JPS58146122A - Ladder type piezoelectric filter - Google Patents

Abstract

PURPOSE:To ensure the high reliability and to make the manufacture easy, by arranging piezoelectric oscillators of a ladder type piezoelectric filter so as to have resonance frequencies in order as increase or decrease, decrease after increase, or increase after decrease. CONSTITUTION:The resonance frequencies of the piezoelectric oscillators of the ladder type piezoelectric filter comprising the piezoelectric oscillators a1-a9 arranged in series and parallel capacitors C are arranged so as to be increased in order from the input terminal to the output terminal, allowing to realize the filter without large ripple and smooth pass band characteristics. Since the resonance frequencies of the oscillators have a tolerance at the manufacture in a prescribed range, the order of arrangement of the piezoelectric oscillators is selected to form the filter. The resonance frequencies can be reduced, reduced after increase, or increased after decrease in order. Thus, the process of the adjustment of frequency characteristics of the piezoelectric oscillators is omitted to manufacture the piezoelectric filter.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a ladder piezoelectric filter. As a ladder type piezoelectric filter, as shown in Fig. 1, a 4551 with a series arm 5 and a pressure W oscillator arranged in parallel 11i1 is used.
Intermediate frequency filters are widely used in radios, transceivers, and other consumer applications.

When constructing this filter, it is first necessary to match the resonant frequency of the vibrator 11 arranged in the series arm with the anti-resonant frequency of the vibrator 11 arranged in the parallel arm. Further, in order to obtain a large guaranteed attenuation amount, the parallel capacitance of the vibrator 11 needs to be small, and the parallel capacitance of the vibrating chill needs to be large.

For this reason, regarding the guaranteed attenuation amount, if a filter is constructed from one type of piezoelectric material, the number of vibrators will be too large, so two types of piezoelectric materials with significantly different Kiloelectric constants are generally used. ing.

Furthermore, the temperature characteristics and aging characteristics of the resonator 1
It is necessary that the resonant frequency of the resonator 1 and the anti-resonant frequency of the vibrator 12 match and have a small deviation, and if a piezoelectric material that satisfies these requirements cannot be obtained, it is necessary to Generates 9-tuples.

Therefore, it is extremely difficult in terms of materials to realize a conveyance filter that requires higher reliability than consumer products with the filter configuration shown in Figure ts1.

Next, the ladder type filter shown in FIG. 2 can overcome the above-mentioned drawbacks, and some of the filters have already been put into practical use after being designed using the operating parameter method. However, when operating parameter design is used, many different types of oscillators A1 to A and h coupling capacitances 01 to C, - are required, resulting in an increase in manufacturing costs.

- On the other hand, when the filter shown in Fig. 2 is designed using the image parameter method, the resonant frequency fr and the capacitance ratio l of the oscillators 1 to A% are equal, and the oscillators at both ends and the 4p parallel capacitance are equal. 24 of the parallel capacitances of the vibrator elements ˜Al&-t, and the coupling capacitances C1 to C, , must all be equal. Therefore, it has the advantage that it can be realized with two types of vibrators with different parallel capacitances and a coupling capacitance of 1 ml till. However, if the resonant frequencies of the resonators are not all equalized, large ripples will occur in the passband of the filter, so each resonator has the disadvantage that the frequency must be adjusted with considerable precision in advance. Ta.

With piezoelectric materials, it is unavoidable that the speed of sound changes slightly when the raw material or manufacturing point changes, and the resonant frequency changes slightly depending on the machining accuracy of the vibrator dimensions, so frequency adjustment as described above is necessary. It has been considered an essential process.

Such adjustment of the frequency v4 requires a large number of manpower and equipment, and is a major factor in increasing the height of the ladder-type piezoelectric filter to 11i1c, as well as being a hindrance during measurement.

An object of the present invention is to provide a ladder-type piezoelectric filter that has high reliability, is easy to manufacture, and is inexpensive.

In the ladder-deaf piezoelectric filter shown in FIG. 121El, matching conditions are not disturbed much even if the resonant frequencies are slightly different between the vibrators whose electrical Ki is close to 1.

The present invention utilizes this property to construct a multi-stage connection structure in which the resonant frequency is slightly shifted between the I and I contact vibrators shown in Fig. 2, and as a result, the overall result is a filter using vibrators with a large difference in resonant frequency. It is designed so that it can be configured.

That is, the present invention uses a ladder-type piezoelectric filter in which piezoelectric vibrators are arranged in series and capacitors are arranged in parallel, and the resonance frequency of the piezoelectric vibrators is output from the input side of the filter. ! A configuration in which the piezoelectric vibrator is arranged so that the resonance frequency increases from the input side of the filter to the input side of the filter, and conversely decreases from the middle of the input side of the filter. It is characterized by a configuration in which J[k: decreases from the input side and inversely increases kl[k] from the input side.
There is.

