JP7043829B2 - Piezoelectric filter device - Google Patents

Description

The present invention relates to a piezoelectric filter device used in communication equipment such as commercial radios and mobile phones.

Piezoelectric filters, for example, piezoelectric filters using a piezoelectric substrate such as an AT-cut crystal plate, generally have an input electrode and an output electrode formed on one surface of the piezoelectric substrate, and are common to the input / output electrodes on the other surface. It has a structure in which an electrode (earth electrode) is formed. Such a configuration is called a two-pole type piezoelectric filter because it has two electrode pairs sandwiching a piezoelectric substrate. However, in order to improve the characteristics of the piezoelectric filter, such a two-pole type has a structure. There is a 4-pole type piezoelectric filter in which a piezoelectric filter is connected in cascade (see, for example, Patent Document 1).

By the way, in communication equipment using such a piezoelectric filter, for example, a commercial radio, the conventional analog system is switched to the digital system for the purpose of effective utilization of frequency bands and improvement of communication confidentiality (privacy protection). Is underway.

Japanese Patent No. 3507206

Some conventional commercial radios can communicate in both analog and digital systems. However, a commercial radio that can communicate using both of these methods is equipped with a piezoelectric filter for an analog system with a wide signal passband and a piezoelectric filter for a digital system with a narrow signal passband. I am trying to switch. Therefore, it is equipped with two piezoelectric filters, one for the analog system with a wide signal passband and the other for the digital system with a narrow signal passband. Is required.

Therefore, it is desired that a single piezoelectric filter can be used for both analog and digital methods.

The present invention has been made in view of the above points, and an object of the present invention is to make it possible to cope with a wide and narrow passband width of a signal by using a single piezoelectric filter.

In the present invention, in order to achieve the above object, it is configured as follows.

That is, in the piezoelectric filter device of the present invention, two piezoelectric filter elements in which an input electrode and an output electrode are formed on one main surface of a piezoelectric substrate and a common electrode is formed on the other main surface are connected in cascade. A piezoelectric filter is provided, the center frequencies of the two piezoelectric filter elements are deviated from each other, the impedances on the input side and the output side of the piezoelectric filter are different from each other, and the input / output directions of the signal to the piezoelectric filter are switched to obtain a signal. A piezoelectric filter device that switches the width of the pass band.
The input terminal of the piezoelectric filter device is switched and connected to the input side or the output side of the piezoelectric filter, and the output terminal of the piezoelectric filter device is connected to the output side or the input side of the piezoelectric filter. A switching means for switching the input / output direction of the signal by switching and connecting to the signal is provided .

According to the present invention, the center frequencies of the two piezoelectric filter elements are shifted from each other, and the input side and output side impedances of the piezoelectric filter in which the two piezoelectric filter elements are connected in cascade are made different. By switching the signal input / output directions, the filter characteristics of the two piezoelectric filter elements can be shifted so that the deviation of the center frequency becomes large or small, whereby the filters of both piezoelectric filter elements can be shifted. The characteristics can be combined to narrow or widen the passband of the signal. Further, since it can be configured by only one piezoelectric filter and one circuit connected to these, it is possible to make a configuration advantageous for space saving.
Further, by controlling the switching means, the input / output direction of the signal with respect to the piezoelectric filter can be easily switched.

It is preferable that the number of the piezoelectric substrates is two, and the input electrode, the output electrode, and the common electrode of each of the two piezoelectric filter elements are formed on each of the piezoelectric substrates.

According to this configuration, an input electrode, an output electrode, and a common electrode are formed on each of the individual piezoelectric substrates to form the piezoelectric filter elements, so that the piezoelectric filter elements are acoustically separated from each other, and the common piezoelectric substrate is used. In addition, as compared with the configuration in which the input electrode, the output electrode and the common electrode of the two piezoelectric filter elements are formed, spurious can be suppressed and the filter characteristics can be improved.

The impedance on the input side and the impedance on the output side are mutually exchanged between the input terminal of the piezoelectric filter device and the switching means, and between the output terminal of the piezoelectric filter device and the switching means. It is preferable to provide different impedance circuits.

