JP2510833Y2 - Ladder type piezoelectric filter for high frequency - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a ladder type piezoelectric filter used in a filtering circuit of a portable mobile radio, an automobile telephone, etc., and is particularly used in a high frequency region of 1 MHz or more. The present invention relates to a ladder type piezoelectric filter.

[Prior Art] Most of the conventional ladder type piezoelectric filters are designed to operate at a response frequency of 455 KHz. Such a filter is constructed by combining a thick-walled small-capacity piezoelectric resonator having a resonance frequency of 455 KHz and a thin-walled large-capacity piezoelectric resonator having an anti-resonance frequency of 455 KHz in series and in parallel, respectively, as shown in FIG. This is a ladder-type filter circuit.

[Problems to be solved by the invention] Recently, as a filter of a radio communication device for a car telephone, 1.2M
Ladder-type piezoelectric filters that operate in high-frequency regions such as Hz and 1.7 MHz have been demanded. However, when trying to meet this demand based on the conventional configuration, the size of the piezoelectric resonator is reduced.
It was practically impossible because it had to be reduced to 2 mm or less compared to 5 mm for 455 KHz.

On the other hand, in the case where the disk-shaped piezoelectric resonator or the rectangular plate-shaped piezoelectric resonator having the above-mentioned size of 5 mm exhibits the vibration in the circumferential direction, as shown in FIGS. Second- and third-order harmonic modes SM and TM appear with the fundamental mode FM having resonant impedance. 455KHz
The resonator uses this fundamental mode FM. In this way, even in the conventional resonator, the second and third harmonic modes S
Since M and TM appear at 1MHz or more, it is possible to use this mode. However, this has a problem that the resonance impedance is relatively small compared to the fundamental mode.

An object of the present invention is to provide a ladder-type piezoelectric filter that can be used in a high frequency range without causing a large change in the shape of a conventional resonator.

[Means for Solving the Problems] The present invention provides a thick-walled small-capacity series branch piezoelectric resonator that exhibits circumferential vibration in a secondary mode or a tertiary mode, and also exhibits circumferential vibration in a secondary mode or a tertiary mode. A series-parallel circuit is formed by a thin-walled and large-capacity parallel branch piezoelectric resonator, and the series branch piezoelectric resonator and the parallel branch piezoelectric resonator have electrodes formed on at least one surface of the series branch piezoelectric resonator and a central electrode through an insulating gap. Part and one or two annular outer electrode parts surrounding them, and the central electrode part region and the one or two outer electrode part regions are polarized such that adjacent regions are in opposite directions, and The electrode part and one or two outer electrode parts are electrically connected.

[Operation] A piezoelectric resonator, which is divided into a center electrode part and one outer electrode part by one insulating gap and polarizes these regions in mutually opposite directions, has a phase of 180 ° with the insulating gap as a boundary. It will be forced to vibrate in a different secondary mode SM. In addition, the piezoelectric resonator, which is divided into a central electrode part and two outer electrode parts by two insulating spaces, and these regions are polarized in opposite directions, has a 180 ° phase difference with the insulating space as a boundary. It will be forced to vibrate in the third mode TM. Therefore, such a secondary mode type piezoelectric resonator or a tertiary mode type piezoelectric resonator can generate resonance and anti-resonance of 1 MHz or more without reducing the size, and therefore these piezoelectric resonators are combined in series and in parallel. This makes it possible to construct a ladder-type piezoelectric filter that obtains a filtering characteristic of 1 MHz or higher.

EXAMPLES Figure 1 shows a serial branch piezoelectric resonator S ₁ to S ₃ thick small capacity, which is inserted in series branch of the ladder-type filter circuit.
In order to explain the manufacturing process of the resonators S _{1 to} S ₃ , first, the electrode 2 formed on one surface of the disk element 1 made of a piezoelectric ceramic such as lead zirconate titanate is removed by annularly removing the electrode layer. The center electrode portion 2a and the outer electrode portion 2b are formed by the formed insulating gap 2c.
Split into and. Next, a predetermined DC high electric field is applied between the central electrode portion 2a and the whole surface electrode 3 on the other surface to polarize the outer electrode portion.
A predetermined direct current high electric field is applied between the 2b and the other whole surface electrode 3 in the opposite direction to polarize. After this polarization, the center electrode portion is formed by the conductive bridge 4 made of a conductive adhesive, solder, or the like arranged so as to straddle a part of the insulating gap 2c.
2a and the outer electrode portion 2b are electrically connected. Thus, the resonators S _{1 to} S _{3 including} the two electrode portions 2a and 2b divided by the insulating gap 2c are formed.

