JPH0259650B2 - - Google Patents

Description

Detailed Description of the Invention (1) Technical Field of the Invention The present invention relates to a piezoelectric ceramic vibrator for a mechanical filter and a mechanical filter.

(2) Technical background Filters play an important role in signal or data transmission. For example, it plays an important role as a timing extraction filter in PCM transmission equipment. Generally, LC filters, that is, electric filters are mainstream as such filters. However, with the progress of LSI technology in recent years, there has been a strong demand for various parts to be smaller, more stable, and more reliable.
LC filters are no longer lacking in functionality. Therefore, there has been a growing trend to use mechanical filters in place of such LC filters.

(3) Prior art and problems Mechanical filters usually consist of a plurality of vibrators, couplers, support wires, etc., and vibrating parts using piezoelectric materials are promising as the vibrators. Especially PCM
Timing extraction filters built into in-home equipment are used at relatively low frequencies (approximately 200kHz),
Conventionally, mechanical filters (ceramic filters) using piezoelectric ceramic resonators in longitudinal vibration mode
has been mainly considered. However, although this type of ceramic filter has the advantage of being inexpensive, it has problems with stability against temperature and aging, and there is also a method of connecting the support wire that holds the piezoelectric ceramic vibrator directly to the electrode surface of the piezoelectric ceramic using solder, etc. Since this method can only be used in a variety of ways, problems such as electrode surface peeling may occur, which poses a problem in terms of component reliability. Furthermore, since piezoelectric ceramic itself is a brittle material, it is necessary to be careful in handling it during manufacturing processes such as cutting and polishing.

(4) Purpose of the Invention In view of the above-mentioned conventional problems and drawbacks, the present invention provides a piezoelectric ceramic vibrator for a mechanical filter that is excellent in stability and reliability and is easy to manufacture, and a mechanical filter comprising the same. The purpose is to

(5) Structure of the Invention In order to achieve the above object, the present invention comprises rectangular parallelepiped piezoelectric ceramics that are polarized in advance in a predetermined direction and that have the same shape and whose centers coincide with the centers of the piezoelectric ceramics. A piezoelectric ceramic vibrator for a mechanical filter is provided, which comprises electrodes made of a pair of constant-elasticity metal pieces bonded to the upper and lower surfaces of the piezoelectric ceramic, respectively, and is polarized in advance in the thickness direction, and the upper and lower surfaces are polarized in advance. A rectangular parallelepiped piezoelectric ceramic having a metal thin film formed on each entire surface of the lower surface, each having the same shape, each having a total length shorter than the total length of the piezoelectric ceramic, and each center of which coincides with the center of the piezoelectric ceramic. As shown in FIG. a connector and a support wire that are connected to each other, the support wire is joined to one of the pair of constant elastic metal thin pieces at the center position of the constant elastic metal thin piece, and the connector is connected to the constant elastic metal thin piece. A mechanical filter is provided which is joined to one of the pair of constant elastic metal thin pieces at a position other than the center position of the thin pieces and is excited in a bending vibration mode.

(6) Examples of the invention The present invention will be explained below with reference to the drawings.

FIG. 1 is a perspective view showing a conventional piezoelectric ceramic vibrator which is the closest type to the present invention as a piezoelectric ceramic vibrator used in a mechanical filter. In this figure, 10 is a piezoelectric ceramic vibrator, which is based on a piezoelectric ceramic 11. The piezoelectric ceramic 11 is polarized in its thickness direction. This polarization is shown as arrow A in the figure. Note that piezoelectric ceramics are generally used after being subjected to such polarization treatment. This is to generate linear distortion with respect to changes in the electric field. This electric field is created by applying an alternating current voltage to the metal thin films 12, 12' (only the top side shown) formed on the top and bottom surfaces of the piezoelectric ceramic 11 as both electrodes. . That is, the piezoelectric ceramic vibrator shown in FIG. 1 utilizes the transverse effect of displacement in a direction perpendicular to the direction of the electric field. This alternating voltage is applied through leads 13 and 13'. In this case, the lead wires 13, 13' are
They are respectively connected to the metal thin films 12 and 12' by soldering or the like.

