JPS63151105A - Ladder type piezoelectric filter - Google Patents

Abstract

PURPOSE:To obtain a single-peak filter characteristic where the extent of attenuation is large in a frequency band higher than the pass band, by connecting the second capacitor between the other terminal of the second piezoelectric resonator and a common potential line. CONSTITUTION:One terminal of the first piezoelectric resonator 16 and that of the second piezoelectric resonator 17 are connected to each other at a connection point 18, and the other terminals are connected to an input terminal 12 out of input terminals 12 and 13 and an output terminal 14 out of output terminals 14 and 15. The first capacitor C1 is connected between said connection point 18 and a common potential line 19 which connects the input terminal 13 and the output terminal 15. The second capacitor C2 is connected between the other terminal of the second piezoelectric resonator 17 and the common potential line 19. Thus, the increase of insertion loss and an influence of insertion loss upon the pass band width are prevented by the action of the second capacitor C2 and the extent of attenuation in a frequency band higher than the pass band is larger though the electrostatic capacity of the first capacitor C1 is not increased.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to clock signal extraction circuits in PCM communications, intermediate frequency amplification circuits for radio receivers, audio intermediate frequency amplification circuits for television receivers, etc. The present invention relates to a ladder type piezoelectric filter having a pass characteristic.

(Prior Art) Various piezoelectric filters are generally known for use in intermediate frequency amplification circuits of radio receivers and audio intermediate frequency amplification circuits of television receivers. FIG. 6 shows one such piezoelectric filter.

The piezoelectric filter 1 is of a ladder type, and includes a two-terminal type first piezoelectric resonator 2. Second piezoelectric resonator 3 and capacitor C
Consisting of One terminal of each of the first piezoelectric resonator 2 and the second piezoelectric resonator 3 is connected to each other, and each other terminal of the first piezoelectric resonator 2 and the second piezoelectric resonator 3 is connected to the input terminal pair 5 of the piezoelectric filter l,
6 and each of the output terminal pairs 7.8 - connected to the blade terminals 5 and 7, respectively. The capacitor C is connected to the first capacitor C.
The connection point 4 between the piezoelectric resonator 2 and the second piezoelectric resonator 3 and the other terminal 6 of the input terminal pair 5.6 and the output terminal pair 7, 8
and a common potential line 9 interconnecting 8.

By the way, in the conventional piezoelectric filter I, the first piezoelectric resonator 2 is used as described above in order to obtain a single peak filter characteristic.
, the second piezoelectric resonator 3 and the capacitor C are connected in a ladder shape. Increasing the capacitance increases the amount of attenuation in the above frequency range, but has the problems of increasing insertion loss and narrowing the pass band.

(Objective of the Invention) The first object of the invention of the present application is to provide a ladder-type piezoelectric filter that has unimodal filter characteristics and has a large amount of attenuation in a frequency range above the passband.

Furthermore, it is an object of the second invention of the present application to provide a ladder-type piezoelectric filter that has unimodal filter characteristics, has a large attenuation amount, has components that are compactly integrated, and is easy to mass-produce. It is.

(Structure of the Invention) Therefore, the first invention of the present application provides a first piezoelectric resonator and a second piezoelectric resonator.
piezoelectric resonators are connected in series between each blade terminal of the pair of input terminals and the pair of output terminals with their one terminals connected to each other, and a first capacitor is connected to the first piezoelectric resonator and a second piezoelectric resonator. The second capacitor is connected between the connection point of the second piezoelectric resonator and the common potential line that interconnects the other terminals of the input terminal pair and the output terminal pair, and the second capacitor is connected to the other terminal of the second piezoelectric resonator. It is characterized in that it is connected between the common potential line and the common potential line. The second capacitor reduces insertion loss, does not change the passband width, and increases attenuation in the frequency range above the passband.

