CN109951172B - Piezoelectric filter device - Google Patents
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- CN109951172B CN109951172B CN201811182466.2A CN201811182466A CN109951172B CN 109951172 B CN109951172 B CN 109951172B CN 201811182466 A CN201811182466 A CN 201811182466A CN 109951172 B CN109951172 B CN 109951172B
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Abstract
The present invention relates to a piezoelectric filter device capable of using a single piezoelectric filter to cope with a width of a passband. A four-pole piezoelectric filter (2) in which two piezoelectric filter elements of a bipolar type are cascade-connected is configured by a first impedance circuit (5) and a second impedance circuit (6), the impedances on the input side and the output side are different, the center frequencies of the two piezoelectric filter elements are shifted from each other, and the input/output directions of signals for the piezoelectric filter (2) are switched by a first switch (3) and a second switch (4), so that the width of the passband width of the signals is switched.
Description
Technical Field
The present invention relates to a piezoelectric filter device used for communication equipment such as a commercial wireless device and a mobile phone.
Background
A piezoelectric filter, for example, a piezoelectric filter using an AT cut quartz plate or the like is generally configured such that an input electrode and an output electrode are formed on one surface of a piezoelectric substrate, and a common electrode (ground electrode) corresponding to the input/output electrode is formed on the other surface. In this structure, since the piezoelectric substrate is sandwiched between two electrode pairs, a so-called bipolar piezoelectric filter is provided, and in order to improve the characteristics of the piezoelectric filter, a four-pole piezoelectric filter is provided in which such a bipolar piezoelectric filter is cascade-connected (for example, refer to patent document 1).
However, in a communication device using the piezoelectric filter, for example, a commercial wireless device, the conversion from the conventional analog system to the digital system is being advanced for the purpose of effectively utilizing a frequency band, improving confidentiality (privacy protection) of communication, and the like.
Patent document 1: japanese patent No. 3507206
Conventional commercial wireless devices include those capable of communicating in both analog and digital modes. However, a commercial wireless device capable of communicating in the above two modes includes a piezoelectric filter for analog mode in which the passband width of a signal is wide and a piezoelectric filter for digital mode in which the passband width of a signal is narrow, and the two piezoelectric filters are switched. Accordingly, the cost increases and space is required in accordance with the two piezoelectric filters including the piezoelectric filter for analog system having a wide passband width of the signal and the piezoelectric filter for digital system having a narrow passband width of the signal.
Therefore, it is desirable to be able to cope with both analog and digital modes by a single piezoelectric filter.
Disclosure of Invention
The present invention has been made in view of the above-described problems, and an object of the present invention is to enable the use of a single piezoelectric filter, corresponding to the width of the passband of a signal.
In the present invention, in order to achieve the above object, the following is constructed.
That is, the piezoelectric filter device of the present invention includes a piezoelectric filter in which two piezoelectric filter elements having an input electrode and an output electrode formed on one principal surface of a piezoelectric substrate and a common electrode formed on the other principal surface so as to face the input electrode and the output electrode are connected in cascade, the center frequencies of the two piezoelectric filter elements being offset from each other, and the impedance on the input side and the impedance on the output side of the piezoelectric filter being different from each other, and the width of the passband width of the signal being switched by switching the input/output directions of the signal for the piezoelectric filter.
According to the present invention, the center frequencies of the two piezoelectric filter elements are deviated from each other, and the impedance of the input side and the output side of the piezoelectric filter in which the two piezoelectric filter elements are cascade-connected is different. Therefore, by switching the input/output directions of signals to/from the piezoelectric filter, the filter characteristics of the two piezoelectric filter elements can be shifted so that the shift in the center frequency becomes larger or smaller. Accordingly, the filter characteristics of the two piezoelectric filter elements are combined, and the passband width of the signal can be narrowed or widened. Further, it is possible to be constituted by only one piezoelectric filter and one circuit connected thereto. Therefore, the structure advantageous for saving space can be achieved.
