭ搬送波信号が加算部１３の出力信号によりパルス幅変調された信号になっている。   The comparison unit 15 compares the amplitude of the output signal of the addition unit 13 (a signal obtained by adding the audio signal and the ultrasonic carrier signal) and the PWM carrier signal, and generates a PWM signal. This PWM signal is a signal obtained by subjecting the PWM carrier signal to pulse width modulation by the output signal of the adder 13.

この比較部１５で得られたＰＷＭ信号の周波数成分は、図３（ｄ）のように、超音波搬送波信号ｆc_usを中心に、ｆc_us±ｆaの成分が含まれる。また、ｆc_pwmを中心に、−２ｆa，−ｆa，＋ｆa，＋２ｆa，の成分が含まれる。また、詳細実験結果を図４に示すが、ＰＷＭ信号が矩形波であるため、ｆc_usの３次高調波、４次高調波、なども含まれる。   The frequency component of the PWM signal obtained by the comparison unit 15 includes a component of fc_us ± fa centering on the ultrasonic carrier signal fc_us as shown in FIG. Further, components of -2fa, -fa, + fa, + 2fa are included with fc_pwm as the center. Further, the detailed experimental results are shown in FIG. 4, and since the PWM signal is a rectangular wave, the third harmonic, the fourth harmonic, etc. of fc_us are also included.

ここで、ＰＷＭ信号の周波数成分のうちの、超音波搬送波信号ｆc_usを中心に、ｆc_us±ｆaの成分は、図６に示した振幅変調出力と同じ周波数成分である。すなわち、図７や図８のような乗算器による変調器を使用することなく、変調出力を得ることができる。   Here, among the frequency components of the PWM signal, the component of fc_us ± fa centering on the ultrasonic carrier signal fc_us is the same frequency component as the amplitude modulation output shown in FIG. That is, a modulated output can be obtained without using a modulator by a multiplier as shown in FIGS.

そして、このＰＷＭ信号はＯＮ／ＯＦＦの繰り返しであるため、駆動部１６でＤ級増幅して、超音波振動子２０用の駆動信号を生成する（図２中のステップＳ２０５）。このＰＷＭ信号から生成した駆動信号を超音波振動子２０に供給することで、超音波音響再生がなされる。   Since this PWM signal is ON / OFF repetition, the drive unit 16 amplifies the class D to generate a drive signal for the ultrasonic transducer 20 (step S205 in FIG. 2). By supplying a drive signal generated from the PWM signal to the ultrasonic transducer 20, ultrasonic acoustic reproduction is performed.

すなわち、本実施形態の手法によれば、乗算器などを用いた変調回路を使用せずに、簡素な回路構成で超音波音響再生が可能になる。
また、ＰＷＭ信号はスイッチングによるＤ級増幅が可能であるため、Ａ級あるいはＢ級増幅が必要であった従来の装置に比較すると、超音波振動子２０を駆動する駆動部１６を簡素化すると共に高効率化することも可能になる。このため、超音波振動子２０を多数配設して、大電力の超音波音響再生を行う場合であっても、実現が容易になる。 That is, according to the method of the present embodiment, it is possible to reproduce ultrasonic sound with a simple circuit configuration without using a modulation circuit using a multiplier or the like.
In addition, since the PWM signal can be class D amplified by switching, the drive unit 16 for driving the ultrasonic transducer 20 is simplified as compared with the conventional device that requires class A or class B amplification. High efficiency can also be achieved. For this reason, even when a large number of ultrasonic transducers 20 are arranged to perform high-power ultrasonic sound reproduction, the realization becomes easy.

なお、本実施形態では、ＰＷＭ搬送波信号は、超音波搬送波信号の２倍の周波数（ｆc_pwm＝２・ｆc_us）であって、超音波搬送波信号に同期した信号であることが条件であったが、この点については、次のように説明できる。   In the present embodiment, the PWM carrier wave signal has a frequency (fc_pwm = 2 · fc_us) that is twice the frequency of the ultrasonic carrier wave signal and is a signal synchronized with the ultrasonic carrier wave signal. This can be explained as follows.

