JP5088924B2 - Piezoelectric ceramic element drive circuit - Google Patents

Description

  The present invention belongs to the technical field of drive circuits for driving high-impedance piezoelectric ceramic elements.

A high signal voltage is required to supply the necessary oscillation power to the high impedance piezoelectric ceramic element.
There is a limit to increasing the power supply voltage of the power amplifier. Therefore, a winding ratio between the primary side and the secondary side can be obtained by connecting a piezoelectric ceramic element in parallel to the secondary side of the transformer using an output transformer to form a resonance circuit and exciting at the resonance frequency of the piezoelectric ceramic element. As a result, the required signal voltage was boosted.

  In FIG. 7, an output transformer 10 is connected to an analog amplifier SEPP (Single Ended Push Pull), and a sine wave having a resonance frequency of the piezoelectric ceramic element 5 is output. A piezoelectric ceramic is obtained by performing parallel resonance that resonates at the resonance frequency of the piezoelectric ceramic element on the secondary side of the transformer, and boosting the voltage on the secondary side with the winding ratio of the primary and secondary to obtain a necessary high voltage. It is applied to the element (see, for example, Patent Document 1).

FIG. 8 shows a half-bridge circuit of a digital amplifier whose output is SEPP. The primary side of the transformer is driven by a rectangular wave having a resonance frequency of the piezoelectric ceramic element, and the other is divided by a capacitor 12 and 13 to divide the power supply voltage by 1 / It is connected to the middle point of the capacitor with the voltage of 2. In the half bridge circuit, one side of the load cannot be grounded, but since a transformer is used, the secondary side can be grounded.
Although not shown, the primary side of the output transformer cannot be grounded even in a full bridge circuit (see, for example, Patent Document 2).
JP 2001-251874 A ([0029], [0030], FIGS. 1 and 2) Japanese Patent Laid-Open No. 11-136041 (FIG. 1)

However, the sine wave drive of the analog amplifier as shown in FIG. 7 has a problem that the power supply efficiency of the amplifier is not good.
In this regard, the digital power amplifier as shown in FIG. 8 amplifies the power of a rectangular wave signal with good power efficiency.
However, in this case, the output of the digital power amplifier, that is, the primary side of the output transformer 10 is a rectangular wave.

  On the other hand, the piezoelectric ceramic element 5 must be applied with a sine wave. That is, even if the primary side input of the output transformer 10 is a rectangular wave, the secondary side output must be a sine wave. For this reason, the coupling coefficient k between the first and second order of the output transformer 10 is made sparse (k ≦ 0.7), the harmonic energy contained in the rectangular wave is consumed as heat loss, and the sine of the fundamental frequency. Only the wave is output to the secondary side. As a result, there is a problem that the loss in the output transformer 10 is large and the overall power efficiency is not good despite the use of a digital power amplifier having a high power supply efficiency. Therefore, there is a problem that a cooling means must be provided.

In order to avoid loss in the output transformer 10, means for inputting the rectangular wave output of the digital power amplifier to the primary side of the output transformer 10 through a filter that passes only the sine wave of the fundamental frequency is conceivable. There is a problem of increasing.
As described above, in order to obtain a high voltage for exciting the high impedance piezoelectric ceramic element, there is a problem in boosting with a transformer.

  In view of the above-described problems of the prior art, the present invention provides a piezoelectric ceramic element driving circuit capable of applying a sine wave voltage higher than a rectangular wave output voltage of a digital power amplifier to a piezoelectric ceramic element without using a step-up transformer. It is a problem to realize.

The present invention has the following configurations in order to solve the above problems.
The first configuration (basic configuration) of the present invention is a piezoelectric ceramic element driving circuit including the following means.
(B) A digital switching amplifier having a SEPP circuit (b) A drive unit for driving the digital switching amplifier with a rectangular wave having a resonance frequency of the drive target piezoelectric ceramic element (c) Connected in parallel with the drive target piezoelectric ceramic element A capacitor and an inductor connecting the parallel circuit and the output point of the digital switching amplifier. The value of the capacitance C of the parallel capacitor and the value of the inductance L of the inductor are the electrodes of the parallel capacitor and the piezoelectric ceramic element. the resonant frequency of the resonant circuit between capacitor C ₁ and consists of said inductor with the same as the resonance frequency f ₀ of the piezoelectric ceramic element at its resonance frequency f _0, the sine wave applied between both ends of the driven piezoelectric ceramic element The voltage is K of the fundamental frequency sine wave component voltage included in the rectangular wave voltage at the output point of Nguanpu (> 1) so that the magnification, the following equation
(R ₁ / ω ₀ L) = ω ₀ (C + C ₁ ) R ₁ = K
However, ω ₀ = 2πf ₀ K> 1
R ₁ : Series resistance value of equivalent circuit of piezoelectric ceramic element
C ₁ : Electrode capacitance of piezoelectric ceramic element
Output circuit characterized by satisfying

