JP2019110490A - Piezoelectric filter device - Google Patents

Abstract

To make it possible to cope with wide and narrow passbands by using a single piezoelectric filter.SOLUTION: Impedances of input and output sides of a 4-pole piezoelectric filter 2 in which two 2-pole piezoelectric filter elements are connected in cascade are made to be different by first and second impedance circuits 5, 6, center frequencies of the two piezoelectric filter elements are offset from each other, and input and output directions of a signal against the piezoelectric filter 2 are switched by first and second changeover switches 3, 4. Thereby, a width of a passband of the signal is switched.SELECTED DRAWING: Figure 1

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a piezoelectric filter device used for communication devices such as commercial wireless devices and mobile phones.

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

  By the way, in a communication device in which such a piezoelectric filter is used, for example, a commercial wireless device, transition from a conventional analog method to a digital method for the purpose of effective use of frequency band, improvement of confidentiality of communication (privacy protection), etc. Is in progress.

Patent No. 3507206 gazette

  Some conventional business radios can communicate in both an analog mode and a digital mode. However, a business-use wireless device that can communicate using both methods includes an analog piezoelectric filter for a wide signal passband width and a digital piezoelectric filter for a narrow signal passband, and both piezoelectric filters are used. I am trying to switch. Therefore, two piezoelectric filters are provided: a piezoelectric filter for an analog system with a wide signal passband width and a piezoelectric filter for a digital system with a narrow signal passband width. Is required.

  For this reason, it is desirable to be able to handle analog and digital systems by using a single piezoelectric filter.

  The present invention has been made in view of the above-described points, and it is an object of the present invention to be able to cope with the wide and narrow passbands of signals using a single piezoelectric filter.

  The present invention is configured as follows to achieve the above object.

  That is, in the piezoelectric filter device of the present invention, two of the piezoelectric filter elements in which the input electrode and the output electrode are formed on one main surface of the piezoelectric substrate and the common electrode is formed on the other main surface are cascaded A piezoelectric filter is provided, the center frequencies of the two piezoelectric filter elements are shifted from each other, the impedances on the input side and the output side of the piezoelectric filter are different from each other, the input / output direction of the signal to the piezoelectric filter is switched, Switch the passband width.

  According to the present invention, since the center frequencies of the two piezoelectric filter elements are mutually shifted and the impedances of the input side and the output side of the piezoelectric filter in which the two piezoelectric filter elements are connected in cascade are made different, By switching the input / output direction of the signal, the filter characteristics of the two piezoelectric filter elements can be shifted so that the deviation of the center frequency becomes larger or smaller, whereby the filters of both piezoelectric filter elements can be shifted. The characteristics may be combined to narrow or widen the passband of the signal. Moreover, since it can comprise only with one piezoelectric filter and one circuit connected to these, it can be set as a structure advantageous to space saving.

  Preferably, 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 respectively formed on one piezoelectric substrate.

  According to this configuration, since the input electrode, the output electrode, and the common electrode are formed on each of the individual piezoelectric substrates to constitute the piezoelectric filter elements, they are acoustically separated from each other, and thus the common piezoelectric substrate 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, the spurious can be suppressed and the filter characteristics can be improved.

  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 the output side or the input side of the piezoelectric filter It is preferable to provide switching means for switching the input / output direction of the signal by switching connection.

  According to this configuration, the input / output direction of the signal to the piezoelectric filter can be easily switched by controlling the switching means. In addition, the circuit configuration can be advantageous for space saving.

  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, the impedance on the input side and the impedance on the output side are mutually set. Preferably, different impedance circuits are provided.

  According to this configuration, the impedance on the input side and 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 is improved.

  As described above, according to the present invention, by switching the input / output direction of the signal to the piezoelectric filter, the filter characteristics of the two piezoelectric filter elements are shifted so that the deviation of the center frequency becomes larger or smaller. The filter characteristics of the two piezoelectric filter elements can be combined to narrow or widen the passband of the signal.

  Therefore, the pass band width of the signal can be switched wide and narrow by a single piezoelectric filter, and, for example, in an industrial radio, the piezoelectric filter device can be used both as analog and digital. it can. As a result, the cost can be reduced as compared with the conventional business wireless device which requires two piezoelectric filters of analog type and digital type piezoelectric filters having different signal passband widths. Space saving can be achieved.