FIG. 2 shows thin-walled and large-capacity parallel-branch piezoelectric resonators P _{1 to} P ₃ which are inserted into the parallel branches of the ladder-type filter circuit, and like the above-described series-branch piezoelectric resonators S _{1 to} S _3. , The electrode 12 formed on one surface of the disc element 11 is divided into a central electrode portion 12a and an outer electrode portion 12b by one insulating circumferential gap 12c, and between the central electrode portion 12a and the entire surface electrode on the other surface, And the outer electrode portion 12b
And the full-surface electrode 13 are polarized in opposite directions, respectively, and then the conductive bridge is arranged so as to straddle a part of the insulating gap.
The central electrode portion and the outer electrode portion are electrically connected by 14;

FIG. 3 shows a high frequency ladder type piezoelectric filter according to the present invention.
20, and the series branch piezoelectric resonators S _{1 to} S ₃ shown in FIG. 1 above.
And the parallel branch piezoelectric resonators P _{1 to} P ₃ shown in FIG. 2 in a case 22 together with a plurality of terminal plates 21 so as to form the ladder type filtering circuit shown in FIG. 7. Stored, each terminal board 21
The input-side connecting branch piece 23a, the output-side connecting branch piece 23b, and the ground-side connecting branch piece 23c that extend from the above project from the opening surface of the case 22. Further, a leaf spring metal plate 24 and a metal spacer 25 are interposed at one end position in the case 22 and the case is
A screw 26 screwed to the other side surface of 22 is screwed to apply a required clamping force for clamping each resonator, thereby ensuring electrical connection of each member. An epoxy resin 28 is sealed in the opening of the case 22 via a shield plate 27.

Next, FIG. 4 shows the filtering characteristics measured for the ladder type piezoelectric filter 20 of the present invention having the above-mentioned basic structure.
The piezoelectric resonators used are as follows.

B) Series branch piezoelectric resonator (S _{1 to} S ₃ ) 3.5mmφ × 0.6mm disk element 1 made of lead zirconate titanate, on one surface of which a center electrode part 2a with a diameter of 1.5mm and an insulating perimeter of 0.5mm width are provided. The gap 2c and the outer electrode portion 2b are formed on the other surface of the disc element 1 by silver baking, and the gap between the center electrode portion 2a and the whole surface electrode 3 and between the outer electrode portion 2b and the whole surface electrode 3 are formed. After applying a direct current voltage of 3 KV / mm in the opposite direction for polarization, silver paint 4 was applied so as to straddle a part of the insulating peripheral space 2c, and the resonance frequency was set to 1.7 MHz.

B) Parallel branch piezoelectric resonator (P _{1 to} P ₃ ) The thickness of the disk element 11 is reduced to 0.35 mm, and the antiresonance frequency is reduced.
It was manufactured under the same conditions as the above-mentioned series branch piezoelectric resonator except that it was set to 1.7 MHz.

As is clear from the result of FIG. 4, the _one using the above-mentioned piezoelectric resonators (S _{1 to} S ₃ , P _{1 to} P ₃ ) can obtain a ladder type piezoelectric filter having a filtering characteristic of 1.7 MHz. did it.

In addition, although the above-described embodiments have described the ladder-type piezoelectric filter using the piezoelectric resonator that exhibits the circumferential vibration in the secondary mode, the series-branch piezoelectric resonators (S _{1 to} S ₃ ) and the parallel-branch piezoelectric resonator ( By arranging P _{1 to} P ₃ ) as shown in FIGS. 5 and 6, it is possible to exhibit circumferential vibration in the third-order mode. That is, as shown in the figure, the electrodes 2 (12) formed on one surface of the device are connected to the two insulating spaces 2c ₁ and 2c.
₂ (12c ₁ , 12c ₂ ) divides the center electrode part 2a (12a) into two outer electrode parts 2b ₁ , 2b ₂ (12b ₁ , 12b ₂ ), and the adjacent electrode part regions are alternately reversed. After being polarized so as to have the polarization axis of, the central electrode portion and the two outer electrode portions are electrically connected by the conductive bridges 4a, 4b (14a, 14b).

