JP4233459B2 - Driving device for ultrasonic vibration element - Google Patents

Description

  The present invention relates to a driving device for an ultrasonic vibration element constituting a super-directional speaker device or the like.

  A super-directional speaker (parametric speaker) using a nonlinear phenomenon of sound waves generally modulates an extremely high frequency carrier wave such as an ultrasonic wave with an audible signal wave and transmits it as a finite amplitude wave. In the sound wave transmitted in this way, secondary waves related to the signal are distributed in a vertical array in the space due to the nonlinear interaction. Thereby, it functions as a super-directional speaker that transmits a signal wave having a sharp directivity and a small side lobe.

  As a super-directional speaker device, for example, there is one disclosed in Patent Document 1. This speaker device includes a coefficient unit, a direct current source adder, a square root converter, a multiplier, a power amplifier, and an ultrasonic vibration element array (hereinafter referred to as a radiator). The operation will be briefly described. An audio signal generated by a modulation signal source or the like is input to a coefficient unit in the speaker device. The coefficient unit multiplies the value of the audio signal by a predetermined coefficient and then outputs it to the DC source adder.

  In the DC source adder, the bias voltage from the DC source is added to the audio signal voltage from the coefficient unit, and the result is output to the square root converter. The square root converter performs square root processing on the input signal from the DC source adder and outputs the processing result to the multiplier. In addition to the input signal from the square root converter, an ultrasonic carrier signal from an ultrasonic band oscillator is input to this multiplier.

  As a result, the multiplier multiplies the input signal from the square root converter by the ultrasonic carrier signal and executes the amplitude modulation processing of the input signal. Thereafter, the modulation signal from the multiplier is output to the power amplifier. In the power amplifier, the power of the modulation signal from the multiplier is amplified and supplied to the radiator. Thereby, the radiator radiates a modulation signal derived from the audio signal as a sound wave.

  This sound wave causes non-linear interaction in the process of propagating in the air as a finite amplitude sound wave that is a powerful ultrasonic wave, and can self-demodulate into a super-directional sound consisting of low-frequency components, etc., and can be heard by the listener. .

Japanese Patent Publication No. 4-58758

  As described above, in the conventional super-directional speaker device, there are a number of configurations such as a coefficient unit, a DC source adder, a square root converter, a multiplier, and a power amplifier as a configuration for driving a radiator which is an ultrasonic vibration element array. A complicated and large-scale processing circuit composed of parts was required.

  For this reason, there existed a subject that the miniaturization of the whole apparatus was restrict | limited and the drift of the various performance in the whole apparatus was also large from the individual difference for every component. Further, when a large number of parts are required, the power consumption is inevitably increased, and the cost is disadvantageous.

  The present invention has been made to solve the above-described problems, and can be configured with a simple circuit without taking a complicated circuit configuration such as a square root converter, and operates with stable performance. An object of the present invention is to obtain a drive device.

  An apparatus for driving an ultrasonic transducer according to the present invention includes a signal input unit that inputs an electric signal in an audible frequency band, a carrier signal generation unit that generates a carrier signal in an ultrasonic frequency band, and a sawtooth based on the carrier signal. Modulation of the pulse width according to the signal level of the input signal from the sawtooth wave signal based on the voltage comparison between the sawtooth wave generator and the sawtooth wave signal and the audible frequency band input signal A pulse width modulation unit that generates a signal and a drive voltage supply unit that drives an ultrasonic vibration element in accordance with the modulation signal and converts an input signal in an audible frequency band into an acoustic signal.

  According to the present invention, a signal input unit that inputs an electric signal in an audible frequency band, a carrier signal generation unit that generates a carrier signal in an ultrasonic frequency band, and a saw tooth that generates a sawtooth wave signal based on the carrier signal. Pulse width modulation that generates a modulated signal with a pulse width corresponding to the signal level of the input signal from the sawtooth wave signal based on the voltage comparison between the sawtooth wave generator and the sawtooth wave signal and the audible frequency band input signal And a drive voltage supply unit that drives an ultrasonic vibration element according to a modulation signal and converts an input signal in an audible frequency band into an acoustic signal, so that a complicated circuit configuration such as a square root converter as in the past Therefore, each component can be configured with an inexpensive and simple circuit and can be operated with stable performance.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of an ultrasonic vibration element driving apparatus according to Embodiment 1 of the present invention, and shows a case where the present invention is applied to a superdirective speaker apparatus. In the figure, a microphone amplifier (signal input unit) 100 amplifies the power of an audio signal input as an audible sound input signal. The bandpass amplifier (signal input unit) 101 is configured by sequentially connecting a highpass amplifier 101a, a limiter 101b, and a lowpass amplifier 101c. The band-pass amplifier 101 removes noise, unnecessary harmonic signals, and high-frequency signals from the audible sound input signal amplified by the microphone amplifier 100, and the voltage is amplified.