FIG. 1 is a schematic block diagram of a piezoelectric filter device according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of the piezoelectric filter of FIG. FIG. 3 is a plan view of the piezoelectric filter of FIG. 2 with the cover removed. FIG. 4 is a schematic view showing the configuration of the piezoelectric filter of FIG. FIG. 5 is a schematic configuration diagram corresponding to FIG. 1 in a state in which the input / output direction of the signal to the piezoelectric filter is switched. FIG. 6 is a diagram showing the filter characteristics when the input / output direction of the signal to the piezoelectric filter is switched to make the digital system or the analog system, (a) shows the filter characteristic when the digital system is used, and (b) shows the analog system. Shows the filter characteristics at the time of. FIG. 7 is a diagram for explaining filter characteristics when the input / output direction of the signal to the piezoelectric filter is digital. FIG. 8 is a diagram for explaining filter characteristics when the input / output direction of a signal to / from the piezoelectric filter is an analog system. FIG. 9 is a diagram showing the filter characteristics in a wide area when the input / output direction of the signal with respect to the piezoelectric filter is switched to make the digital system or the analog system, (a) shows the filter characteristic when the digital system is The filter characteristic in the case of an analog system is shown.

  Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

  FIG. 1 is a schematic block 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 switches 3 and 4 as switching means for switching the input / output direction of the signal to the piezoelectric filter 2, and the input side and output of the piezoelectric filter 2. The first and second impedance circuits 5 and 6 are provided to make the impedance on the side different.

  In the present invention, the input / output direction of the signal to / from the piezoelectric filter 2 is switched. First, in the state where the input / output direction of the signal is not switched The configuration will be described. FIG. 1 shows the state in which the input / output direction of the signal is not switched, that is, the state in the input / output direction of the same signal as in the conventional case.

  The piezoelectric filter 2 of this embodiment is a four-pole piezoelectric filter in which two two-pole piezoelectric filter elements are cascaded as described later.

  2 is a longitudinal 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 cover 10 removed, and FIG. 4 is a piezoelectric filter of FIG. FIG. 2 is a schematic view showing a configuration of 2.

  The piezoelectric filter 2 according to this embodiment includes a ceramic base 7, two first and second piezoelectric filter elements 8 and 9 stored in the base 7, and a lid 10 for hermetically sealing the base 7. Is equipped. The lid 10 is made of, for example, a metal plate such as Kovar.

  The base 7 in this embodiment is made of a ceramic multilayer substrate having alumina or the like as a base material. In this embodiment, the base 7 is a flat lower layer 7a having a substantially rectangular shape in plan view, a middle layer 7b forming a step formed on the upper side of the lower layer 7a, and a frame formed on the outer peripheral part on the middle layer 7b. It is a three-layer configuration with the upper layer 7c to be configured. In the base 7, the three layers 7 a to 7 c constitute 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 respectively include first and second piezoelectric substrates 11 and 12 made of, for example, an AT-cut quartz substrate.

  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 holding and mounting the first piezoelectric substrate 11 and a first output pad 15 , And the first ground pad 16 are formed. Similarly, a second input pad 17 for holding and mounting the second piezoelectric substrate 12 electromechanically, a second output pad 18 and a second ground pad 19 are formed.

  On the back surface (lower surface) which is one main surface of the first piezoelectric substrate 11 of the first piezoelectric filter element 8, rectangular input electrodes 111 and output electrodes 112 are formed in parallel at intervals. The respective electrodes 111 and 112 are drawn out to opposing corners of the first piezoelectric substrate 11 and are electrically connected to the first input pad 14 and the first output pad 15 by the 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) which is the other main surface of the first piezoelectric substrate 11. The common electrode 113 is drawn to the other corner of the first piezoelectric substrate 11 and is electrically connected to the first ground pad 16 by the conductive adhesive 20.

  Also in the second piezoelectric substrate 12 of the second piezoelectric filter element 9, rectangular input electrodes 121 and output electrodes 122 are formed on the back surface, similarly to the first piezoelectric substrate 11. Each of the electrodes 121 and 122 is drawn out to the facing corner of the second piezoelectric substrate 12 and is electrically connected to the second input pad 17 and the second output pad 18 by the conductive adhesive 20. A common electrode 123 which is a rectangular ground electrode corresponding to the input electrode 121 and the output electrode 122 is formed on the surface of the second piezoelectric substrate 12. The common electrode 123 is drawn to the other corner of the second piezoelectric substrate 12 and is electrically connected to the second ground pad 19 by the conductive adhesive 20.

  On the bottom of the base 7, six first to sixth external connection terminals 21 to 26 for surface mounting shown in FIG. 1 and FIG. 4 are formed. These external connection terminals 21 to 26 are connected to the first input pad 14, the first output pad 15, the first ground pad 16, the first input pad 14, the first output pad 15, and the The second input pad 17 is electrically connected to the second output pad 18 and the second ground pad 19. Therefore, the 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 through the pads 14 to 19 and the conductive adhesive 20, respectively. 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 The eleven output electrodes 112 and the third external connection terminal 23 are connected to each other.

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

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

  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 have GND terminals, as shown in FIG. 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 form a coupling capacitor C3. Commonly connected.

