WO2011024329A1 - Ultrasonic sound reproduction method and ultrasonic sound reproduction device - Google Patents

Ultrasonic sound reproduction method and ultrasonic sound reproduction device Download PDF

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WO2011024329A1
WO2011024329A1 PCT/JP2009/071794 JP2009071794W WO2011024329A1 WO 2011024329 A1 WO2011024329 A1 WO 2011024329A1 JP 2009071794 W JP2009071794 W JP 2009071794W WO 2011024329 A1 WO2011024329 A1 WO 2011024329A1
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signal
ultrasonic
pwm
carrier signal
frequency
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French (fr)
Japanese (ja)
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利根川寛
佐藤宏
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フォスター電機株式会社
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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

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  • the present invention relates to an ultrasonic acoustic reproduction method and an ultrasonic acoustic reproduction apparatus, and more particularly to a technique that enables efficient ultrasonic reproduction with a simple circuit configuration.
  • 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 having a sharp directivity toward a narrow range. Sound reproduction is realized.
  • the modulation circuit used as the ultrasonic sound reproducing device first, as shown in FIG. 8, a DC component is superimposed on the audio signal from the audio signal source 1 by the DC superimposing unit 2. Then, the ultrasonic carrier signal Sc_us from the carrier generation unit 3 is modulated by the multiplication unit 4 with the DC superimposed audio signal. With such an ultrasonic sound reproducing apparatus, an amplitude-modulated output having the frequencies fc (kHz) and fc ⁇ fa (kHz) shown in FIG. 6 can be obtained.
  • a modulation circuit based on a Weaver SSB circuit having oscillators 3a and 3b, phase shifters 5a and 5b, multipliers 4a, 4b, 4c and 4d, and LPFs 6a and 6b may be used. is there.
  • FIG. 9 since four multipliers 4a, 4b, 4c, and 4d are required, there is a problem that the circuit configuration becomes complicated.
  • 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.
  • the invention of the ultrasonic sound reproduction method is as follows: 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 to generate a triangular or sawtooth PWM carrier signal that is twice the frequency of the ultrasonic carrier signal and synchronized with the ultrasonic carrier signal; A PWM signal generated by comparing the amplitude of the output signal of the adder and the PWM carrier wave signal is output as a drive signal for the ultrasonic transducer.
  • the invention of the ultrasonic sound reproducing device 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 and synchronized with 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; Is provided.
  • an ultrasonic carrier signal having a frequency twice or more the upper limit frequency of the audio signal is generated by the ultrasonic carrier signal generator. Then, the audio signal and the ultrasonic carrier wave signal are added by the adding unit.
  • a PWM carrier signal generating unit generates a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal and synchronized with the ultrasonic carrier signal.
  • the output signal of the adder and the PWM carrier signal are compared in amplitude by the comparator, thereby generating a PWM signal. Furthermore, a drive signal for the ultrasonic transducer is generated by the drive unit based on the PWM signal.
  • 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.
  • ultrasonic acoustic reproduction can be performed with a simple circuit configuration without using a modulation circuit using a multiplier or the like.
  • the PWM signal can be amplified by class D by a switching circuit, the drive circuit for driving the ultrasonic transducer can be simplified and the efficiency can be increased.
  • FIG. 1 is an explanatory view schematically showing a configuration of a main part of the ultrasonic sound reproducing device 10 according to the first embodiment of the present invention. Note that the ultrasonic sound reproducing method is executed by operating the ultrasonic sound reproducing device 10.
  • the audio signal source 11 is a signal source that generates an audio signal Sa to be reproduced by ultrasonic acoustic reproduction.
  • the audio signal Sa means an audible signal existing in the audible frequency range.
  • the audio signal source 11 does not have to be built in the ultrasonic reproduction apparatus 10, and may be various external audio apparatuses, microphones, or the like.
  • an audio circuit that receives an audio signal from an external audio device or a microphone and amplifies it to a predetermined level may be provided.
  • the ultrasonic carrier signal generator 12 generates an ultrasonic carrier signal Sc_us having a frequency fc_us that is a frequency that is at least twice the upper limit frequency fa_max of the audio signal Sa to be reproduced and is a carrier wave for ultrasonic acoustic reproduction.
  • the adder 13 adds the audio signal Sa and the ultrasonic carrier signal Sc_us.
  • synchronized means that the state of 2 ⁇ fc_us coincides with fc_pwm is continuously maintained without shifting even if the frequency is less than 1 Hz with respect to the frequency doubling relationship.
  • the amplitude of the ultrasonic carrier signal Sc_us is desirably equal to the maximum amplitude of the audio signal Sa, and is desirable for performing ultrasonic acoustic reproduction in an efficient state without distortion. Further, it is more desirable that the amplitude of the PWM carrier signal Sc_pwm is twice that of the ultrasonic carrier signal Sc_us in order to perform ultrasonic acoustic reproduction in an efficient state without distortion.
  • the comparison unit 15 compares the amplitude of the output signal of the addition unit 13 (a signal obtained by adding the audio signal Sa and the ultrasonic carrier signal Sc_us) and the PWM carrier signal Sc_pwm, and generates a PWM signal S_pwm.
