JP2000114917A - Balance type acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a configuration of a balance type acoustic wave filter which suitably corresponds to a balance input-output type, is also excellent in withstand power property and is also extremely excellent in phase characteristic difference and amplitude characteristic difference. SOLUTION: Relating to an acoustic wave filter (a) formed by cascading a ladder type filter and a lattice type filter, the capacitive component for lattice type filter is obtained by one or more pairs of comb-shaped electrodes 18 and also, the longitudinal direction of electrode fingers of the electrodes 18 is made nonparallel to the propagation direction of surface acoustic waves. In this case, the electrodes 18 are provided in such a manner that the longitudinal direction of their electrode fingers is especially 90 deg.±15 deg. to the propagation direction of surface acoustic waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter used for a mobile communication device such as a mobile phone.
The present invention relates to a so-called balanced surface acoustic wave filter such as an unbalanced input-balanced output and a balanced input-unbalanced output type.

[0002]

2. Description of the Related Art A surface acoustic wave filter for mobile communication basically has to be small in size with the miniaturization of mobile phones.
Low loss in the pass band for power saving;
It is required that a desired amount of attenuation be obtained in an attenuation range determined by the system used and the circuit design of the mobile phone.

The surface acoustic wave filter includes a propagation type, a resonator type, a ladder type, and a lattice type, and a type suitable for the required specifications is selected and used. The ladder type is often used because of its high steepness. Further, in a high-frequency circuit portion near the antenna to which a large power is applied, only a ladder-type filter is used because of its high power durability.

As shown in FIG. 10, a conventional ladder type surface acoustic wave filter 101 has a first input / output terminal pair 106.
a, 106b and a second input / output terminal pair 107a, 107b
The series surface acoustic wave resonators 102a to 102d and the parallel surface acoustic wave resonators 103a to 103c are alternately connected in cascade, and the terminals 106b and 107b are connected to the ground G. It was a filter.

[0005]

However, the conventional surface acoustic wave filter is an unbalanced-unbalanced type, and when used in a connection portion with a mixer, as described below, the unbalanced-balanced type is not used. There is a problem that a balun is required separately for conversion.

FIG. 9 shows a block diagram of a receiving circuit near an antenna of a portable telephone. In the figure, the arrows indicate the flow direction of the received signal. A signal received from an antenna (not shown) is amplified through a low-noise amplifier 23, then an interference signal is removed by an unbalanced surface acoustic wave filter 24, and is converted into a low-frequency signal by a mixer 26. Here, since the mixer 26 has a balanced input, it is necessary to connect a balun 25 for unbalanced-balanced conversion to the subsequent stage of the unbalanced surface acoustic wave filter 24.

A brief description of the balun 25 will be given with reference to FIG. The configuration of the ladder type filter is the same as that of FIG. 10, and the output from the second input / output terminal pair 107a, 107b which is an unbalanced terminal pair is
08a and 108b. The balun 25 is an impedance converter using inductive coupling. To reduce the conversion loss, it is necessary to increase the size of the balun 25 to a certain extent, which is several times larger than that of the surface acoustic wave filter.
In addition, the use of a separate balun hinders cost reduction and weight reduction.

For this reason, there is a strong demand for a conventional unbalanced ladder-type filter having a high steepness and excellent power durability to be balanced. In particular, the phase characteristic difference is 180 ° ± 10 °
It is desired that the amplitude characteristic difference be within 0.5 dB.

Accordingly, the present invention provides a configuration of a balanced surface acoustic wave filter which is suitable for a balanced input / output type, has excellent power durability, and has a very excellent difference in phase characteristics and amplitude characteristics. Aim.

[0010]

A balanced surface acoustic wave filter according to the present invention is a surface acoustic wave filter in which a ladder type filter and a lattice type filter are connected in cascade. The above-mentioned comb-shaped electrode is obtained, and the longitudinal direction of the electrode finger of the comb-shaped electrode is not parallel to the propagation direction of the surface acoustic wave.

In particular, it is characterized in that the longitudinal direction of the electrode fingers of the comb-like electrode is arranged at 90 ° ± 15 ° with respect to the propagation direction of the surface acoustic wave.

A balanced surface acoustic wave filter according to the present invention is a surface acoustic wave filter in which a ladder filter and a lattice filter are connected in cascade, and the capacitance component of the lattice filter is a pair of comb teeth. And the resonance frequency of the lattice type filter is set lower than the center frequency of the surface acoustic wave filter.

