JP2003234636A - Surface acoustic wave filter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a balanced operation type surface acoustic wave filter device with excellent amplitude balance performance and phase balance performance. <P>SOLUTION: A plurality of IDTs (11-13 or 21-23) composed by crossing comb- line electrodes are provided on a piezoelectric substrate (10). The electrode fingers of the comb-line electrodes constituting the IDTs (11-13 or 21-23) are arranged with the width and interval of about 1/4 wavelength of surface acoustic waves excited by the IDTs (11-13 or 21-23). A plurality of resonator type surface acoustic wave elements (1A or 2A) constituted in such a manner are provided. In this case, one (1A) of the surface acoustic wave elements and the other (2A) are cascade-connected and wiring (W1A-W4A) constituting the cascade connection is turned to a floating state in terms of an electric circuit from the ground circuit of the surface acoustic wave filter device. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a differential type (balanced operation type) surface acoustic wave filter device.

[0002]

2. Description of the Related Art A surface acoustic wave filter device converts an electric signal and a surface acoustic wave (SAW) by a comb-shaped electrode (interdigital transducer: IDT) made of thin film metal provided on a piezoelectric body. It is a device that transmits and receives signals, and is used in surface acoustic wave filters, surface acoustic wave resonators, delay circuits, and the like. This surface acoustic wave device has come to be widely used in the field of mobile communication such as a mobile phone due to its merit that it can be made thin and compact.

It is natural that a surface acoustic wave filter for an RF stage used in mobile communication or the like is required to have a low loss and a steep out-of-band cutoff characteristic. (Differential input and / or differential output type) has been required. Behind this is the commercialization / cost reduction of balanced input type (balanced output type) ICs.

The balanced operation type filter is required to have good amplitude balance performance and phase balance performance. As a conventional method for obtaining good amplitude balance performance and phase balance performance, there is a method in which a balun coil is connected to a surface acoustic wave filter of non-differential drive to extract a differential signal. However, in the method of connecting the balun coil to the surface acoustic wave filter of the non-differential drive, the structure of the filter circuit becomes large and the cost of the circuit component also becomes high. Therefore, development of a differential (balanced operation) surface acoustic wave filter that can be directly connected to a balanced IC is desired.

As a conventional configuration example of a surface acoustic wave filter for differentially driving a balanced input IC, there is one shown in FIG. 1 of the following Document 1: Document 1. G. Endoh et. Al “High Performance Balanced
Type SAW Filters in the Range of 900MHz and 1.9 GH
z ”, Proc, IEEE Ultrason. Sympo., p41-44 (1997) In this reference 1, the structure of the SAW filter is the same as the conventional one, and the balanced output terminals are left with the interstage IDT on the unbalanced input side grounded. However, an attempt has been made to directly differentially drive the output-side IDT that is connected to the output side of the I. However, in this method, as described in Reference 1, both the amplitude balance performance and the phase shift balance performance are satisfactory. The performance has not been realized.The cause is SA of the conventional structure.
In the W filter, a floating impedance component associated with an IDT for which differential signal processing is performed exists asymmetrically with respect to the differential circuit operation. This is described in Document 2 below.

Reference 2. PJEdmonson et. Al., “Effect
of Stay Coupling on the Balanceof a Differential
LSAW Front-End Resonator-filter for Wireless / Mobil
e Circuits ”, Proc. IEEE Ultrason. Sympo., p361-36
4 (1999)

[0007]

If the influence of the above-mentioned asymmetrical stray impedance (particularly the asymmetry of stray capacitance between the wiring pattern of the IDT and the piezoelectric substrate) is not managed,
A balanced operation type surface acoustic wave filter device having good amplitude balance performance and phase balance performance cannot be obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a balanced operation type surface acoustic wave filter device having good amplitude balance performance and phase balance performance.

[0009]

A surface acoustic wave filter device according to an embodiment of the present invention includes a piezoelectric substrate and a plurality of surface acoustic wave elements formed on the substrate of the piezoelectric substrate. ing. One of the plurality of surface acoustic wave elements,
A first comb tooth-shaped electrode having an unbalanced signal terminal or a balanced signal terminal, a second comb tooth-shaped electrode arranged on one side of the first comb tooth-shaped electrode, and a first comb tooth-shaped electrode And a third comb-teeth-shaped electrode arranged on the other side of the electrode. The other of the plurality of surface acoustic wave elements is a fourth comb-tooth-shaped electrode having first and second balanced signal terminals, and a fifth comb-tooth-shaped electrode arranged on one side of the second comb-tooth-shaped electrode. And a sixth comb-tooth-shaped electrode arranged on the other side of the second comb-tooth-shaped electrode.