  Thus, 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 first and second two-pole piezoelectric filter elements 8 and 9 are cascaded. A 4-pole piezoelectric filter 2 connected 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 prior art.

  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 shapes close to a rectangular shape, and the input / output electrodes 121 and 122 have shapes close to a square, with different aspect ratios, thereby suppressing spurious. The electrode shapes of both piezoelectric filter elements 8 and 9 may be the same.

  The piezoelectric filter device 1 according to this embodiment is used for a business-use radio device, for example, a transceiver for the outdoors, in which the transition from the analog system to the digital system is in progress.

  In the piezoelectric filter device 1 of this embodiment, the single piezoelectric filter 2 is configured as follows so as to be compatible with 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 that constitute the piezoelectric filter 2 are offset from each other. In this embodiment, the center frequency of the first piezoelectric filter element 8 is 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 shifted by several kHz, for example, 1 kHz, higher than the nominal frequency. In addition, the center frequency of the second piezoelectric filter element 9 is shifted by several kHz, for example, 1 kHz lower than the nominal frequency. 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 offset 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 deposition on each of the electrodes 111 to 113 and 121 to 123 of each of the piezoelectric filter elements 8 and 9.

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

  Furthermore, in the piezoelectric filter device 1, the impedance on the input side of the piezoelectric filter 2 and the impedance on the output side are made different. 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 resistor R1 and a first capacitor C1. 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 resistor R2 and a second capacitor C2.

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

  The first changeover switch 3 includes a movable contact 3a connected to a 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 3 b is connected to the first impedance circuit 5 and to the second fixed contact 4 c of the second changeover switch 4. The second fixed contact 3 c is connected to the first fixed contact 4 b of the second changeover switch 4.

  The second changeover switch 4 includes a movable contact 4a connected to a 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 4 b is connected to the second impedance circuit 6 and also connected to the second fixed contact 3 c of the first changeover switch 3 as described above.

  In this embodiment, in 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. Thereby, the signal from the input terminal 27 is inputted to the first external connection terminal 21 which is the first terminal (# 1) of the piezoelectric filter 2 through the first impedance circuit 5, and the first piezoelectric filter element 8 and the The signal is output from the fourth external connection terminal 24 which is the fourth terminal (# 4) of the piezoelectric filter 2 through the two piezoelectric filter element 9, and is output from the output terminal 28 through the second impedance circuit 6.

  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. As a result, the signal from the input terminal 27 is transmitted to the fourth external connection terminal 24 which is the fourth terminal (# 4) of the piezoelectric filter 2 through the first impedance circuit 5, the first changeover switch 3 and the second changeover switch 4. Through the second piezoelectric filter element 9 and the first piezoelectric filter element 8 to output from the first external connection terminal 21 which is the No. 1 terminal (# 1) of the piezoelectric filter 2, and the second impedance circuit 6 It outputs from the output terminal 28 via it.

Thus, by switching the first and second changeover switches 3 and 4 to switch the input / output direction of the signal to the piezoelectric filter 2, the cascaded first and second piezoelectric filter elements whose center frequencies are shifted from each other The input and output directions of the signals of 8 and 9 are switched, the pass band width of the signal is narrow in the digital method, and the pass band width of the signal is wide in the analog method.

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

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

  Next, the change of the pass band width of the signal by switching the input / output direction of the signal to the piezoelectric filter 2 will be described.

  7, when the input / output direction of the signal with respect to the piezoelectric filter 2 is digital, that is, the signal is inputted 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 when it outputs from the 4th external connection terminal 24 which is four.

  In FIG. 8, when the input / output direction of the signal to / from the piezoelectric filter 2 is analog, that is, the signal is inputted from the fourth external connection terminal 24 which is the fourth terminal # 4 of the piezoelectric filter 2, It is a figure for demonstrating the filter characteristic when it outputs from the 1st external connection terminal 21 which is 1. FIG.

  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 impedance on the input side and the output side of the piezoelectric filter 2 is 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 have a frequency S, which in this example is as described above. Is offset 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.

  Thus, when the impedance on the input side is larger than the impedance on the output side, the filter characteristic of the piezoelectric filter element on the input side is shifted to the high frequency side (plus side), and the piezoelectric filter on the output side The filter characteristics of the element shift to the lower frequency side (negative side).

  Therefore, in the digital method, as shown in FIG. 7B, the filter characteristic P1 of the first piezoelectric filter element 8 on the input side is shifted to the high frequency side and the second piezoelectric filter element 9 on the output side. The filter characteristic P2 shifts to the low 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, as shown in FIG. 7C, the pass band width of the signal becomes narrow, which corresponds to the digital system.