FIG. 2 is a perspective view showing a piezoelectric ceramic vibrator for a mechanical filter according to the present invention. Note that the same reference numbers or symbols are given to the same components throughout the drawings. As is clear from the figure, the piezoelectric ceramic vibrator 20 for a mechanical filter of the present invention further includes thin metal pieces 21 and 2 on the upper and lower surfaces of the piezoelectric ceramic vibrator 10 of FIG.
1'. Since these serve as electrodes, the lead wires 13, 13' are connected to parts of these metal thin pieces 21, 21', respectively, rather than to the metal thin films 12, 12' in FIG. 1. Further, a connector and a support wire, which will be described later, are connected via these thin metal pieces 21 or 21'.

In the case of FIG. 1, the lead wire, connector, and support wire are bonded to the metal thin films 12, 12';
It is disadvantageous mainly in terms of strength, has manufacturing difficulties as a piezoelectric ceramic vibrator for mechanical filters, and is also disadvantageous in terms of stability and reliability. However, according to the present invention, a metal thin piece (not a metal thin film) is introduced as shown in FIG. 2, so that the above-mentioned difficulties and disadvantages are completely eliminated. What should be noted is that these metal flakes do not just eliminate these difficulties and disadvantages, but also produce new effects that will be described later.

The metal flakes 21, 21' have the same shape.
In short, exactly the same thing is provided on the top and bottom surfaces of the piezoelectric ceramic 11. If these metal flakes 2
If 1 and 21' are not the same, vibration purely in the longitudinal direction of the piezoelectric ceramic 11 cannot be obtained, and unnecessary bending vibration will occur. Further, the metal thin pieces 21, 21' are made of a constant elastic metal material.
It is generally known that the frequency temperature coefficient of a constant modulus metal material can be controlled by appropriately changing the heat treatment temperature of the constant modulus metal. Using this technology, for example, if the frequency temperature coefficient of the piezoelectric ceramic has a positive value, the heat treatment temperature is adjusted so that the temperature coefficient of the constant elastic metal material becomes negative, and the piezoelectric ceramic and constant elastic The frequency temperature coefficient of the composite vibrator made of a metal piece can be made to be zero temperature coefficient. In the end, metal flakes 21,2
1' and piezoelectric ceramic 11 make temperature compensation possible. Furthermore, the centers of these thin metal pieces 21, 21' are made to coincide with the center of the piezoelectric ceramic 11. This is to prevent unnecessary bending vibrations from occurring. The total length of these thin metal pieces 21, 21' is made shorter than the total length of the piezoelectric ceramic. In this case, these metal flakes 2
Although it is conceivable to make the total length of 1 and 21' the same as the total length of the piezoelectric ceramic (that is, to create a sandwich structure by sandwiching the piezoelectric ceramic between these thin metal pieces), in the present invention, we intentionally set the total length of the two pieces to be the same. will be established. This is because when these are configured as mechanical filters, there are advantages in that impedance adjustment is easy and third-order spurious can be easily removed (described later).

When an alternating current voltage is applied between the lead wires 13 and 13' of the piezoelectric ceramic vibrator 20 (FIG. 2) constructed as described above, the piezoelectric ceramic vibrator 20 operates under the longitudinal first mode of a predetermined frequency. is excited. In fact, in addition to the first mode, higher odd-order modes are also excited. However, these excitations are spurious. FIG. 3 is a graph showing the frequency response characteristics of the piezoelectric ceramic vibrator 20 shown in FIG. 2, in which the horizontal axis shows the frequency and the vertical axis shows the attenuation Loss. In this figure, response waveforms L ₁ , L ₃ and L ₅ are the first waveforms of longitudinal vibration, respectively.
Represents the next mode, the third mode and the fifth mode. Incidentally, since the metal thin pieces 21 and 21' have the same shape and are arranged in the same manner, spurious waves other than the vertical odd-order mode do not appear.