  The oscillation circuit (carrier signal generation unit) 102 generates a reference carrier signal having an ultrasonic band frequency of 40 kHz and outputs the reference carrier signal to the sawtooth wave generation circuit 103. The sawtooth wave generation circuit (sawtooth wave generation unit) 103 charges and discharges the capacitor C1 in synchronization with the reference carrier signal from the oscillation circuit 102 to generate a sawtooth wave signal.

  The pulse width modulation circuit (pulse width modulation unit) 104 includes a comparator that compares the voltage of the audible sound input signal amplified by the bandpass amplifier 101 and a 40 kHz sawtooth wave signal, and a pulse width corresponding to the comparison result. The modulated signal is generated. The driver circuit 105 has an amplifier for lowering the output impedance of the modulation signal from the pulse width modulation circuit 104, and controls opening / closing of the power FETs Q1 and Q2 of the switching element 106 by the modulation signal.

  The high-power amplifier circuit (drive voltage supply unit) includes a switching element 106, an inductance element 107, an output transformer 108, a capacitor 109, a high-speed switching diode 111, a ring coil 112, and the like until the ultrasonic vibration element 110 is connected. The

  The switching element 106 controls opening / closing of energization to the inductance element 107 side or the transformer 108 side. The electromotive force energy for driving the ultrasonic vibration element 110 is obtained by the opening / closing operation by the switching element 106. For this reason, the switching element 106 needs to be reliably controlled for opening and closing, and is preferably composed of a high-voltage power FET or the like that can carry a large current.

  The inductance element 107 is a coil having a winding number of 20 t, and a current flows when the switching element 106 is in an open state, and generates a large electromotive force energy when the switching element 106 is in a closed state. In the following description, the inductance element is also referred to as a coil.

  In the output transformer 108, the capacitor 109 and the ring coil 112 are connected to the primary coil 108a, and the ultrasonic vibration element 110 is connected to the secondary coil 108b. The ultrasonic vibration element 110 is supplied.

  The capacitor 109 is a power supply smoothing capacitor connected to one end of the inductance element 107 and the output transformer 108. Ideally, the power supply smoothing capacitor has zero external resistance when the power supply is viewed from the load side. Therefore, for example, a large capacity of 1000 μF or more is desirable.

  Furthermore, the energization to the capacitor 109 side is switched by the switching element 106 at 40 kHz. For this reason, for example, when the loss angle tangent (tan δ) is high, heat is generated and the life is shortened. Therefore, it is desirable that the capacitor 109 has a small loss.

  The ultrasonic vibration element 110 is a radiator of a speaker using a piezoelectric element or the like, and sends an audible electric signal as an ultrasonic acoustic signal into a medium such as air. The high speed switching diode 111 completely cuts off the current in the direction opposite to the electromotive voltage. The ring coil 112 corrects the current waveform in order to drive the ultrasonic vibration element 110 efficiently.

Next, the operation will be described.
FIG. 2 is a diagram showing signal waveforms in each part of the ultrasonic vibration element driving apparatus according to the first embodiment, and the operation will be described with reference to this figure. In FIG. 2, each signal waveform is represented by a graph in which the horizontal axis represents time and the vertical axis represents the signal level.

  First, as an input signal of the microphone amplifier 100, an audible sound (reference voltage is 0 V) as shown in FIG. The audible sound signal amplified by the microphone amplifier 100 is input to the band pass amplifier 101 at the next stage. The high-pass filter 101a in the band-pass amplifier 101 amplifies a component of the signal from the microphone amplifier 100 that is equal to or higher than a preset frequency band, and outputs the amplified component to the next-stage limiter 101b.

  The limiter 101b clips a signal component exceeding the maximum value or minimum value of a preset frequency band of the signal, and outputs a signal within a range defined by the maximum value and the minimum value. Here, it is assumed that, for example, a range of 500 Hz to 8.5 kHz is preset as the pass frequency band.