One electrode of the second comb-teeth electrode and one electrode of the fifth comb-teeth electrode are electrically connected via a first wiring; The other electrode and the other electrode of the fifth comb-teeth-shaped electrode are electrically connected via a second wiring; one electrode of the third comb-teeth-shaped electrode and the sixth comb-teeth-shaped electrode The one electrode is electrically connected through a third wiring; the other electrode of the third comb-tooth-shaped electrode and the other electrode of the sixth comb-tooth-shaped electrode are electrically connected through a fourth wiring. Connected.

Here, each of the first to fourth wirings forms a stray capacitance with another electrode via the piezoelectric substrate.

The stray capacitance of the first wiring and the stray capacitance of the second wiring are made to coexist so that the balance between the first and second balanced signal terminals falls within a desired range. Stray capacitance of the wiring and the fourth
It is configured such that the stray capacitances of the wirings coexist.

Alternatively, in the surface acoustic wave filter device according to the embodiment of the present invention, a plurality of interdigital converters having comb-shaped electrodes intersecting each other are provided on the piezoelectric substrate, and the interdigital converters are provided. A plurality of resonator-type surface acoustic wave elements are provided in which the electrode fingers of the comb-teeth-shaped electrodes that are formed are arranged with a width and an interval of approximately ¼ wavelength of the surface acoustic wave excited by the interdigital converter. ing.

Here, one of the surface acoustic wave elements and the other of the surface acoustic wave elements are connected in cascade, and the wiring forming the cascade connection is electrically floating from the ground circuit of the surface acoustic wave filter device. It is configured to be in a state.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave filter device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining the structure of a surface acoustic wave filter device (unbalanced input / balanced output surface acoustic wave filter cascade-connected in a vertical arrangement) according to an embodiment of the present invention.

In FIG. 1, the piezoelectric substrate 10 is made of, for example, a single crystal of lithium tantalum oxide (LiTaO ₃ ).
It was obtained by cutting in the direction rotated by 36 ° in the Y-axis direction around the X-axis (hereinafter abbreviated as LTA).

On the piezoelectric substrate 10, an unbalanced input surface acoustic wave element 1A and a balanced output surface acoustic wave element 2 are provided.
A is formed in a vertical arrangement. Surface acoustic wave element 1A
Are interdigital converters (hereinafter abbreviated as IDTs) 11 to 13 formed by intersecting comb-shaped electrodes made of a metal thin film such as aluminum, and a grating-shaped reflector (hereinafter abbreviated as Gr) made of a metal thin film such as aluminum. Yes) 14-1
It is equipped with 5. Further, the surface acoustic wave element 2A is formed by intersecting comb-teeth electrodes of a thin film made of metal such as aluminum.
Gr of DT21-23 and thin film made of metal such as aluminum
24 to 25 are provided. Gr14 and Gr15 are I
Arranged along the propagation direction of the surface acoustic wave excited by the DT 12 (or the IDTs 11 and 13) (left and right direction in FIG. 1), Gr24 and Gr25 are IDTs 21 and 23
(Or the IDT 22) is arranged along the propagation direction of the surface acoustic wave excited (left-right direction in FIG. 1).

Here, each surface acoustic wave element 1A, 2A is
The electrode finger pitch (distance between centers of a pair of adjacent electrode fingers; electrode period), electrode finger line width, opening length (substantial crossing length of electrode fingers), number of electrode finger pairs, and other pattern shapes should be approximately the same. Is formed. In other words, IDTs 11-1
The electrode fingers constituting 3, 21 to 23 are composed of electrodes (hereinafter referred to as solid electrodes) arranged at a width and an interval of about 1/4 wavelength of the surface acoustic wave excited by the IDT. FIG. 1 shows a resonator type surface acoustic wave filter having such a configuration.