  A second configuration of the present invention is a piezoelectric ceramic element driving circuit according to the first configuration, wherein a DC blocking capacitor is connected in series with the inductor of the output circuit.

  A third configuration of the present invention is a piezoelectric ceramic element driving circuit, characterized in that, in the first configuration or the second configuration, the duty ratio of the rectangular wave of the driving unit is variable by an external signal. .

  According to a fourth configuration of the present invention, there is provided a piezoelectric ceramic element driving circuit characterized in that the time position of the rectangular wave of the driving unit is variable by an external signal in the first configuration or the second configuration. is there.

  The fifth configuration of the present invention is characterized in that, in the first configuration or the second configuration, the duty ratio of the rectangular wave and the time position of the rectangular wave of the driving unit are each variable by an external signal. It is a piezoelectric ceramic element drive circuit.

According to the first configuration (basic configuration) of the present invention, the output of a digital switching amplifier driven by a rectangular wave of a driving unit is applied to a parallel circuit of a piezoelectric ceramic element and a capacitor via an inductor in series. Therefore, the frequency of the rectangular wave is set to the resonance frequency of the piezoelectric ceramic element.
This is shown in FIG. 6 (a).

The piezoelectric ceramic element is generally expressed by an equivalent circuit as shown in (b) of FIG. 6, since this is the impedance of the series resonant circuit capacitor C ₂ and the inductor L ₁ becomes zero when operating at the resonant frequency of the piezoelectric element, The equivalent circuit is as shown in FIG. C ₁ is Ri interelectrode capacitance der piezoceramic element, R ₁ is Ru series resistor der of the equivalent circuit. And in this basic configuration, inductance and capacitance of the capacitor of the inductor is set to a value such resonance frequency of the resonance circuit consisting of the parallel circuit and the inductor electrode capacitance C ₁ and the capacitor becomes the resonance frequency of the piezoelectric ceramic element Has been.

  That is, this resonance circuit functions to extract a sine wave component having the same frequency from a rectangular wave signal having the same frequency as the resonance frequency of the piezoelectric ceramic element, which is supplied from a rectangular wave power source.

As an order of explanation, as shown in FIG. 6E, when the circuit after the inductor is driven by a sine wave power source of voltage V, the voltage V _q applied to both ends of the piezoelectric ceramic element becomes any value. Let's see.
The inductance of the inductor L, and the capacitance of the capacitor C, and the resonance frequency of the piezoelectric ceramic element and f _0.
V _q applied to the piezoelectric ceramic element is a voltage between bc obtained by dividing the power supply voltage V by the impedance between ab and the impedance between bc.
Impedance Zb between _ab and impedance Zbc between _ab and _bc is expressed by Equation 1.

Therefore, V _q is expressed by Equation 2.

Here, if ω at the resonance frequency f ₀ is ω ₀ , Equation 3 is established.

  From Equation 3, Equation 2 becomes Equation 4.

Formula 5 is established from Formula 4 ,

The value of Equation 5 as K, Compared viewed Equation 4 and Equation 5, the amplitude of the voltage V _q applied to the piezoelectric element indicates that becomes K times the magnitude of the supply voltage V.
That is, Formula 6 is established.

Therefore, when you want multiplied by K times the magnitude of the supply voltage to the piezoelectric ceramic element is to say may be obtained inductance L and capacitance C values of Equation 5 ing and K.
If the piezoelectric ceramic element to be used is determined, C ₁ , R ₁ , and ω ₀ in Formula 5 are determined as known numbers, so that L and C can be easily obtained.
In the above, the case of driving with a sine wave power source has been described, but on the assumption of this, the case of driving with a rectangular wave will be described.