  • the drive unit 16 Based on the PWM signal S_pwm generated by the comparison unit 15, the drive unit 16 performs class D amplification using a switching operation of a switching element and generates a drive signal Sd for driving the ultrasonic transducer. .
  • the filter unit 18 is a filter unit including a low-pass filter or a band-pass filter that passes a signal having a frequency near the ultrasonic carrier frequency fc_us and attenuates other frequency components. It should be noted that the filter unit 18 can be modified such as being built in the drive unit 16 or omitted.
  • the ultrasonic transducer 20 is an electroacoustic transducer such as a transducer that generates ultrasonic vibrations based on the drive signal Sd generated by the drive unit 16.
  • an audio signal Sa having a frequency fa (see FIG. 3A) is input from the audio signal source 11 (step S20 in FIG. 2).
  • the audio signal Sa is a general audible signal, that is, an audio signal.
  • the upper limit frequency fa_max of the audio signal is set to 20 kHz, for example.
  • the ultrasonic carrier signal Sc_us (see FIG. 3B) of the ultrasonic carrier frequency fc_us selected to be at least twice the upper limit frequency fa_max of the audio signal Sa is generated by the ultrasonic carrier signal generator 12 (see FIG. 3B). Step S201 in FIG.
  • the ultrasonic carrier frequency fc_us it is desirable to select a frequency that is at least twice the upper limit frequency fa_max of the audio signal and that can vibrate the ultrasonic transducer 20 efficiently.
  • the ultrasonic carrier frequency fc_us is set to 40 kHz.
  • the ultrasonic carrier signal Sc_us and the audio signal Sa are added by the adder 13 (step S202 in FIG. 2).
  • the adder 13 instead of amplitude modulation using a multiplier, simple addition or superposition may be performed.
  • the PWM carrier signal generation unit 14 has a frequency twice that of the above ultrasonic carrier signal Sc_us and is synchronized with the ultrasonic carrier signal Sc_us, and is a triangular wave or sawtooth PWM carrier signal Sc_pwm (FIG. 3). (See (c)) is generated (step S203 in FIG. 2).
  • the PWM carrier frequency fc_pwm of the PWM carrier signal Sc_pwm is set to 80 kHz.
  • the ultrasonic carrier signal Sc_us and the PWM carrier signal Sc_pwm are multiplied or divided by using a signal generated by a common oscillator. It is desirable to generate by such as.
  • the ultrasonic carrier signal Sc_us and PWM The carrier signal Sc_pwm is shifted together, and the above-mentioned condition of double the frequency and the synchronization state is not lost.
  • the comparison unit 15 compares the amplitude of the output signal of the addition unit 13 (a signal obtained by adding the audio signal Sa and the ultrasonic carrier signal Sc_us) and the PWM carrier signal Sc_pwm, and the PWM signal corresponding to the comparison result. S_pwm is generated. This PWM signal S_pwm is in a state corresponding to a signal obtained by subjecting the PWM carrier signal Sc_pwm to pulse width modulation by the output signal of the adder 13.
  • the frequency component of the PWM signal S_pwm obtained by the comparison unit 15 includes a component of fc_us ⁇ fa centering on the ultrasonic carrier frequency fc_us, as shown in FIG.
  • the frequency component of the PWM signal S_pwm obtained by the comparison unit 15 includes ⁇ 2fa, ⁇ fa, + fa, + 2fa around the PWM carrier frequency fc_pwm as shown in FIG. , Components are included.
  • FIG. 4 Since the PWM signal S_pwm is a rectangular wave signal waveform, the third harmonic, the fourth harmonic, etc. of fc_us are also included.
  • the frequency component of fc_us ⁇ fa centering on the ultrasonic carrier frequency fc_us is the same frequency component as the amplitude modulation output shown in FIG. That is, by using the method of the present embodiment, a modulated output can be obtained without using a modulator that is a multiplier having the circuit configuration shown in FIGS.
  • the drive unit 16 Since this PWM signal S_pwm is ON / OFF repetition, the drive unit 16 amplifies the class D to generate a drive signal Sd for the ultrasonic transducer 20 (step S205 in FIG. 2). By supplying the drive signal Sd generated from the PWM signal S_pwm to the ultrasonic transducer 20, ultrasonic acoustic reproduction is performed.
  • ultrasonic sound reproduction can be performed with a simple circuit configuration based on addition and amplitude comparison without using a modulation circuit using a multiplier or the like.
  • the drive unit 16 for driving the ultrasonic transducer 20 is simplified as compared with the conventional device that required class A or class B amplification. At the same time, it becomes possible to increase the efficiency. For this reason, even when a large number of ultrasonic transducers 20 are arranged to perform high-power ultrasonic sound reproduction, it is easy to realize an ultrasonic sound reproduction device.
  • fc_pwm 2 ⁇ fc_us
  • the frequency fc_pwm of the PWM carrier signal Sc_pwm corresponds to the sampling frequency fs of discrete signal processing.
  • a sampling frequency fs 80 kHz
  • components up to 40 kHz can be accurately reproduced, but frequency components exceeding 40 kHz cause aliasing and appear as an image in a band of 40 kHz or less.