Further, the second invention of the present application provides electrode patterns for one and the other of the pair of input terminals, electrode patterns for one and the other of the pair of output terminals, and terminals for each of the first piezoelectric resonator and the second piezoelectric resonator. and a common potential electrode pattern that interconnects the other electrode pattern of the input terminal pair and the other electrode pattern of the output terminal pair, The circuit board is characterized in that the first piezoelectric resonator, the second piezoelectric resonator, the first capacitor, and the second capacitor are mounted on this circuit board. The first piezoelectric resonator, the second piezoelectric resonator, the first capacitor, and the second capacitor are integrated on a single circuit board to form a ladder-shaped piezoelectric filter.

(Effects of the Invention) According to the first invention of the present application, even if the capacitance of the first capacitor is greatly reduced, the amount of attenuation can be increased by the second capacitor. It is possible to obtain a ladder-type piezoelectric filter having unimodal filter characteristics with no reduction and a large amount of attenuation in a frequency range higher than the passband.

Further, according to the second invention of the present application, since the filter components are compactly integrated on one circuit board, the degree of integration of the components is high, and the filter is compact and has excellent mass productivity, and is smaller than the passband. Also, it is possible to obtain a ladder-type piezoelectric filter having a single peak filter characteristic with a large amount of attenuation in a high frequency range.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

A circuit diagram of an embodiment of a ladder-type piezoelectric filter according to the present invention is shown in FIG.

The ladder type piezoelectric filter 11 has a pair of input terminals 12.1
3, an output terminal pair 14.15, a two-terminal first piezoelectric resonator I6, a two-terminal second piezoelectric resonator 17, a first capacitor C3, and a second capacitor C1.

The first piezoelectric resonator 16 and the second piezoelectric resonator I7 both have 1. It utilizes the energy-trapped thickness-shear vibration mode of a piezoelectric substrate. One terminal of the first piezoelectric resonator 16 and the second piezoelectric resonator 17 are connected to each other at a connection point 18, and the other terminals of the first piezoelectric resonator 16 and the second piezoelectric resonator 17 are connected to each other at the input terminal pair 12. Each of the terminal pairs 14 and 15 is connected to the terminals 12 and 14, respectively.

The first capacitor CI is connected to the connection point 18 between the first IE electric resonator 16 and the second piezoelectric resonator 17, and to each of the input terminal pair 12.13 and the output terminal pair 14.15. and a common potential line I9 that interconnects the two.

Further, the second capacitor C1 is connected to the second piezoelectric resonator 17.
and the common potential line 19.

With the above circuit configuration, in order to increase the amount of attenuation in the frequency range above the passband, the first capacitor C
Even if the capacitance of I is not increased, the second capacitor C1
Due to this effect, there is no increase in insertion loss or influence on the passband width, and the amount of attenuation in the frequency range above the passband can be increased.

The capacitance value of the second capacitor C1 is in the range of 0.2 times to 0.4 times the capacitance value of the first capacitor C1 (
It is preferable to set it to 0.2G+<Ct<0.40+). This means that C3≦0.20. Then the second capacitor C
This is because the effect of , is small, and when 0.4C≦C3, the second capacitor C3 has an adverse effect on the phase linearity of the filter.

In the ladder-type piezoelectric filter 11 of FIG. 1 described above, the standard signal generator 21 having an output resistance of R8 is connected between the input terminal pair 12 and 13 through the impedance matching resistor R, and the output Terminal pair 14.1
When a resistor R3 for impedance matching and a high frequency voltmeter 22 were connected between the terminals 5 and 5 and the filter characteristics were measured, filter characteristics as shown by the solid line in FIG. 2 were obtained.

Also, the conventional ladder type piezoelectric filter shown in Figure 6! When we measured the filter characteristics in the same way as above, we found that
Filter characteristics as shown by dotted lines in FIG. 2 were obtained.

As is clear from a comparison of the above filter characteristics, the ladder type piezoelectric filter 11 shown in Fig. 1 has an attenuation of about 8 dB at 10 MHz compared to the ladder type piezoelectric filter 1 shown in Fig. 6. You can see that it's getting bigger.