  Next, the low-pass amplifier 101c amplifies a component equal to or lower than a preset frequency band for the signal from the limiter 101b, and then applies this to one end of the comparator input in the pulse width modulation circuit 104 in the next stage.

  In this way, noise, unnecessary harmonic signals and high frequency signals are removed from the audible sound signal amplified by the microphone amplifier 100 by the band pass amplifier 101 at the next stage, and the voltage is amplified. A signal waveform to which a bias is applied in the range of 500 Hz to 8.5 kHz by the bandpass amplifier 101 is a waveform shown in FIG.

  On the other hand, the oscillation circuit 102 applies the pulse signal of the ultrasonic band of 40 kHz generated by itself to the gate of the first FET (Field Effect Transistor) Q 1 in the sawtooth wave generation circuit 103. The signal waveform from the oscillation circuit 102 is the waveform shown in FIG. The FET Q1 is in an open state (on state) only during a period in which the pulse signal in the signal waveform of FIG. 2c is on.

  When the pulse signal from the oscillation circuit 102 is off, the FET Q1 is turned off and the capacitor C1 is gradually charged by the constant current circuit composed of the FET Q2 and the FET Q3 based on the reference voltage + B. At this time, when the pulse signal from the oscillation circuit 102 is turned on and the FET Q1 is turned on, the charge accumulated in the capacitor C1 is discharged to the ground via the FET Q1.

  The capacitor C1 is directly connected to the output of the sawtooth wave generation circuit 103. Thereby, the output of the sawtooth wave generating circuit 103 becomes a sawtooth signal waveform as shown in d of FIG. 2 in synchronization with the output from the oscillation circuit 102 shown in c of FIG. In the figure, the sawtooth wave signal and the audible sound input signal are displayed in an overlapping manner in order to explain the relationship with the signal e described later.

  The output signal (sawtooth wave signal d) from the sawtooth wave generation circuit 103 is applied to the other end of the input of the comparator in the pulse width modulation circuit 104 (the input end where the output from the bandpass amplifier 101 is not applied). Is done. In this way, the comparator in the pulse width modulation circuit 104 compares the voltage of the sawtooth signal d and the audible sound input signal b, and generates a modulation signal having a pulse width corresponding to the comparison result.

  More specifically, the pulse width modulation circuit 104 is set to a low level when the voltage of the sawtooth wave signal d is lower than that of the audible sound input signal b, and conversely, the voltage of the sawtooth wave signal d is higher than that of the audible sound input signal b. An output signal is generated so as to become high level during the period. Thereby, as shown in d and e of FIG. 2, the pulse width is set according to the signal level relationship between the sawtooth wave signal and the audible sound input signal, that is, according to the signal level at each sampling point of the audible sound input signal. A changing signal e is generated.

  Here, the comparator of the pulse width modulation circuit 104 can be configured using a stable and inexpensive OP amplifier or the like, and does not require a complicated processing circuit as in the prior art, and at each sampling point of the audible sound input signal. It is possible to obtain a pulse width modulation signal corresponding to the signal level.

  A pulse width modulation signal from the pulse width modulation circuit 104 is input to the driver circuit 105. The driver circuit 105 inverts the potential of the pulse width modulation signal e. As a result, the pulse width modulation signal e becomes a pulse signal f having an amplitude corresponding to the signal level at each sample time of the audible sound input signal. This pulse signal f is output from the pulse width modulation circuit 104 to the switching element 106.

  As a result, the inductance element 107, the output transformer 108, the high-speed switching diode 111, the ring coil 112 having a winding number 2t, and the ultrasonic vibration element 110, which are loads hanging on the capacitor 109, are supplied at a high-speed power supply voltage of 40 kHz of the pulse signal f. To zero.

  More specifically, the pulse signal f from the driver circuit 105 is input to the gates of the power FETs Q1 and Q2 constituting the switching element 106, respectively. Here, when the pulse signal f is in the on state (H level), the FETs Q1 and Q2 are in the on state, a current flows through the inductance element 107 formed of a coil with 20 turns, and energy corresponding to the pulse width is stored.

  On the other hand, when the pulse signal f is turned off (L level), the FETs Q1 and Q2 are turned off, and due to the energy accumulated in the inductance element 107, the current is switched to the high speed switching diode 111, the ring coil 112 having 2t turns, and the output. It flows to the transformer 108.