  • 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.
  • 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.
  • the PWM signal S_pwm may include the component of the ultrasonic carrier signal Sc_us modulated with the audio signal. found. Further, by satisfying the condition of the PWM carrier signal Sc_pwm in a state of being synchronized with the ultrasonic carrier signal Sc_us, an extra component is added to the component of the ultrasonic carrier signal Sc_us modulated with the audio signal included in the PWM signal S_pwm. It was found that no beat component was included.
  • the conditions of the present embodiment that is, the PWM carrier signal Sc_pwm having a frequency twice that of the ultrasonic carrier signal Sc_us, and the PWM carrier signal Sc_pwm synchronized with the ultrasonic carrier signal Sc_us are not intended. It became clear that ultrasonic sound reproduction could not be performed. That is, the conditions of the present embodiment are clearly different from the conventionally known techniques, and are clearly critical conditions.
  • an ultrasonic carrier signal Sc_us having a frequency twice or more the upper limit frequency of the audio signal is generated and added to the audio signal, and the frequency is twice that of the ultrasonic carrier signal Sc_us.
  • a triangular wave or sawtooth wave PWM carrier signal Sc_pwm synchronized with the sonic carrier wave signal Sc_us is generated, the amplitude of the added signal and the PWM carrier wave signal Sc_pwm is compared, and the PWM signal S_pwm is output, whereby the audio signal and the ultrasonic carrier wave signal Sc_us Is added as a PWM signal S_pwm in a pulse width modulated state.
  • ultrasonic sound reproduction is performed by supplying the PWM signal S_pwm to the ultrasonic transducer. That is, ultrasonic sound reproduction can be performed with a simple circuit configuration based on addition and amplitude comparison without using a modulation circuit using a multiplier or the like. Moreover, since the PWM signal S_pwm can be amplified by class D by switching, it is possible to simplify the drive circuit for driving the ultrasonic transducer and increase the efficiency.

Abstract

Ultrasonic sound reproduction becomes possible by a simple circuit structure. Provided are an ultrasonic carrier wave signal generation unit for generating an ultrasonic carrier wave signal which has a frequency at least twice the frequency of the upper limit frequency of an audio signal to be reproduced, and which becomes a carrier wave for ultrasonic sound reproduction; an addition unit for adding the audio signal and the ultrasonic carrier wave signal; a PWM carrier wave signal generation unit for generating a triangular or sawtooth PWM carrier wave signal which has a frequency twice the frequency of the ultrasonic carrier wave signal and which is synchronized with the ultrasonic carrier wave signal; a comparison unit which compares amplitudes between the output signal of the addition unit and the PWM carrier wave signal and generates a PWM signal; and a driving unit which generates a driving signal of an ultrasonic oscillator on the basis of the PWM signal generated by the comparison unit.

Description

超音波音響再生方法および超音波音響再生装置Ultrasonic sound reproducing method and ultrasonic sound reproducing apparatus
　本発明は超音波音響再生方法と超音波音響再生装置とに関し、特に、簡易な回路構成により効率の良い超音波再生を可能とする技術に関する。 The present invention relates to an ultrasonic acoustic reproduction method and an ultrasonic acoustic reproduction apparatus, and more particularly to a technique that enables 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、この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、狭い範囲に向けた鋭指向性の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 having a sharp directivity toward a narrow range. Sound reproduction is realized.
　たとえば、図６に示されるように、周波数ｆｃ（ｋＨｚ）の超音波搬送波信号Ｓc_usを、周波数ｆａ（ｋＨｚ）の音声信号Ｓaで変調することで、超音波搬送波信号の両脇に周波数ｆｃ±ｆａ（ｋＨｚ）の超音波信号が得られる。 For example, as shown in FIG. 6, by modulating an ultrasonic carrier signal Sc_us having a frequency fc (kHz) with an audio signal Sa having a frequency fa (kHz), frequencies fc ± fa are provided on both sides of the ultrasonic carrier signal. An ultrasonic signal of (kHz) is obtained.
　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では、まず、図８に示されるように、音声信号源１からの音声信号に直流重畳部２で直流成分を重畳する。そして、搬送波生成部３からの超音波搬送波信号Ｓc_usを、乗算部４において直流重畳音声信号で変調する。このような超音波音響再生装置により、図６に示す周波数ｆｃ（ｋＨｚ），ｆｃ±ｆａ（ｋＨｚ）の振幅変調出力が得られる。 In the modulation circuit used as the ultrasonic sound reproducing device, first, as shown in FIG. 8, a DC component is superimposed on the audio signal from the audio signal source 1 by the DC superimposing unit 2. Then, the ultrasonic carrier signal Sc_us from the carrier generation unit 3 is modulated by the multiplication unit 4 with the DC superimposed audio signal. With such an ultrasonic sound reproducing apparatus, an amplitude-modulated output having the frequencies fc (kHz) and fc ± fa (kHz) shown in FIG. 6 can be obtained.