本実施形態の方式において、ＰＷＭ搬送波信号ｆc_pwmは、離散的信号処理のサンプリング周波数ｆｓにあたる。信号をサンプリング周波数ｆｓ＝８０ｋＨｚでサンプリングした場合、４０ｋＨｚ以下の成分までは正確に再現できるが、４０ｋＨｚ以上の成分はエイリアシングを起こして４０ｋＨｚ以下の帯域に像となってあらわれる。このようになると、もとの信号とエイリアシングによる像とを分離することができない。このようにエイリアシングによる像を分離できない現象は望ましくない状態であるため、従来はフィルタリングなどによってエイリアシングが発生しないようにしていた。しかし、本件出願の発明者は、エイリアシングを特定の状況において積極的に利用することで、超音波音響再生に活用できることを見いだした。   In the system of this embodiment, the PWM carrier signal fc_pwm corresponds to the sampling frequency fs of discrete signal processing. When the signal is sampled at the sampling frequency fs = 80 kHz, components up to 40 kHz can be accurately reproduced, but components above 40 kHz cause aliasing and appear as an image in a band of 40 kHz or less. In this case, the original signal and the aliased image cannot be separated. Since the phenomenon in which an image cannot be separated due to aliasing in this way is an undesirable state, aliasing has conventionally been prevented by filtering or the like. However, the inventors of the present application have found that aliasing can be used for ultrasonic sound reproduction by actively using aliasing in a specific situation.

たとえば、４０ｋＨｚの正弦波信号と１ｋＨｚの正弦波信号とからなる、以下の数式で示される信号を想定する。
sin(2π・1000・t)＋sin(2π・40000・t)，
この信号を時刻ｔで微分すると、角速度、すなわち周波数が求まる。
d／dt・｛sin(2π・1000・t)＋sin(2π・40000・t)｝
＝2π・1000・cos(2π・1000・t)＋2π・40000・cos(2π・40000・t)，
この信号をｆｓ＝８０ｋＨｚでサンプリングした場合には、４１ｋＨｚの成分がｆｓの１／２にかかり、４０ｋＨｚ以下の領域に折り返されて分離できなくなるので、４０ｋＨｚを中心に±１ｋＨｚの信号成分が現れる。このように、ｆｓ＝８０ｋＨｚでＰＷＭ変調することにより、４０ｋＨｚの搬送波で振幅変調した場合と同じスペクトラムの信号が得られる。 For example, assume a signal represented by the following formula, which is composed of a 40 kHz sine wave signal and a 1 kHz sine wave signal.
sin (2π · 1000 · t) + sin (2π · 40000 · t),
Differentiating this signal at time t gives the angular velocity, that is, the frequency.
d / dt · {sin (2π · 1000 · t) + sin (2π · 40000 · t)}
= 2π · 1000 · cos (2π · 1000 · t) + 2π · 40000 · cos (2π · 40000 · t),
When this signal is sampled at fs = 80 kHz, a component of 41 kHz is applied to 1/2 of fs and is folded back into a region of 40 kHz or less and cannot be separated, so that a signal component of ± 1 kHz appears around 40 kHz. Thus, by performing PWM modulation at fs = 80 kHz, a signal having the same spectrum as that obtained when amplitude modulation is performed with a 40 kHz carrier wave can be obtained.

いっぽう、以上の４０ｋＨｚの正弦波信号と１ｋＨｚの正弦波信号とからなる、以上の数式で示される信号を、ｆｓ＝１６０ｋＨｚでサンプリングした場合には、各成分はｆｓの１／２より小さいため、何ら問題なく分離することができる。この場合には、以上ｆｓ＝８０ｋＨｚの場合のような、振幅変調と同じ周波数成分の信号は得られないことになる（図５参照）。   On the other hand, when the signal represented by the above formula consisting of the above 40 kHz sine wave signal and 1 kHz sine wave signal is sampled at fs = 160 kHz, each component is smaller than 1/2 of fs. It can be separated without any problems. In this case, a signal having the same frequency component as that of amplitude modulation as in the case of fs = 80 kHz cannot be obtained (see FIG. 5).

このように、超音波搬送波信号の２倍の周波数のＰＷＭ搬送波信号の条件を満たすことで、ＰＷＭ信号中に、音声信号で変調された超音波搬送波信号の成分が含まれることが判明した。また、超音波搬送波信号と同期がとれた状態のＰＷＭ搬送波信号という条件を満たすことで、ＰＷＭ信号中に含まれる、音声信号で変調された超音波搬送波信号の成分に、余分なビート成分が含まれないことが判明した。   Thus, it has been found that by satisfying the condition of the PWM carrier signal having a frequency twice that of the ultrasonic carrier signal, the component of the ultrasonic carrier signal modulated by the audio signal is included in the PWM signal. In addition, by satisfying the condition of the PWM carrier wave signal in synchronization with the ultrasonic carrier wave signal, an extra beat component is included in the component of the ultrasonic carrier wave signal modulated by the audio signal contained in the PWM signal. It turned out not to be.