Looking at the frequency component of the rectangular wave that continues repeatedly, it contains a sine wave with the same frequency as the fundamental frequency of the rectangular wave and a sine wave with an odd multiple, and the higher the frequency, the smaller the amplitude. Yes.
If the power source is a square wave having the same frequency as the resonance frequency of the piezoelectric ceramic element as in FIG. 6 (d), composed of a inter-electrode capacitance C ₁ and the capacitor and inductor also piezoelectric its resonant frequency square wave power and A resonance circuit having the same resonance frequency as the ceramic element functions as a filter for extracting a sine wave having the fundamental frequency from the power source rectangular wave.

Then, the repetition frequency of the square wave f, when the square wave time width (pulse width) was set to A, and the amplitude V _S of the rectangular wave in the power supply, the fundamental frequency sine wave that contains an amplitude V _P-P It is known that there is a relationship of Formula 7 by Fourier analysis.

  Af in the equation is a ratio (duty ratio) of A to the repetition period of the rectangular wave. When the duty ratio is 50%, sin (πAf) is 1, and thus Equation 8 is obtained.

Accordingly, in FIG. 6D, when the amplitude of the power source rectangular wave is V _S , the voltage V _q applied to both ends of the piezoelectric ceramic element is expressed by Equation 6 and Equation 8 from Equation 9.

That is, when the duty ratio is 50%, a sine wave voltage 4 K / π times the amplitude of the rectangular wave is applied to both ends of the piezoelectric ceramic element.
Thus, once the piezoelectric ceramic element to be used is determined, the necessary applied voltage V _q , resonance frequency f ₀ , interelectrode capacitance C ₁ , and equivalent resistance R ₁ are determined as known numbers. if the power supply voltage applied is determined, because also determined amplitude V _S of the rectangular wave, seeking K from first V _S and V _q by equation 9, the inductance L and capacitance C of the capacitor of the inductor by equation 5 from the obtained K is The required high voltage _Vq can be applied to the piezoelectric ceramic element.

Thus, the present invention uses a power efficient digital switching amplifier, does not use a lossy step-up transformer to convert a rectangular wave into a sine wave, and uses a resonant circuit filter that resonates at the resonance frequency of the piezoelectric ceramic element. it allows to reduce the loss, there is a remarkable effect of the 4 K / [pi times as high sinusoidal voltage higher than the voltage of the rectangular wave output from the digital switching amplifier can be applied to the piezoelectric ceramic element.

The digital switching amplifier used in the present invention is best used with a low output impedance.
Also, the output is best not a sinusoidal wave but a rectangular wave.
It is best to apply a voltage to the piezoelectric ceramic element so that one terminal can be connected to ground.

Hereinafter, embodiments of the piezoelectric ceramic element driving circuit of the present invention will be described with reference to the drawings.
FIG. 1A shows a circuit configuration of a first embodiment of the drive circuit according to the present invention.
Constitute a digital switching power amplifier SEPP with two N-channel power MOS FET _{M 1} and _{M 2.} The drain D of the MOS FET M ₁ is connected to a power supply _{V CC,} the source S is the source S of the MOS FET _{M 2} is connected to the drain D of the MOS FET _{M 2} is connected to ground.
Has become a connection point of the drain D of the source S and the MOS FET _{M 2} of MOS FET M ₁ is an output terminal, connected to the inductor 3 via the capacitor 6 of the DC component blocking, the output of the inductor 3 and the capacitor 4 It is connected to a parallel circuit with the piezoelectric ceramic element 5. The other end of the parallel circuit is grounded with the source of the MOS FET _{M 2.} The drive unit 1 alternately drives the gates of the MOS FETs M ₁ and M ₂ with a rectangular wave having the same frequency as the resonance frequency of the piezoelectric ceramic element 5. That, M ₂ when M ₁ is turned on is turned off, M ₁ is off driven such M ₂ is turned on.

By this operation, the output end a, M ₁ is turned on, M ₂ appears a voltage lowered by D-S voltage of the power supply voltage V _CC at the time of off, when the opposite, D-S voltage from the ground potential Only a high voltage will appear. Since all of these voltages are on one side with respect to the ground potential, they contain a direct current component. However, since the direct current component is unnecessary for driving the piezoelectric ceramic element, it is blocked by the capacitor 6. The capacitance of the capacitor 6 is sufficiently large so as not to affect the resonance frequency of the resonance circuit composed of the inductor 3 and the capacitance between the electrodes of the capacitor 4 and the piezoelectric ceramic element.