　また、図９に示されるように、発振器３ａ，３ｂ、移相器５ａ，５ｂ，乗算器４ａ，４ｂ，４ｃ，４ｄ、ＬＰＦ６ａ，６ｂを有するWeaver方式ＳＳＢ回路に基づく変調回路が用いられることもある。この場合、図９のように、４個の乗算器４ａ，４ｂ，４ｃ，４ｄが必要になるため、回路構成が複雑になる問題がある。 Also, as shown in FIG. 9, a modulation circuit based on a Weaver SSB circuit having oscillators 3a and 3b, phase shifters 5a and 5b, multipliers 4a, 4b, 4c and 4d, and LPFs 6a and 6b may be used. is there. In this case, as shown in FIG. 9, since four multipliers 4a, 4b, 4c, and 4d are required, there is a problem that 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に記載されたものなどが存在している。 In addition, as such an ultrasonic sound reproducing device, for example, the one described in Patent Document 1 below exists.
特開２００３－１５３３７０号公報JP 2003-153370 A
　以上説明した各種の超音波音響再生装置では、いずれの場合も乗算器を用いて変調を行う必要がある。このため、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を有していた。 In the various ultrasonic sound reproducing apparatuses described above, in any case, it is necessary to perform modulation using a multiplier. For this reason, a compatible DSP and analog multiplier are required, and the configuration of the modulation circuit is complicated, and the cost is high.
　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。 The present invention that solves the above problems is as described below.
　（１）超音波音響再生方法の発明は、
　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倍の周波数であって前記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されたＰＷＭ信号を超音波振動子の駆動信号として出力する。 (1) The invention of the ultrasonic sound reproduction method is as follows:
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 to generate a triangular or sawtooth PWM carrier signal that is twice the frequency of the ultrasonic carrier signal and synchronized with the ultrasonic carrier signal;
A PWM signal generated by comparing the amplitude of the output signal of the adder and the PWM carrier wave signal is output as a drive signal for the ultrasonic transducer.
　（２）超音波音響再生装置の発明は、
　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倍の周波数であって前記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、
を備える。 (2) The invention of the ultrasonic sound reproducing device
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 and synchronized with 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;
Is provided.
　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が、超音波搬送波信号生成部により生成される。そして、音声信号と超音波搬送波信号とが加算部で加算される。また、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に同期した三角波あるいは鋸波のＰＷＭ搬送波信号が、ＰＷＭ搬送波信号生成部で生成される。 In the present invention, an ultrasonic carrier signal having a frequency twice or more the upper limit frequency of the audio signal is generated by the ultrasonic carrier signal generator. Then, the audio signal and the ultrasonic carrier wave signal are added by the adding unit. In addition, a PWM carrier signal generating unit generates a triangular or sawtooth PWM carrier signal having a frequency twice that of the ultrasonic carrier signal and synchronized with the ultrasonic carrier signal.
　そして、加算部の出力信号と、ＰＷＭ搬送波信号とが、比較部で振幅比較されることで、ＰＷＭ信号が生成される。さらに、ＰＷＭ信号に基づいて超音波振動子の駆動信号が駆動部によって生成される。 Then, the output signal of the adder and the PWM carrier signal are compared in amplitude by the comparator, thereby generating a PWM signal. Furthermore, a drive signal for the ultrasonic transducer is generated by the drive unit based on the PWM signal.
　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。 Thereby, 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.
　すなわち、加算と振幅比較とによってＰＷＭ信号を生成することにより、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回路による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。 That is, by generating a PWM signal by addition and amplitude comparison, 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 amplified by class D by a switching circuit, 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. 超音波音響再生装置の特性を数式により示す説明図である。It is explanatory drawing which shows the characteristic of an ultrasonic acoustic reproduction apparatus by numerical formula. 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実施形態を詳細に説明する。 Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
　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が動作することにより、超音波音響再生方法が実行される。 FIG. 1 is an explanatory view schematically showing a configuration of a main part of the ultrasonic sound reproducing device 10 according to the first embodiment of the present invention. Note that the ultrasonic sound reproducing method is executed by operating 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Ｓaを生成する信号源である。ここで、音声信号Ｓaとは、可聴周波数範囲に存在する可聴信号を意味している。なお、この音声信号源１１は、超音波再生装置１０に内蔵されていなくともよく、外部の各種オーディオ装置やマイクロフォンなどであってもよい。また、音声信号源１１の代わりに、外部のオーディオ装置やマイクロフォンからの音声信号を受けて、所定のレベルまで増幅する増幅回路を備えていてもよい。 The audio signal source 11 is a signal source that generates an audio signal Sa to be reproduced by ultrasonic acoustic reproduction. Here, the audio signal Sa means an audible signal existing in the audible frequency range. Note that the audio signal source 11 does not have to be built in the ultrasonic reproduction apparatus 10, and may be various external audio apparatuses, microphones, or the like. Further, instead of the audio signal source 11, an audio circuit that receives an audio signal from an external audio device or a microphone and amplifies it to a predetermined level may be provided.
　超音波搬送波信号生成部１２は、再生すべき音声信号Ｓaの上限周波数ｆa_max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周波数ｆc_usの、超音波搬送波信号Ｓc_usを生成する。 The ultrasonic carrier signal generator 12 generates an ultrasonic carrier signal Sc_us having a frequency fc_us that is a frequency that is at least twice the upper limit frequency fa_max of the audio signal Sa to be reproduced and is a carrier wave for ultrasonic acoustic reproduction.