  As described above, an electromotive voltage is applied to the primary coil 108a of the output transformer 108 in accordance with the pulse width of the pulse signal f. As a result, a signal whose amplitude is modulated by the 40 kHz carrier signal from the oscillation circuit 102 is applied to the ultrasonic vibration element 110.

  As described above, the capacitor 109 is switched at a high speed of 40 kHz and charged / discharged, so that a capacitor with a small loss (small tan δ) is used.

  From the above, to the audible sound input signal, the pulse signal whose pulse width is changed in the previous stage according to the level of the signal applied to the pulse width modulation circuit 104 is added. The frequency of the pulse signal is set to a carrier frequency (40 kHz), and the pulse width is configured to increase as the frequency of the audible sound input signal increases.

  In addition, the pulse signal is set so that the level of the audible sound input signal is high and effective according to the level of the audible sound input signal, and the level of the audible sound input signal is low and invalid. Try to lower the level. Note that the width of the entire pulse is a width (time) determined by the carrier frequency.

Next, the operation of the above-described high output amplifier circuit will be described in more detail.
FIG. 3 is a diagram for explaining the configuration and operation of the high-power amplifier circuit in FIG. 1, and will be described with reference to this figure.
When the pulse signal f from the driver circuit 105 is applied to the gates of the power FETs Q1 and Q2 in the switching element 106, the FETs Q1 and Q2 are turned on at a portion where the pulse level of the pulse signal f is high.

  When the FETs Q1 and Q2 are turned on, a current Ia flows from the power source to the coil 107 and the FETs Q1 and Q2 by the potential + BB from the DC power source connected to one end of the coil 107 (indicated by the solid arrow in the figure). At this time, no current flows through the coil 112 and the output transformer 108 due to the diode 111.

  The current value of the current Ia increases in proportion to time due to the inductance L1 of the inductance element 107. The upper limit of the current value is a value limited by a very small internal resistance of the inductance L1, and can be increased to near infinity if the power source, the coil constituting the circuit, etc. can withstand the increase in the current value. .

  As the current value of the current Ia increases, the electromotive voltage E1 at both ends of the inductance element 107 increases. The signal waveform in the inductance element 107 at this time becomes a waveform as shown in g of FIG. 2, and a large amount of power is generated when the level of the pulse signal f shifts from the high level to the low level.

  When the pulse signal f is in a low level period and the FETs Q1 and Q2 are turned off, the current Ib is converted into the diode 111, the coil by the back electromotive voltage E1 across the inductance element 107, as indicated by the dashed arrows in the figure. 112 and the output transformer 108 side.

  At this time, counter electromotive voltages E2 and E3 are generated in the coil 112 and the primary coil 108a of the output transformer 108 by the current Ib. These electromotive voltages E2 and E3 are voltages obtained by dividing the electromotive voltage E1 and are proportional to the inductances of the coil 112 and the coil 108a.

  Through the above-described process, a voltage E3 corresponding to the pulse width is generated for the primary coil 108a of the output transformer 108. The voltage E3 is converted into a voltage from the primary side coil 108a having a winding number of 7t through the secondary side coil 108b having a winding number of 2t and supplied to the ultrasonic vibration element 110.

  As described above, a signal having a voltage level corresponding to each pulse width is applied to the ultrasonic vibration element 110, and as a result, the ultrasonic vibration element 110 is driven by the amplitude-modulated signal of 40 kHz.

  When the FETs Q1 and Q2 are turned off, the electromotive voltage E1 rapidly decreases, but the current Ib gradually increases due to the inductances of the coils 112 and 108a and then decreases. Thereby, the signal waveform applied to the ultrasonic vibration element 110 becomes a waveform shown in h of FIG.

  In FIG. 2 h, the signal waveform applied to the ultrasonic vibration element 110 and the audible sound input signal are overlapped. As shown in the figure, it can be seen that the signal applied from the output transformer 108 to the ultrasonic vibration element 110 is a signal having a level corresponding to the pulse width of the audible sound input signal.

  As described above, according to the first embodiment, the bandpass amplifier 101 that inputs an electrical signal in the audible frequency band, the oscillation circuit 102 that generates the carrier signal in the ultrasonic frequency band, and the carrier signal as a reference. A pulse width corresponding to the signal level of the input signal from the sawtooth wave signal based on the result of voltage comparison between the sawtooth wave signal and the input signal of the audible frequency band. A square-width conversion circuit including a pulse-width modulation circuit 104 that generates a modulation signal and a high-power amplification circuit that drives the ultrasonic vibration element 110 in accordance with the modulation signal and converts an input signal in an audible frequency band into an acoustic signal. Each component can be configured with a simple circuit with an inexpensive operational amplifier and can be operated with stable performance without taking a complicated circuit configuration such as a detector.