FIG. 4 is a perspective view showing an embodiment of the mechanical filter of the present invention using the piezoelectric ceramic vibrator 20 of FIG. 2. FIG. Two cases are shown as a plurality of piezoelectric ceramic vibrators, and each is distinguished by suffixes a and b. Reference numeral 41 in this figure represents a support line, which serves to mechanically support the piezoelectric ceramic vibrators 20a and 20b. Therefore, each piezoelectric ceramic vibrator is connected at its node. This node is located at the center of each of the metal flakes 21a' and 21b'. Further, 42 is a connector. Note that this connector 42 consists of a pair of thin metal pieces 21a',
There may be a plurality of pieces as long as they connect 21b'. However, with the connector 42, the thin metal piece 21
After connecting the metal thin pieces 21a and 21b',
It is not allowed to connect 1b with a connector. This is because the input and output are short-circuited. It is joined to the thin metal pieces 21a' and 21b' at a position other than the node. This coupler 42 is excited in a bending vibration mode. The signal input side of the mechanical filter 40 thus constructed is IN, and the filtered output is obtained from the output side OUT.

The mechanical filter 40 constructed as shown in FIG. 4 produces the special effects described below. The first effect is that impedance adjustment is easy. With the recent trend toward LSI, it is often required to create a difference between the input impedance Zin and the output impedance Zout of this mechanical filter 40. Specifically, Zin<Zout
It is. This is a condition based on a design requirement to suppress voltage attenuation in the mechanical filter 40 as small as possible when LSI-formed C-MOS circuits are connected to the input side and the output side of the mechanical filter 40.

The reason for producing the above first effect will be explained. FIG. 5 is a sectional view of the piezoelectric ceramic vibrator 20a shown in FIG.
This shows the case where a is cut in the length direction. FIG. 6 is a sectional view of the piezoelectric ceramic vibrator 20b shown in FIG. 4, and the direction of the cross section is the same as that in FIG. 5. A piezoelectric ceramic vibrator 20a (FIG. 5) on the side related to the input impedance Zin and a piezoelectric ceramic vibrator 20 on the side related to the output impedance Zout.
The difference from b (Fig. 6) lies in the presence or absence of slits S.
This slit S can be easily formed using, for example, a laser, and thereby the conduction between the metal thin films on both sides of the slit S is cut off. When there is no slit S (Fig. 5),
The total length of the electrode is L _P , and when there is a slit S (Fig. 6), the total length of the electrode is L _M. Here L _P ＞
The difference in length of L _M is related to the magnitude of Z _io and Z _put . 7 shows the piezoelectric ceramic vibrator 20a of FIG. 5 and the piezoelectric ceramic vibrator 2 of FIG.
0b is an equivalent circuit diagram common to 0b. In this diagram, L
is the equivalent inductance component, C is the equivalent capacitance component,
C _d is the damping capacity, R is the equivalent resistance, and the resonant frequency _r is It is determined by Note that _r in the case of FIG. 5 and _r in the case of FIG. 6 are the same. This is because the vibration frequency of a longitudinally vibrating piezoelectric ceramic depends only on its total length (the total lengths of the piezoelectric ceramics 11a and 11b are the same). Here, when the dimensions of the piezoelectric ceramic and the metal flake are constant, comparing the magnitude of the equivalent inductance L in Figures 5 and 6, the electrode area is larger in the case without the slit S in Figure 5. , the electrical-mechanical conversion efficiency is good and L is small. In other words, the equivalent inductance without the slit S (determining Z _io ) is smaller than the equivalent inductance with the slit S (determining Z _put ), and the expected Z _io < Z _put holds true. do. It should be noted that this is satisfied simply by the presence or absence of the slit S.

Next, a second effect obtained by the mechanical filter 40 configured as shown in FIG. 4 will be described. This second effect is that the third-order spurious mode can be easily suppressed. In conclusion, it is best to choose the relationship between L _P and L _M in Figure 6 as L _M ≒ 2/3 L _P. In practice, it is sufficient for a mechanical filter to satisfy this relationship only for the piezoelectric ceramic vibrator on the output side. As mentioned above, if we assume a sandwich structure in which piezoelectric ceramics (each having the same total length) are sandwiched between thin metal pieces, the relationship between L _M and L _P should be set to L _M ≒ 2/3 L _P. is not possible.

FIG. 8 is a graph showing the frequency response characteristics of the mechanical filter 40 of FIG. 4 that satisfies L _M ≒ 2/3 L _P , and the horizontal and vertical axes are the frequency and attenuation Loss, as in FIG. 3. shows. As shown in this graph, the third-order spurious mode _L3 is significantly suppressed. Also, the fifth spurious mode
_L5 is also considerably suppressed due to its function as a mechanical filter.

