JPS58146121A - Ceramic filter - Google Patents

Abstract

PURPOSE:To reduce the response of unnecessary frequency at the outside of bands, by using a width longitudinal oscillation ceramic oscillator having different plate thickness for a ceramic filter of ladder constitution. CONSTITUTION:The ceramic filter of ladder form is constituted with ceramic oscillators 1, 1' and a capacitor C. As the ceramic oscillators 1, 1', using the width as lengthwise direction, the ceramic oscillators comprising a piezoelectromagnetic plate 5, metallic thin film electrodes 6a, 6b, 6c, and 6d, separation bands 7a, 7b, and terminals 9a, 9b are used. In using different plate thickness tO for the ceramic oscillators, the resonance frequency of the main oscillation (width longitudinal oscillation fundamental wave) is made equal and the resonance frequencies of the ternary mode and succeeding is made different, the unnecessary frequency response at the outside of band is reduced and the S/N of a filter output signal is improved remarkably.

Description

Detailed Description of the Invention (a) Technical Field of the Invention The present invention relates to a ceramic filter using an energy confinement type ceramic resonator in which mechanical vibration energy is concentrated in a part of the piezoelectric ceramic resonator.・9 Ceramic filters with improved loss characteristics ◎ (1)) Background of the technology A ceramic resonator made of piezoelectric ceramic material and metal thin film electrodes is used. - Ceramic filters are small and have no v441. In addition to features such as no need for coils, good compatibility with recent RC and PSR, and the high performance of piezoelectric ceramic materials, it will increasingly be used in intermediate frequency filters for wireless communication equipment and various other communication devices. There is a tendency for the range of use to be expanded.

(C) Prior art and problems A conventional ceramic filter will be explained using FIGS. 1 to 4.

FIG. 1 is a diagram showing an example of the configuration of a ceramic filter. In the figure, 1.1' is a ceramic resonator, and C is a capacitor.

Figure llF2 is a perspective view of a thickness-longitudinal ceramic resonator that fully utilizes thickness-longitudinal vibration. In the figure, 2 is a piezoelectric ceramic plate,
3 is a metal thin film electrode, and 4 is a support.

FIG. 3 is a diagram showing an example of the configuration of a nine-width vertical ceramic vibrator using width-longitudinal vibration. (IL) is a perspective view of the width-longitudinal ceramic vibrator, and (b) is a top view of the width-longitudinal ceramic vibrator. In the figure, 5 is a piezoelectric ceramic plate, 6a to 6d are metal thin film electrodes, γa and b are separation bands, 8 is a red stamp indicating the polarization direction, 9a and 9b are terminals, W is the width of the vibrator, and to is Board thickness, 2 is length.

Figure 4 is a diagram showing an example of the frequency/loss characteristics of a conventional ceramic filter.In Figure 0, the horizontal axis is frequency, the vertical axis is loss, and A indicates the unnecessary response. The energy trapping type ceramic oscillator used in the ceramic filter of this structure utilizes the thickness vibration of the plate, and there are nine thickness vertical ceramic oscillators. For example, as shown in FIG. 2, if metal thin film electrodes 3 are formed by vapor deposition on both sides of a piezoelectric ceramic plate 2 having a thickness ζ↓, and the peripheral part of the piezoelectric ceramic plate 2 is held by a metal holder 4. In addition to this, there is a thick vertical ceramic resonator that is connected to the metal thin film electrode 3 and confines most of the vibration energy in a portion facing the metal thin film electrode 3.

The resonant frequency of the nine-thickness vertical ceramic vibrator and thickness-shear ceramic vibrator that utilizes the full thickness vibration of the plate mentioned above is (1)
As shown in the formula and (4), it is determined by the thickness of the ceramic resonator.

f Chiku KS! ! ＜ = x X m [Hz]
-... (2) where, in formulas (1) and (2), fnVi is the resonant frequency (H2) of the thickness vertical ceramic resonator, and fm is the resonant frequency CHz of the thickness shear ceramic resonator.

