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DESCRIPTION JPH02113799

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DESCRIPTION JPH02113799
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
piezoelectric speakers, and more particularly to digital speakers which can be directly driven by
digitized audio signals such as PCM18. [Prior Art] As shown in FIG. 2, in a digital audio system,
an audio signal in the form of an analog signal is modulated by a PCM modulator 1 into a digital
signal, which passes through a transmission / recording / reproduction system, Again, it is
converted to an analog signal by the PCM demodulator 2 and turned into a speaker 3. As the
speaker 3, speakers of various types such as an electromagnetic type, an electrostatic type, or a
piezoelectric type are used. In digital audio systems, analog audio signals are converted to digital
signals for transmission / recording / reproduction, so it is possible to realize very high S / N
ratio and large kinamink range. . (Technical problem to be solved by the invention) In the
conventional digital audio system, the original sound can not be reproduced unless an analog
audio signal is inputted to the speaker 3. Therefore, it has been necessary to connect a
demodulator like the PCM demodulator 2 and having an A / A conversion capability between the
transmission / recording / reproduction system and the speaker 3. As a result, since the very
expensive PCM demodulator is required, the cost of the entire system becomes quite high, and it
has been a factor that prevents the system from being miniaturized, reduced in weight and
reduced in power consumption. An object of the present invention is to provide a digital speaker
which can directly input a digitized audio signal to reproduce an original sound. [Means for
Solving the Technical Problems] The present invention is a speaker utilizing bending vibration
due to the piezoelectric effect, and it is possible to directly drive with a digitized audio signal. In
the speaker of the present invention, the piezoelectric vibrating element is attached to the elastic
diaphragm. This piezoelectric vibrating element is made of piezoelectric ceramic in which
electrodes are formed on both main surfaces, and has a plurality of piezoelectric vibrating
portions driven for each bit signal of the digital input signal. Also, the plurality of piezoelectric
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vibration units are characterized in that the piezoelectric constants d of the plurality of
piezoelectric vibration units are different from each other so as to generate a sound pressure
corresponding to the weight of each bit digit of the digital input signal. . [Operation] A digitized
voice signal is in the form of a binary code, and in the present invention, a plurality of
piezoelectric vibration units are bits each time each bit signal of the binary code is input to each
piezoelectric vibration unit. It is driven every technique.
Then, the piezoelectric constants d of the respective piezoelectric vibrating parts are made
different from each other, whereby the piezoelectric vibrating parts generate a sound pressure
corresponding to the weight of each bit. Therefore, the plurality of piezoelectric vibration units
are directly driven by the digital input signal, and as a result, the waveform of the PAM wave and
hence the original sound is reproduced. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS.
1 and 3 are a plan view and a cross-sectional view taken along the line III-I of a piezoelectric
speaker according to an embodiment of the present invention. This embodiment is applied to a
digital speaker for direct driving by a 5-bit PCM signal. A disc-shaped piezoelectric vibrating
element 12 is attached on a disc-shaped elastic diaphragm 1 = 41 made of a metal material such
as brass using a conductive adhesive (not shown). The piezoelectric vibrating element 12 has a
structure in which a common electrode 14 is formed on the lower surface of a disk-shaped
piezoelectric ceramic, and a first to fourth divided electrodes 15 to 18 in the upper surface. In
the region where the first to fourth divided electrodes 15 to 18 are formed, the piezoelectric
ceramic layer interposed between the common electrode 14, each of the divided electrodes 15 to
18, and the common electrode 14 The 1st-4th piezoelectric vibration parts 21-24 are comprised.
The first to fourth piezoelectric vibrating units 21 to 24 are configured to be individually driven
by the focus signals of the PCM signal, as described later. Furthermore, the degree of polarization
of the piezoelectric ceramic layer interposed between the divided electrodes 15, 16 and 17 and
the common electrode 14 in each of the piezoelectric vibrating portions 21 to 24 is different, and
the piezoelectric constant d is different. . The reason why the piezoelectric constant d is different
is that, as will be described later, when the piezoelectric vibrating portions 21 to 24 are driven
for each focusing digit of the digital input signal, a sound pressure corresponding to the weight
of the bit digit is generated. To make it possible. That is, the piezoelectric constants d of the
plurality of piezoelectric vibrating portions 21 to 24 differ from each other to such an extent that
sound pressure can be generated according to the weight of the bit digit. Specifically, in the
present embodiment, the polarization of the piezoelectric ceramic layer in each of the
piezoelectric vibrating portions 21 to 24 is performed under the following conditions. However,
"one" polarization was performed by processing for 30 minutes at a temperature of 60 ° C. As
described above, in the present embodiment, the ratio of the piezoelectric constant d31 of the
first to fourth piezoelectric vibrating portions 21 to 24 is set to 38: 75: 150: 300 = 2 ° + 2 ′ +
22: 23. At the time of driving, as shown in FIG. 1, the lead wire 31 is connected to the elastic
diaphragm 11. The lead wire 31 is electrically connected to the common electrode 14 via the
elastic diaphragm 11 and a conductive adhesive (not shown).
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The lead wires 32 to 35 are electrically connected to the electrodes 15 to 18 on the upper
surfaces of the first to fourth piezoelectric vibrating portions 21 to 24, respectively. The elastic
diaphragm 11 may be made of an insulating material, or the piezoelectric vibrating element 12
may be attached to the elastic diaphragm 11 using an insulating adhesive such as an epoxy resin,
in which case the common Electrical extraction may be performed directly from the electrode 14.