Specifically, the surface acoustic wave device 1A includes an IDT 12 having an unbalanced signal terminal P01, and the IDT 12
The IDT 11 arranged on the left side of the IDT 11, the IDT 13 arranged on the right side of the IDT 12, and Gr 14 and Gr 15 arranged on the left and right with the IDTs 11 to 13 interposed therebetween. One electrode 12a of the central IDT 12 is connected to the unbalanced signal terminal P01, and the other electrode 12b is grounded to the ground circuit of the filter.

Similarly, the surface acoustic wave device 2A includes an IDT 22 having balanced signal terminals P11 and P12, and an IDT 22
IDT21 arranged on the left side of T22, IDT23 arranged on the right side of IDT22, and these IDTs 21 to 2
It includes Gr24 and Gr25 which are arranged on the left and right sides with 3 in between. One electrode 22a of the central IDT 22 is connected to one balanced signal terminal P11, and the other electrode 12b is connected to the other balanced signal terminal P12.

Surface acoustic wave element 1A and surface acoustic wave element 2A
Are cascade-connected via wirings W1A to W4A.
That is, the one electrode 11b of the IDT 11 and the one electrode 21b of the IDT 21 are electrically connected to each other via the first wiring W1A, and the other electrode 11a of the IDT 11 and the other electrode 21a of the IDT 21 are connected via the second wiring W2A. It is electrically connected. Similarly, one electrode 13b of the IDT 13 and I
One electrode 23b of the DT 23 is electrically connected via the third wiring W3A, and the other electrode 13a of the IDT 13 and I
The other electrode 23a of DT23 is electrically connected through the fourth wiring W4A.

In the above-mentioned cascade connection, the wirings W1A to W4
A is not grounded and is floating from the ground circuit. Therefore, between each of the wirings W1A to W4A and the ground circuit, via the piezoelectric substrate 10 (dielectric),
The stray capacitances Cx1 to Cx4 are formed.

What is important here is the wiring W1A and the wiring W.
The asymmetry of the stray capacitance (capacitance) associated with the wiring W1A and the wiring W2A has more influence on the balance of the filter than the asymmetry of the impedance (inductance + DC resistance) due to the difference in length of 2A. That's a big thing (this is empirically known). Therefore, from the viewpoint of balance (of course, the inductance of the wiring W1A / resistance and the inductance of the wiring W2A /
It is desirable that both the wiring W1A and the wiring W2A have capacitances Cx1 and Cx2 that do not make a large difference (the difference is as small as possible), although the resistance does not exceed a near value. Similarly, from the standpoint of balance (although the inductance / resistance of the wiring W3A and the inductance / resistance of the wiring W4A have never exceeded close to each other), both wiring W3A and wiring W4A
It is desirable to have capacitance components Cx3 and Cx4 that do not make a large difference (the difference is as small as possible).

If the wiring W2A is grounded to the ground circuit, Cx2 is apparently infinite in view of the magnitude of impedance, and a large difference occurs between Cx1 and Cx2, resulting in a difference between IDT11 and IDT21. Wiring W1
The asymmetry of the capacitance of A and the wiring W2A increases. However, the wiring W1A and the wiring W2A
If both of them are floating (not grounded) from the ground circuit, capacitances Cx1 and Cx2 remain in these wirings, even if Cx1 ≠
Even with Cx2, the asymmetry of the capacitance is significantly reduced compared to the case where the wiring W1A or the wiring W2A is grounded (that is, the balanced transmission path between the IDT 11 and the IDT 21 is better balanced). .

Similarly, if the wiring W4A is grounded to the ground circuit, Cx4 is apparently infinite from the viewpoint of the magnitude of impedance, and a large difference occurs between Cx3 and Cx4, and IDT13 and IDT23. The asymmetry of the capacitance in the wiring W3A and the wiring W4A between and becomes large. However, if both the wiring W3A and the wiring W4A are floated from the ground circuit (not grounded), capacitances Cx3 and Cx4 remain in these wirings, and even if Cx3 ≠ Cx4, the wiring W3A Or wiring W4
Compared to the case where A is grounded, the asymmetry of capacitance is significantly reduced (that is, IDT13 and IDT
Better balance of the balanced transmission line with 23).