According to the present invention, it is not necessary to correct variations in the resonance frequency of each piezoelectric vibrator caused by rounding and variations in manufacturing conditions, which are characterized by different resonance frequencies of each piezoelectric vibrator, but it is even convenient. Therefore, it is possible to eliminate the drawbacks of the conventional filter, and the filter can be constructed without the troublesome step of frequency adjustment.

Hereinafter, the present invention will be explained according to Examples.

[Example 1] Nine piezoelectric vibrators as shown in FIG. A ladder-type piezoelectric filter having a capacitance of 1,000,000 is selected as a representative example of the present invention and will be explained.

The piezoelectric vibrators arranged in series in the third Iiiil have a parallel capacitance c of 102 to 105PF, and an II quantity ratio l of 5.
．． 13-5.27.

The resonance sharpness (is 1920~2060.Also, the A end Ki1 row Ic&iif of the piezoelectric vibrator", Lp a@ is l and (is about the same as the piezoelectric vibrator a, ~a, but the parallel capacitance C
It is 207 to 211PF, which is 12 times en1. Further, the coupling capacitance C is set to 1850 to 1920PF.

Regarding the shape of the piezoelectric vibrator, town and a are plate thickness 0.65.
Full-surface electrode configuration with a diameter of 4.36 cm, a plate thickness of 0.80 m, p diameter of 4.39 m, and y electrode diameter of 3.17 m.
n partial electrode configuration. Then, the resonance frequency of the piezoelectric vibrator was set at 5° as shown in Figure @4. In other words, the lowest resonant frequency that is allowed to be incorporated into the filter! 567
．． Vibrators belonging to each of nine frequency ranges from 90 KHz to 300 K 56α6 kkh are sequentially arranged as piezoelectric vibrators 18 to a. Of these a.

For the seven piezoelectric vibrators from ~a, frequency selection 1
Classified by 1K. The '+t fluctuation of 21cHx up to 55 & 5G0.20 is almost the same as the variation K due to the normal manufacturing method of piezoelectric vibrators, and the piezoelectric vibrators from a to a Hatake require frequency adjustment. Not at all.

In this embodiment, it is only necessary to adjust the frequency of the piezoelectric vibrators 11 and a at both ends.

The passband characteristics of the filter of the present invention are shown by solid lines in Figure 5.

In addition, the dotted line in the same figure shows the filter characteristics designed using the conventional image parameter method, and the common □
All vibration frequencies! 59.25 k)h K frequency wLI
It can be seen that both 1 and Toge, which were subjected to Il adjustment, exhibit smooth passband characteristics.

In addition, the chain 1 in the same figure indicates the parallel capacitance Co of each piezoelectric vibrator.
, capacitance ratio d, resonance sharpness (This is similar to the previous example, but the resonance frequency of piezoelectric vibrators 11 to a9 is 558.20kHz.
~560.20 kHz/) were randomly incorporated without following the structure of the present invention.

In each case, the terminal impedance is 150Ω.

As is clear from the above examples, piezoelectric vibrators with 5 different frequencies are randomly placed! [If combined, the passband characteristics of the filter will be disturbed and large ripples will occur. On the other hand, if the resonant frequency of the piezoelectric vibrator is arranged so that it increases in order from the input side as in the present invention, the passband will not be disturbed and it will be completely different from the case where each piezoelectric vibrator is precisely adjusted. It is clear that the same effect as in Example 1 can be obtained from the principle of the present invention even if the piezoelectric vibrators are arranged so that their resonant frequencies decrease in order from the input side. be.

[Example 2].

This is an example of a ladder lid filter consisting of the same nine piezoelectric vibrators and eight capacitors as in Example 1. In reality l, in the irises 3 diagram, fi mover 1. The parallel capacitance of ~a is l of the parallel capacitance of each of the vibrators 12 ~ in the central portion.

However, in Example 2, the parallel capacitance e, capacitance ratio α, and resonance sharpness (1) of all the vibrators are exactly the same as those of the vibrator in Example 1.

In Example 2, the oscillators were changed from the input side to the output side of the filter, and the resonant frequencies were set as shown in FIG. 4. Here, the resonant frequency of the vibrator that can be incorporated into the filter is 557.90 to 560.
．． 60- to 2-7-, and since the vibrator can be realized with the same shape, there is no need for frequency adjustment in this case. 300 manufactured piezoelectric vibrators
All that is required is to classify and incorporate a frequency sorter K that sorts by Hz.

The passband operation attenuation characteristic at this time is shown in diagram jI6. f・±3.5k compared to the embodiment IK of the present invention shown in FIG.
It can be seen that other than a small ripple occurring around Hz, good characteristics are obtained. Further, ripples of this level generally do not pose a problem at all (for example, in a group carrier filter).

[Example 3] In Examples 1 and 2, the number of frequency classifications of the piezoelectric vibrator was nine.