According to this configuration, the impedance on the input side and the impedance on the output side of the piezoelectric filter can be set by the impedance circuit.

The piezoelectric substrate is preferably a quartz substrate.

According to this configuration, the frequency temperature characteristic becomes good.

As described above, according to the present invention, by switching the input / output direction of the signal with respect to the piezoelectric filter, the filter characteristics of the two piezoelectric filter elements are shifted so that the deviation of the center frequency thereof becomes large or small. This allows the filter characteristics of both piezoelectric filter elements to be combined to narrow or widen the passband of the signal.

Therefore, the pass band of a signal can be switched between wide and narrow by a single piezoelectric filter. For example, in a commercial radio, the piezoelectric filter device can be used for both analog and digital systems. can. As a result, the cost can be reduced and the cost can be reduced as compared with the conventional commercial radio that requires two piezoelectric filters, that is, a piezoelectric filter for an analog system and a piezoelectric filter for a digital system, which have different signal passband widths. Space can be saved.

FIG. 1 is a schematic configuration diagram of a piezoelectric filter device according to an embodiment of the present invention. FIG. 2 is a vertical cross-sectional view of the piezoelectric filter of FIG. FIG. 3 is a plan view of the piezoelectric filter of FIG. 2 with the lid removed. FIG. 4 is a schematic diagram showing the configuration of the piezoelectric filter of FIG. FIG. 5 is a schematic configuration diagram corresponding to FIG. 1 in a state where the input / output directions of signals with respect to the piezoelectric filter are switched. FIG. 6 is a diagram showing the filter characteristics when the input / output direction of the signal with respect to the piezoelectric filter is switched to the digital system or the analog system. FIG. 6A shows the filter characteristics when the digital system is used, and FIG. 6B shows the filter characteristics when the digital system is used. The filter characteristics at the time of are shown. FIG. 7 is a diagram for explaining the filter characteristics when the input / output direction of the signal with respect to the piezoelectric filter is a digital method. FIG. 8 is a diagram for explaining the filter characteristics when the input / output direction of the signal with respect to the piezoelectric filter is an analog method. FIG. 9 is a diagram showing the filter characteristics in a wide range when the input / output direction of the signal with respect to the piezoelectric filter is switched to the digital system or the analog system, and (a) shows the filter characteristics when the digital system is used, and (b) shows the filter characteristics. The filter characteristics in the case of the analog method are shown.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a piezoelectric filter device 1 according to an embodiment of the present invention.

The piezoelectric filter device 1 of this embodiment includes a piezoelectric filter 2, first and second switching switches 3 and 4 as switching means for switching the input / output direction of a signal with respect to the piezoelectric filter 2, input side and output of the piezoelectric filter 2. The first and second impedance circuits 5 and 6 for making the impedances on the side different are provided.

In the present invention, the input / output direction of the signal with respect to the piezoelectric filter 2 is switched, but first, on the premise that the input / output direction of the signal is not switched, that is, the input / output direction of the same signal as before is assumed. The configuration will be described. Note that FIG. 1 shows a state in which the input / output direction of the signal is not switched, that is, a state in which the input / output direction of the signal is the same as in the conventional case.

The piezoelectric filter 2 of this embodiment is a 4-pole type piezoelectric filter in which two 2-pole type piezoelectric filter elements are connected in series as described later.

2 is a vertical cross-sectional view of the piezoelectric filter 2 of FIG. 1, FIG. 3 is a plan view of the piezoelectric filter 2 of FIG. 2 with the lid 10 removed, and FIG. 4 is a plan view of the piezoelectric filter of FIG. 2. It is a schematic diagram which shows the structure of 2.

The piezoelectric filter 2 of this embodiment includes a ceramic base 7, two first and second piezoelectric filter elements 8 and 9 housed in the base 7, and a lid 10 for airtightly sealing the base 7. It is equipped with. The lid 10 is made of a metal plate such as Kovar.