  In addition, a modulator composed of a sawtooth wave generation circuit 103, a pulse width modulation circuit 104 and a driver circuit 105, an amplifier such as a bandpass amplifier 101, an ultrasonic vibration element serving as a radiator, and a surrounding configuration are respectively Since it can be configured with a simple circuit, it is easy to integrate the three constituent units.

Embodiment 2. FIG.
FIG. 4 is a circuit diagram showing a configuration of an ultrasonic vibration element driving apparatus according to Embodiment 2 of the present invention. The ultrasonic vibration element driving apparatus according to the second embodiment has the same basic configuration as that of the first embodiment, but differs in the configuration around the driver circuit, the switching element, and the ultrasonic vibration element. In the driver circuit 105A, an amplifier is connected in parallel to make the output impedance lower than that in the configuration of FIG.

  The switching element 106A switches the modulation signal of 40 kHz by the FET Q1 whose output of the driver circuit 105A is connected to the gate. Here, since the driver circuit 105A outputs the modulated signal amplified by the configuration of FIG. 1, it is desirable that the FET Q1 is configured by a high-voltage power FET that can carry a larger current.

  The output transformer 108A is a drive transformer for driving the ultrasonic vibration element in the same manner as the output transformer 108 shown in FIG. 1. However, the output transformer 108A is different from the one shown in FIG. 1 in that the coil 112 is not provided on the primary side of the output transformer. The number of turns of the coil is different. Note that the components denoted by the same reference numerals as those in FIG. 1 are the same or corresponding configurations, and thus redundant description is omitted.

Next, the operation will be described.
Here, since the operation up to the pulse width modulation circuit 104 is the same as that in the first embodiment, the description thereof will be omitted, and the operation of the circuit after the switching element 106A will be described.
When the pulse signal f shown in FIG. 2 from the driver circuit 105A is applied to the gate of the power FET Q1 in the switching element 106A, the FET Q1 is turned on at a portion where the pulse level of the pulse signal f is high.

  The pulse signal f has a signal level amplified by the driver circuit 105 in FIG. 1 by the driver circuit 105A in which two amplifiers are connected in parallel as described above in order to further reduce the output impedance.

  When the FET Q1 is turned on, the potential + BB from the DC power supply is short-circuited via the output transformer 108A and the FET Q1. On the other hand, when the pulse signal f is in a low level period and the FET Q1 is turned off, the potential + BB is applied to the output transformer 108A.

  This electromotive voltage is converted into a voltage from the primary side coil having a small number of turns of the output transformer 108A through the secondary side coil having a large number of turns, and is supplied to the ultrasonic vibration element 110. The power supply voltage is turned on / off at high speed by a 40 kHz modulation signal from the switching element 106A.

  As described above, even in the configuration shown in FIG. 4, a signal having a voltage level corresponding to each pulse width is applied to the ultrasonic vibration element 110, and as a result, the ultrasonic vibration element 110 is driven by the amplitude-modulated signal of 40 kHz. .

  In the first embodiment, when the pulse signal from the switching element 106 is in the on state, the coil 107 stores energy, and when the pulse signal is in the off state, a current flows through the output transformer 108 as indicated by the dashed arrow in FIG. . For this reason, the + BB power supply voltage does not need to be so high, and a general IC drive voltage of 5V operates sufficiently.

  On the other hand, in the second embodiment, the coil 107 as in the first embodiment is not provided, and the application of the power supply voltage to the output transformer 108A is merely turned on and off by the switching element 106A. Thus, in order to drive the ultrasonic vibration element 110 with a large amplitude, a general IC drive voltage of 5V is insufficient and the power supply voltage must be increased.

  Further, when the ultrasonic vibration element 110 serving as the capacitive system is driven by the transformer 108A serving as the inductor system, it is most efficiently driven to resonate the load of the transformer and the vibrator to the switching frequency (40 kHz) by the pulse signal. it can. That is, when the transformer load is viewed from the drain side of the FET Q1 of the switching element 106A, the large-capacity ultrasonic vibration element 110 is excited by resonating with the carrier frequency of the finite amplitude sound wave.