FIG. 9 is a graph used to explain the reason why the third-order spurious mode is significantly suppressed. x is the length of the intermediate position), and the vertical axis shows the piezoelectric ceramic 11
The distortion D appearing in a and 11b is shown. In the first place, piezoelectric ceramics convert mechanically strained alternating current voltage, and utilize the fact that positive or negative charges are induced by this mechanical strain.
Then, focusing only on the third excitation mode, the total amount of positive charge (indicated by the hatched region 91) induced by strain on the positive side and the total amount of negative charge induced by strain on one side. amount (hatching area 9
2,93) cancel each other out, and the induced charge eventually becomes zero. In other words, the third excitation mode does not appear as a filter output. This is the reason why the third-order spurious mode is suppressed.

(7) Effects of the invention As explained above, according to the present invention, stability,
A mechanical filter is realized that is highly reliable and easy to manufacture, and has special effects such as easy impedance adjustment and easy suppression of third-order spurious modes.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a conventional piezoelectric ceramic vibrator of the type closest to the present invention as a piezoelectric ceramic vibrator used in a mechanical filter, and FIG. 2 is a perspective view showing a piezoelectric ceramic vibrator for a mechanical filter of the present invention. 3 is a graph showing the frequency response characteristics of the piezoelectric ceramic vibrator 20 shown in FIG. 2, and FIG. 4 is a graph showing the frequency response characteristics of the piezoelectric ceramic vibrator 20 shown in FIG.
5 is a cross-sectional view of the piezoelectric ceramic vibrator 20a shown in FIG. 4, and FIG. 6 is a cross-sectional view of the piezoelectric ceramic vibrator 20a shown in FIG. 4. A sectional view of the vibrator 20b, FIG. 7 is a cross-sectional view of the piezoelectric ceramic vibrator 20 of FIG.
FIG. 8 is a graph showing the frequency response characteristic of the mechanical filter 40 of FIG. 4 that satisfies L _M ≒ 2/3 L _P. The figure is a graph used to explain the reason why the third-order spurious mode is significantly suppressed. 11a, 11b...piezoelectric ceramic, 12a,
12a', 12b, 12b'...metal thin film, 20a,
20b...Piezoelectric ceramic vibrator, 21a, 21
a', 21b, 21b'...metal thin piece, 41...support wire, 42...connector, S...slit.

Claims (1)

[Scope of Claims] 1. A rectangular parallelepiped piezoelectric ceramic that has been polarized in advance in a predetermined direction; A piezoelectric ceramic vibrator for a mechanical filter, characterized in that it is composed of an electrode made of a pair of constant elastic metal pieces that are bonded together. 2. A rectangular parallelepiped piezoelectric ceramic which is polarized in advance in the thickness direction and has metal thin films formed on its entire upper and lower surfaces, and which has the same shape and whose total length is shorter than the total length of the piezoelectric ceramic. It has a plurality of piezoelectric ceramic vibrators each having a plurality of piezoelectric ceramic vibrators each comprising a pair of constant-elastic metal pieces and electrodes bonded to the upper and lower surfaces of the piezoelectric ceramic so that the center of each vibrator coincides with the center of the piezoelectric ceramic. , further comprising a coupler and a support wire connected between the plurality of piezoelectric ceramic vibrators, and the support wire is bonded to one of the pair of constant elastic metal thin pieces at a central position of the constant elastic metal thin piece. The mechanical filter is further characterized in that the connector is joined to one of the pair of constant elastic metal thin pieces at a position other than the center position of the constant elastic metal thin pieces, and is excited in a bending vibration mode. 3 In at least one of the plurality of piezoelectric ceramic vibrators, the total length L _p of the piezoelectric ceramic
3. The mechanical filter according to claim 2, wherein the total length L _M of each of the constant elastic metal thin pieces satisfies L _M ≈2/3 L _P . 4. The mechanical filter according to claim 2, wherein in at least one of the plurality of piezoelectric ceramic vibrators, a slit is provided in each of the metal thin films parallel to each end face of each of the constant elastic metal thin pieces.