The base 7 of this embodiment is made of a ceramic multilayer substrate using alumina or the like as a base material. In this embodiment, the base 7 has a flat plate-shaped lower layer 7a having a substantially rectangular plan view, a middle layer 7b forming a step portion formed on the upper portion of the lower layer 7a, and a frame portion formed on an outer peripheral portion on the middle layer 7b. It is a three-layer structure with the constituent upper layer 7c. In the base 7, these three layers 7a to 7c form a storage recess 13 having a step portion for storing and holding the first and second piezoelectric filter elements 8 and 9.

The first and second piezoelectric filter elements 8 and 9 include, for example, the first and second piezoelectric substrates 11 and 12 made of an AT-cut quartz substrate, respectively.

On the upper surface of the middle layer 7b of the base 7, that is, on the stepped portion of the storage recess 13 of the base 7, a first input pad 14 for electrically mechanically holding and mounting the first piezoelectric substrate 11 and a first output pad 15 are provided. , The first earth pad 16 is formed. Similarly, a second input pad 17, a second output pad 18, and a second earth pad 19 for electrically mechanically holding and mounting the second piezoelectric substrate 12 are formed.

Rectangular input electrodes 111 and output electrodes 112 are formed in parallel on the back surface (lower surface), which is one of the main surfaces of the first piezoelectric substrate 11 of the first piezoelectric filter element 8, at intervals. Each of these electrodes 111 and 112 is drawn out to the opposite corners of the first piezoelectric substrate 11 and is electrically connected to the first input pad 14 and the first output pad 15 by a conductive adhesive 20, respectively. There is.

A common electrode 113, which is a rectangular ground electrode corresponding to the input electrode 111 and the output electrode 112, is formed on the surface (upper surface) of the other main surface of the first piezoelectric substrate 11. The common electrode 113 is drawn out to another corner of the first piezoelectric substrate 11 and is electrically connected to the first ground pad 16 by a conductive adhesive 20.

Similarly to the first piezoelectric substrate 11, a rectangular input electrode 121 and an output electrode 122 are formed on the back surface of the second piezoelectric substrate 12 of the second piezoelectric filter element 9, respectively. Each of these electrodes 121 and 122 is drawn out to the opposite corners of the second piezoelectric substrate 12, and is electrically connected to the second input pad 17 and the second output pad 18 by a conductive adhesive 20. On the surface of the second piezoelectric substrate 12, a common electrode 123, which is a rectangular ground electrode corresponding to the input electrode 121 and the output electrode 122, is formed. The common electrode 123 is drawn out to another corner of the second piezoelectric substrate 12, and is electrically connected to the second ground pad 19 by a conductive adhesive 20.

Six first to sixth external connection terminals 21 to 26 for surface mounting shown in FIGS. 1 and 4 are formed on the bottom surface of the base 7. These external connection terminals 21 to 26 have a first input pad 14, a first output pad 15, a first earth pad 16, and a first via wiring (wiring pattern, via, etc.) (not shown) formed inside the base 7. It is electrically connected to the two input pads 17, the second output pad 18, and the second earth pad 19. Therefore, these external connection terminals 21 to 26 are electrically connected to the electrodes 111 to 113 and 121 to 123 of the first and second piezoelectric substrates 11 and 12, respectively, via the pads 14 to 19 and the conductive adhesive 20. It is connected to the.

Specifically, as shown in FIG. 4, the input electrode 111 and the first external connection terminal 21 of the first piezoelectric substrate 11, the common electrode 113 and the second external connection terminal 22 of the first piezoelectric substrate 11, and the first piezoelectric substrate are shown. The output electrode 112 of 11 and the third external connection terminal 23 are connected to each other.

Further, the output electrode 122 and the fourth external connection terminal 24 of the second piezoelectric board 12, the common electrode 123 and the fifth external connection terminal 25 of the second piezoelectric board 12, and the input electrode 121 and the sixth external connection of the second piezoelectric board 12 are connected. The terminals 26 are connected to each other.

In addition, in FIGS. 1 and 4, the terminal numbers (pin numbers) # 1 to # 6 of the external connection terminals 21 to 26 are also shown, and the first external connection terminal 21 which is the first terminal # 1 is shown. The conventional input terminal and the fourth external connection terminal 24, which is the fourth terminal # 4, correspond to the conventional output terminals, respectively.