Preferably, the piezoelectric substrates are provided in 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, the input electrode, the output electrode, and the common electrode are formed on the individual piezoelectric substrates, and the piezoelectric filter element is configured. Therefore, the piezoelectric filter elements are separated from each other acoustically, and the filter characteristics can be improved by suppressing the spurious emission, compared with a configuration in which the input electrode, the output electrode, and the common electrode of the two piezoelectric filter elements are formed on the common piezoelectric substrate.
Preferably, the present invention includes: and a switching unit that switches the input terminal of the piezoelectric filter device to be connected to the input side or the output side of the piezoelectric filter, and switches the output terminal of the piezoelectric filter device to be connected to the output side or the input side of the piezoelectric filter, thereby switching the input/output direction of the signal.
According to this configuration, by controlling the switching means, the input/output direction of the signal to the piezoelectric filter can be easily switched. Further, the circuit configuration can be advantageous in saving space.
Preferably, impedance circuits for making the impedance on the input side and the impedance on the output side different from each other are provided between the input terminal and the switching unit of the piezoelectric filter device and between the output terminal and the switching unit of the piezoelectric filter device, respectively.
According to this configuration, the impedance circuits can set the impedance of the input side and the output side of the piezoelectric filter, respectively.
Preferably, the piezoelectric substrate is a quartz substrate.
According to this structure, the frequency temperature characteristic is made good.
As described above, according to the present invention, by switching the input/output directions of signals to/from the piezoelectric filter elements, the filter characteristics of the two piezoelectric filter elements can be shifted so that the deviation of the center frequencies thereof becomes larger or smaller, and the filter characteristics of the two piezoelectric filter elements can be combined, thereby making it possible to narrow or widen the passband width of the signals.
Therefore, the width of the passband of the signal can be switched by a single piezoelectric filter, and for example, in a commercial wireless device, the piezoelectric filter device can be used in both analog and digital modes. Accordingly, compared with the conventional example of a commercial wireless device in which two piezoelectric filters, i.e., an analog piezoelectric filter and a digital piezoelectric filter, having different passband widths of a desired signal, the cost can be reduced and space can be saved.
Drawings
Fig. 1 is a schematic configuration 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. 1.
Fig. 3 is a plan view of the piezoelectric filter of fig. 2 with the cover removed.
Fig. 4 is a schematic view illustrating a structure of the piezoelectric filter of fig. 2.
Fig. 5 is a schematic configuration diagram corresponding to fig. 1 in a state in which the input/output direction of signals to the piezoelectric filter is switched.
Fig. 6 is a diagram showing filter characteristics when the input/output direction of a signal to the piezoelectric filter is switched to a digital mode or an analog mode, (a) shows filter characteristics when the signal is in the digital mode, and (b) shows filter characteristics when the signal is in the analog mode.
Fig. 7 is a diagram for explaining filter characteristics when the input/output direction of signals to/from the piezoelectric filter is digital.
Fig. 8 is a diagram for explaining filter characteristics when the input/output direction of signals to/from the piezoelectric filter is in the analog mode.
Fig. 9 is a diagram showing filter characteristics in a wide area when the input/output direction of a signal to the piezoelectric filter is switched to a digital mode or an analog mode, (a) shows filter characteristics in the digital mode, and (b) shows filter characteristics in the analog mode.
Description of the reference numerals
1. Piezoelectric filter device
2. Piezoelectric filter
3. First switch
4. Second change-over switch
5. First impedance circuit
6. Second impedance circuit
7. Base seat
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
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying 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; a first changeover switch 3 and a second changeover switch 4 as switching means for switching the input/output direction of a signal to the piezoelectric filter 2; and a first impedance circuit 5 and a second impedance circuit 6 for making the impedance of the input side and the output side of the piezoelectric filter 2 different.
In the present invention, although the input/output direction of the signal to the piezoelectric filter 2 is switched, first, the configuration of the piezoelectric filter 2 will be described on the premise of a state in which the input/output direction of the signal is not switched, that is, the same input/output direction of the signal as in the related art. 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 that in the conventional case.
The piezoelectric filter 2 of this embodiment is a four-pole piezoelectric filter in which two piezoelectric filter elements of a bipolar type are cascade-connected as described later. Here, "cascade connection" means that an output electrode of one of the bipolar piezoelectric filter elements is connected to an input electrode of the other bipolar piezoelectric filter element.