FIG. 1B is a diagram in which the piezoelectric ceramic element 5 of FIG. 1A is replaced with an equivalent circuit during operation at the resonance frequency.
Thus, the drive unit 1 and the digital switching power amplifier 2 is equivalent to the rectangular wave power supply (d) of FIG. 6, the capacitor 6, the inductor 3, the operation of the resonant circuit composed of the capacitor 4 and the inter-electrode capacitance C ₁ Except for the fact that it has no effect, FIG. 1 (b) is the same as the circuit of FIG. 6 (d), and the operation described in FIG. Become.

FIG. 2 shows a circuit of a second embodiment of the drive circuit according to the present invention. The piezoelectric ceramic element is shown as an equivalent circuit when operating at a resonance frequency, as in FIG.
1 in that, in that the source S of the MOS FET _{M 2} digital switching power amplifier 7 is connected to the negative power source _{-V CC.} The driving by the driving unit 1 is the same as in the case of FIG. M ₁ is _{M 2} When on off, _{M 1} is _{M 2} is turned on when off. Thus, the output point a is or are connected to the connected or -V _CC to supply V _CC, a rectangular wave amplitude is obtained close to twice the substantially V _CC.

Since this rectangular wave has almost plus / minus waveform with the ground potential interposed therebetween and does not include a DC component, the DC blocking capacitor 6 as shown in FIG. 1 is unnecessary and is not used.
The other points are the same as in FIG.

FIG. 3 shows a third embodiment in which the power MOS FET is a P channel type on the positive power supply side and an N channel type complementary type (complementary) on the negative power supply side. This method is exactly the same as the output format of CMOS IC. Since the digital switching power amplifier of FIG. 3 is a complementary SEPP circuit, the driving of the drive unit 8 is different from the case of FIGS. 1 and 2, and the MOS FETs M ₃ and M ₂ are driven by the same-polar rectangular wave.
Since both + V _CC and -V _CC are used as the power source, the DC component is not included in the output from the output point a as in the case of FIG. 2, and therefore no DC component blocking capacitor is used.

Next, power control by the drive unit will be described.
As described in the effect of the invention, the time width (pulse width) of the rectangular wave is A, the amplitude is V _S , and the amplitude V _P-P of the sine wave of the frequency f included in the rectangular wave of the repetition frequency f is between. There is a relationship of Formula 7. Therefore, the amplitude of the sine wave changes by changing the duty ratio Af. When the duty ratio Af is 0.5, the term of sin becomes 1 and becomes maximum, and otherwise, it becomes smaller according to the sin curve.
Therefore, by changing the pulse width A, the sine wave voltage applied to the piezoelectric ceramic element 5 can be changed, so that the power output to the piezoelectric ceramic element 5 can be changed. That is, power control is possible.

FIG. 4 is a diagram showing the difference in the amplitude of the sine wave when the duty ratio is 0.5 and 1/6 at a certain K with the time axis of the rectangular wave and the time axis of the sine wave coincident. is there.
(A) is a rectangular wave with a duty ratio of 0.5 at the top and 1/6 at the bottom.
(B) is a corresponding sine wave where the larger amplitude has a duty ratio of 0.5 and the smaller amplitude has a duty ratio of 1/6. By changing the duty ratio from 0.5 to 1/6, the amplitude of the sine wave is halved.
Since the pulse width can be easily controlled by a known technique, the power control can be easily performed by sending a pulse width control signal to the driving unit shown in FIGS.

  In addition, in the repetitive waveform of the rectangular wave, it is possible to easily control at which point in one cycle the rectangular wave is raised by a well-known technique. it can.

FIG. 5 shows that the phase of a sine wave having a half amplitude corresponding to a square wave having a duty ratio of 1/6 in FIG. It is a figure which shows having moved so that it may align with the sine wave.
Thus, the amplitude and phase of the sine wave applied to the piezoelectric ceramic element can be controlled by sending a control signal to the drive unit.
In a scanning sonar that transmits and receives waves by arranging tens or hundreds of piezoelectric ceramic elements, it is necessary to change the beam direction and to suppress side lobes.

