JP2002100960A - Multiband rf surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small multiband RF SAW filter, which satisfies the characteristic of each filter and whose bandwidth is wide. SOLUTION: The multiband SAW filter is composed of two piezoelectric substrates, in which at least one each of double-band SAW filters are formed on main faces. The double-band SAW filters, whose specific bandwidths are adjacent, are formed on the same piezoelectric substrate, and electrode film thicknesses are made nearly equal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-band RF surface acoustic wave filter, and more particularly to a miniaturized multi-band RF surface acoustic wave filter.

[0002]

2. Description of the Related Art Recently, a surface acoustic wave filter (hereinafter referred to as SA) has been developed.
W filters) are widely used in the field of communications and have excellent characteristics such as high performance, small size, and mass productivity, and are therefore often used particularly in mobile phones and the like. Conventionally, in a cellular type mobile phone, it was possible to secure a sufficient line with a single band RF filter, but recently, the number of subscribers to the mobile phone has rapidly increased, so it has become necessary to add an assigned frequency. . For this reason, the mobile phone has to cope with the transmission and reception RF filter by using a multi-band system. For example, 900MHz in North America
The dual system of the /1.9 GHz band and the 800 MHz / 1.8 GHz band in Europe has been put into practical use, and with this, multi-band RF filters have been adopted as the transmission and reception RF filters.

On the other hand, Japanese cellular cellular phones (PDs)
In C), the reception frequency band of the terminal is 8 as shown in FIG.
10MHz to 843MHz band (RA band), 870MHz
~ 885MHz band (RB band) and 1477MHz ~ 15
01 MHz band (RC band, not shown), transmission frequency band is 893 MHz to 898 MHz (TA band), 92 MHz
5MHz to 960MHz (TB band) and 1429MHz
１４1453 MHz (TC band, not shown) has been allocated. In particular, the reception RB band and the transmission T
Since the A band is close, the RF filter in the RB band has 8
10d indicated by α in the figure from 93 MHz to 898 MHz
B or more attenuation is required. In particular, mobile terminals are required to be miniaturized.
That is, a so-called multi-band RF surface acoustic wave filter (hereinafter, multi-band RFS) in which the SAW filters of the RA band, the RB band, and the RC band are housed in one package, for example, a miniaturized package having a size of about 3.0 mm × 3.0 mm.
AW filter).

[0004] It is possible to form a multi-band RF SAW filter by separately forming the above-mentioned RA, RB, and RC band SAW filters and accommodating them in a single package. There was a problem of becoming too much. Therefore, the primary and tertiary longitudinally coupled dual mode S of the RA and RB bands whose frequency bands are close to each other
An AW filter (hereinafter, referred to as a dual mode SAW filter) is formed on one piezoelectric substrate, and a dual mode SAW filter in the RC band is formed on the other piezoelectric substrate, and these are accommodated in one package. A so-called 2-chip-1 package type has been manufactured. FIG. 5 shows the above two chips.
FIG. 3 is a plan view showing a configuration of a one-package type multi-band RF SAW filter, including a package 20, a piezoelectric substrate 22 having two 800 MHz band dual-mode SAW filters FA and FB formed on a main surface, 1.5
And a piezoelectric substrate 23 on which a dual-mode SAW filter FC in the GHz band is formed. An adhesive is applied to the concave portion 21 of the package 20, and the piezoelectric substrates 22 and 23 are placed and fixed thereon, and the input / output pad electrodes of the dual mode SAW filters FA and FB are connected to the package 20.
Input / output terminal electrodes IN1, OUT1 and IN2, OUT
2 with bonding wires 24, 25, 26, respectively.
27, connect to dual mode SAW filters FA and FB
Of the package 20 and the ground terminal electrodes 30, 30,.
8. Connect with. Similarly, for the dual mode SAW filter FC, the input / output pad electrodes and the package 2
In addition, the input / output terminal electrodes IN3 and OUT3 of No. 0 are connected by bonding wires, and the ground pad electrodes and the ground terminal electrodes 30 and 30 of the package 20 are connected by bonding wires to form a multi-band RF SAW filter. ing.