Km is a constant (Hz/m) determined by the material of the thickness-longitudinal ceramic resonator, and KS is a constant (Hz/m) determined by the material of the thickness-shear ceramic resonator.

t is the plate thickness (m) of the vertical ceramic resonator.

is the plate thickness (m) of the thickness-shear ceramic resonator, and n and m are the orders (1, 3, 5...).

That is, the resonance frequency of the thickness-longitudinal ceramic resonator and the thickness-shear resonator is inversely proportional to the plate thickness.

In addition to the above-mentioned vertical ceramic vibrator and 9-thick ceramic vibrator, the energy trapping type ceramic vibrator used in the ceramic filter with the terminal type configuration shown in Fig. 1 includes the piezoelectric There is also a width-vertical ceramic vibrator shown in FIG. 3, which alleviates the constraints imposed by the selection of the dimensional ratio of the ceramic plates and the selection of the supporting means. For more information,
This is shown in Japanese Patent Application No. 123,252/1983.

That is, the conventional ceramic filter uses the above-mentioned thickness vertical ceramic oscillator and thickness shear ceramic oscillator as the ceramic oscillators 1 and 1' shown in FIG.

However, such conventional ceramic filters have the following drawbacks. That is, since the conventional Ceramic Filter Co., Ltd. uses the above-mentioned thickness vertical ceramic vibrator, thickness shear ceramic vibrator, and width vertical ceramic vibrator having the same plate thickness as the ceramic vibrators 1 and 1' in Fig. 331, When using the main vibration of a ceramic resonator (for example, the thickness-shear fundamental wave), higher-order modes (thickness-shear WE
Third order.

Even in the 5th mode), the resonant frequencies of each ceramic oscillator match, and as shown in Figure 4, an unnecessary response A appears in the attenuation range, worsening the frequency and loss characteristics outside the band. . That is, since sufficient loss cannot be obtained in the attenuation region, unneeded signals are mixed in, worsening the 87N of the filter output signal and causing deterioration in the performance of the device. As a result, in conventional ceramic filters,
Unnecessary response A in the attenuation range? It is necessary to provide a suppressing circuit at the output stage of the ceramic filter shown in FIG. 1, which has the drawback of increasing the size of the device configuration.

(d) Object of the Invention The present invention eliminates the drawbacks of the conventional ceramic filter by providing a high-performance ceramic filter that suppresses the frequency response outside the band, which is difficult to achieve with the conventional ladder-shaped ceramic filter, and suppresses the attenuation. This is a book whose purpose is to eliminate circuits that suppress unnecessary responses in Sakai. A piezoelectric ceramic plate having a narrow part in which the width of the center part in the longitudinal direction is smaller than the width of both ends, and metal thin films formed on one side surface and the other side surface of the piezoelectric ceramic plate, respectively, in the longitudinal direction. At least two ceramic oscillators configured of electrodes separated by a separation band are connected in series so as to narrow the narrow width portion at different positions, and at least one ceramic oscillator is provided with a capacitor between the ceramic oscillators connected in series. Embodiments of the invention The embodiments of the ceramic filter of the present invention will be explained in detail with reference to FIGS. 5 to 8. O Figure 5 is a diagram showing an example of plate thickness/resonant frequency equality of a width-vertical ceramic resonator. In the figure, the horizontal axis is the plate thickness of the ceramic resonator, the vertical axis is the resonant frequency of the ceramic resonator, and the solid line is Fundamental wave characteristics of width-longitudinal vibration.

The broken line is the third-order mode characteristic of width-longitudinal vibration, and the dashed line is the fundamental wave characteristic of thickness-longitudinal vibration.

FIG. 6 is a diagram showing an example of frequency and loss characteristics of a width-longitudinal ceramic vibrator. In the figure, the horizontal axis is frequency, and the vertical axis is
Loss, destruction! is the characteristic of the widthwise vertical ceramic vibrator with the plate thickness ta, and the solid line is the characteristic of the widthwise vertical ceramic vibrator with the plate thickness tbO.