As shown in FIG. 1, the second external connection terminal 22 connected to the common electrode 113 of the first piezoelectric substrate 11 and the fifth external connection terminal 25 connected to the common electrode 123 of the second piezoelectric substrate 12 are GND terminals. As each is grounded.

The third external connection terminal 23 connected to the output electrode 112 of the first piezoelectric filter element 8 and the sixth external connection terminal 26 connected to the input electrode 121 of the second piezoelectric filter element 9 are connected to the coupling capacitor C3. Connected in common.

In this way, the output electrode 112 of the first piezoelectric filter element 8 and the input electrode 121 of the second piezoelectric filter element 9 are connected to each other, and the two 2-pole type first and second piezoelectric filter elements 8 and 9 are longitudinally connected. A connected 4-pole type piezoelectric filter 2 is configured.

The above is the configuration of the piezoelectric filter 2 on the premise that the input / output direction of the signal is not switched, that is, the input / output direction of the same signal as in the conventional case.

In this embodiment, as shown by the broken line in FIG. 3, the aspect ratio of the rectangular input / output electrodes 111 and 112 of the first piezoelectric filter element 8 and the rectangular input / output electrodes 121 and 122 of the second piezoelectric filter element 9 The input / output electrodes 111 and 112 have a shape close to a rectangle, and the input / output electrodes 121 and 122 have a shape close to a square so as to suppress spurious. The electrode shapes of both piezoelectric filter elements 8 and 9 may be the same.

The piezoelectric filter device 1 of this embodiment is used for a commercial radio device, for example, an outdoor transceiver, for which the transition from the analog system to the digital system is in progress.

The piezoelectric filter device 1 of this embodiment is configured as follows so that a single piezoelectric filter 2 can be used for an analog system and a digital system.

First, the center frequencies of the first piezoelectric filter element 8 and the second piezoelectric filter element 9 constituting the piezoelectric filter 2 are deviated from each other. In this embodiment, the center frequency of the first piezoelectric filter element 8 is set higher than the center frequency of the second piezoelectric filter element 9.

As described above, the nominal frequency of the piezoelectric filter device 1 of the present embodiment used for the outdoor transceiver is, for example, 50.85 MHz.

On the other hand, the center frequency of the first piezoelectric filter element 8 is deviated from the nominal frequency by several kHz, for example, 1 kHz. Further, the center frequency of the second piezoelectric filter element 9 is deviated from the nominal frequency by several kHz, for example, 1 kHz. Therefore, in this embodiment, the center frequency of the first piezoelectric filter element 8 and the center frequency of the second piezoelectric filter element 9 are deviated from each other by 2 kHz.

The adjustment of the center frequency of the piezoelectric filter elements 8 and 9 is performed, for example, by partial vapor deposition on the electrodes 111 to 113, 121 to 123 of the piezoelectric filter elements 8 and 9.

The piezoelectric filter device 1 switches the input / output direction of a signal with respect to the piezoelectric filter 2 between an analog method and a digital method. Therefore, as shown in FIG. 1, the first and second changeover switches 3 and 4 are provided.

Further, in the piezoelectric filter device 1, the impedance on the input side and the impedance on the output side of the piezoelectric filter 2 are different from each other. Therefore, the piezoelectric filter device 1 includes the first and second impedance circuits 5 and 6.

The first impedance circuit 5 is provided between the input terminal 27 of the piezoelectric filter device 1 and the first changeover switch 3, and includes a first resistance R1 and a first capacitor C1. Further, the second impedance circuit 6 is provided between the output terminal 28 of the piezoelectric filter device 1 and the second changeover switch 4, and includes a second resistance R2 and a second capacitor C2.

In this embodiment, the impedance of the first impedance circuit 5 on the input side is, for example, 360Ω // 9pF, and the impedance of the second impedance circuit 6 on the output side is, for example, 160Ω // 5pF.