If the equivalent facing area difference between the wiring W1A and the ground circuit is reduced by increasing the width of the wiring W1A and narrowing the width of the wiring W2A, for example, the asymmetry of the capacitance in the wiring W1A and the wiring W2A is obtained. Can be further reduced. Similarly, for example, if the width of the wiring W3A is widened and the width of the wiring W4A is narrowed to reduce the equivalent facing area difference between these wirings and the ground circuit, the wiring W3A
The asymmetry of the capacitance of A and the wiring W4A can be further reduced.

To what extent the asymmetry of the capacitance component can be tolerated is determined by the product of the present invention.
It depends on how much the final balance (amplitude balance and phase balance) is managed. Although specific values of Cx1 to Cx4 or specific values of capacitance ratio Cx2 / Cx1 and capacitance ratio Cx4 / Cx3 cannot be shown, wiring is performed so that desired balance (amplitude balance / phase balance) can be obtained. It is sufficiently possible to experimentally determine the pattern arrangement / area / length, etc. of W1A to W4A.

Specifically, the balanced signal terminals (P11 to P1
The balance in 2) is within the desired range (for example, the amplitude characteristic is ±
The stray capacitance Cx1 of the wiring W1A and the stray capacitance Cx1 of the wiring W2A coexist and the stray capacitance C of the wiring W3A is set to 1 dB and the phase balance is within ± 10 °.
x3 and the stray capacitance Cx4 of the wiring W4A coexist (that is, the wirings W1A to W4A are not grounded). When the equilibrium of a certain prototype sample does not fall within the desired range, for example, by changing the wiring method and / or the area of any of the wirings W1A to W4A, the impedance balance on the wiring is changed. Make a prototype sample of. When the balance of this other prototype sample falls within a desired range (for example, the amplitude characteristic is ± 1 dB and the phase balance is ± 10 °), the pattern shape / area / arrangement / length etc. at that time are set as design values. The surface acoustic wave filter device may be mass-produced by adopting it. Such trial and error work is easy for those skilled in the art.

The above "desired range of equilibrium" will be described more specifically with reference to FIGS. Figure 4
FIG. 5 is a diagram illustrating a characteristic example (amplitude characteristic and standing wave ratio: VSWR) of the surface acoustic wave filter device according to the embodiment of the present invention. Here, the characteristics of a filter (50 Ω system unbalanced input / balanced output type) using the LTA substrate 10 are illustrated. Further, FIG. 5 is a diagram for explaining a characteristic example (amplitude balance characteristic and phase balance characteristic) of the surface acoustic wave filter device according to the embodiment of the present invention.

The SAW filter used for the measurement of FIG.
For example, the surface acoustic wave filter having the structure shown in FIG. 1 is used. The input of this filter (corresponding to P01 in FIG. 1) is connected to a signal source having an output impedance of 50Ω, and the output of this filter (corresponding to P11 to P12 in FIG. 1) is terminated by a load resistance of 50Ω. As illustrated in FIG. 4, this filter has a center frequency of approximately 942.5 MHz and has a bandpass characteristic of passing 922.5 MHz to 962.5 MHz. The VSWR in the pass frequency band is within a practically sufficiently small value (VSWR is approximately 2.5 or less).

Amplitude balance characteristic T in the pass frequency band
FIG. 5 illustrates the F and phase balance characteristics (enlarged scale). From the example of FIG. 5, the amplitude characteristic within the pass frequency band (922.5 MHz to 962.5 MHz) is within ± 1 dB, and the phase balance characteristic is also within ± 7 °. For example, in order to obtain such characteristics, the pattern shape / area / arrangement / length etc. of FIG.
It may be determined by appropriately using conventional design data and / or by trial and error.

Although the input / output impedance is set to 50Ω in the above example, the filter element (surface acoustic wave element 1
A, 2A, etc.) by appropriately changing / operating the electrode finger opening length, the number of electrode fingers, etc.
(Ω, 100Ω, 150Ω, 200Ω, etc.), the same effect can be obtained.

Further, by changing the impedance design of the filter (surface acoustic wave element) at the input stage and the output stage by appropriately selecting the electrode finger opening length, the number of electrode fingers, etc., the elastic surface having different input and output impedances can be obtained. Wave filters (eg, 50Ω unbalanced input 200Ω balanced output, 200Ω balanced input 50Ω unbalanced output, 100Ω balanced input 100Ω balanced output, etc.) can also be implemented.