Further, by using the third-order mode type piezoelectric resonator having this configuration, it is possible to provide a filter having a higher frequency.

In each of the above-mentioned embodiments, the electric connection between the central electrode portion and the outer electrode portion, which are formed by dividing the piezoelectric resonator on one surface, is made by the conductive bridge. However, as shown in FIG. When assembled with the terminal plate 21 in the terminal plate 22, the terminal plate arranged on one surface side of the piezoelectric resonator is provided with a contact for contacting with and holding the central electrode part and another contact for contacting with the outer electrode part. The electrical connection between the center electrode portion and the outer electrode portion can be ensured by various configurations such as the use of, and in this case, the conductive bridge can be omitted.

Further, in each of the above-mentioned embodiments, the disk-shaped piezoelectric resonator is used, but the same applies to the case of using the plate-shaped piezoelectric resonator, and the number of series branch piezoelectric resonators and parallel branch piezoelectric resonators to be used is The amount of attenuation can be increased as needed by increasing or decreasing it as needed.

[Advantages of the Invention] As described above, according to the present invention, it is possible to obtain characteristics that can be used in a high frequency region without causing a large change in the shape of the piezoelectric resonator, and thus, it has been impossible to obtain it at all. There is an excellent effect that a ladder filter for high frequency of 1 MHz or more can be easily provided.

[Brief description of drawings]

The accompanying drawings show an embodiment of the present invention, FIG. 1 shows series-branch piezoelectric resonators S _{1 to} S ₃ , FIG. 1A is a plan view, and FIG. 1B is a diagram with radial waveforms. A cross-sectional view taken along the line A-A, 2nd
Figure shows a parallel branch piezoelectric resonator P ₁ to P _3, second spinal plan view, the second Zuro the second spinal shown with radial waveform B-
A sectional view taken along line B, FIG. 3 is a longitudinal side view of the ladder-type piezoelectric filter 20, FIG. 4 is a waveform diagram showing the filtering characteristic of the ladder-type piezoelectric filter 20, and FIG. 5 is another example of a series-branch piezoelectric resonator S ₁ indicates to S _3, 5 spinal plan view, C-C line cross-sectional view of a fifth cerebrospinal fifth Zuro is shown with radial wave, the parallel branches piezoelectric resonator of FIG. 6 is also another example 6A and 6B show P _{1 to} P ₃ , FIG. 6A is a plan view, FIG. 6B is a sectional view taken along the line DD of FIG. 6A showing a waveform in the radial direction, and FIG. 7 is a ladder type filter circuit diagram. . Further, FIG. 8 is a graph showing the relationship between impedance and frequency of the conventional resonator, and FIG. 9 is a waveform chart in the circumferential direction. S _{1 to} S ₃ … Series branch piezoelectric resonators P _{1 to} P ₃ … Parallel branch piezoelectric resonators 2, 12… Electrodes 2a, 12a… Center electrode parts 2b, 2b ₁ , 2b ₂ , 12b, 12b ₁ , 12b ₂ … Outer electrode portion 2c, 2c ₁ , 2c ₂ , 12c, 12c ₁ , 12c ₂ ... Insulating gap 4a, 4b, 14a, 14b ... Conductive bridge

Claims (1)

(57) [Scope of utility model registration request] 1. A thick-walled small-capacity series branch piezoelectric resonator exhibiting circumferential vibration in a secondary mode or a tertiary mode, and a thin-wall large-capacity parallel branch piezoelectric resonance also exhibiting circumferential vibration in a secondary mode or a tertiary mode. And a parallel-branch piezoelectric resonator, the series-branched piezoelectric resonator and the parallel-branched piezoelectric resonator have electrodes formed on at least one surface thereof and a central electrode portion and one or two electrodes surrounding the central electrode portion through an insulating gap. And the outer electrode part region of the central electrode part and one or two outer electrode part regions are polarized so that the adjacent regions are in opposite directions, and the central electrode part and one or two outer parts are polarized. A high-frequency ladder-type piezoelectric filter characterized in that it is electrically connected to an electrode portion.