Fig. 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 in a state in which the cover 10 is removed, and fig. 4 is a schematic diagram showing the structure of the piezoelectric filter 2 of fig. 2.
The piezoelectric filter 2 of this embodiment includes: a ceramic susceptor 7; two piezoelectric filter elements, namely a first piezoelectric filter element 8 and a second piezoelectric filter element 9, are accommodated in the chassis 7; and a lid 10 for hermetically sealing the base 7. The cover 10 is made of a metal plate such as kovar (コ).
The susceptor 7 of this embodiment is composed of a ceramic multilayer substrate using alumina or the like as a base material. In this embodiment, the susceptor 7 has a three-layer structure of a flat plate-like lower layer 7a having a substantially rectangular planar shape in plan view, a middle layer 7b constituting a step portion formed on an upper portion of the lower layer 7a, and an upper layer 7c constituting a frame portion formed on an outer peripheral portion of the middle layer 7 b. The base 7 has three layers 7a to 7c, and a housing recess 13 having a stepped portion for housing and holding the first piezoelectric filter element 8 and the second piezoelectric filter element 9 is formed.
The first piezoelectric filter element 8 and the second piezoelectric filter element 9 include, for example, a first piezoelectric substrate 11 and a second piezoelectric substrate 12 each made of an AT-cut quartz substrate.
A first input pad 14, a first output pad 15, and a first ground pad 16 for electrically and mechanically holding the first piezoelectric substrate 11 are formed on the upper surface of the middle layer 7b of the base 7, that is, on the step portion of the housing recess 13 of the base 7. Similarly, a second input pad 17, a second output pad 18, and a second ground pad 19 for electrically and mechanically holding the second piezoelectric substrate 12 are formed.
Rectangular input electrodes 111 and output electrodes 112 are formed in parallel with each other at a distance from each other on one principal surface (lower surface) of the first piezoelectric substrate 11 of the first piezoelectric filter element 8. The electrodes 111 and 112 are led out to the opposite corners of the first piezoelectric substrate 11, and are electrically connected to the first input pad 14 and the first output pad 15 via the conductive adhesive 20.
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 other main surface (upper surface) of the first piezoelectric substrate 11. The common electrode 113 is led out to the other corner of the first piezoelectric substrate 11, and is electrically connected to the first ground pad 16 via the conductive adhesive 20.
Similarly to the first piezoelectric substrate 11, the second piezoelectric substrate 12 of the second piezoelectric filter element 9 is also formed with rectangular input electrodes 121 and rectangular output electrodes 122 on the back surface thereof. The electrodes 121 and 122 are led out to the opposite corners of the second piezoelectric substrate 12, and are electrically connected to the second input pad 17 and the second output pad 18 via 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 led out to the other corner of the second piezoelectric substrate 12, and is electrically connected to the second ground pad 19 via the conductive adhesive 20.
On the bottom surface of the base 7, first to sixth external connection terminals 21 to 26, which are six external connection terminals for surface mounting shown in fig. 1 and 4, are formed. These external connection terminals 21 to 26 are electrically connected to the first input pad 14, the first output pad 15, the first ground pad 16, the second input pad 17, the second output pad 18, and the second ground pad 19 via wiring (wiring pattern, via hole, or the like) formed in the base 7 and not shown. Accordingly, the external connection terminals 21 to 26 are electrically connected to the electrodes 111 to 113, 121 to 123 of the first piezoelectric substrate 11 and the second piezoelectric substrate 12 via the pads 14 to 19 and the conductive adhesive 20, respectively.
Specifically, as shown in fig. 4, the input electrode 111 of the first piezoelectric substrate 11 is connected to the first external connection terminal 21, the common electrode 113 of the first piezoelectric substrate 11 is connected to the second external connection terminal 22, and the output electrode 112 of the first piezoelectric substrate 11 is connected to the third external connection terminal 23.
The output electrode 122 of the second piezoelectric substrate 12 is connected to the fourth external connection terminal 24, the common electrode 123 of the second piezoelectric substrate 12 is connected to the fifth external connection terminal 25, and the input electrode 121 of the second piezoelectric substrate 12 is connected to the sixth external connection terminal 26.