Specifically, (1) the surface acoustic wave of at least one of the electrode fingers of the comb-teeth-shaped electrode which constitutes the IDT (11 to 13) of one (1A) of the surface acoustic wave element. The width dimension in the excitation direction (horizontal direction in FIG. 1) is set to the surface acoustic wave excitation direction (FIG. 1) of the electrode fingers of the comb-teeth-shaped electrodes that form the other (2A) IDT (21 to 23) of the surface acoustic wave element. By setting the width of the surface acoustic wave filter device to be different from the width dimension of the surface acoustic wave filter device, the design value of the input and / or output impedance of the surface acoustic wave filter device can be changed.

(2) I of one (1A) of the surface acoustic wave element
The opening length of at least one electrode finger of the electrode fingers of the comb-teeth-shaped electrode forming the DT (11 to 13) constitutes the IDT (21 to 23) of the other surface acoustic wave element (2A). The design value of the input and / or output impedance of the surface acoustic wave filter device can be changed by making the opening length of the electrode fingers of the comb-shaped electrode different.

(3) Two electrode fingers of the comb-teeth-shaped electrode are paired, and when the distance between the centers of the pair of electrode fingers is the electrode period, it is included in one surface acoustic wave element (1A). By designing the electrode period of at least one pair of electrode fingers different from the electrode period of the electrode fingers included in the other surface acoustic wave element (2A), the design value of the input and / or output impedance of the filter device is set. Can be changed.

(4) The total number of electrode fingers included in one surface acoustic wave element (1A) is the other surface acoustic wave element (2A).
The design value of the input and / or output impedance of the filter device can be changed by making the number different from the total number of electrode fingers included in.

(5) One of the surface acoustic wave elements (1A) is
A plurality of grating reflectors (14-) formed on the piezoelectric substrate (10) so as to sandwich the IDT (11-13) along the propagation direction of the surface acoustic wave excited by the IDT (11-13). 15), and the other surface acoustic wave element (2A) is IDT (21-23).
A plurality of grating reflectors (24 to 25) are formed on the piezoelectric substrate (10) so as to sandwich the IDT (21 to 23) along the propagation direction of the surface acoustic wave excited by. it can. In this case, the total number of reflective electrode fingers forming the grating reflectors (14 to 15) included in one of the surface acoustic wave elements (1A) is the grating reflector included in the other surface acoustic wave element (2A). The design value of the input and / or output impedance of the filter device can be changed by making the number different from the total number of the reflective electrode fingers forming (24 to 25).

(6) The total number of IDTs (11 to 13) included in one surface acoustic wave element (1A) is different from the total number of IDTs (21 to 23) included in the other surface acoustic wave element (2A). By doing so, the design value of the input and / or output impedance of the filter device can be changed.

(7) The electrode of the IDT forming each surface acoustic wave element so that the transmission frequency characteristic of one surface acoustic wave element (1A) is different from the transmission frequency characteristic of the other surface acoustic wave element (2A). The number of fingers, the opening length, the electrode period, etc. may be changed.

FIG. 2 is a view for explaining the structure of a surface acoustic wave filter device (an unbalanced input / balanced output surface acoustic wave filter having a side-by-side arrangement and a cascade connection) according to another embodiment of the present invention. The difference between FIG. 1 and FIG. 2 lies in the method of arranging two surface acoustic wave elements connected in cascade. That is, in FIG. 1, the surface acoustic wave element 1A and the surface acoustic wave element 2A are vertically arranged and cascaded in the drawing, but in FIG. 2, the surface acoustic wave element 1B and the surface acoustic wave element 2B are horizontally arranged in the drawing. And are connected in cascade. Wiring W1A in FIGS.
~ W4A and wiring W1B ~ W4B are different, but wiring W
It is common that both 1A to W4A and the wirings W1B to W4B are floated from the ground circuit, and each wiring has a stray capacitance (between the ground circuit).