Next, a specific configuration of the ladder type piezoelectric filter 11 having the circuit configuration shown in FIG. 1 is shown in FIG. 3.

As shown in FIG. 3, the first piezoelectric resonator 16 of FIG. 1 is mounted on a single rectangular circuit board 23. Second piezoelectric resonator 17
．． A first capacitor CI and a second capacitor C2 are mounted.

The circuit board 23 is made of, for example, a ceramic substrate and has a certain width. As shown in FIG. 4, electrode patterns 12 and 13 corresponding to one terminal 12 and the other terminal 13 of the input terminal pair 12.13 in FIG. 1 are formed on one main surface of the circuit board 23, respectively. Electrode patterns 14 and 15 corresponding to one terminal 14 and the other terminal 15 of the output terminal pair 1=1.15 in FIG. 1, respectively, are formed on the top and bottom. The first piezoelectric resonator 16 and the second piezoelectric resonator are also disposed on the one main surface of the circuit board 23.
A connection point that connects each one terminal of the piezoelectric resonator 17 to each other! A connection electrode pattern 18 corresponding to 8 is formed, and a common potential electrode pattern 19 corresponding to the common potential line 19 is formed. This common potential electrode pattern I9 connects the electrode pattern 13 corresponding to the other terminal I3 of the input terminal pair 12.13 and the i-pole pattern 15 corresponding to the other terminal 15 of the output terminal pair 14.15 to each other. .

In addition, in FIG. 4 above, the electrode patterns corresponding to the connection lines or connection points of components in the circuit of FIG. There is.

Both the first piezoelectric resonator 16 and the second piezoelectric resonator 17 mounted on the circuit board 23 have electrodes 25 on both opposing main surfaces of a piezoelectric substrate 24 having a constant width, as shown in FIG. and 26 are formed. and,
These electrodes 25 and 26 face each other approximately at the center of the piezoelectric substrate 24, and the piezoelectric substrate 24, which is polarized in the longitudinal direction perpendicular to the width direction, forms an energy trapping structure at the portion facing the electrodes 25 and 26. Thickness shear vibration is performed.

The electrode 25 is drawn out from approximately the center of one main surface on which it is formed, through the - end surface of the piezoelectric substrate 24, until it reaches a part of the other main surface. This is a terminal 25a. Similarly, the electrode 26 is drawn out from approximately the center of the other main surface on which it is formed, passes through the other end surface of the piezoelectric substrate 24, and reaches a part of the one main surface. is the other terminal 26a.

On the other hand, both the first capacitor C0 and the second capacitor C2 are chip-shaped multilayer capacitors.

As can be seen from FIGS. 3 and 4, the first piezoelectric resonator 16 has one electrode pattern 1 of the input terminal pair 12.13.
The second piezoelectric resonator 17 has its terminals 26a and 25a conductively bonded to the output terminal pair 14 and the connection electrode pattern 18 with solder or conductive adhesive, respectively.
．． The electrodes 26a and 25a are electrically conductively bonded to one of the electrode patterns 14 of 15 and the connection electrode pattern 18, respectively, in the same manner as described above. Also, the first capacitor C
The terminals 31 and 32 of the capacitor I are conductively bonded to the connection electrode pattern 18 and the common potential electrode pattern 19 with solder or conductive adhesive, respectively, and the terminals 33 and 34 of the second capacitor C2 are bonded to the common potential electrode pattern 19, respectively. It is conductively bonded to the potential electrode pattern 19 and the N-pole pattern 15 of the other terminal 15 of the output terminal pair 1c 15 in the same manner as described above.

The above 1″LL scraping pattern 12.14 and the common potential voltage
j; The pattern 19 has lead terminals 3 each having a certain width.
5', 36, and 37 are firmly bonded with conductive adhesive such as solder. And, the outer 11 parts of the circuit board 23 are made of a resin-like exterior resin (not shown).
The technique is overturned.