FIG. 1 is a diagram showing the frequency/loss characteristics of an embodiment of the ceramic filter of the present invention.

In the figure, the horizontal axis represents frequency and the vertical axis represents loss.

, FIG. 8 is a diagram showing the frequency/loss characteristics of another embodiment of the ceramic filter of the present invention. In FIG. 2, the horizontal axis is the frequency and the vertical axis is the loss.

The ceramic filter of the present invention has a width-vertical ceramic vibrator shown in FIG. Using two vertical ceramic oscillators with different widths 0 In other words, ceramic oscillators with different plate thicknesses are used as the oscillators 1.1' of the ceramic filter having the ladder-like configuration shown in Fig. 1. The width-vertical ceramic vibrator has a characteristic that when the width of the vibrator is constant and the plate thickness is varied, the resonance frequency changes as shown in FIG. In other words, the fundamental wave resonant frequency of width-longitudinal vibration of a 1-width vertical ceramic resonator is less influenced by the shape ratio determined by the width of the resonator (W in Figure 3) and the plate thickness ((71; to) in Figure 3, and is almost constant. Since it is determined by the width dimension, there is little change, but the third mode of width longitudinal vibration has characteristics that are affected by the shape ratio, and the resonant frequency of thickness longitudinal vibration is inversely proportional to the plate thickness, so the resonant frequency of the transducer plate Changing the thickness (to in FIG. 3) significantly changes the resonant frequency.

For example, when comparing a wide vertical ceramic vibrator with a plate thickness taft and a wide vertical ceramic vibrator with a plate thickness tb'l, as shown in Figure 6, in the main vibration (width longitudinal vibration fundamental wave), the resonant frequency are almost equal, but the resonant frequency of the third mode is fa in the case of a wide vertical ceramic vibrator having a plate thickness ta1r, and fb in the case of a wide vertical ceramic vibrator having a plate thickness tb.

To be sure, the resonant frequencies are different in the fifth and subsequent modes as well. In this way, the resonant frequencies other than the main vibration are significantly different between the widthwise vertical ceramic vibrator having the plate thickness ta and the widthwise vertical ceramic vibrator having the plate thickness tb6.

Therefore, a width-longitudinal ceramic resonator with a plate thickness ta and a plate thickness t
When vertical ceramic oscillators with width b are used as ceramic oscillators 1 and 1' of the ladder-shaped ceramic filter shown in FIG. 1, respectively, the frequency/loss characteristics of the ceramic filter become as shown in FIG. 7. In other words, when vertical ceramic oscillators with different thicknesses are used in a ladder-shaped ceramic filter, the resonant frequencies other than the main vibration of each width vertical ceramic oscillator are different, so it is possible to minimize loss outside the band. The extraneous frequency response can be reduced.

That is, the ceramic filter of the present invention uses vertical ceramic resonators with different widths in the ladder circuit to reduce the unnecessary frequency response outside the band. In addition, here, we have explained a case in which two width vertical ceramic oscillators with different plate thicknesses are used in the ladder-shaped ceramic filter shown in Fig. 1. However, two or more width vertical ceramic oscillators The unnecessary frequency response outside the band can also be reduced in the ladder-type ceramic filter used.
It is only necessary to change the plate thickness of the vertical ceramic resonator.

In a ceramic filter having a ladder-like configuration using two width-vertical ceramic oscillators, the plate thicknesses ta and tbQ of each width-vertical ceramic oscillator are controlled to obtain a width-vertical ceramic oscillator having a plate thickness tag as shown in Fig. 6. When the frequency fc and the frequency faXt of a widthwise vertical ceramic resonator with a plate thickness tb are matched, the deterioration of the frequency and loss characteristics due to the resonance of the widthwise vertical ceramic vibrator with a plate thickness tb is the same as that of a widthwise vertical ceramic resonator with a plate thickness tb. Since it is suppressed by the anti-resonance of the vibrator, a ceramic filter having the frequency/loss characteristics shown in FIG. 8 can be obtained. That is, by matching the resonant frequency of the third-order mode of the width-ceramic resonator with the plate thickness tb and the anti-resonance frequency of the third-order mode of the width-longitudinal ceramic resonator with the plate thickness tat, the eighth As shown in the figure, unnecessary frequency responses outside the band are effectively suppressed, and the frequency/loss characteristics can be improved more effectively.