In the configuration of FIG. 2, the stray capacitance C of the wiring W1B
The wirings W1B to W are composed of y1 and the stray capacitance Cy2 of the wiring W2B.
The impedance balance (capacitance asymmetry) between 2B is improved, and the impedance balance (capacitance asymmetry) between the wirings W3B and W4B is improved by the stray capacitance Cy3 of the wiring W3B and the stray capacitance Cy4 of the wiring W4B. As a result, a balanced operation type surface acoustic wave filter device having excellent amplitude balance performance and phase balance performance is realized.

Although not shown, the surface acoustic wave elements 1A and 2A as shown in FIG. 1 and the surface acoustic wave elements 1B and 2B as shown in FIG. 2 are formed on the same piezoelectric substrate 10. Embodiments are also possible.

The surface acoustic wave element 1A of FIG. 1 or the surface acoustic wave element 1B of FIG. 2 is a balanced type, and the surface acoustic wave element 2A of FIG. 1 or the surface acoustic wave element 2B of FIG. 2 is an unbalanced type. Such an embodiment is also possible.

Further, the terminal P01 of the surface acoustic wave element 1A or 1B of FIG. 1 or 2 is used as an output terminal, and the terminal P11 of the surface acoustic wave element 2A or 2B of FIG. 1 or 2 is used.
An embodiment in which P12 is used as an input terminal is also possible.

FIG. 3 is a view for explaining the structure of a surface acoustic wave filter device (balanced input / balanced output surface acoustic wave filter of cascade connection arranged in cascade) according to still another embodiment of the present invention. The difference between FIG. 1 and FIG. 3 is that two are connected in cascade.
One of the surface acoustic wave elements (1A) is an unbalanced type or a balanced type. That is, FIG. 1 shows an unbalanced input / balanced output type surface acoustic wave filter device, while FIG. 3 shows a balanced input / balanced output type surface acoustic wave filter device.

Specifically, in FIG. 1, the unbalanced signal terminal P01 is connected to one electrode 12a of the IDT 12 and the other electrode 1 thereof.
2b is grounded to the ground circuit, but in FIG.
One balanced signal terminal P01 * on one electrode 12a of T12
Is connected to the other electrode 12b, and the other balanced signal terminal P02 is connected to the other electrode 12b.
* Is connected.

The vertically arranged surface acoustic wave elements 1A and 2A shown in FIG. 3 may be arranged horizontally as shown in FIG.

The configuration of the embodiment shown in FIGS. 1 to 3 can be summarized as follows. That is, an interdigital converter (11 to 13 or 21 to 2) formed by intersecting comb-shaped electrodes on a piezoelectric substrate (10).
A plurality of 3) are provided. The electrode fingers of the comb-shaped electrodes forming the interdigital converter (11 to 13 or 21 to 23) are the interdigital converter (11).
13 to 21 or 21 to 23), the surface acoustic waves are arranged with a width of, for example, a quarter wavelength and an interval. A plurality of resonator type surface acoustic wave elements (1A or 2A) configured in this manner are provided. Then, one (1A) of the surface acoustic wave elements and the other (2A) of the surface acoustic wave elements.
A) are connected in cascade.

Here, the wiring (W
1A to W4A) are configured so as to be in an electrically floating state from the ground circuit of the surface acoustic wave filter device (if a stray capacitance is formed in each wiring, any wiring other than the ground circuit) It doesn't matter that it is connected to the.

Wirings (W1A to W) that constitute the cascade connection.
4A), at least one is disconnected from the ground circuit. As the wiring, for example, I in FIG.
When considering the wiring connected to the electrode 12b of the DT 12, the wiring connected to the electrode 12b is not separated from the ground circuit. "At least one is separated from the ground circuit" is an expression in consideration of such a situation. Further, for example, in the embodiment in which the configuration of FIG. 1 and the configuration of FIG. 3 are formed on the same substrate 10, the wirings W2A and W4A are grounded to the ground circuit in the configuration of FIG. 1, but the configuration of FIG. Then wiring W1A
An embodiment is conceivable in which none of W4A to W4A is grounded to the ground circuit. "At least one is separated from the ground circuit" is an expression in consideration of such a situation.

The present invention is not limited to the above embodiments, and various modifications and changes can be made at the stage of carrying out the invention without departing from the spirit of the invention. Also,
The respective embodiments may be combined as appropriate as much as possible, and in that case, the effect of the combination can be obtained.

Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of constituent elements disclosed in this application. For example, even if one or more constituent elements are deleted from all the constituent elements shown in the embodiment, if at least one of the effect of the present invention or the effect of implementing the present invention is obtained, the constituent element is The deleted configuration can be extracted as an invention.

<Effects of Embodiment> Focusing on the floating impedance component of the IDT that performs differential signal processing (balanced signal processing) (mainly, the floating capacitance between the ground circuit in the wiring of the balanced signal path), the interstage IDT The wiring of is not configured to be grounded to the ground circuit. This allows for differential (balanced) input or differential (balanced) output or differential (balanced)
It is possible to obtain a surface acoustic wave filter device (in particular, a surface acoustic wave filter device used in the field of mobile communication) that enables input / output, has excellent amplitude balance property and phase balance property, and can be driven with low impedance.

[0056]

EFFECTS OF THE INVENTION A balanced operation type surface acoustic wave filter device having good amplitude characteristics / phase balance performance can be realized.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a structure of a surface acoustic wave filter device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a structure of a surface acoustic wave filter device according to another embodiment of the present invention.

FIG. 3 is a diagram illustrating a structure of a surface acoustic wave filter device according to still another embodiment of the present invention.

FIG. 4 is a surface acoustic wave filter device according to an embodiment of the present invention (50Ω system balanced output E using an LTA substrate).
Characteristics example of GSM-Rx filter (amplitude characteristics and VSW
FIG.

FIG. 5 is a diagram illustrating a characteristic example (amplitude balance characteristic and phase balance characteristic) of the surface acoustic wave filter device according to the embodiment of the present invention.

[Explanation of symbols]

1A, 1B, 2A, 2B ... Surface acoustic wave element (resonator type surface acoustic wave element); 10 ... Piezoelectric substrate; 11-13, 21
~ 23 ... Comb-shaped electrodes (interdigital converter / ID
T; functional element); 14, 15, 24, 25 ... Reflector; P
01 ... unbalanced signal terminal; P01 *, P02 *, P11,
P12 ... Balanced signal terminal; W1A to W4A, W1B to W4
B ... Signal line; Cx1 to Cx4, Cy1 to Cy4 ... Stray capacitance (stray impedance).

Claims (12)

