JPS5821444B2 - Energy Tojikomegata Atsuden Tairohaki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an energy confinement type piezoelectric filter that eliminates unnecessary responses. In particular, the present invention relates to an energy confinement type piezoelectric filter that eliminates unnecessary responses. This invention relates to an energy confinement type filter in which electrodes are arranged close to each other in parallel.

FIG. 1 is a diagram showing an example of the configuration of a conventional energy confinement type piezoelectric filter, in which electrodes 2, 2', 3, 3
' is provided, electrode 2 is connected to input line 8, electrode 3 is connected to output line 9
In addition, the electrodes 2', 3' are connected to a common line 10.

Furthermore, Fig. 2 shows a conventional example using multiple piezoelectric plates.
Electrodes 4, 4', 5, 5' are provided on both sides of the piezoelectric plate 1, and electrodes 6, 6', 7 are provided on both sides of the other pressure heavy plate 1'.
．． 7' is provided, the electrode 4 is connected to the input wire, the electrode 4' is connected to the common line, and the electrode 5, 5' is connected to the electrode 6 through the capacitor 11.
6', the electrode 7 is connected to the output line 9, and the electrode 7' is connected to the common line 10.
It is used in a so-called tandem configuration.

In addition to crystal and piezoelectric ceramics, piezoelectric crystals such as lithium tantalate and lithium niobate are used as the piezoelectric material.

FIG. 3 is a diagram showing the electric field distribution in the piezoelectric plate of the corrugator shown in FIGS. 1.2, and 12 is the line of electric force.

The electric field distribution has a component perpendicular to the surface of the piezoelectric body 1 (hereinafter,
At the same time, a component parallel to the plane of the piezoelectric plate (hereinafter referred to as a parallel electric field) is generated in the gap between adjacent electrodes.

Here, the excitation mode due to the vertical electric field and the excitation mode due to the parallel electric field will be explained with reference to FIG.

As shown in Figure 3, the axis perpendicular to the piezoelectric plate surface is the Xi axis,
The parallel axis is the Xi axis (where i, j = 1°2 or 3,
i=j), the vertical electric field component can be expressed as E, and the parallel electric field component as E.

In the presence of N1 piezoelectric constant di In the presence of , the electric field E causes a strain of 5 J-d JE .

When these elastic waves accompanied by distortion propagate in the thickness direction, resonance occurs at a frequency determined by the speed of the Atsukichi elastic wave.

For example, in a lithium tantalate Z-cut plate, X i
=X 3=ηTsumugi,X.

If =x is the X axis, there are piezoelectric constants d33 and d15, so the vertical electric field causes a longitudinal strain S8, and the parallel electric field causes a shear strain S5.These generate standing waves in the thickness direction, so the vertical electric field causes Resonance of the thickness longitudinal wave is obtained, and on the other hand, resonance of the thickness shear wave is generated at a frequency different from that of the thickness longitudinal wave due to the parallel electric field.

In addition, in the case of lithium tantalate X-cut plate, xl−==x
, = X axis, Xj = x3 - Z axis, piezoelectric constant d15
1 dlfs and d:3. is not zero, the vertical electric field, that is, the electric field in the X-axis direction E1 causes a slight strain S5
= d 15 Ft 1 and 56-d, 6E1 are generated, and a thickness shear wave is generated, and a parallel electric field, that is, a Z-axis direction electric field E3, is generated on the piezoelectric plate surface, 51 = d3, E3 is generated, and a thickness longitudinal wave is generated.

As a result, the resonances of the thickness longitudinal wave and the thickness shear wave occur at different frequencies.

In general, energy confinement type piezoelectric filters use a resonance mode caused by vertical electric field excitation, so resonance caused by parallel electric field excitation can occur as an unnecessary response and can deteriorate the characteristics of the filter. .

In order to solve the above drawbacks of the conventional example, the present invention provides two parallel rectangular auxiliary electrodes in addition to the energy confinement electrode on the same piezoelectric plate constituting the energy confinement type filter. 31 One or more such vibrators are provided on the same piezoelectric plate, and their electrodes are placed in parallel with the electrodes to trap energy. The present invention provides an energy confinement type piezoelectric filter that eliminates unnecessary responsiveness of the filter by connecting the filter to the filter.

Below is the drawing 3! Examples will be explained in more detail.

FIG. 4 tl shows an energy confinement type piezoelectric filter according to the present invention. In this figure, the same symbols as in FIG. 1 indicate the same things.
Reference numerals 14 and 14' denote auxiliary electrodes for configuring the parallel electric field excitation vibration 4 (oscillator), which are provided on both sides of the piezoelectric plate 1.