　加算部１３は、音声信号Ｓaと超音波搬送波信号Ｓc_usとを加算する。 The adder 13 adds the audio signal Sa and the ultrasonic carrier signal Sc_us.
　ＰＷＭ搬送波信号生成部１４は、超音波搬送波信号Ｓc_usの周波数である超音波搬送波周波数ｆc_usの２倍の周波数（２・ｆc_us＝ｆc_pwm）であって、超音波搬送波信号Ｓc_usに同期した三角波あるいは鋸波のＰＷＭ搬送波信号Ｓc_pwmを生成する。 The PWM carrier signal generation unit 14 has a frequency twice the ultrasonic carrier frequency fc_us (2 · fc_us = fc_pwm) that is the frequency of the ultrasonic carrier signal Sc_us, and is a triangular wave or a sawtooth wave synchronized with the ultrasonic carrier signal Sc_us. PWM carrier signal Sc_pwm is generated.
　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、２・ｆc_usがｆc_pwmに一致した状態が継続的に保たれていることを意味する。 Here, “synchronized” means that the state of 2 · fc_us coincides with fc_pwm is continuously maintained without shifting even if the frequency is less than 1 Hz with respect to the frequency doubling relationship.
　なお、超音波搬送波信号Ｓc_usの振幅は、音声信号Ｓaの最大振幅と等しくすることが望ましく、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。また、ＰＷＭ搬送波信号Ｓc_pwmの振幅は超音波搬送波信号Ｓc_us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更に望ましい。 It should be noted that the amplitude of the ultrasonic carrier signal Sc_us is desirably equal to the maximum amplitude of the audio signal Sa, and is desirable for performing ultrasonic acoustic reproduction in an efficient state without distortion. Further, it is more desirable that the amplitude of the PWM carrier signal Sc_pwm is twice that of the ultrasonic carrier signal Sc_us in order to perform ultrasonic acoustic reproduction in an efficient state without distortion.
　比較部１５は、加算部１３の出力信号（音声信号Ｓaと超音波搬送波信号Ｓc_usとが加算された信号）と、ＰＷＭ搬送波信号Ｓc_pwmとを振幅比較して、ＰＷＭ信号Ｓ_pwm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 Sa and the ultrasonic carrier signal Sc_us) and the PWM carrier signal Sc_pwm, and generates a PWM signal S_pwm.
　駆動部１６は、比較部１５で生成されたＰＷＭ信号Ｓ_pwmに基づいて、スイッチング素子のスイッチング動作などを用いたＤ級増幅を行って、超音波振動子を駆動するための駆動信号Ｓｄを生成する。 Based on the PWM signal S_pwm generated by the comparison unit 15, the drive unit 16 performs class D amplification using a switching operation of a switching element and generates a drive signal Sd for driving the ultrasonic transducer. .
　フィルタ部１８は、超音波搬送波周波数ｆc_us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、省略するといった変形も可能である。 The filter unit 18 is a filter unit including a low-pass filter or a band-pass filter that passes a signal having a frequency near the ultrasonic carrier frequency fc_us and attenuates other frequency components. It should be noted that the filter unit 18 can be modified such as being 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Ｓｄ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。 The ultrasonic transducer 20 is an electroacoustic transducer such as a transducer that generates ultrasonic vibrations based on the drive signal Sd generated by the drive unit 16.
　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から周波数ｆaの音声信号Ｓa（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Ｓa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る。そして、このオーディオ信号の上限周波数ｆa_maxを、たとえば、２０ｋＨｚと定めておく。 That is, in the ultrasonic sound reproducing apparatus 10 described above, first, an audio signal Sa having a frequency fa (see FIG. 3A) is input from the audio signal source 11 (step S20 in FIG. 2). The audio signal Sa is a general audible signal, that is, an audio signal. The upper limit frequency fa_max of the audio signal is set to 20 kHz, for example.
　ここで、音声信号Ｓaの上限周波数ｆa_maxの２倍以上に選択された超音波搬送波周波数ｆc_usの超音波搬送波信号Ｓc_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）。 Here, the ultrasonic carrier signal Sc_us (see FIG. 3B) of the ultrasonic carrier frequency fc_us selected to be at least twice the upper limit frequency fa_max of the audio signal Sa is generated by the ultrasonic carrier signal generator 12 (see FIG. 3B). Step S201 in FIG.
　この超音波搬送波周波数ｆc_usとしては、音声信号の上限周波数ｆa_maxの２倍以上の周波数であり、かつ、超音波振動子２０を効率よく振動させることが可能な周波数を選択することが望ましい。 As the ultrasonic carrier frequency fc_us, it is desirable to select a frequency that is at least twice the upper limit frequency fa_max of the audio signal and that can vibrate the ultrasonic transducer 20 efficiently.
　たとえば、ここでは、上述した音声信号の上限周波数ｆa_maxが２０ｋＨｚであったため、超音波搬送波周波数ｆc_usとして４０ｋＨｚに設定する。 For example, here, since the upper limit frequency fa_max of the audio signal is 20 kHz, the ultrasonic carrier frequency fc_us is set to 40 kHz.