With such a configuration, the first piezoelectric resonator 16 and the second piezoelectric resonator 17 are mounted on one circuit board 23. In the above embodiment, the first piezoelectric resonator 16 and the second piezoelectric resonator
The piezoelectric resonators 17 are arranged substantially parallel to the longitudinal direction of the rectangular circuit board 23. Further, the first capacitor CI and the second capacitor C7 are also arranged between lead terminals 35 and 37 and between lead terminals 36 and 37, respectively.

As a result, components are compactly mounted on one circuit board 23, and a ladder-type piezoelectric filter having a simple structure and easy assembly can be obtained.

In the above embodiment, the lead terminals 35, 36 and 37 are not essential, and these lead terminals 35.
36 and 37 are glued to the electrode bag 12. By extending a part of +4 and 19 to the side surface of the circuit board 23 and using this extended part as a terminal, and bonding a cover member made of a material such as ceramic to the component mounting surface of the circuit board 23, a depth-shaped part is formed. It is possible to construct a piezoelectric filter.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a ladder-type piezoelectric filter according to the first invention of the present application, FIG. 2 is a filter characteristic diagram of the ladder-type piezoelectric filter of FIG. 1 and a conventional ladder-type piezoelectric filter, and FIG. A perspective view showing the specific structure of the ladder type piezoelectric filter according to the second invention, FIG. 4 is a plan view of the electrode pattern of the circuit board used in the ladder type piezoelectric filter of FIG. FIG. 6 is a perspective view of a first piezoelectric resonator and a second piezoelectric resonator used in the ladder-type piezoelectric filter shown in the figure, and FIG. 6 is a circuit diagram of a conventional ladder-type piezoelectric filter. 11... Ladder type piezoelectric filter, 12.13... Input terminal pair, 14.15... Output terminal pair, 16... First piezoelectric resonator, 17... Second piezoelectric resonator, 18 ...Connection point, 19...Common potential line, C,...First capacitor, C3...Second capacitor. Patent applicant Murata Manufacturing Co., Ltd. Representative Patent attorney Aoyama Aoyama and 2 others Figure 1

Claims (2)

[Claims] (1) A piezoelectric filter consisting of an input terminal pair, an output terminal pair, a two-terminal first piezoelectric resonator, a two-terminal second piezoelectric resonator, a first capacitor, and a second capacitor. One terminal of each of the first piezoelectric resonator and the second piezoelectric resonator is connected to each other, and the other terminal of each of the first piezoelectric resonator and the second piezoelectric resonator is connected to one of the input terminal pair and the output terminal pair, and The first capacitor is connected between the connection point of the first piezoelectric resonator and the second piezoelectric resonator and a common potential line that interconnects each other of the input terminal pair and the output terminal pair, and the second capacitor is A ladder-type piezoelectric filter, characterized in that it is connected between the other terminal of the second piezoelectric resonator and the common potential line. (2) A piezoelectric filter in which a two-terminal first piezoelectric resonator, a two-terminal second piezoelectric resonator, a first capacitor, and a second capacitor are mounted on a single circuit board. The circuit board includes electrode patterns for one and the other of the pair of input terminals of the piezoelectric filter, electrode patterns for one and the other of the pair of output terminals, and one of each of the first piezoelectric resonator and the second piezoelectric resonator. A connection electrode pattern that connects the terminals of the terminals to each other, and a common potential electrode pattern that connects the other electrode pattern of the input terminal pair and the other electrode pattern of the output terminal pair to each other are formed, The piezoelectric resonator is connected between one electrode pattern of the pair of input terminals and the connection electrode pattern, and the second piezoelectric resonator is connected between the electrode pattern of one of the pair of output terminals and the connection electrode pattern. The first capacitor is connected between the connection electrode pattern and the common potential electrode pattern, and the second capacitor is connected between one electrode pattern of the output terminal pair and the common potential electrode pattern. A ladder-type piezoelectric filter characterized by being connected.