The first changeover switch 3 includes a movable contact 3a connected to the first external connection terminal 21 which is the first terminal (# 1) of the piezoelectric filter 2, and first and second fixed contacts 3b and 3c. .. The first fixed contact 3b is connected to the first impedance circuit 5 and also to the second fixed contact 4c of the second changeover switch 4. The second fixed contact 3c is connected to the first fixed contact 4b of the second changeover switch 4.

The second changeover switch 4 includes a movable contact 4a connected to the fourth external connection terminal 24 which is the fourth terminal (# 4) of the piezoelectric filter 2, and first and second fixed contacts 4b and 4c. .. The first fixed contact 4b is connected to the second impedance circuit 6 and is also connected to the second fixed contact 3c of the first changeover switch 3 as described above.

In this embodiment, in the case of the digital system, the movable contacts 3a and 4a of the first and second changeover switches 3 and 4 are connected to the first fixed contacts 3b and 4b as shown in FIG. As a result, the signal from the input terminal 27 is input to the first external connection terminal 21 which is the first terminal (# 1) of the piezoelectric filter 2 via the first impedance circuit 5, and the first piezoelectric filter element 8 and the first are used. 2 The output is output from the fourth external connection terminal 24, which is the fourth terminal (# 4) of the piezoelectric filter 2, via the piezoelectric filter element 9, and is output from the output terminal 28 via the second impedance circuit 6.

Further, in the case of the analog system, as shown in FIG. 5, the movable contacts 3a and 4a of the first and second changeover switches 3 and 4 are switched and connected to the second fixed contacts 3c and 4c side. As a result, the signal from the input terminal 27 is sent to the fourth external connection terminal 24, which is the fourth terminal (# 4) of the piezoelectric filter 2, via the first impedance circuit 5, the first changeover switch 3, and the second changeover switch 4. Is input to, and is output from the first external connection terminal 21 which is the first terminal (# 1) of the piezoelectric filter 2 via the second piezoelectric filter element 9 and the first piezoelectric filter element 8, and the second impedance circuit 6 is output. It is output from the output terminal 28 via the output terminal 28.

By switching the first and second changeover switches 3 and 4 in this way to switch the signal input / output direction to the piezoelectric filter 2, the first and second piezoelectric filter elements connected in cascade with their center frequencies deviated from each other. The input / output directions of the signals with respect to 8 and 9 are switched, and the pass band width of the signal is narrowed in the case of the digital system and widened in the pass band width of the signal in the analog system.

FIG. 6 is a diagram showing filter characteristics when the input / output direction of a signal is switched in the piezoelectric filter device 1 of this embodiment, and FIG. 6A shows the filter characteristics when the digital system is used, and is the same diagram. (B) shows the filter characteristics in the case of the analog method. In FIG. 6, the vertical axis represents the signal attenuation (dB), and the horizontal axis represents the signal frequency (kHz). The vertical axis is Scale 1dB, that is, 1dB / div, and the horizontal axis is Center 50.85MHz, Span 50kHz, that is, the range of ± 25kHz centered on the center frequency 50.85MHz, and the scale is 5kHz / div. ..

In this embodiment, the pass band of the signal in the digital system is 10 kHz / 3 dB, whereas the pass band of the signal in the analog system can be as wide as 12.5 kHz / 3 dB. ..

Next, it will be described that the pass band width of the signal is changed by switching the input / output direction of the signal with respect to the piezoelectric filter 2.

FIG. 7 shows when the input / output direction of the signal to the piezoelectric filter 2 is digital, that is, the signal is input from the first external connection terminal 21 which is the first terminal # 1 of the piezoelectric filter 2, and the fourth terminal # It is a figure for demonstrating the filter characteristic at the time of output from the 4th external connection terminal 24 which is 4.

FIG. 8 shows the case where the input / output direction of the signal to the piezoelectric filter 2 is an analog method, that is, the signal is input from the fourth external connection terminal 24 which is the fourth terminal # 4 of the piezoelectric filter 2, and the first terminal # It is a figure for demonstrating the filter characteristic at the time of output from the 1st external connection terminal 21 which is 1.