　そして、この超音波搬送波信号Ｓc_usと音声信号Ｓa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、重畳を行えばよい。 Then, the ultrasonic carrier signal Sc_us and the audio signal Sa are added by the adder 13 (step S202 in FIG. 2). Here, instead of amplitude modulation using a multiplier, simple addition or superposition may be performed.
　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Ｓc_usの２倍の周波数であって、該超音波搬送波信号Ｓc_usに同期した状態の、三角波あるいは鋸波のＰＷＭ搬送波信号Ｓc_pwm（図３（ｃ）参照）を生成する（図２中のステップＳ２０３）。 On the other hand, the PWM carrier signal generation unit 14 has a frequency twice that of the above ultrasonic carrier signal Sc_us and is synchronized with the ultrasonic carrier signal Sc_us, and is a triangular wave or sawtooth PWM carrier signal Sc_pwm (FIG. 3). (See (c)) is generated (step S203 in FIG. 2).
　この場合、以上の超音波搬送波周波数ｆc_usが４０ｋＨｚであるため、ＰＷＭ搬送波信号Ｓc_pwmのＰＷＭ搬送波周波数ｆc_pwmとして８０ｋＨｚに設定する。 In this case, since the above ultrasonic carrier frequency fc_us is 40 kHz, the PWM carrier frequency fc_pwm of the PWM carrier signal Sc_pwm is set to 80 kHz.
　ここで、超音波搬送波信号Ｓc_usとＰＷＭ搬送波信号Ｓc_pwmとを同期させるためには、超音波搬送波信号Ｓc_usとＰＷＭ搬送波信号Ｓc_pwmとを、共通の発振器で生成された信号を用いて、逓倍や分周などにより生成することが望ましい。 Here, in order to synchronize the ultrasonic carrier signal Sc_us and the PWM carrier signal Sc_pwm, the ultrasonic carrier signal Sc_us and the PWM carrier signal Sc_pwm are multiplied or divided by using a signal generated by a common oscillator. It is desirable to generate by such as.
　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、基本となる発振器が生成する信号の周波数にずれが生じたとしても、超音波搬送波信号Ｓc_usとＰＷＭ搬送波信号Ｓc_pwmとが共にずれることになり、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。 In this way, even if the frequency of the signal generated by the basic oscillator is shifted by using multiplication or division using the signal from the common oscillator, the ultrasonic carrier signal Sc_us and PWM The carrier signal Sc_pwm is shifted together, and the above-mentioned condition of double the frequency and the synchronization state is not lost.
　また、比較部１５は、加算部１３の出力信号（音声信号Ｓaと超音波搬送波信号Ｓc_usとが加算された信号）と、ＰＷＭ搬送波信号Ｓc_pwmとを振幅比較して、比較結果に相当するＰＷＭ信号Ｓ_pwmを生成する。このＰＷＭ信号Ｓ_pwmは、ＰＷＭ搬送波信号Ｓc_pwm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相当する状態になっている。 The comparison unit 15 compares the amplitude of the output signal of the addition unit 13 (a signal obtained by adding the audio signal Sa and the ultrasonic carrier signal Sc_us) and the PWM carrier signal Sc_pwm, and the PWM signal corresponding to the comparison result. S_pwm is generated. This PWM signal S_pwm is in a state corresponding to a signal obtained by subjecting the PWM carrier signal Sc_pwm 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Ｓ_pwmの周波数成分は、図３（ｄ）に示されるように、超音波搬送波周波数ｆc_usを中心に、ｆc_us±ｆaの成分が含まれる。また、同様に、この比較部１５で得られたＰＷＭ信号Ｓ_pwmの周波数成分には、図３（ｄ）に示されるように、ＰＷＭ搬送波周波数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Ｓ_pwmが矩形波の信号波形であるため、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 S_pwm obtained by the comparison unit 15 includes a component of fc_us ± fa centering on the ultrasonic carrier frequency fc_us, as shown in FIG. Similarly, the frequency component of the PWM signal S_pwm obtained by the comparison unit 15 includes −2fa, −fa, + fa, + 2fa around the PWM carrier frequency fc_pwm as shown in FIG. , Components are included. The detailed experimental results are shown in FIG. 4. Since the PWM signal S_pwm is a rectangular wave signal waveform, the third harmonic, the fourth harmonic, etc. of fc_us are also included.
　ここで、ＰＷＭ信号Ｓ_pwmの周波数成分のうちの、超音波搬送波周波数ｆc_usを中心にしたｆc_us±ｆaの周波数成分は、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、本実施形態の手法を用いることで、図８や図９に示される回路構成の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, of the frequency components of the PWM signal S_pwm, the frequency component of fc_us ± fa centering on the ultrasonic carrier frequency fc_us is the same frequency component as the amplitude modulation output shown in FIG. That is, by using the method of the present embodiment, a modulated output can be obtained without using a modulator that is a multiplier having the circuit configuration shown in FIGS.