Next, the operation of the above embodiment will be described. As shown in FIG. 4, the MSB (sign
focus) of the most significant bit digit in the PCM signal input signal of 5 hints is inverted by the
in-hook 36 and is inputted from the lead wire 31 to the common electrode 14. On the other
hand, on each of the electrodes 15 to 18 on the "two-faced side" of each of the piezoelectric
vibrating portions 21 to 24, bit signals of each bit digit from the lead wires 32 to 35 (LSB, bit 2,
bit sequentially from lower bit digit) 3) and the focus signal of bit 4) are input. Since the first to
fourth piezoelectric vibrating portions 21 to 24 have different piezoelectric constants (131
different from each other) such that the sound pressure ratio when driven alone is 2 ° + 2 ′:
22: 2 ′ By inputting each focus signal as in the above, the piezoelectric vibration units 21 to 24
generate sound pressure corresponding to the weight of the bit digit. Therefore, by combining
the sound pressures generated by the first to fourth piezoelectric vibration units 21 to 24, the
digitized sound signal is converted to a sound wave. However, as it is, the waveform of the
reproduced sound is a P A M wave. Therefore, it is preferable to combine a low pass filter that
passes a band of 1/2 or less of the zambling frequency, or to place an acoustic low pass filter on
the front of the speaker in order to make it approach the original sound. That is, by combining
such a low pass filter or an acoustic low pass filter, the PAM wave can be made into a continuous
sound pressure waveform. 5 (a) to 5 (d) are plan views showing modified examples of the split
electrode. As shown in FIG. 5A, divided electrodes 15a to 18a having different shapes and sizes
may be formed to form first to fourth piezoelectric vibrating portions having different areas.
Further, as shown in FIG. 5 (b), a square plate-like elastic diaphragm 11. The first to fourth
piezoelectric vibrating portions may be configured by forming rectangular divided electrodes
15b to 18b on a. Further, as shown in FIG. 5 (c), by forming divided electrodes 1.5c to 18c on the
plurality of piezoelectric ceramic plates 13a to 13d 'respectively, the first to fourth piezoelectric
vibrations are obtained. You may form a part.
That is, the piezoelectric vibrating element of the present invention does not necessarily have to
be integrally configured as in the embodiment of FIG. 1, and a plurality of piezoelectric vibrating
elements may be individually attached to an elastic diaphragm. Further, as shown in FIG. 5 (d), a
disc-shaped split electrode 1.56 is formed at the center of the disc-shaped piezoelectric seraminic
plate affixed to the elastic diaphragm 11, and an annular ring is concentrically formed around
the disc-shaped split electrode 1.56. The first to fourth piezoelectric vibrating portions may be
arranged concentrically by forming the divided electrodes 16 d to 18 d. FIG. 6 is a sectional view
showing a modification of FIG. 1 embodiment. Here, the piezoelectric vibrating element 12
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having the same structure as that of the piezoelectric vibrating element 2 of the embodiment
shown in FIG. That is, it has a bimorph structure in which piezoelectric vibrating elements are
attached to both sides of the elastic diaphragm. In this structure, similar operation can be
performed by connecting the corresponding divided electrodes on the upper surface and the
lower surface and connecting the corresponding bit signal to each piezoelectric vibrating unit as
shown in FIG. Further, in the above embodiment, the case of electro-acoustic conversion of 5-bit
PCM signal has been described, but the present invention is also applied to the case of
reproducing digital signals of other numbers of bits such as 8-bit and 16-bit. be able to. In that
case, it is possible to directly convert an audio signal digitized in the same manner as that
described above by simply changing the number and weighting of the piezoelectric vibration
parts according to the number of bits. The present invention can also be applied to the case
where digital signals of modulation schemes other than PCM modulation are converted into
sounds. According to the present invention, according to the present invention, the piezoelectric
constants d of the plurality of piezoelectric vibration units driven for each bit signal of the digital
input signal are made different, and the weight of each bit digit is generated. Since a weight of
17.4 = J is generated so as to generate a sound pressure corresponding to V, voice can be
reproduced by directly inputting each via signal to a plurality of piezoelectric vibration parts.
Therefore, it is possible to obtain high-quality reproduced sound only by directly connecting with
an amplifier that outputs a digital signal, and it is possible to omit an expensive PCM
demodulator. Therefore, the price of the digital audio system can be effectively reduced, and the
system can be miniaturized, reduced in weight and reduced in consumption. Furthermore, since a
plurality of piezoelectric vibrating parts are disposed on the elastic diaphragm and the
piezoelectric constants are made relatively different from each other, the mass productivity is
excellent, and hence the cost is low and the reliability is high. It is possible to realize a high
quality digital speaker.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a plan view of an embodiment of the present invention, FIG. 2 (a block diagram showing
an outline of a J digital audio system, FIG. 3 is a sectional view taken along the line II-III of FIG. 1
is a block diagram for explaining the method of driving the embodiment of FIG. 1, FIGS. 5 (a) to 5
(d) are plan views showing modifications of the divided electrodes, and FIG. 6 is another
embodiment of the present invention. FIG. 2 is a cross-sectional view of an example to explain the
present invention.
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In the figure, 1] denotes an elastic diaphragm, 12 denotes a piezoelectric vibration element, 14
denotes a common electrode, 15 to 18 denote split electrodes, and 21 to 24 denote first to fourth
piezoelectric vibration portions.
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