This auxiliary electrode 13, 13'. 14 and 14' are rectangular and are provided close to each other, and the auxiliary electrodes 13 and 13' and the auxiliary electrodes 14 and 14' have the same dimensions, respectively, as shown.

The electrodes 13, 13' and 14, 14' are connected to the conductor 1, respectively.
5 to form one parallel electric field excitation vibrator.

The electrodes 13 and 13' are connected to the output line 9, and the electrodes 14 and 14' are connected to the common line 10.

Now, when the auxiliary electrodes 13, 13', 14, and 14' are not connected to the output line 9 and the common line 10, the configuration is the same as that in FIG. 1, so an input signal is applied to the input line 8. Then, the wave output due to the vertical electric field appears as the main signal, and the resonance frequency component of the parallel electric field-excited vibration between the electrodes 2, 2' and 3, 3' appears on the output line 9 as an unnecessary response.

Next, when the auxiliary electrodes 13, 13' and 14°14' are connected to the output line 9 and the common line 10, respectively, parallel electric field excitation vibrators are inserted in parallel on the output side, but parallel Since the resonant frequency of electric field excitation vibration is determined by the thickness of the piezoelectric plate 1, the auxiliary electrodes 13, 13' and 14
, 14', the resonant frequency of the parallel electric field excitation resonator formed by the electrodes 2, 2' and 3, 3' matches the resonant frequency of the parallel electric field excitation by the electrodes 2, 2' and 3, 3'.

Therefore, unnecessary responses due to parallel electric field excitation between electrodes 2, 2' and 3, 3' can be avoided by auxiliary electrodes 13, 13' and 1.
A common line 10 is passed through the vibrator constituted by 4 and 14'.
Since the output line 9 is short-circuited to the output line 9, there is almost no current flowing through the output line 9.

On the other hand, since the parallel electric field excitation vibration is not excited at the frequency in the passband of the transducer which suppresses the resonant frequency of the vertical electric field excitation, the auxiliary electrodes 13, 13' and 14, 14' become mere capacitors.

The capacitance of this capacitor is smaller than the parallel capacitance of the vibrator at the electrodes 3 and 3', and has almost no effect on the characteristics.

In this way, by configuring the energy confinement type piezoelectric filter as shown in FIG. 4, unnecessary responses of the filter can be eliminated.

In the above embodiments, the auxiliary electrodes 13, 13' and 14,
14' is connected to the output side, but the same effect can be obtained when connected to the input side.

In addition, auxiliary electrodes 13, 13' and 14 are provided on the same piezoelectric plate.
, 14' are provided and connected in parallel to the input side and the output side, respectively, the effect of unnecessary response removal becomes even more remarkable.

FIG. 5 shows another embodiment of the energy confinement type piezoelectric filter according to the present invention, in which the same symbols as in FIG. 2 indicate the same things, and electrodes 4, 4', 5,5'
and 6, 6', 7.7' and supplementary electrodes 13, 13' and 1
4, 14' are provided on the same piezoelectric body.

And between electrodes 4, 4' and 5, 5' and between electrodes 6, 6'
and 7°1' are arranged in close proximity to obtain the required mechanical connection, but electrodes 4, 4', 5, 5' and electrodes 6, 6', ? , 7' are placed sufficiently apart from each other so as not to be mechanically coupled, and are electrically coupled via a capacitor 11 in a tandem configuration.

Further, the auxiliary electrodes 13, 13', 14, 14' are the electrodes 4, 4
'5.5', 6:6', 7, 7' are provided at a sufficiently distant position so as not to be mechanically coupled, thereby forming a parallel electric field excitation vibrator.

This vibrator is connected in parallel with the connection capacitor 11.

This effect is caused by the frequency of the unwanted response caused by the parallel electric field applied between the electrodes 4, 4' and 5, 5' and between the electrodes 6, 6' and 7.7', as explained with reference to FIG. coincides with the resonant frequency of the parallel electric field excitation vibrator composed of the auxiliary electrodes 13, 13' and 14°14'.

Therefore, since unnecessary responses are short-circuited by the common line 10,
There is almost no damage to the output line 9.

In the passband of the filter, auxiliary electrodes 13, 13'14, 14'
Since it acts simply as a capacitor, it forms part of the connecting capacitor.

In addition, in the tandem configuration shown in FIG. 5, auxiliary electrodes 13, 13', 1
If parallel electric field excitation vibrators similar to those configured with 4 and 14' are connected in parallel, the effect of eliminating unnecessary responses will be even more remarkable.

Furthermore, it has almost no effect on the characteristics of the passband, as explained in FIG.