　そして、このＰＷＭ信号Ｓ_pwm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Ｓｄを生成する（図２中のステップＳ２０５）。このＰＷＭ信号Ｓ_pwmから生成された駆動信号Ｓｄ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 S_pwm is ON / OFF repetition, the drive unit 16 amplifies the class D to generate a drive signal Sd for the ultrasonic transducer 20 (step S205 in FIG. 2). By supplying the drive signal Sd generated from the PWM signal S_pwm 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、加算と振幅比較による簡素な回路構成で超音波音響再生が可能になる。 That is, according to the method of the present embodiment, ultrasonic sound reproduction can be performed with a simple circuit configuration based on addition and amplitude comparison without using a modulation circuit using a multiplier or the like.
　また、ＰＷＭ信号Ｓ_pwm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、超音波音響再生装置を実現することが容易になる。 Further, since the PWM signal S_pwm 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 required class A or class B amplification. At the same time, it becomes possible to increase the efficiency. For this reason, even when a large number of ultrasonic transducers 20 are arranged to perform high-power ultrasonic sound reproduction, it is easy to realize an ultrasonic sound reproduction device.
　なお、本実施形態では、ＰＷＭ搬送波信号Ｓc_pwmは、超音波搬送波信号Ｓc_usの２倍の周波数（ｆc_pwm＝２・ｆc_us）であって、超音波搬送波信号Ｓc_us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 signal Sc_pwm is a signal having a frequency (fc_pwm = 2 · fc_us) twice that of the ultrasonic carrier signal Sc_us and synchronized with the ultrasonic carrier signal Sc_us. However, this point can be explained as follows.
　本実施形態の方式において、ＰＷＭ搬送波信号Ｓc_pwmの周波数ｆc_pwmは、離散的信号処理のサンプリング周波数ｆsに相当する。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を超える周波数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表れる。このようになると、元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 frequency fc_pwm of the PWM carrier signal Sc_pwm corresponds to the sampling frequency fs of discrete signal processing. When a signal is sampled at a sampling frequency fs = 80 kHz, components up to 40 kHz can be accurately reproduced, but frequency components exceeding 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)，
　以上の信号を時刻または時間を意味するｔで微分すると、図７の式に示されるように、角速度が求まる。 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),
When the above signals are differentiated by t which means time or time, the angular velocity is obtained as shown in the equation of FIG.
　さらに、この図７に示される式を２πで割ると、以下に示されるように、周波数が求まる。
1000・cos(2π・1000・t)＋40000・cos(2π・40000・t)，
　この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、図４に示されるように、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。 Further, when the equation shown in FIG. 7 is divided by 2π, the frequency is obtained as shown below.
1000 ・ cos (2π ・ 1000 ・ t) +40000 ・ cos (2π ・ 40000 ・ t),
When this signal is sampled at a sampling frequency fs = 80 kHz, a component of 41 kHz is applied to ½ of fs, and is folded back into a region of 40 kHz or less and cannot be separated. Therefore, as shown in FIG. A signal component of ± 1 kHz appears in the center. In this way, 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.
　一方、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、４０ｋＨｚの２倍より高い周波数のｆs＝１６０ｋＨｚでサンプリングした場合には、各成分はｆsの１／２より小さくなるため、何ら問題なく分離することができる。この場合には、上述した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。この様子を図５に示す。 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, which is a frequency higher than twice 40 kHz, each component is fs. Therefore, it can be separated without any problem. In this case, a signal having the same frequency component as that of amplitude modulation as in the case of fs = 80 kHz described above cannot be obtained. This is shown in FIG.
　このように、超音波搬送波信号Ｓc_usの２倍の周波数のＰＷＭ搬送波信号Ｓc_pwmの条件を満たすことで、ＰＷＭ信号Ｓ_pwm中に、音声信号で変調された超音波搬送波信号Ｓc_us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Ｓc_usと同期がとれた状態のＰＷＭ搬送波信号Ｓc_pwmという条件を満たすことで、ＰＷＭ信号Ｓ_pwm中に含まれる、音声信号で変調された超音波搬送波信号Ｓc_us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, by satisfying the condition of the PWM carrier signal Sc_pwm having a frequency twice that of the ultrasonic carrier signal Sc_us, the PWM signal S_pwm may include the component of the ultrasonic carrier signal Sc_us modulated with the audio signal. found. Further, by satisfying the condition of the PWM carrier signal Sc_pwm in a state of being synchronized with the ultrasonic carrier signal Sc_us, an extra component is added to the component of the ultrasonic carrier signal Sc_us modulated with the audio signal included in the PWM signal S_pwm. It was found that no beat component was included.