FIG. 6 is a plan view showing a detailed configuration of the dual mode SAW filter. Three IDTs are provided on the main surface of a piezoelectric substrate (not shown) along the propagation direction of the surface wave.
The electrodes 31, 32, and 33 are arranged close to each other, and grating reflectors (hereinafter, referred to as reflectors) 3 are provided on both sides thereof.
4a and 34b. Then, the IDT electrodes 31, 3
Reference numerals 2 and 33 denote a pair of comb-shaped electrodes each having a plurality of electrode fingers interposed therebetween, and connect one comb-shaped electrode of the IDT electrode 31 to the input IN and ground the other comb-shaped electrode. Further, one of the IDT electrodes 32 and 33 is connected to the comb-shaped electrode and the output OUT, and the other comb-shaped electrode is grounded to form a dual mode SAW filter.

FIGS. 7 and 8 each show a dual mode SAW filter F prototyped on the same piezoelectric substrate with the configuration shown in FIG.
9 shows an example of filter characteristics of A and FB. A dual-mode SAW filter FA (FB) using 36XYX LiTaO ₃ as the piezoelectric substrate, the electrode thickness of the aluminum alloy (8.3% λ: λ is the electrode period of the IDT electrode) is the same as each other.
The number of IDT electrodes 31 is 15.5 (31.5 pairs), the number of IDT electrodes 32 and 33 is 10.5 (21.5 pairs), and the reflector 34
The numbers of a and 34b are each 100 (100), and the intersection length is
In each filter characteristic example when 58 λ (30 λ) is set, the pass band characteristic and the attenuation characteristic are overwritten.

[0007]

However, two dual-mode SAW filters RA and R having close frequency bands are used.
In a conventional multi-band RF SAW filter in which Bs are formed on the same piezoelectric substrate, a dual mode SAW filter FA (with a specific bandwidth of about 4%) and an FB (with a specific bandwidth of about 1.7%)
%) At the same time, the thickness of the IDT electrode must be the same (for example, 8.5% λ). As is well known, when lithium tantalate (LiTaO ₃ ) is used for the piezoelectric substrate, the electromechanical coupling coefficient increases in proportion to the electrode film thickness. For this reason, when designing a relatively wide band filter such as the dual mode SAW filter FA, it is necessary to increase the electrode film thickness, but the bandwidth is narrow as in the dual mode SAW filter FB. If the filter is formed with the same thickness as the filter FA having a wide bandwidth, the bandwidth becomes too wide as shown in FIG. 8 and the frequency indicated by P (893 MHz)
, There is a problem that the attenuation standard (10 dB or more) cannot be satisfied. Furthermore, dual mode S of RC band
Although the frequency of the AW filter FC is high, the electrode pattern can be reduced in size, but the substrate size cannot be reduced so much due to mechanical restrictions of the mounter when mounting. This results in an increase in the size of the substrate of the filter FC in consideration of the basic suction device of the mounter for automatically mounting the piezoelectric substrate in the package. In other words, a substrate suction device suitable for sucking and mounting a large-sized piezoelectric substrate cannot suction a small substrate due to a large suction port. Because you have to do it. As a result, there is a problem that there is a limit in reducing the size of the multi-band RF SAW filter. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a small multiband RFSA satisfying the characteristics of each filter.
It is intended to provide a W filter.

[0008]