In fig. 1 and 4, the terminal numbers (pin numbers) #1 to #6 of the external connection terminals 21 to 26 are collectively shown, and the first external connection terminal 21, which is the terminal #1, corresponds to a conventional input terminal, and the fourth external connection terminal 24, which is the terminal #4, corresponds to a conventional output terminal.
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 grounded as ground terminals, respectively.
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 in common.
As described above, 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 four-pole piezoelectric filter 2 in which the first piezoelectric filter element 8 and the second piezoelectric filter element 9, which are two piezoelectric filter elements each of the bipolar type, are cascade-connected is configured.
The above is a configuration of the piezoelectric filter 2 assuming that the input/output direction of the signal is not switched, that is, the input/output direction of the signal is the same as the conventional one.
In this embodiment, as shown by the broken line in fig. 3, the aspect ratio of the rectangular input electrode 111 and output electrode 112 of the first piezoelectric filter element 8 is made different from the aspect ratio of the rectangular input electrode 121 and output electrode 122 of the second piezoelectric filter element 9, the input electrode 111 and output electrode 112 are formed in a substantially rectangular shape, the input electrode 121 and output electrode 122 are formed in a substantially square shape, and the spurious emission is suppressed. The electrode shapes of the two piezoelectric filter elements 8 and 9 may be the same.
The piezoelectric filter device 1 of this embodiment is used for a commercial wireless device that is being shifted from an analog mode to a digital mode, such as an outdoor radio transceiver.
In the piezoelectric filter device 1 of this embodiment, the piezoelectric filter device 2 is configured as follows so as to be capable of being used in an analog mode and a digital mode.
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 made higher than the center frequency of the second piezoelectric filter element 9. Here, the center frequency is defined as the frequency of the arithmetic average of the passband on the lower side and the passband on the upper side in the bandpass filter.
The nominal frequency of the piezoelectric filter device 1 of the present embodiment, which is used for an outdoor radio transceiver as described above, is 50.85MHz, for example.
In contrast, the center frequency of the first piezoelectric filter element 8 is shifted from the nominal frequency by several kHz, for example, by 1kHz. In addition, the center frequency of the second piezoelectric filter element 9 is shifted from the nominal frequency by several kHz, for example, by 1kHz. 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 2kHz.
The center frequency of the piezoelectric filter elements 8 and 9 is adjusted by, for example, partial vapor deposition or the like on the electrodes 111 to 113 and 121 to 123 of the piezoelectric filter elements 8 and 9.
The piezoelectric filter device 1 switches the input/output direction of the signal to the piezoelectric filter 2 between the analog mode and the digital mode. Therefore, as shown in fig. 1, the first switch 3 and the second switch 4 are provided.
Further, in the piezoelectric filter device 1, the impedance of the input side and the impedance of the output side of the piezoelectric filter 2 are made different. Accordingly, the piezoelectric filter device 1 includes the first impedance circuit 5 and the second impedance circuit 6.
The first impedance circuit 5 is provided between the input terminal 27 of the piezoelectric filter device 1 and the first 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 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//9pF, and the impedance of the second impedance circuit 6 on the output side is, for example, 160 Ω//5pF.
The first switch 3 includes a movable contact 3a connected to a first external connection terminal 21, which is a terminal #1 of the piezoelectric filter 2, and a first fixed contact 3b and a second fixed contact 3c. The first fixed contact 3b is connected to the first impedance circuit 5 and 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 change-over switch 4 includes a movable contact 4a connected to a fourth external connection terminal 24, which is a terminal #4 of the piezoelectric filter 2, and a first fixed contact 4b and a second fixed contact 4c. The first fixed contact 4b is connected to the second impedance circuit 6 and, as described above, to the second fixed contact 3c of the first switch 3.
In this embodiment, in the digital mode, the movable contacts 3a, 4a of the first switch 3 and the second switch 4 are connected to the first fixed contacts 3b, 4b side as shown in fig. 1. Accordingly, the signal from the input terminal 27 is input to the first external connection terminal 21, which is the No. 1 terminal (# 1) of the piezoelectric filter 2, via the first impedance circuit 5, and is output from the fourth external connection terminal 24, which is the No. 4 terminal (# 4) of the piezoelectric filter 2, via the first piezoelectric filter element 8 and the second piezoelectric filter element 9, and is output from the output terminal 28 via the second impedance circuit 6.