[Claims] 1. A piezoelectric substrate comprising a piezoelectric substrate and a plurality of surface acoustic wave elements formed on the substrate of the piezoelectric substrate, wherein one of the plurality of surface acoustic wave elements is an unbalanced signal terminal or A first comb tooth-shaped electrode having a balanced signal terminal, and
A second comb-teeth electrode arranged on one side of the comb-teeth electrode and a third comb-teeth electrode arranged on the other side of the first comb-teeth electrode; The other of the surface acoustic wave elements is a fourth comb-tooth-shaped electrode having first and second balanced signal terminals, and a fifth comb-tooth-shaped electrode arranged on one side of the second comb-tooth-shaped electrode. And a sixth comb-tooth electrode arranged on the other side of the second comb-tooth electrode; one electrode of the second comb-tooth electrode and one of the fifth comb-tooth electrode. The electrode is electrically connected via a first wiring; the other electrode of the second comb-teeth-shaped electrode and the other electrode of the fifth comb-teeth-shaped electrode are electrically connected via a second wiring. The third comb-teeth electrode and the sixth comb-teeth electrode are electrically connected to each other through a third wiring; and the third comb-teeth electrode is electrically connected to the third comb-teeth electrode. The other side of Wherein the other electrode of the sixth interdigital electrodes of via the fourth wiring are electrically connected; the first
To each of the fourth wirings form a stray capacitance between the fourth wiring and the other electrode via the piezoelectric substrate; to the extent that the balance at the first and second balanced signal terminals falls within a desired range, The stray capacitance of the first wiring and the stray capacitance of the second wiring coexist, and the stray capacitance of the third wiring and the stray capacitance of the fourth wiring coexist. Balanced surface acoustic wave filter device. 2. A plurality of interdigital converters, which are formed by intersecting comb-teeth-shaped electrodes, are provided on a piezoelectric substrate, and the electrode fingers of the comb-teeth-shaped electrodes that form the interdigital converter are the interdigital converters. A plurality of resonator-type surface acoustic wave elements arranged at a width and an interval of about ¼ wavelength of the surface acoustic wave excited by the transducer, wherein one of the surface acoustic wave elements and the surface acoustic wave are provided. The other surface of the wave element is cascade-connected, and the wiring forming the cascade connection is configured so as to be in a floating state in an electric circuit from the ground circuit of the surface acoustic wave filter device. Wave filter device. 3. The surface acoustic wave filter device according to claim 2, wherein at least one of the wirings forming the cascade connection is separated from the ground circuit. 4. One of the surface acoustic wave elements includes an interdigital converter connected to the unbalanced signal terminal and the ground circuit, and the other of the surface acoustic wave elements is connected to the balanced signal terminal. The surface acoustic wave filter device according to claim 2, wherein the surface acoustic wave filter device is configured to include an interdigital converter that is not connected to the ground circuit. 5. One of the surface acoustic wave elements includes an interdigital converter connected to a balanced signal terminal but not connected to the ground circuit, and the other of the surface acoustic wave elements is connected to a balanced signal terminal. The surface acoustic wave filter device according to claim 2, wherein the surface acoustic wave filter device is configured to include an interdigital converter that is connected to the ground circuit but is not connected to the ground circuit. 6. The width dimension in the surface acoustic wave excitation direction of at least one of the electrode fingers of the comb-teeth-shaped electrode forming the interdigital converter of one of the surface acoustic wave elements is defined as follows. The input and / or output of the filter device is made different from the width dimension in the surface acoustic wave excitation direction of the electrode fingers of the comb-shaped electrodes that constitute the other interdigital converter of the surface acoustic wave element. The surface acoustic wave filter device according to any one of claims 2 to 5, wherein the impedance design value is changed. 7. The opening length of at least one electrode finger of the electrode fingers of the comb-teeth-shaped electrode forming one of the interdigital converters of one of the surface acoustic wave elements is set to the other of the surface acoustic wave elements. In the configuration, the design value of the input and / or output impedance of the filter device is changed by making it different from the opening length of the electrode fingers of the comb-teeth-shaped electrode that composes the interdigital converter. The surface acoustic wave filter device according to any one of claims 2 to 6, which is characterized in that. 8. The pair of electrode fingers of the comb-teeth-shaped electrode is a pair, and at least one of the surface acoustic wave elements is included when the distance between the centers of the pair of electrode fingers is the electrode period. By changing the electrode period of the pair of electrode fingers different from the electrode period of the electrode fingers included in the other surface acoustic wave element, the design value of the input and / or output impedance of the filter device is changed. The surface acoustic wave filter device according to any one of claims 2 to 7, wherein the surface acoustic wave filter device is configured to: 9. The input of the filter device, wherein the total number of the electrode fingers included in one of the surface acoustic wave elements is different from the total number of the electrode fingers included in the other of the surface acoustic wave elements. 9. The surface acoustic wave filter device according to claim 2, wherein the design value of the output impedance and / or the output impedance is changed. 10. One of the surface acoustic wave elements is arranged to sandwich the part of the interdigital converter along a propagation direction of a surface acoustic wave excited by a part of the interdigital converter. A plurality of grating-shaped reflectors formed on the substrate; the other of the surface acoustic wave elements is arranged along the propagation direction of the surface acoustic wave excited by the other portion of the interdigital converter. An interdigital converter is sandwiched between the plurality of other grating reflectors formed on the piezoelectric substrate, and the total number of reflective electrode fingers forming the grating reflector included in one of the surface acoustic wave elements is , The total number of the reflective electrode fingers constituting the grating reflector included in the other of the surface acoustic wave elements is different. , Input and / or elastic surface wave filter device according to any one of claims 2 to 9, characterized by being configured to change the design value of the output impedance of the filter device. 11. The total number of the interdigital converters included in one of the surface acoustic wave elements is different from the total number of the interdigital converters included in the other of the surface acoustic wave elements. The surface acoustic wave filter device according to any one of claims 2 to 9, which is configured to change a design value of input and / or output impedance of the filter device. 12. The surface acoustic wave device according to claim 2, wherein one frequency characteristic of the surface acoustic wave device is different from the other frequency characteristic of the surface acoustic wave device. The surface acoustic wave filter device according to item 1.