That is, when a plurality of vertical ceramic vibrators with different widths and different thicknesses are used in a ceramic filter having a ladder-like configuration, and the condition of the plate thickness of each vertical ceramic vibrator is A (i.e.,
When the resonant frequency of the 3rd mode of a vertical ceramic vibrator with a certain width matches the anti-resonant frequency of the 3rd mode of a vertical ceramic vibrator with another width (9 o'clock), the frequency and loss characteristics can be further improved. be.

(ω As explained in detail in ``Effects of the Invention'', the ceramic filter of the present invention has the following effects:
The frequency and loss characteristics can be completely improved by simply changing the plate thickness of the vertical ceramic resonator for each usage width, so the 8/N ratio of the filter output signal is greatly improved, making it easy to achieve high performance characteristics that could not be obtained with conventional ceramic filters. It is effective in improving the performance, downsizing, and economical of various communication systems.
Its industrial value is enormous.

[Brief explanation of drawings]

Fig. 1 shows an example of the configuration of a ceramic filter, Fig. 2 shows an example of the structure of a thickness-longitudinal ceramic resonator using thickness-longitudinal vibration, and Fig. 4 shows an example of frequency and loss characteristics of a conventional ceramic filter. Figure 5 is a diagram showing an example of plate thickness and resonant frequency characteristics of a width-longitudinal ceramic resonator and a thickness-lengthwise ceramic resonator, and Figure 6 is a diagram showing an example of frequency and loss characteristics of a width-lengthwise ceramic resonator. 1 is a diagram showing the frequency/loss characteristics of one embodiment of the ceramic filter of the present invention, and FIG. 8 is a diagram showing the frequency/loss characteristics of another embodiment of the ceramic filter of the present invention. In the figure, 1.1' is a ceramic resonator, 2.5 is a piezoelectric ceramic plate, 3.6a to 6d are metal thin film electrodes, numbers are supports, numbers a and 7b are separation bands, and 8 is an arrow indicating the polarization direction. f4','
1, 9a and 9b are terminals. Perforated mushroom ztffi m, baya `` Mushroom S Mouth y # Otsu 1 Rod 70 Procedural amendment (method) 1. Indication of it l'l 3 Sleeve 11 4-R ・Relationship with ICf'l Patent applicant Address 1015 Nakahara-ku, Yozaki-shi, Kanagawa (522) Name Fujitsu Limited 1 Agent Address 1 Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture] 1015 Odanaka Fujitsu Limited 8, l+li 11: (7 'l, $I'1.6
Attachment Selection (1) The third line of page 13 of the specification of the present application, ``The vibrator...conventional cellar'' has been corrected as follows. ``A diagram showing an example of the configuration of a vibrator, Figure 3 is a diagram showing an example of the configuration of a width-vertical ceramic vibrator using #gold, and Figure 4 is a conventional ceramic.''

Claims (1)

[Claims] The whole is polarized in the thickness direction, and 1f in the central part in the length direction
! A piezoelectric ceramic plate having a nine-narrow width smaller than the width of both ends, and metal thin films formed on one side and the other side of the piezoelectric ceramic plate at different positions in the length direction. At least two ceramic oscillators each consisting of electrodes and membrane electrodes separated by a separation band are connected in series so as to narrow the area, and at least one capacitor is connected in differential series between the series-connected ceramic oscillators. The ceramic filter 0 is characterized in that the thickness of at least one ceramic oscillator among the ceramic oscillators connected in series is different from the thickness of the other ceramic oscillators.