Here, as shown in Figure 7, the configuration consists of 9 piezoelectric vibrators and 8 capacitors, and the piezoelectric vibrators are connected in order from the input side to 1"*9"ly...v Let's say m's. Then, as shown in FIG. 8, the resonance frequency setting is gradually increased from the input side, and the center vibrator 1. Set the highest frequency, and then gradually set it lower. vibrator a, and 1. As in Example 1, is twice the parallel capacitance of the central vibrators a, ~a, and a
;, z,, S, az, at, ;, <tobe are set to the same frequency range, and each frequency range is set to the same frequency range as in Examples 1 and 20.
The sample was taken every 600 hours.

The operational attenuation characteristics at this time are shown in solid lines in Figure 9. Note that the dotted line is the characteristic of the image parameter design shown in the first embodiment. Therefore, by applying Embodiment 3, a filter with good characteristics can be realized even if piezoelectric vibrators with a large difference in resonance frequency are placed adjacent to each other compared to Embodiment 1. This is not necessary for the oscillators 4 to a% in the center, as the oscillators at both ends are separated by r8 and a-. Furthermore, even if all nine piezoelectric vibrators have the same parallel capacitance in the configuration of Example 3, the operation attenuation characteristics are good and large ripples do not appear.

Further, in this embodiment, the resonance frequency of the piezoelectric vibrator is minimized by Ka/, so that the resonance frequency is decreased from 11 to 1, and a
The J[J! It is clear from this. Furthermore, the piezoelectric vibrator with the maximum or minimum resonant frequency in the array of these vibrators does not have to be located in the center of the array of all piezoelectric vibrators in the filter, and its position may be biased toward the input side or output side. However, the operational attenuation characteristics are almost the same, except that the design is somewhat more difficult.

The above embodiments have been described for the case where both the input side and the output side of the filter are one end, but as shown in FIG.
It goes without saying that the present invention can also be applied as is to a ladder-carried piezoelectric filter in which either the input side or the output side is one end and the other is a stripped end, as shown in No. uIll.

In addition, in the filter of the present invention, the coupling capacitances arranged in parallel positions are allowed to vary by about ±5- from the designed value. Filter KI again! It is clear that depending on the required standard value, the variation in coupling capacitance and the selection range of piezoelectric vibrators can be made larger than the values in the embodiments.

As detailed above, according to the present invention, the frequency range of the piezoelectric vibrator incorporated in the ladder-type piezoelectric filter can be allowed to be quite wide.

Therefore, according to the present invention, a piezoelectric filter can be manufactured without the step of adjusting the frequency characteristics of a piezoelectric vibrator, and its industrial value is extremely large.

[Brief explanation of the drawing]

Figure 1 shows a ladder piezoelectric filter in which piezoelectric vibrators are arranged in each of the series arm and the parallel arm. Figure 2 shows a highly stable ladder deaf piezoelectric filter with a piezoelectric vibrator in the series arm and a capacitor in the parallel arm. FIG. 3 is a diagram showing the configuration of the ladder-type piezoelectric filter according to the embodiment, and FIG. 84 is a diagram showing the frequency setting of the vibrator according to the embodiment of the present invention. The solid line in FIG. 5 shows the passband characteristics of the filter. FIG. 6 shows the passband characteristics of the filter according to the embodiment of the present invention. FIG. 7 shows the configuration of a ladder filter in an embodiment of the present invention. This figure shows the configuration of a ladder-type piezoelectric fiber in which one of the output sides is a T end and the other is a right end. In the figure, 11, 12, mu1@4p~,...-
g AIL-IAla, a, &, a4.
a,, a, a,, a,, a,, a,. al, Hatake,, a4. l,, l,, a,, a,
, IL, is a piezoelectric vibrator, CIt C,, C, # +-
...-*c, -ffi, c, -1, c indicates capacity. Figure 1 °) Raku-otzu Graduation B Standard 5 Figure-6-4-2 几子2 Su4 +4
Yami Wataru Akira (Mitsuru H,) Kamu Figure -6-4-2mu +? Su4- +RoR Bow Shibeotsu Danruni ((Riiiot) Ryo q Ku-ro -4-2f, +;l 14
-+6m5! I Self 0 (It H Otsu) Distortion lO figure

Claims (2)

[Claims] (1) In a ladder-type piezoelectric filter in which a piezoelectric vibrator is placed in a series arm and a capacitor is placed in a parallel arm, is the piezoelectric vibrator arranged so that its resonant frequency increases in order from the input end to the output end? , or a ladder-type piezoelectric filter characterized in that the filters are arranged in decreasing order. (2) In a ladder-type piezoelectric filter in which a piezoelectric vibrator is placed in the series arm and a capacitor is placed in the parallel arm, the resonance/frequency of the piezoelectric vibrator increases sequentially from the input end and decreases in the opposite direction. A ladder-type piezoelectric filter characterized in that it is arranged so that J[k decreases from the input end and increases inversely KIIIK from the middle.