In the analog mode, as shown in fig. 5, the movable contacts 3a and 4a of the first switch 3 and the second switch 4 are switched and connected to the second fixed contacts 3c and 4c. Accordingly, the signal from the input terminal 27 is input to the fourth external connection terminal 24, which is the No. 4 terminal (# 4) of the piezoelectric filter 2, via the first impedance circuit 5, the first change-over switch 3, and the second change-over switch 4, and is output from the first external connection terminal 21, which is the No. 1 terminal (# 1) of the piezoelectric filter 2, via the second piezoelectric filter element 9 and the first piezoelectric filter element 8, and is output from the output terminal 28 via the second impedance circuit 6.
By switching the first and second switches 3, 4 in this way and switching the input/output directions of signals to/from the piezoelectric filter 2, the input/output directions of signals to/from the first piezoelectric filter element 8 and the second piezoelectric filter element 8, 9, which are cascade-connected with each other with their center frequencies being shifted from each other, are switched, and in the digital mode, the passband width of the signals is narrowed, and in the analog mode, the passband width of the signals is widened. Fig. 6 is a diagram showing filter characteristics when the input/output directions of signals are switched in the piezoelectric filter device 1 according to the embodiment, in which (a) of the diagram shows filter characteristics in the digital system, and (b) of the diagram shows filter characteristics in the analog system. In fig. 6, the vertical axis represents the attenuation amount (dB) of the signal, and the horizontal axis represents the frequency (kHz) of the signal. The vertical axis has 1dB scale, the horizontal axis has a range of + -25 kHz centered on a center frequency of 50.85MHz (nominal frequency), and the 1 scale has 2kHz.
In this embodiment, the passband width of the signal in the digital mode is 10kHz/3dB, whereas the passband width of the signal in the analog mode can be widened to 12.5kHz/3dB.
Next, a description will be given of a change in the passband width of the signal by switching the input/output direction of the signal to the piezoelectric filter 2.
Fig. 7 is a diagram for explaining filter characteristics when signals are input from the first external connection terminal 21, which is the terminal #1 of the piezoelectric filter 2, and output from the fourth external connection terminal 24, which is the terminal #4, when the input/output direction of signals to/from the piezoelectric filter 2 is digital.
Fig. 8 is a diagram for explaining filter characteristics when signals are input from the fourth external connection terminal 24, which is the terminal #4 of the piezoelectric filter 2, and output from the first external connection terminal 21, which is the terminal #1, when the input/output direction of signals to/from the piezoelectric filter 2 is in the analog mode.
Fig. 7 and 8 (a) show the filter characteristics P1 of the first piezoelectric filter element 8 and the filter characteristics P2 of the second piezoelectric filter element 9 when the impedances of the input side and the output side of the piezoelectric filter 2 are the same. As shown in fig. 7 (a) and 8 (a), the center frequency of the first piezoelectric filter element 8 is shifted from the center frequency of the second piezoelectric filter element 9 by the frequency S, and in this example, by 2kHz as described above.
In this embodiment, as described above, the impedance of the input side of the piezoelectric filter 2 is larger than the impedance of the output side.
When the impedance on the input side is larger than the impedance on the output side in this way, the filter characteristic of the piezoelectric filter element on the input side shifts to the side with high frequency (positive side), and the filter characteristic of the piezoelectric filter element on the output side shifts to the side with low frequency (negative side).
Accordingly, in the digital system, as shown in fig. 7 (b), the filter characteristic P1 of the first piezoelectric filter element 8 on the input side shifts to the side of high frequency, the filter characteristic P2 of the second piezoelectric filter element 9 on the output side shifts to the side of low frequency, and the shift in center frequency between the first piezoelectric filter element 8 and the second piezoelectric filter element 9 increases.
As a result, when the filter characteristics of the first piezoelectric filter element 8 and the second piezoelectric filter element 9 are combined, the passband width of the signal becomes narrower as shown in fig. 7 (c), corresponding to the digital system.