Further, the lattice type filter is characterized in that its inductance component is obtained by a bonding wire or a line.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the basic configuration of a balanced surface acoustic wave filter 1 according to the present invention. The surface acoustic wave filter 1 has 4
A 2 ° Y-cut lithium tantalate (LiTaO ₃ ) single crystal substrate is provided with a series surface acoustic wave resonator 2a composed of IDT (interdigital transducer) electrodes on a substrate.
To 2d, a ladder-type filter similarly composed of parallel surface acoustic wave resonators 3a to 3c also composed of IDT electrodes, and a capacitor as a lumped constant element (composed of comb-shaped electrodes)
4 and a coil (consisting of lines such as bonding wires and meander lines) 5 are formed as a lattice filter.

The terminals 6b, 7b are connected to the terminal pairs 6a, 6
b and 7a, 7b are connected to the ground G in order to be unbalanced terminals.

In this manner, the capacitance component of the lattice type filter is obtained by one or more comb-shaped electrodes, and the longitudinal direction of the electrode fingers is not parallel to the propagation direction of the surface acoustic wave (preferably 90 °). ± 15 °). Further, the inductance component is obtained by the coil.

Further, the resonance frequency of the comb-shaped electrode of the lattice type filter is set to be much lower than the center frequency of the surface acoustic wave filter 1.

FIG. 2 shows a transmission amplitude characteristic 10 of the balanced surface acoustic wave filter according to the present invention. As is clear from FIG. 2, a low loss is achieved in the pass band 9 and a high attenuation is achieved in other regions.

FIGS. 3A to 3D are diagrams for explaining the balance operation of the balanced surface acoustic wave filter according to the present invention. 3A shows a transmission phase characteristic 11a from the terminal 6a to the terminal 8a, FIG. 3B shows a transmission phase characteristic 11b from the terminal 6a to the terminal 8b, and FIG.
3D shows the transmission amplitude characteristic to the terminal 6a.
6 shows the transmission amplitude characteristic to the line b. Phase characteristic diagram 3 (a)
3 (b) are completely shifted from each other by 180 °, and the amplitude characteristics of FIGS. 3 (c) and 3 (d) are at most 0.
The characteristic has a difference of 25 dB.

As described above, the capacitance component of the lattice type filter is obtained by one or more pairs of comb-shaped electrodes, and the longitudinal direction of the electrode fingers of the comb-shaped electrodes is not parallel (preferably 90 °) to the propagation direction of the surface acoustic wave. (± 15 °), so that unnecessary surface acoustic waves are less likely to be excited, whereby the comb-like electrodes of the lattice filter function as pure capacitors.

Further, since the resonance frequency of the comb-shaped electrode of the lattice filter is set lower than the center frequency of the surface acoustic wave filter, a pure capacitance component can be obtained.

Further, since the lattice component of the lattice type filter is obtained by using a bonding wire or a line, it is possible to reduce the size while maintaining the same characteristics as those of the related art.

Thus, the phase characteristics and the amplitude characteristics of the balanced surface acoustic wave filter of the present invention can satisfy the desired balance characteristics. (Phase characteristic difference is 180 ° ±
In the present invention, the substrate material is a 42 ° Y-cut LiTaO3 single crystal, but the substrate material is a 36 ° to 42 ° Y-cut LiTaO ₃ single crystal or a 64 ° Y-cut. Various piezoelectric materials such as LiNbO ₃ single crystal can be used. In the present invention, the number of resonators is seven, but it goes without saying that the number and the like can be appropriately changed according to required specifications.

[0025]

Next, a description will be given of an embodiment in which a ladder type surface acoustic wave filter according to the present invention is experimentally manufactured. First, a manufacturing process will be described. Photolithography was performed using a stepper (reduction projection exposure machine) and an RIE (Reactive Ion Etching) apparatus.

The substrate material (42 ° Y-cut of LiTaO ₃ ) was subjected to ultrasonic cleaning with acetone, IPA or the like to remove organic components. Next, after the substrate was sufficiently dried by a clean oven, an electrode was formed. An Al-Cu (2% by weight) material was formed into a film using a sputtering apparatus for forming the electrode. The electrode thickness is about 200
0 °.

Next, a resist was spin-coated to a thickness of about 0.5 μm, and desired patterning was performed by a stepper. As the stepper, a reticle (corresponding to a photomask of a contact exposure machine) serving as an original for patterning is used. In the stepper, the image can be reduced and projected to 1/5 by the optical system, so the pattern on the reticle is 5 times the size of the exposure pattern, and the resolution is 5 times as large as that of a conventional contact exposure machine that performs 1: 1 exposure. Can be realized.

Next, an unnecessary portion of the resist was dissolved with an alkali developing solution in a developing device to form a desired resist pattern. Then, the Al-Cu electrode was etched by the RIE apparatus, and the patterning of the electrode was completed.

Thereafter, a film of SiO ₂ was formed by a sputtering device, and the film was etched by an RIE device or the like to complete a protective film pattern.