  On the other hand, in the analog method in which the input / output direction of the signal is reversed, as shown in FIG. 8B, the filter characteristic P2 of the second piezoelectric filter element 9 on the input side is shifted to the higher frequency side As a result, the filter characteristic P1 of the first piezoelectric filter element 8 on the output side is shifted to the lower frequency side, and the deviation of the center frequencies of the first and second piezoelectric filter elements 8 and 9 is reduced.

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

  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 of the piezoelectric filter 2 and the impedance on the output side. The shift amount can be increased by increasing the difference between the impedance on the input side of the piezoelectric filter 2 and the impedance on the output side.

  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 shift to the high frequency side and the piezoelectric filter on the output side The filter characteristics of the element shifted to lower frequencies.

  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 are shifted to lower frequency side, contrary to the above. The filter characteristics of the piezoelectric filter element on the side shift to the higher frequency side.

  Therefore, in this case, when the signal is inputted from the first external connection terminal 21 which is the first terminal # 1 of the piezoelectric filter 2 and is outputted from the fourth external connection terminal 24 which is the fourth terminal # 4. The filter characteristic is the same as that of FIG. 8C, that is, the filter characteristic having a wide pass band width of the signal corresponding to the analog system. Further, when the signal is inputted from the fourth external connection terminal 24 which is the fourth terminal # 4 of the piezoelectric filter 2 and outputted from the first external connection terminal 21 which is the first terminal # 1, as shown in FIG. The same filter characteristics as in c), that is, narrow filter characteristics of the passband width of the signal corresponding to the digital system.

  That is, the analog system and the digital system are reversed in the above embodiment.

  FIG. 9 is a diagram showing wide-range filter characteristics when the input / output direction of the signal is switched in the piezoelectric filter device 1 of this embodiment, and FIG. 9 (a) shows the filter characteristics in the digital system. The figure (b) has shown the filter characteristic at the time of an analog system.

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

  As described above, according to the present embodiment, by switching the input / output direction of the signal with respect to the single piezoelectric filter 2, the pass band width of the signal can be switched to be wide or narrow. Therefore, in the professional wireless apparatus provided with the piezoelectric filter device 1 of the present embodiment, the piezoelectric filter device 1 can be used both as an analog system and a digital system.

  As a result, the number of piezoelectric filters can be reduced compared to the conventional business wireless device that requires two piezoelectric filters, one for analog type and the other for digital type, with 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 respectively on the individual piezoelectric substrates 11 and 12, they are acoustically separated from each other, It becomes a high quality thing with few spurious.

  Furthermore, since the piezoelectric filter 4 has the same basic configuration as the existing four-pole piezoelectric filter except that the center frequencies of the two-pole piezoelectric filter elements 8, 9 are mutually shifted, the existing four-pole piezoelectric It can be implemented inexpensively without major changes in filter design.

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

  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 The area of the electrode of the piezoelectric filter element may be reduced by about 40% at the maximum as compared with the area of the electrode of the other piezoelectric filter element.

  For example, when 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, ripples become large, and the signal passband width is further narrowed. be able to.

  If the area of the electrode is reduced to more than 40%, the insertion loss is undesirably increased.

  In the above embodiment, the present invention is applied to switching of the pass band width of the signal corresponding to the analog system and the digital system of the business radio, but the present invention is not limited to such application, for example, in a plurality of communication channels. The present invention may be applied to switching of the passband width 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.

Reference Signs List 1 piezoelectric filter device 2 piezoelectric filter 3 first changeover switch 4 second changeover switch 5 first impedance circuit 6 second impedance circuit 7 base 8 first piezoelectric filter element 9 second piezoelectric filter element 11 first piezoelectric substrate 12 second piezoelectric Substrate 21 first external connection terminal 24 fourth external connection terminal 27 input terminal 28 output terminal

Claims (5)

A piezoelectric filter in which two of the piezoelectric filter elements having an input electrode and an output electrode formed on one main surface of the piezoelectric substrate and a common electrode formed on the other main surface are cascaded;
The center frequencies of the two piezoelectric filter elements are mutually offset,
The impedances of the input side and the output side of the piezoelectric filter are different from each other,
Switching the width direction of the signal passband by switching the input / output direction of the signal to the piezoelectric filter,
Piezoelectric filter device characterized in that. The number of the piezoelectric substrates is two, and the input electrodes, the output electrodes, and the common electrodes of the two piezoelectric filter elements are formed on the respective piezoelectric substrates.
The piezoelectric filter device according to claim 1. 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 the output side or the input side of the piezoelectric filter Switching means for switching the input / output direction of the signal by switching connection to
The piezoelectric filter device according to claim 1. 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, the impedance on the input side and the impedance on the output side are mutually set. Different impedance circuits are provided, respectively
The piezoelectric filter device according to claim 3. The piezoelectric substrate is a quartz substrate;
The piezoelectric filter device according to any one of claims 1 to 4.

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