　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Ｓc_usの２倍の周波数のＰＷＭ搬送波信号Ｓc_pwm、超音波搬送波信号Ｓc_usと同期したＰＷＭ搬送波信号Ｓc_pwm、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、従来から知られた技術とは明らかに異なるものであり、臨界的に意義のある条件であることが明らかである。 Therefore, it is intended that the conditions of the present embodiment, that is, the PWM carrier signal Sc_pwm having a frequency twice that of the ultrasonic carrier signal Sc_us, and the PWM carrier signal Sc_pwm synchronized with the ultrasonic carrier signal Sc_us are not intended. It became clear that ultrasonic sound reproduction could not be performed. That is, the conditions of the present embodiment are clearly different from the conventionally known techniques, and are clearly critical 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Ｓc_usを生成して音声信号と加算し、超音波搬送波信号Ｓc_usの２倍の周波数であって、超音波搬送波信号Ｓc_usと同期した三角波あるいは鋸波のＰＷＭ搬送波信号Ｓc_pwmを生成し、加算信号とＰＷＭ搬送波信号Ｓc_pwmとを振幅比較してＰＷＭ信号Ｓ_pwmを出力することにより、音声信号と超音波搬送波信号Ｓc_us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Ｓ_pwmとして出力される。よって、このＰＷＭ信号Ｓ_pwm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、加算と振幅比較とによる簡素な回路構成で、超音波音響再生が可能になる。また、ＰＷＭ信号Ｓ_pwm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 Sc_us having a frequency twice or more the upper limit frequency of the audio signal is generated and added to the audio signal, and the frequency is twice that of the ultrasonic carrier signal Sc_us. A triangular wave or sawtooth wave PWM carrier signal Sc_pwm synchronized with the sonic carrier wave signal Sc_us is generated, the amplitude of the added signal and the PWM carrier wave signal Sc_pwm is compared, and the PWM signal S_pwm is output, whereby the audio signal and the ultrasonic carrier wave signal Sc_us Is added as a PWM signal S_pwm in a pulse width modulated state. Therefore, ultrasonic sound reproduction is performed by supplying the PWM signal S_pwm to the ultrasonic transducer. That is, ultrasonic sound reproduction can be performed with a simple circuit configuration based on addition and amplitude comparison without using a modulation circuit using a multiplier or the like. Moreover, since the PWM signal S_pwm can be amplified by class D by switching, it is possible to simplify the drive circuit for driving the ultrasonic transducer and increase the efficiency.
　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Ｓc_usの超音波搬送波周波数ｆc_usとしての４０ｋＨｚ、ＰＷＭ搬送波信号Ｓc_pwmのＰＷＭ搬送波周波数ｆc_pwmとしての８０ｋＨｚは一例であり、他の任意の周波数を採用することが可能である。すなわち、適用する超音波音響再生装置や部品において適した周波数を採用することが可能である。 Other embodiments:
The specific numerical values used in the description of the above embodiment, 40 kHz as the ultrasonic carrier frequency fc_us of the ultrasonic carrier signal Sc_us, and 80 kHz as the PWM carrier frequency fc_pwm of the PWM carrier signal Sc_pwm are examples, and other arbitrary frequencies are used. It is possible to adopt. That is, it is possible to employ a frequency suitable for the applied ultrasonic sound reproducing device or component.
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)

  1. 　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倍の周波数であって前記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された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 that is twice the frequency of the ultrasonic carrier signal and synchronized with the ultrasonic carrier signal;
    The 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 for the ultrasonic transducer.
    An ultrasonic sound reproducing method characterized by the above.
  2. 　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倍の周波数であって前記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 and synchronized with 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:
  3. 　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倍の周波数であって前記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 and synchronized with 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:
  4. 　前記超音波搬送波信号生成部は、
    　前記超音波搬送波信号の振幅を前記音声信号の最大振幅と等しくし、
    　前記ＰＷＭ搬送波信号の振幅を前記超音波搬送波信号の振幅の２倍となるようにする、
    ことを特徴とする請求項２－３のいずれか一項に記載の超音波音響再生装置。     The ultrasonic carrier wave signal generator is
    Making the amplitude of the ultrasonic carrier signal 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 any one of claims 2-3.
  5. 　前記駆動部は、スイッチング回路により構成され、前記ＰＷＭ信号に応じたスイッチングを行うことで前記駆動信号を生成する、
    ことを特徴とする請求項２－３のいずれか一項に記載の超音波音響再生装置。     The drive unit is configured by a switching circuit, and generates the drive signal by performing switching according to the PWM signal.
    The ultrasonic sound reproducing device according to any one of claims 2-3.
  6. 　前記超音波搬送波信号生成部は、前記超音波搬送波信号の振幅を前記音声信号の最大振幅と等しくし、前記ＰＷＭ搬送波信号の振幅を前記超音波搬送波信号の振幅の２倍となるようにし、
    　前記駆動部は、スイッチング回路により構成され、前記ＰＷＭ信号に応じたスイッチングを行うことで前記駆動信号を生成する、
    ことを特徴とする請求項２－３のいずれか一項に記載の超音波音響再生装置。     The ultrasonic carrier signal generation unit makes the amplitude of the ultrasonic carrier signal equal to the maximum amplitude of the audio signal, and makes the amplitude of the PWM carrier signal twice the amplitude of the ultrasonic carrier signal,
    The drive unit is configured by a switching circuit, and generates the drive signal by performing switching according to the PWM signal.
    The ultrasonic sound reproducing device according to any one of claims 2-3.
PCT/JP2009/071794 2009-08-24 2009-12-28 Ultrasonic sound reproduction method and ultrasonic sound reproduction device WO2011024329A1 (en)

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