Next, the substrate was diced along a dicing line and divided into chips. Each chip was mounted on a die bonder, picked up, and bonded to a cavity in the SMD package with a die bond resin containing Si resin as a main component. Thereafter, a temperature of about 160 ° was applied to dry and harden. The SMD package had a 3 mm square laminated structure, and the chip size was 1.6 × 1.0 mm.

Next, a 30 μm φ Au wire is wire-bonded to the pad portion of the SMD package and the Al pad on the chip, and then the lid is put on the package.
Sealed with a seam sealer and completed.

Next, a specific configuration will be described.

FIG. 6 shows a first embodiment of a balanced surface acoustic wave filter according to the present invention. An electrode 15 for bonding wires 17a to 17d is provided on the package 15.
a to 15e were formed.

In FIG. 6, the electrode 15a is an input electrode,
The electrodes 15c and 15d are output electrodes, and the electrodes 15b and 15
e is a ground electrode. A predetermined electrode on the single crystal substrate 16 and an electrode of the package are connected to bonding wires 17a to
Connected at 17d. A ladder filter and a lattice filter were formed on the single crystal substrate 16. That is, the ladder-type filter includes the surface acoustic wave resonators 2a to 2d, 3a to
3c and an electrode pattern 19 for electrically connecting the resonators. On the other hand, the lattice filter was composed of a capacitor 18 using a comb-shaped electrode for obtaining a capacitance component and a coil formed by bonding wires 17e and 17f for obtaining an inductance component.

The comb-teeth electrode 18 serving as a capacitor is shown in FIG.
As shown in (b), the resonance frequency is set so as to be significantly lower than the center frequency of the filter (at least 200 MHz), and near the center frequency of the filter, the ideal frequency shown in FIG. It is set so as to have characteristics (13a and 14a) equivalent to the impedance characteristic 13 of the capacitor.

Further, in order to avoid an adverse effect due to unnecessary resonance, they are arranged at an angle of about 90 ° from the propagation direction of the surface acoustic wave. It should be noted that a reflector for increasing the Q value of the resonance was not formed because it was unnecessary.

FIG. 4 shows the correlation between the inductance L of the coil constituting the lattice type filter and the insertion loss of the lattice type filter. Inductance and capacitance are calculated assuming no loss. If the magnitudes of the reactances of the coil and the capacitor are made equal at the center frequency of the filter, the insertion loss of the filter is minimized. There). The optimum coil inductance L when the center frequency is 1930 [MHz] is 4.1 [nH]. The degree of balance hardly deteriorates even if the inductance deviates from this value.

In this embodiment, in order to make the inductance of the bonding wire close to 4.1 [nH], electrodes for connecting the bonding wire are arranged at the ends of the single crystal substrate. In this embodiment, an inductance of about 1.6 [nH] is obtained.

FIG. 7 shows a second embodiment of the balanced surface acoustic wave filter according to the present invention. The package 15 is shown in FIG.
And the same.

In FIG. 7, the electrode 15c is an input electrode,
The electrodes 15a and 15d are output electrodes and the electrodes 15b and 15
e is a ground electrode. The predetermined electrodes on the single crystal substrate 16 and the electrodes of the package are connected to the bonding wires 20a to 20a.
Connected at 20d.

In this embodiment, in order to increase the inductance of the coil constituting the lattice type filter, one coil is formed by four bonding wires. That is, the bonding wires 20e to 20h formed one coil, and the bonding wires 20i to 20l formed another coil. The connection between the bonding wires was performed via the electrode pattern of the jump island formed on the single crystal substrate 16. As a result, an inductance of 4.1 [nH] was realized, and the insertion loss of the lattice filter could be minimized.

FIG. 8 shows a third embodiment of the balanced surface acoustic wave filter according to the present invention. The package 15 is shown in FIG.
And the same.

In FIG. 8, the electrode 15c is an input electrode,
The electrodes 15a and 15d are output electrodes and the electrodes 15b and 15
e is a ground electrode. A predetermined electrode on the single crystal substrate 16 and an electrode of the package are connected to bonding wires 21a to 21a.
Connected at 21d. In the present embodiment, the lattice filter coil is constituted by a meander line 22 formed on a single crystal substrate. The line width is 5 μm, the length is 2.7 mm,
An inductance of 4.1 [nH] is realized.

In this case, since the electrode cross-sectional area is smaller than that of the coil formed by the bonding wires in the embodiment shown in FIGS. 6 and 7, the conductor loss is slightly increased, but the structure is simpler because the number of wires to be bonded is small. I was able to.

The surface acoustic wave resonator constituting the ladder type surface acoustic wave filter has a logarithm of the IDT electrode of 40 to 120.
On the other hand, the crossing width is 10 to 30 wavelengths, and the wavelength of the surface acoustic wave is different between the series resonator and the parallel resonator. The number of reflective electrodes was set to 20 for both the series resonator and the parallel resonator.