According to a first aspect of the present invention, there is provided a multi-band RF surface acoustic wave filter comprising at least one longitudinally coupled multimode surface acoustic wave on a main surface. Multi-band RF in which a plurality of piezoelectric substrates with filters are housed in one package
In the surface acoustic wave filter, a plurality of longitudinally coupled multi-mode surface acoustic wave filters having a relative bandwidth close to each other are formed on one of the piezoelectric substrates, and the thickness of the electrodes is made substantially equal. This is a surface acoustic wave filter. The invention according to claim 2 is characterized in that the longitudinally coupled multimode surface acoustic wave filter is a first-order to third-order longitudinally coupled dual-mode surface acoustic wave filter. It is a wave filter. The invention according to claim 3 has a pass band of 810 MHz to 843 M
A first- and third-order longitudinally-coupled dual-mode surface acoustic wave filter having a pass band of 870 Hz is provided on the first piezoelectric substrate.
MHz ~ 885MHz and 1477MHz ~ 1501M
The first and second longitudinally-coupled dual-mode surface acoustic wave filters at Hz are formed on the second piezoelectric substrate,
A multi-band RF surface acoustic wave filter characterized in that the piezoelectric substrate described above is housed in one package. The invention according to claim 4 has a pass band of 925 MHz to 960 M
A first-to-third longitudinally-coupled dual-mode surface acoustic wave filter having a pass band of 893 Hz is provided on the first piezoelectric substrate.
MHz ~ 898MHz and 1429MHz ~ 1453M
The first and second longitudinally-coupled dual-mode surface acoustic wave filters at Hz are formed on the second piezoelectric substrate,
A multi-band RF surface acoustic wave filter characterized in that the piezoelectric substrate described above is housed in one package.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1 is a plan view showing the configuration of a multi-band SAW filter according to the present invention, which includes a package 1, a piezoelectric substrate 2 having a dual mode SAW filter FA formed on a main surface, and two piezoelectric substrates 2 formed on a main surface. Piezoelectric substrate 3 on which double mode SAW filters FB and FC are formed
Consists of Recess 4 of package 1 coated with adhesive
The piezoelectric substrates 2 and 3 are accommodated and fixed by bonding.
The input / output pad electrodes of the dual mode SAW filter FA and the input / output terminal electrodes IN1 and OUT1 of the package 1 are connected by bonding wires 5 and 6, and the ground pad electrode of the dual mode SAW filter FA and the ground electrode of the package 1 are connected. The terminals 7, 7 are connected by bonding wires 8, 8.

Further, similarly to the case of the dual mode SAW filter FA, the input / output pad electrodes of the dual mode SAW filters FB and FC and the input / output terminal electrodes IN2, OUT2 and IN3 and OUT3 of the package 1 are connected. The bonding wires 9, 10 and 11, 12 are connected to each other, and the ground pad electrodes of the dual mode SAW filters FB, FC and the ground terminal electrodes 7, 7... Of the package 1 are connected by bonding wires 8, 8. Connect,
A multi-band RF SAW filter is configured.

A feature of the present invention is that in forming a multi-band SAW filter, instead of forming ones having close center frequencies on the same piezoelectric substrate, ones having close fractional bandwidths, for example, a PDC receiving RF. In the example of the filter, forming dual mode SAW filters FB and FC,
The dual mode SAW filter RA is formed on another piezoelectric substrate. The reason is that when LiTaO ₃ is used for the piezoelectric substrate as described above, the electromechanical coupling coefficient increases in proportion to the film thickness. In other words, as the thickness of the electrode is increased, it has a property that it is suitable for a wide band but not for a narrow band. Therefore, by forming the dual mode SAW filters FB and FC having close relative bandwidths on the same substrate, not only the mounter is not restricted but suitable for miniaturization, but also the electrode film thickness can be configured to be the same. This is because the manufacturing process is also simplified.

FIGS. 2 and 3 show examples of filter characteristics of the dual mode SAW filters FB and FC which are experimentally produced with the configuration shown in FIG. Double mode SAW filters FB and FC having the same electrode thickness (3.5% λ: wavelength of λ excited surface wave) are formed on the same piezoelectric substrate (36 ゜ YX LiTaO ₃ ), and a double mode SAW filter is formed. The number of IDT electrodes 31 of the FB (FC) is 31.5 pairs (24.5 pairs),
The logarithm of 3 is 21.5 pairs (16.5 pairs), the number of reflectors 34a and 34b is 100 each (100), and the intersection length is 30λ (30λ).
Each filter characteristic example in the case of setting is shown.

As is apparent from the characteristics shown in FIG. 2, the pass band width of the dual mode SAW filter FB is narrowed, and an attenuation of 10 dB or more can be secured at the frequency indicated by P (893 MHz). Then, as shown in FIG.
The filter characteristics of the z-band dual mode SAW filter FC are also good. Further, since the dual mode SAW filters FB and FC are formed on the same piezoelectric substrate 3, it is possible to realize an area approximately equal to that of the piezoelectric substrate 2 without providing a useless margin. The use of a suitable substrate suction device did not hinder the operation of the mounter.