In contrast, in the analog system in which the input/output direction of the signal is reversed, as shown in fig. 8 (b), the filter characteristic P2 of the second piezoelectric filter element 9 on the input side shifts to the side of higher frequency, the filter characteristic P1 of the first piezoelectric filter element 8 on the output side shifts to the side of lower frequency, and the shift in the center frequency between the first piezoelectric filter element 8 and the second piezoelectric filter element 9 is reduced.
As a result, when the filter characteristics of the first piezoelectric filter element 8 and the second piezoelectric filter element 9 are combined, the passband width of the signal becomes wider as shown in fig. 8 (c), corresponding to the analog system.
The amounts of offset of the filter characteristics P1 and P2 of the first piezoelectric filter element 8 and the second piezoelectric filter element 9 can be adjusted by the difference between the impedance of the input side and the impedance of the output side of the piezoelectric filter 2. The offset amount can be increased by increasing the difference between the impedance of the input side and the impedance of the output side of the piezoelectric filter 2.
In this embodiment, since the impedance of the input side of the piezoelectric filter 2 is larger than the impedance of the output side, the filter characteristic of the piezoelectric filter element on the input side shifts to the side having a high frequency, and the filter characteristic of the piezoelectric filter element on the output side shifts to the side having a low frequency.
In contrast, when the impedance of the input side of the piezoelectric filter 2 is smaller than the impedance of the output side, the filter characteristic of the piezoelectric filter element on the input side shifts to the low frequency side, and the filter characteristic of the piezoelectric filter element on the output side shifts to the high frequency side.
Therefore, in this case, when a signal is input from the first external connection terminal 21 which is the terminal #1 of the piezoelectric filter 2 and output from the fourth external connection terminal 24 which is the terminal #4, the filter characteristics similar to those of fig. 8 (c), that is, the filter characteristics having a wide passband width of the signal according to the analog method are obtained. When a signal is input from the fourth external connection terminal 24, which is the terminal #4 of the piezoelectric filter 2, and output from the first external connection terminal 21, which is the terminal #1, the filter characteristics similar to those of fig. 7 (c), that is, the filter characteristics having a narrow passband width of the signal corresponding to the digital system are obtained.
That is, the analog system is inverted from the digital system in comparison with the above-described embodiment.
Fig. 9 is a diagram showing a wide area filter characteristic when the input/output direction of a signal is switched in the piezoelectric filter device 1 of this embodiment, where (a) of the diagram shows a filter characteristic in a digital system and (b) of the diagram shows a filter characteristic in an analog system.
As shown in fig. 9, the filter characteristics of the digital system and the analog system are identical except for the passband of the signal.
As described above, according to the present embodiment, the width of the passband width of the signal can be switched by switching the input/output direction of the signal to/from the single piezoelectric filter 2. Therefore, in the commercial wireless device including the piezoelectric filter device 1 of the present embodiment, the piezoelectric filter device 1 can be used in both the analog system and the digital system.
Accordingly, compared with the conventional example commercial wireless device in which two piezoelectric filters, i.e., an analog piezoelectric filter and a digital piezoelectric filter, having different passband widths of a desired signal, the number of piezoelectric filters can be reduced, and accordingly, the cost can be reduced, and a space can be saved.
Further, since the first piezoelectric filter element 8 and the second piezoelectric filter element 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 and become high-quality elements with less spurious emissions.
Further, since the piezoelectric filter 4 has the same basic structure as the conventional four-pole piezoelectric filter except that the center frequencies of the bipolar piezoelectric filter elements 8 and 9 are shifted from each other, the design of the conventional four-pole piezoelectric filter does not need to be changed greatly, and the piezoelectric filter can be implemented at low cost.
As another embodiment of the present invention, the piezoelectric filter elements 8 and 9 may be configured by forming the electrodes 111 to 113 and 121 to 123 on a single common piezoelectric substrate.
In the above embodiment, the areas of the electrodes 111 to 113 of the first piezoelectric filter element 8 are the same as the areas of the electrodes 121 to 123 of the second piezoelectric filter element 9, but as another embodiment of the present invention, the area of the electrode of one of the piezoelectric filter elements may be reduced by at most about 40% compared with 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 characteristic of increasing the ripple can be achieved, and the passband width of the signal can be further narrowed.