In this embodiment, the electrode is an AlCu electrode, but another material such as Al may be used. Further, although the protective film is made of SiO2, other materials such as Si and SiN may be used.

[0047]

According to the balanced surface acoustic wave filter of the present invention, a surface acoustic wave filter having excellent power durability can be realized. As a result, the balun can be eliminated, and the size, weight, and cost of the mobile phone can be reduced.

Further, the capacitance component of the lattice filter is obtained by one or more comb-shaped electrodes, and the longitudinal direction of the electrode fingers of the comb-shaped electrode is non-parallel to the propagation direction of the surface acoustic wave (preferably ± 90 °). 15 °), unnecessary surface acoustic waves are less likely to be excited, whereby the comb-shaped electrodes of the lattice filter function as pure capacitors.

Further, since the resonance frequency of the comb-like electrode of the lattice type filter is set lower than the center frequency of the surface acoustic wave filter, a pure capacitance component can be obtained.

In the lattice type filter, the inductance component is obtained by a bonding wire or a line, so that the size can be reduced while maintaining the same characteristics as the conventional one.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of a balanced surface acoustic wave filter according to the present invention.

FIG. 2 is a diagram showing transmission amplitude characteristics of a balanced surface acoustic wave filter according to the present invention.

FIGS. 3A to 3D are characteristic diagrams showing a balance operation of the balanced surface acoustic wave filter according to the present invention.

FIG. 4 is a diagram showing a correlation between inductance and insertion loss of a coil constituting a lattice type filter portion of the balanced type surface acoustic wave filter according to the present invention.

FIGS. 5A and 5B are characteristic diagrams showing an ideal capacitor and an impedance characteristic of a surface acoustic wave resonator, respectively.

FIGS. 6A and 6B are schematic plan views showing a first embodiment of a balanced surface acoustic wave filter according to the present invention, wherein FIG. 6A is a plan view of a surface acoustic wave filter, and FIG.

FIGS. 7A and 7B are schematic plan views showing a second embodiment of a balanced surface acoustic wave filter according to the present invention, wherein FIG. 7A is a plan view of a surface acoustic wave filter, and FIG.

FIGS. 8A and 8B are schematic plan views showing a third embodiment of a balanced surface acoustic wave filter according to the present invention, wherein FIG. 8A is a plan view of a surface acoustic wave filter, and FIG.

FIG. 9 is a partial block diagram of a mobile phone in which a balanced-unbalanced surface acoustic wave filter is used.

FIG. 10 is an equivalent circuit diagram of a conventional unbalanced ladder type surface acoustic wave filter.

FIG. 11 is an equivalent circuit diagram in which a balun is added to a conventional unbalanced ladder type surface acoustic wave filter to obtain a balanced-unbalanced filter.

[Explanation of symbols]

 1: balanced-unbalanced surface acoustic wave filters 2a to 2d: series surface acoustic wave resonators 3a to 3c: parallel surface acoustic wave resonators 4: capacitors 5: coils 6, 106: first input / output terminal pair 7, 107: Second input / output terminal pair 8, 108: Balanced terminal pair 9: Pass band 10: Transmission amplitude characteristic 11: Transmission phase characteristic 12: Transmission phase characteristic 13: Impedance characteristic of ideal capacitor 14: Surface acoustic wave resonator Impedance characteristics 15: Package 16: Single crystal substrate 17, 20, 21: Wire 18: Capacitor using comb electrode 19: Electrode pattern 22: Meander line 23: Low noise amplifier 24: Unbalanced surface acoustic wave filter 25, 109 : Balun 26: Mixer 101, 111: Unbalanced ladder filter 102: Series surface acoustic wave resonator 103: Parallel elasticity table Wave resonator

Claims (4)

[Claims] 1. A surface acoustic wave filter comprising a ladder-type filter and a lattice-type filter connected in cascade, wherein a capacitance component of the lattice-type filter is obtained by a pair or more of comb-like electrodes. A balanced surface acoustic wave filter characterized in that a longitudinal direction of an electrode finger of an electrode is not parallel to a propagation direction of a surface acoustic wave. 2. The balance according to claim 1, wherein a longitudinal direction of the electrode fingers of the comb-shaped electrode is disposed at 90 ° ± 15 ° with respect to a propagation direction of the surface acoustic wave. Type surface acoustic wave filter. 3. A surface acoustic wave filter comprising a ladder-type filter and a lattice-type filter connected in cascade, wherein a capacitance component of the lattice-type filter is obtained by one or more comb-shaped electrodes. Characterized in that the resonance frequency is set lower than the center frequency of the surface acoustic wave filter. 4. The balanced surface acoustic wave filter according to claim 1, wherein the lattice type filter is configured to obtain its inductance component by a bonding wire or a line.