したがって、本実施形態の条件、すなわち、超音波搬送波信号の２倍の周波数のＰＷＭ搬送波信号、超音波搬送波信号と同期したＰＷＭ搬送波信号、という条件を外れることで、意図している超音波音響再生が行えなくなることが明らかになった。すなわち、本実施形態の条件は、臨界的に意義のある条件であることが明らかである。   Therefore, by deviating from the conditions of the present embodiment, that is, the PWM carrier signal having a frequency twice that of the ultrasonic carrier signal and the PWM carrier signal synchronized with the ultrasonic carrier signal, the intended ultrasonic sound reproduction is performed. It became clear that can not be done. That is, it is clear that the conditions of this embodiment are critically significant conditions.

以上詳細に説明したように、音声信号の上限周波数の２倍以上の周波数の超音波搬送波信号を生成して音声信号と加算し、超音波搬送波信号の２倍の周波数であって、超音波搬送波信号と同期した三角波あるいは鋸波のＰＷＭ搬送波信号を生成し、加算信号とＰＷＭ搬送波信号とを振幅比較してＰＷＭ信号を出力することにより、音声信号と超音波搬送波信号とが加算された状態の加算信号がパルス幅変調された状態のＰＷＭ信号として出力される。よって、このＰＷＭ信号を超音波振動子に供給することで、超音波音響再生がなされる。すなわち、乗算器などを用いた変調回路を使用せずに、簡素な回路構成で超音波音響再生が可能になる。また、ＰＷＭ信号はスイッチングによるＤ級増幅が可能であるため、超音波振動子を駆動する駆動回路を簡素化すると共に高効率化することも可能になる。   As described in detail above, an ultrasonic carrier signal having a frequency that is twice or more the upper limit frequency of the audio signal is generated and added to the audio signal, and the ultrasonic carrier signal has a frequency twice that of the ultrasonic carrier signal. A triangular wave or sawtooth wave PWM carrier signal synchronized with the signal is generated, the amplitude of the sum signal and the PWM carrier signal is compared, and the PWM signal is output, so that the audio signal and the ultrasonic carrier signal are added. The addition signal is output as a PWM signal in a state of pulse width modulation. Therefore, ultrasonic sound reproduction is performed by supplying this PWM signal to the ultrasonic transducer. That is, ultrasonic acoustic reproduction can be performed with a simple circuit configuration without using a modulation circuit using a multiplier or the like. In addition, since the PWM signal can be class D amplified by switching, the drive circuit for driving the ultrasonic transducer can be simplified and the efficiency can be increased.

その他の実施形態:
上記実施形態の説明に用いた具体的数値、超音波搬送波信号の４０ｋＨｚ、ＰＷＭ搬送波信号の８０ｋＨｚは一例であり、他の周波数とすることも可能である。すなわち、適用する超音波音響再生装置において適した周波数を用いることが可能である。 Other embodiments:
The specific numerical values, 40 kHz of the ultrasonic carrier signal, and 80 kHz of the PWM carrier signal used in the description of the above embodiment are examples, and other frequencies may be used. That is, it is possible to use a frequency suitable for the applied ultrasonic sound reproducing apparatus.

１０ 超音波音響再生装置
１１ 音声信号源
１２ 超音波搬送波生成部
１３ 加算部
１４ ＰＷＭ搬送波信号生成部
１５ 比較部
１６ 駆動部
１８ フィルタ部
２０ 超音波振動子 DESCRIPTION OF SYMBOLS 10 Ultrasonic sound reproduction apparatus 11 Audio | voice signal source 12 Ultrasonic carrier wave generation part 13 Addition part 14 PWM carrier wave signal generation part 15 Comparison part 16 Drive part 18 Filter part 20 Ultrasonic transducer

Claims (6)