The case where the present invention is applied to a multi-band RF SAW filter for receiving a PDC system has been described above. As for a multi-band RF SAW filter for transmission, a dual mode SAW in a TB band (925 MHz to 960 MHz) is used.
The filter is mounted on one piezoelectric substrate in the TA band (893MHz ~ 898M
Hz) and TC band (1429MHz-1453MHz) dual mode SAW
If the filter is formed on another piezoelectric substrate, the size is reduced and the multi-band RF SAW having good filter characteristics is formed.
Filters can be configured. Further, although an example in which lithium tantalate is used for the piezoelectric substrate has been described, it is needless to say that the present invention can be applied to a piezoelectric substrate such as lithium niobate, lithium tetraborate, and langasite. Also, the description has been given of the first-order / third-order longitudinally coupled dual mode SAW filter.
Secondary-secondary longitudinally coupled dual mode filter or primary-two
It can also be applied to a next-to-third-order longitudinally coupled multi-mode SAW filter.

[0015]

As described above, the present invention has an excellent effect that a multi-band RF SAW filter having a small size and excellent filter characteristics can be realized according to the first aspect of the present invention. Further, according to the invention of claim 2, 1
Since the next-third-order longitudinally coupled dual mode SAW filter is used, an excellent effect of realizing a small-sized multi-band RF SAW filter having a wide bandwidth is exhibited. Further, according to the third aspect of the invention, an excellent effect that a multiband RFSAW filter for reception used in a PDC mobile phone in Japan can be realized in a small size can be obtained. Further, according to the invention of claim 4, there is an excellent effect that a transmission multi-band RF SAW filter used in a PDC mobile phone in Japan can be realized in a small size.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a multi-band RF SAW filter according to the present invention.

FIG. 2 is a diagram illustrating filter characteristics of a dual mode SAW filter FB in an RB band (870 MHz to 885 MHz).

Fig. 3 RC band (1477MHz to 1501MHz band)
FIG. 5 is a diagram showing filter characteristics of the dual mode SAW filter FC.

FIG. 4 is a diagram of frequency allocation of a mobile phone system (PDC).

FIG. 5 is a plan view showing a configuration of a conventional multi-band RF SAW filter.

FIG. 6 is a diagram showing an electrode configuration of a conventional primary-tertiary-order longitudinally coupled dual-mode SAW filter.

FIG. 7 is a diagram illustrating filter characteristics of a dual-mode SAW filter FA in the RA band (810 MHz to 843 MHz).

FIG. 8 shows an RB having the same electrode thickness as an RA band filter.
FIG. 9 is a diagram illustrating filter characteristics of a band dual mode SAW filter FB.

[Explanation of symbols]

1. Package 2, 3, Piezoelectric substrate 4, Package recess 5, 6, 9, 10, 11, 12, Bonding wire for input / output 7, Ground terminal electrode of package 8, Ground Bonding wire IN1, IN2, IN3 Package input terminal electrode OUT1, OUT2, OUT3 Package output terminal electrode FA, FB, FC ... Dual mode SAW filter

Claims (4)

[Claims] 1. A multi-band RF surface acoustic wave filter in which a plurality of piezoelectric substrates having at least one longitudinally coupled multi-mode surface acoustic wave filter formed on a main surface are housed in one package. A multi-band RF surface acoustic wave filter characterized by forming a plurality of longitudinally coupled multi-mode surface acoustic wave filters having specific bandwidths close to each other and making electrode thicknesses substantially equal. 2. The multi-band R according to claim 1, wherein the longitudinally-coupled multi-mode surface acoustic wave filter is a first-order / third-order longitudinally-coupled dual-mode surface acoustic wave filter.
F surface acoustic wave filter. 3. A pass band of 810 MHz to 843 MHz.
Are placed on the first piezoelectric substrate with a pass band of 870 MHz.
z ~ 885MHz and 1477MHz ~ 1501MHz
Wherein two first- and third-order longitudinally-coupled double-mode surface acoustic wave filters are formed on a second piezoelectric substrate, and the first and second piezoelectric substrates are housed in one package. Band RF surface acoustic wave filter. 4. A pass band of 925 MHz to 960 MHz.
And a third-order longitudinally coupled double-mode surface acoustic wave filter having a pass band of 893 MHZ on the first piezoelectric substrate.
z ~ 898MHz and 1429MHz ~ 1453MHz
Wherein two first- and third-order longitudinally-coupled double-mode surface acoustic wave filters are formed on a second piezoelectric substrate, and the first and second piezoelectric substrates are housed in one package. Band RF surface acoustic wave filter.