7 and 8, (a) shows the filter characteristic P1 of the first piezoelectric filter element 8 and the filter characteristic P2 of the second piezoelectric filter element 9 when the impedances on the input side and the output side of the piezoelectric filter 2 are the same. There is. As shown in FIGS. 7 (a) and 8 (a), the center frequency of the first piezoelectric filter element 8 and the center frequency of the second piezoelectric filter element 9 are frequencies S, and in this example, as described above. It is off by 2 kHz.

In this embodiment, as described above, the impedance on the input side of the piezoelectric filter 2 is larger than the impedance on the output side.

When the impedance on the input side is larger than the impedance on the output side in this way, the filter characteristics of the piezoelectric filter element on the input side shift to the higher frequency side (plus side), and the piezoelectric filter on the output side becomes. The filter characteristics of the element shift to the lower frequency side (minus side).

Therefore, in the digital system, as shown in FIG. 7B, the filter characteristic P1 of the first piezoelectric filter element 8 on the input side is shifted to the higher frequency side, and the second piezoelectric filter element 9 on the output side is used. The filter characteristic P2 of the above shifts to the lower frequency side, and the deviation of the center frequency of the first and second piezoelectric filter elements 8 and 9 becomes large.

As a result, when the filter characteristics of the first and second piezoelectric filter elements 8 and 9 are combined, the pass band width of the signal becomes narrow as shown in FIG. 7 (c), which corresponds to the digital method.

On the other hand, in the analog method in which the signal input / output directions are reversed, the filter characteristic P2 of the second piezoelectric filter element 9 on the input side shifts to the higher frequency side, as shown in FIG. 8 (b). Then, the filter characteristic P1 of the first piezoelectric filter element 8 on the output side shifts to the lower frequency side, and the deviation of the center frequency of the first and second piezoelectric filter elements 8 and 9 becomes smaller.

As a result, when the filter characteristics of the first and second piezoelectric filter elements 8 and 9 are combined, the pass band width of the signal becomes wide as shown in FIG. 8 (c), and it corresponds to the analog method.

The shift amount of the filter characteristics P1 and P2 of the first and second piezoelectric filter elements 8 and 9 can be adjusted by the difference between the impedance on the input side and the impedance on the output side of the piezoelectric filter 2. The shift amount can be increased by increasing the difference between the impedance on the input side and the impedance on the output side of the piezoelectric filter 2.

In this embodiment, since the impedance on the input side of the piezoelectric filter 2 is larger than the impedance on the output side, the filter characteristics of the piezoelectric filter element on the input side are shifted to the side having a higher frequency, and the piezoelectric filter on the output side is used. The filter characteristics of the element have shifted to the lower frequency side.

On the other hand, when the impedance on the input side of the piezoelectric filter 2 is smaller than the impedance on the output side, the filter characteristics of the piezoelectric filter element on the input side shift to the lower frequency side and output, contrary to the above. The filter characteristics of the piezoelectric filter element on the side shift to the side with a higher frequency.

Therefore, in this case, when the signal is input from the first external connection terminal 21 which is the first terminal # 1 of the piezoelectric filter 2 and output from the fourth external connection terminal 24 which is the fourth terminal # 4. , The same filter characteristics as in FIG. 8C, that is, the filter characteristics having a wide pass band width of the signal corresponding to the analog method. Further, when the signal is input from the 4th external connection terminal 24 which is the 4th terminal # 4 of the piezoelectric filter 2 and output from the 1st external connection terminal 21 which is the 1st terminal # 1, the above FIG. 7 ( It has the same filter characteristics as c), that is, a filter characteristic having a narrow pass band width of a signal corresponding to the digital method.

That is, the analog method and the digital method are reversed from the above embodiment.

FIG. 9 is a diagram showing a wide range of filter characteristics when the input / output direction of a signal is switched in the piezoelectric filter device 1 of this embodiment, and FIG. 9A shows the filter characteristics in the digital system. FIG. 3B shows the filter characteristics in the analog system.

As shown in FIG. 9, the filter characteristics of the digital system and the analog system are exactly the same except for the signal pass band.

As described above, according to the present embodiment, the pass band width of the signal can be switched between wide and narrow by switching the input / output direction of the signal with respect to the single piezoelectric filter 2. Therefore, in the commercial radio device provided with the piezoelectric filter device 1 of the present embodiment, the piezoelectric filter device 1 can be used for both the analog system and the digital system.