In order to suppress the side lobes, the excitation amplitude for the arranged piezoelectric ceramic elements must be weighted by a window function such as Hamming, Hanning, Chebyshev or the like according to the arrangement position.
In order to change the beam direction, it is necessary to change the excitation phase according to the arrangement position of the piezoelectric ceramic elements.

In the piezoelectric ceramic element driving circuit of the present invention, as described above, a signal for controlling the pulse width of the switching rectangular wave generated in the driving unit and a signal for controlling the rising position of the rectangular wave are sent to the driving unit. by sending, it is possible to control the sine wave of amplitude and phase applied to the piezoelectric ceramic element, the scanning two Ngusona and other phases beam direction control and sidelobes in phased array using the driving circuit of the present invention Sufficient suppression can be performed.

It is a figure which shows the circuit structure of the 1st Example of this invention drive circuit. It is a figure which shows the circuit structure of the 2nd Example of this invention drive circuit. It is a figure which shows the circuit structure of the 3rd Example of this invention drive circuit. In the drive circuit of the present invention, it is a diagram for explaining that the amplitude of a sine wave applied to the piezoelectric ceramic element is changed by changing the pulse width A of the rectangular wave of the drive unit. It is a figure explaining change of the phase of the sine wave applied to a piezoelectric ceramic element by changing the time position of the rectangular wave of a drive part in the present invention drive circuit. FIG. 6 is a diagram illustrating the principle of the drive circuit according to the present invention. When a resonance circuit that resonates at a resonance frequency of a piezoelectric ceramic element is driven by a rectangular wave having a resonance frequency, a high voltage sine is K times the fundamental frequency sine wave component voltage included in the rectangular wave amplitude. It is explanatory drawing that a wave is applied to a piezoelectric ceramic element. It is a piezoelectric ceramic element drive circuit diagram using a conventional analog power amplifier and a step-up transformer. It is a piezoelectric ceramic element drive circuit diagram using a conventional digital power amplifier and a step-up transformer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Drive part 2 Digital switching power amplifier 3 Inductor 4 Capacitor 5 Piezoceramic element 6 Capacitor 7 Digital switching power amplifier 8 Drive part 9 Digital switching power amplifier 10 Output transformer 11 Analog amplifier 12 Capacitor 13 Capacitor

Claims (5)

A piezoelectric ceramic element driving circuit comprising the following means.
(B) A digital switching amplifier having a SEPP circuit (b) A drive unit for driving the digital switching amplifier with a rectangular wave having a resonance frequency of the drive target piezoelectric ceramic element (c) Connected in parallel with the drive target piezoelectric ceramic element A capacitor and an inductor connecting the parallel circuit and the output point of the digital switching amplifier. The value of the capacitance C of the parallel capacitor and the value of the inductance L of the inductor are the electrodes of the parallel capacitor and the piezoelectric ceramic element. the resonant frequency of the resonant circuit between capacitor C ₁ and consists of said inductor with the same as the resonance frequency f ₀ of the piezoelectric ceramic element at its resonance frequency f _0, the sine wave applied between both ends of the driven piezoelectric ceramic element The voltage is K of the fundamental frequency sine wave component voltage included in the rectangular wave voltage at the output point of Nguanpu (> 1) so that the magnification, the following equation
(R ₁ / ω ₀ L) = ω ₀ (C + C ₁ ) R ₁ = K
However, ω ₀ = 2πf ₀ K> 1
R ₁ : Series resistance value of equivalent circuit of piezoelectric ceramic element
C ₁ : Electrode capacitance of piezoelectric ceramic element
Output circuit characterized by satisfying   2. The piezoelectric ceramic element driving circuit according to claim 1, wherein a direct current blocking capacitor is connected in series with the inductor of the output circuit.   3. The piezoelectric ceramic element driving circuit according to claim 1, wherein the duty ratio of the rectangular wave of the driving unit is variable by an external signal.   3. The piezoelectric ceramic element driving circuit according to claim 1, wherein the time position of the rectangular wave of the driving unit is variable by an external signal.   3. The piezoelectric ceramic element driving circuit according to claim 1, wherein the duty ratio of the rectangular wave and the time position of the rectangular wave of the driving unit are variable by an external signal.

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