Further, if the area of the electrode is reduced by more than 40%, the insertion loss increases, which is not preferable.
In the above-described embodiment, the present invention is applicable to switching of the passband width of a signal corresponding to an analog system and a digital system of a commercial wireless device, but the present invention is not limited to the above-described application, and may be applied to switching of the passband width of a signal corresponding to a wide-bandwidth channel and a narrow-bandwidth channel among a plurality of communication channels, for example.
In the above embodiment, the quartz substrate is used as the piezoelectric substrate, but a ceramic substrate or a polycrystalline substrate having piezoelectric characteristics may also be used.
Claims (7)
1. A piezoelectric filter device comprising a piezoelectric filter in which two piezoelectric filter elements are connected in cascade, wherein an input electrode and an output electrode are formed on one principal surface of a piezoelectric substrate, a common electrode is formed on the other principal surface of the piezoelectric filter element so as to face the input electrode and the output electrode,
the respective center frequencies of the two piezoelectric filter elements deviate from each other,
the impedance of the input side and the impedance of the output side of the piezoelectric filter are different from each other,
by switching the input/output direction of the signal to the piezoelectric filter, the width of the passband width of the signal is switched,
wherein the piezoelectric filter device comprises:
and a switching unit that switches the input terminal of the piezoelectric filter device to be connected to the input side or the output side of the piezoelectric filter, and switches the output terminal of the piezoelectric filter device to be connected to the output side or the input side of the piezoelectric filter, thereby switching the input/output direction of the signal.
2. The piezoelectric filter device according to claim 1, wherein,
there are two of said piezoelectric substrates,
the input electrode, the output electrode, and the common electrode of each of the two piezoelectric filter elements are formed on the two piezoelectric substrates, respectively.
3. The piezoelectric filter device according to claim 1, wherein,
impedance circuits for making the impedance on the input side and the impedance on the output side different from each other are provided between the input terminal and the switching means of the piezoelectric filter device and between the output terminal and the switching means of the piezoelectric filter device, respectively.
4. A piezoelectric filter device according to any one of claims 1 to 3, wherein,
the piezoelectric substrate is a quartz substrate.
5. The piezoelectric filter device according to claim 1, wherein the piezoelectric filter device comprises:
a first impedance circuit connected to the signal input terminal of the piezoelectric filter device and having a predetermined impedance;
a second impedance circuit connected to the signal output terminal of the piezoelectric filter device and having an impedance lower than the predetermined impedance;
a first changeover switch which is connected to the first impedance circuit and which, when the piezoelectric filter device is of a digital type, switches the first impedance circuit to the input side of the piezoelectric filter, and when the piezoelectric filter device is of an analog type, switches the first impedance circuit to the output side of the piezoelectric filter; and
a second switch connected to the second impedance circuit, and switching the second impedance circuit to the output side of the piezoelectric filter when the piezoelectric filter device is of a digital type, and switching the first impedance circuit to the input side of the piezoelectric filter when the piezoelectric filter device is of an analog type,
the two switches switch the input/output direction of the signal to the piezoelectric filter according to whether the piezoelectric filter device is of the digital type or the analog type, so as to switch the width of the passband width of the signal in the piezoelectric filter.
6. A piezoelectric filter device according to claim 5, wherein,
the piezoelectric substrate is a quartz substrate.
7. The piezoelectric filter device according to claim 6, wherein,
the quartz substrate is an AT cut quartz plate.
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| Application Number | Priority Date | Filing Date | Title |
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| JP2017243682A JP7043829B2 (en) | 2017-12-20 | 2017-12-20 | Piezoelectric filter device |
| JP2017-243682 | 2017-12-20 |
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| CN109951172A CN109951172A (en) | 2019-06-28 |
| CN109951172B true CN109951172B (en) | 2023-07-21 |
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Also Published As
| Publication number | Publication date |
|---|---|
| JP2019110490A (en) | 2019-07-04 |
| CN109951172A (en) | 2019-06-28 |
| JP7043829B2 (en) | 2022-03-30 |
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