  As described above, in the configuration according to the second embodiment, a power supply voltage of several tens of volts, which is higher than a general 5V IC drive voltage, is required to increase drive efficiency.

  As described above, according to the second embodiment, the switching element 106A that opens and closes the connection with the ground according to the signal level of the modulation signal from the pulse width modulation circuit 104 is provided in series with the switching element 106A. One end of the primary side coil is connected to the power source, the other end is connected to the switching element, and a high output is output from an output transformer 108A that supplies a power source voltage to the ultrasonic vibration element 110 provided in the secondary side coil. Since the amplifier circuit is configured, it can be configured with a simpler circuit than the first embodiment and can be operated with stable performance.

It is a circuit diagram which shows the structure of the drive device of the ultrasonic vibration element by Embodiment 1 of this invention. FIG. 4 is a diagram illustrating signal waveforms in respective parts of the ultrasonic vibration element driving device according to the first embodiment. It is a figure for demonstrating the structure and its operation | movement of the high output amplifier circuit in FIG. It is a circuit diagram which shows the structure of the drive device of the ultrasonic vibration element by Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Microphone amplifier (signal input part), 101 Band pass amplifier (signal input part), 101a High pass amplifier, 101b Limiter, 101c Low pass amplifier, 102 Oscillation circuit (carrier signal generation part), 103 Sawtooth wave generation circuit (sawtooth wave generation) Part), 104 pulse width modulation circuit (pulse width modulation part), 105, 105A driver circuit, 106, 106A switching element, 107 inductance element, 108, 108A output transformer, 109, 109A capacitor, 110 ultrasonic vibration element, 111 high speed Switching diode, 112 Ring coil.

Claims (7)

A signal input unit for inputting an electric signal in an audible frequency band;
A carrier signal generator for generating a carrier signal in an ultrasonic frequency band;
A sawtooth wave generator for generating a sawtooth wave signal based on the carrier signal;
A pulse width modulation unit that generates a modulation signal having a pulse width corresponding to the signal level of the input signal from the sawtooth wave signal based on a result of voltage comparison between the sawtooth wave signal and the input signal of the audible frequency band; ,
A drive device for an ultrasonic vibration element, comprising: a drive voltage supply unit that drives the ultrasonic vibration element in accordance with the modulation signal and converts an input signal in the audible frequency band into an acoustic signal.   The drive voltage supply unit includes a switching element that opens and closes a connection to the ground according to the signal level of the modulation signal from the pulse width modulation unit, an inductor in which the switching element and one end are connected in series, and the other end is connected to a power source A power supply voltage is applied to the ultrasonic vibration element provided in the secondary coil, one end of the primary coil is connected to the power source, the other end is connected to the switching element, and the element is provided in parallel with the inductor element. The ultrasonic vibration element driving apparatus according to claim 1, further comprising an output transformer for supplying the ultrasonic vibration element.   The drive voltage supply unit is provided in series with the switching element that opens and closes the connection with the ground according to the signal level of the modulation signal from the pulse width modulation unit, and one end of the primary side coil is connected to the power source. The superstructure according to claim 1, further comprising an output transformer connected to the switching element and having an other end connected to the switching element and supplying a power supply voltage to an ultrasonic vibration element provided in a secondary coil. Drive device for acoustic vibration element. The signal input unit has an audible frequency bandpass filter,
4. The pulse width modulation unit performs voltage comparison between an input signal whose frequency band is limited by the band-pass filter and a sawtooth wave signal, according to claim 1. Drive device for ultrasonic vibration element.   The sawtooth wave generator includes a capacitor and a switching element that charges and discharges the capacitor according to a carrier signal from the carrier signal generator, and generates a sawtooth wave signal by charging and discharging the capacitor. The drive device for an ultrasonic vibration element according to any one of claims 1 to 4.   When generating the sawtooth wave signal, the sawtooth wave generator resets the signal level of the sawtooth wave signal based on the pulse at the frequency of the carrier signal from the carrier signal generator and determines its phase. 6. The ultrasonic vibration element driving device according to claim 1, wherein the ultrasonic vibration element driving device is a driving device.   The pulse width modulation unit has a comparator that compares the voltage of the sawtooth wave signal and the input signal of the audible frequency band, and based on the comparison result of the comparator, the sawtooth wave signal corresponds to the signal level of the input signal. The ultrasonic vibration element driving apparatus according to any one of claims 1 to 6, wherein a modulation signal having a pulse width is generated.

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