再生すべき音声信号の上限周波数の２倍以上の周波数であって超音波音響再生の搬送波となる超音波搬送波信号を生成し、
前記音声信号と前記超音波搬送波信号とを加算し、
前記超音波搬送波信号の２倍の周波数の三角波あるいは鋸波のＰＷＭ搬送波信号を生成し、
前記加算部の出力信号と前記ＰＷＭ搬送波信号とを振幅比較して生成したＰＷＭ信号を超音波振動子の駆動信号として出力する、
ことを特徴とする超音波音響再生方法。 Generating an ultrasonic carrier signal having a frequency that is at least twice the upper limit frequency of the audio signal to be reproduced and serving as a carrier for ultrasonic acoustic reproduction;
Adding the audio signal and the ultrasonic carrier signal;
Generating a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal;
A PWM signal generated by comparing the amplitude of the output signal of the adding unit and the PWM carrier wave signal is output as a drive signal of the ultrasonic transducer;
An ultrasonic sound reproducing method characterized by the above. 再生すべき音声信号の上限周波数の２倍以上の周波数であって超音波音響再生の搬送波となる超音波搬送波信号を生成する超音波搬送波信号生成部と、
前記音声信号と前記超音波搬送波信号とを加算する加算部と、
前記超音波搬送波信号の２倍の周波数の三角波あるいは鋸波のＰＷＭ搬送波信号を生成するＰＷＭ搬送波信号生成部と、
前記加算部の出力信号と前記ＰＷＭ搬送波信号とを振幅比較してＰＷＭ信号を生成する比較部と、
前記比較部で生成されたＰＷＭ信号に基づいて超音波振動子の駆動信号を生成する駆動部と、
を備えたことを特徴とする超音波音響再生装置。 An ultrasonic carrier signal generator that generates an ultrasonic carrier signal that is a frequency that is at least twice the upper limit frequency of the audio signal to be reproduced and that serves as a carrier for ultrasonic acoustic reproduction;
An adder for adding the audio signal and the ultrasonic carrier signal;
A PWM carrier signal generator for generating a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal;
A comparison unit that generates a PWM signal by performing amplitude comparison between the output signal of the addition unit and the PWM carrier wave signal;
A drive unit that generates a drive signal of the ultrasonic transducer based on the PWM signal generated by the comparison unit;
An ultrasonic sound reproducing apparatus comprising: 再生すべき音声信号の上限周波数の２倍以上の周波数であって超音波音響再生の搬送波となる超音波搬送波信号を生成する超音波搬送波信号生成部と、
前記音声信号と前記超音波搬送波信号とを加算する加算部と、
前記超音波搬送波信号の２倍の周波数の三角波あるいは鋸波のＰＷＭ搬送波信号を生成するＰＷＭ搬送波信号生成部と、
前記加算部の出力信号と前記ＰＷＭ搬送波信号とを振幅比較してＰＷＭ信号を生成する比較部と、
前記比較部で生成されたＰＷＭ信号に基づいて超音波振動子の駆動信号を生成する駆動部と、
前記駆動部で生成された駆動信号により超音波振動を発生させる超音波振動子と、
を備えたことを特徴とする超音波音響再生装置。 An ultrasonic carrier signal generator that generates an ultrasonic carrier signal that is a frequency that is at least twice the upper limit frequency of the audio signal to be reproduced and that serves as a carrier for ultrasonic acoustic reproduction;
An adder for adding the audio signal and the ultrasonic carrier signal;
A PWM carrier signal generator for generating a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal;
A comparison unit that generates a PWM signal by performing amplitude comparison between the output signal of the addition unit and the PWM carrier wave signal;
A drive unit that generates a drive signal of the ultrasonic transducer based on the PWM signal generated by the comparison unit;
An ultrasonic transducer that generates ultrasonic vibrations by a drive signal generated by the drive unit;
An ultrasonic sound reproducing apparatus comprising: 前記超音波搬送波信号の振幅は前記音声信号の最大振幅と等しく、
前記ＰＷＭ搬送波信号の振幅は前記超音波搬送波信号の振幅の２倍である、
ことを特徴とする請求項２−３記載の超音波音響再生装置。 The amplitude of the ultrasonic carrier signal is equal to the maximum amplitude of the audio signal;
The amplitude of the PWM carrier signal is twice the amplitude of the ultrasonic carrier signal.
The ultrasonic sound reproducing device according to claim 2. 前記駆動部は、スイッチング回路により構成される、
ことを特徴とする請求項２−４のいずれか一項に記載の超音波音響再生装置。 The driving unit is configured by a switching circuit.
The ultrasonic sound reproducing device according to any one of claims 2 to 4, wherein 前記ＰＷＭ搬送波信号は、前記超音波搬送波信号に同期した状態である、
ことを特徴とする請求項２−５のいずれか一項に記載の超音波音響再生装置。 The PWM carrier signal is in a state synchronized with the ultrasonic carrier signal.
The ultrasonic sound reproducing device according to any one of claims 2 to 5, wherein
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