Furthermore, in the embodiment shown in FIGS. 4 and 5, the auxiliary electrode 1
3, 13', 1414' are electrodes 2, 2', 3, 3',
4, 4', 5° 5', 6, 6', 7, 7' can be formed at the same time, so no special process is required in manufacturing the filter.

FIG. 6 shows experimental results showing the effect of eliminating unnecessary responses according to the present invention.

FIG. 6a shows the characteristics of the two-resonator energy confinement type piezoelectric filter having the configuration shown in FIG.

Here, a Z-cut plate (approximately 300 μm thick) of lithium tantalate is used as the piezoelectric substrate, and the main response is the 3-wavelength longitudinal wave.
It supports the following overtones.

In the above piezoelectric plate, a thickness longitudinal wave is excited by vertical electric field excitation, and a thickness shear wave is excited by parallel electric field excitation, and since the sound speed ratio of the thickness longitudinal wave and the thickness shear wave is 1:0.58, the thickness longitudinal wave is excited. The frequency ratio between the third-order and the thickness-slip fifth-order overtone is 3:2.9, and an unnecessary response corresponding to the thickness-slip is observed on the lower frequency side of about the third order with respect to the main mode.

On the other hand, according to the configuration shown in FIG. 4 in which the parallel electric field excitation vibrators according to the present invention are provided on the same substrate, unnecessary responses due to thickness shear waves are significantly reduced, as shown in FIG. 6.

By the way, the electrode dimensions used in this experiment are electrodes 2, 2',
3 and 3' are both 0 and 8 mm wide and 1.5 mm long, the gap between electrodes 2 and 3 is 0.7 mm, and the auxiliary electrode 13.13
', 14, 14' are both width 0.6 mrrt and length 2.
0 mrrt, and the auxiliary electrode 13. :! :14 gap is 0.4 mm.

Note that the following precautions must be taken when configuring the parallel electric field excitation vibrator.

That is, even if the auxiliary electrodes 13' and 14' are not provided, the auxiliary electrodes 13 and 14 constitute a parallel electric field excitation vibrator.

However, in this case, the electric field distribution does not have a vertically symmetrical distribution as shown by E in Figure 4, so the vertical electric field component causes resonance that coincides with the main response frequency of the filter, and the passband characteristic adversely affect.

Opposite to this the auxiliary electrode 13.14 13'.

14' is provided, and auxiliary electrodes 13, 13', and 14°1 are provided.
It was experimentally confirmed that if 4' are interconnected, the electric field distribution becomes vertically symmetrical, and there is almost no excitation due to the vertical electric field.

Therefore, as for the electrode configuration of the parallel electric field excitation vibrator that contributes to the purpose of the present invention, it is important to provide the electrodes so as to overlap the front and back surfaces of the piezoelectric plate.

As explained above, the present invention eliminates unnecessary responses by providing an auxiliary electrode on the same plate as the piezoelectric plate on which the energy confinement electrode is provided, and therefore improves the characteristics of the filter with a simple structure. It is possible to provide an energy confinement type piezoelectric filter that is extremely effective in practical terms.

[Brief explanation of the drawing]

1 and 2 are diagrams showing an example of the configuration of a conventional energy confinement type piezoelectric filter, FIG. 3 is a diagram showing the electric field distribution in the piezoelectric plate, and FIG. 5 is a block diagram of one embodiment of the present invention, FIG. 5 is a block diagram of another embodiment of the present invention, and FIG. 6 is an implementation diagram showing the effects of the present invention. 1...Piezoelectric plate, 2, 2', 3, 3',
4.4'. 5, 5', 6, 6', 7.7'... Electrode, 8... Input line, 9... Output line, 1o
... Curve common line, 11... Curve connection capacitor, 13,1
3', 14, 14'...Auxiliary electrode.

Claims (1)

[Claims] In an energy confinement type piezoelectric filter consisting of one energy confinement type three-terminal thickness vibrator or a plurality of the three-terminal thickness vibrators connected via a capacitor, configured on 11 piezoelectric substrates, 2 on the surface of the piezoelectric plate
first and second rectangular electrodes are provided in parallel and close to each other,
third and fourth rectangular electrodes having the same dimensions as the first and second rectangular electrodes are provided on the back surface of the piezoelectric plate, facing each other;
By connecting the first and third electrodes and the second and fourth electrodes facing each other on the front and back surfaces of the piezoelectric plate, a resonant frequency that matches the unnecessary response frequency of the piezoelectric filter is created. By configuring one parallel electric field excitation oscillator having a parallel electric field excitation oscillator, and connecting the - or plural parallel electric field excitation oscillators in parallel with the input terminal, the output terminal, or any vibrator of the energy confinement oscillator. , an energy confinement type piezoelectric filter characterized by eliminating unnecessary responses.