This reduces the number of piezoelectric filters compared to conventional commercial radios that require two piezoelectric filters, one for analog and the other for digital, which have different signal passbands. Therefore, the cost can be reduced and the space can be saved.

Further, since the first and second piezoelectric filter elements 8 and 9 are configured by forming the electrodes 111 to 113 and 121 to 123 on the individual piezoelectric substrates 11 and 12, respectively, they are acoustically separated from each other. High quality with less spurious.

Further, since the piezoelectric filter 4 has the same basic configuration as the existing 4-pole type piezoelectric filter except that the center frequencies of the 2-pole type piezoelectric filter elements 8 and 9 are shifted from each other, the existing 4-pole type piezoelectric filter 4 has the same basic configuration. It can be implemented inexpensively without major changes in the filter design.

As another embodiment of the present invention, the electrodes 111 to 113 and 121 to 123 may be formed on a single common piezoelectric substrate to form the piezoelectric filter elements 8 and 9, respectively.

In the above embodiment, the area of the electrodes 111 to 113 of the first piezoelectric filter element 8 and the area of the electrodes 121 to 123 of the second piezoelectric filter element 9 are the same, but as another embodiment of the present invention, on the other hand. The area of the electrode of the piezoelectric filter element may be reduced by up to about 40% with respect to the area of the electrode of the other piezoelectric filter element.

For example, if the area of the electrodes 111 to 113 of the first piezoelectric filter element 8 is smaller than the area of the electrodes 121 to 123 of the second piezoelectric filter element 9, the ripple becomes large and the pass band width of the signal is further narrowed. be able to.

If the area of the electrode is made smaller than 40%, the insertion loss increases, which is not preferable.

In the above embodiment, it is applied to the switching of the passband width of the signal corresponding to the analog system and the digital system of the commercial radio, but the present invention is not limited to such an application, and for example, in a plurality of communication channels. , May be applied to switch the passband of a signal corresponding to a wide bandwidth channel and a narrow bandwidth channel.

In the above embodiment, a quartz substrate is used as the piezoelectric substrate, but a ceramic substrate or a polycrystalline substrate having piezoelectric characteristics may be used.

1 Piezoelectric filter device 2 Piezoelectric filter 3 1st changeover switch 4 2nd changeover switch 5 1st impedance circuit 6 2nd impedance circuit 7 Base 8 1st piezoelectric filter element 9 2nd piezoelectric filter element 11 1st piezoelectric substrate 12 2nd piezoelectric Board 21 1st external connection terminal 24 4th external connection terminal 27 Input terminal 28 Output terminal

Claims (4)

A piezoelectric filter in which two piezoelectric filter elements having an input electrode and an output electrode formed on one main surface of a piezoelectric substrate and a common electrode formed on the other main surface are connected in cascade is provided.
The center frequencies of the two piezoelectric filter elements are offset from each other.
The impedances on the input side and output side of the piezoelectric filter are different from each other.
A piezoelectric filter device that switches the input / output direction of a signal with respect to the piezoelectric filter to switch the width of the pass band of the signal.
The input terminal of the piezoelectric filter device is switched and connected to the input side or the output side of the piezoelectric filter, and the output terminal of the piezoelectric filter device is connected to the output side or the input side of the piezoelectric filter. A switching means for switching the input / output direction of the signal by switching and connecting to the signal is provided.
A piezoelectric filter device characterized by that. There are two piezoelectric substrates, and the input electrode, the output electrode, and the common electrode of each of the two piezoelectric filter elements are formed on each piezoelectric substrate.
The piezoelectric filter device according to claim 1. The impedance on the input side and the impedance on the output side are mutually exchanged between the input terminal of the piezoelectric filter device and the switching means, and between the output terminal of the piezoelectric filter device and the switching means. Different impedance circuits are provided, respectively.
The piezoelectric filter device according to claim 1 or 2. The piezoelectric substrate is a quartz substrate.
The piezoelectric filter device according to any one of claims 1 to 3 .

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