JP2003023341A - Balanced operation type surface acoustic wave filter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balance operation type surface acoustic wave(SAW) filter device with which the terminal resistance (nominal value) of an unbalanced terminal can be easily made equal with the terminal resistance (nominal value) of a balanced terminal. SOLUTION: This SAW filter device is composed of a first SAW element 1 provided with first comb-line electrode groups 24-26 while having an unbalanced terminal 21 and a pair of balanced terminals 22 and 23 and a second SAW element 2 provided with second comb-line electrode groups 27-29. The unbalanced terminal 21 is connected to one terminal 25b of serial electrode structures 25 and 28 serially connecting one part 25a of the first comb-line electrode groups and one part 28a of the second comb- line electrode groups. One balanced terminal 22 is connected to one terminal 24a+27a of parallel electrode structures 24 and 27 parallelly connecting a first other part 24 of the first comb-line electrode groups and a first other part 27 of the second comb-line electrode groups. The other balanced terminal 23 is connected to one terminal 26a+29a of parallel electrode structures 26 and 29 parallelly connecting a second other part 26 of the first comb-line electrode groups and a second other part 29 of the second comb-line electrode groups.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a balanced operation type surface acoustic wave filter device which is used, for example, in a reception / transmission bandpass filter of a mobile phone.

[0002]

2. Description of the Related Art Surface acoustic wave filter devices (surface acou
stic wave filter device; also referred to as SAW filter) is formed by forming comb-teeth electrodes on a piezoelectric substrate. Since this surface acoustic wave filter device is a passive element, it can operate without a power supply, and since it is small and lightweight, it is often used in mobile phones and the like that require high-density mounting of electronic components.

In recent years, as a circuit for mobile communication used in a mobile phone or the like, one including a balanced operation circuit is becoming mainstream. In this case, the surface acoustic wave filter device used before or after the balanced operation circuit is configured as an unbalanced / balanced operation type (unbalanced input / balanced output type or balanced input / unbalanced output type). In such circuits, the input and output termination resistors (nominal termination impedance) are different,
About 50Ω to 200Ω is desired.

[0004]

Conventionally, unbalanced input / balanced output type surface acoustic wave filters are well known. An example thereof is the surface acoustic wave filter disclosed in Japanese Patent Laid-Open No. 09-326669. In the surface acoustic wave filter of this publication, a pair of comb-teeth-shaped electrodes are arranged on the left and right of the comb-teeth-shaped electrode connected to the unbalanced input terminal, and a pair of balanced outputs is formed from the pair of left-right comb-teeth-shaped electrodes. It is designed to be taken out. In such a conventional configuration, for example, when the termination resistance of the comb-teeth-shaped electrodes on the unbalanced input side is designed to be 50Ω, the termination resistance of the pair of left and right comb-teeth-shaped electrodes is 1 respectively.
It becomes 00Ω, and the termination resistance of the balanced output becomes 200Ω. In the surface acoustic wave filter having such a configuration, it is not easy in designing the surface acoustic wave filter to set the balanced output termination resistance to 50Ω, which is the same as the unbalanced input termination resistance.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a balanced operation type elastic surface having a structure in which the terminating resistance of an unbalanced terminal and the terminating resistance of a balanced terminal can be easily equalized. A wave filter device is provided.

[0006]

In order to achieve the above object, a balanced operation type surface acoustic wave filter device according to the present invention includes a piezoelectric substrate (10) and the piezoelectric substrate (10).
It comprises a plurality of surface acoustic wave elements (1, 2) formed on it and comprises at least one unbalanced terminal (21) and at least one pair of one and the other balanced terminal (22, 23). In this balanced operation type surface acoustic wave filter device (100), the plurality of surface acoustic wave elements (1,
2) includes at least first and second surface acoustic wave elements, the first surface acoustic wave element (1) includes a first comb tooth-shaped electrode group (24 to 26), and The surface acoustic wave element (2) includes a second comb tooth-shaped electrode group (27 to 29).

The unbalanced terminal (21) is connected to a part (25a) of the first comb-teeth electrode group (24 to 26) and the second unbalanced terminal (21).
One end (25) of the series electrode structure (25, 28) in which a part (28a) of the comb tooth-shaped electrode group (27 to 29) is connected in series.
b). The other end (28b) of the series electrode structure (25, 28) is grounded, for example.

The one balanced terminal (22) is composed of the first other portion (24) of the first comb-teeth electrode group (24-26) and the second comb-teeth electrode group (27-29). The first other part (27)
One parallel electrode structure in which and are connected in parallel (24, 27)
Is connected to one end (24a + 27a). The other end (24b, 27b) of this parallel electrode structure (24, 27) is grounded, for example.

The other balanced terminal (23) is connected to the second other portion (26) of the first comb-teeth electrode group (24-26) and the second comb-teeth electrode group (27-29). Second Other Department (29)
Another parallel electrode structure in which and are connected in parallel (26, 29)
Is connected to one end (26a + 29a). The other ends (26b, 29b) of the parallel electrode structure (26, 29) are grounded, for example.

In the above structure, assuming that the input termination resistance and the output termination resistance of each comb-teeth-shaped electrode (or interdigital converter IDT) are both 50Ω, for example, one end of the series electrode structure (25, 28). (25
The terminating resistance in b) (terminating resistance of unbalanced terminal) is 50.
Ω + 50Ω = 100Ω.

On the other hand, the one parallel electrode structure (2
The terminating resistance at one end (24a + 27a) of 4, 27) is 100Ω // 100Ω = 50Ω, and the terminating resistance at one end (26a + 29a) of the other parallel electrode structure (26, 29) is 100Ω // 100Ω = 50Ω. Therefore, one end (24a + 27a) of the one parallel electrode structure (24, 27) and the other parallel electrode structure (26,
The termination resistance between one end (26a + 29a) of 29) (termination resistance between the balanced terminals) is 50Ω + 50Ω = 100Ω, which is the same as the termination resistance of the unbalanced terminal of 100Ω.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A balanced operation type 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 illustrating the configuration of a balanced operation type surface acoustic wave filter device 100 according to an embodiment of the present invention. In the following description, the comb-teeth-shaped electrodes (24 to 29) forming the surface acoustic wave filter will be appropriately referred to as interdigital converters (abbreviated IDTs).

The surface acoustic wave filter device 100 shown in FIG.
A plurality of (here, two) surface acoustic wave elements 1 and 2 are provided on the piezoelectric substrate 10, and at least one unbalanced terminal (signal port) 21 and at least one pair of balanced terminals (signal port) 22 and 23 are provided. It is configured to include. In this balanced operation type surface acoustic wave filter device 100, the piezoelectric substrate 10 can be made of, for example, lithium tetraborate or lithium tantalate. On this substrate 10, a comb-shaped electrode 2 made of, for example, an aluminum alloy or a copper alloy is formed.
4-29 are formed.

The first surface acoustic wave element 1 includes a first comb tooth-shaped electrode group (24 to 26), and the second surface acoustic wave element 2 includes a second comb tooth shaped electrode group (27 to 29). Is included. In this embodiment, the first comb tooth-shaped electrode group (24-26) includes three IDTs 24-26 and two reflectors 12, 13.
The second comb-teeth electrode group (27 to 29) is composed of three IDTs 27 to 29 and two reflectors 14 and 15 and is arranged in a row along the surface wave propagation direction of the piezoelectric substrate 10. There is. The elements 1 and 2 are arranged in a row in a direction substantially orthogonal to the surface wave propagation direction.

A pair of IDTs arranged in three rows (24 to 26 and 2)
7-29), the central IDTs 25 and 28 are connected in series and connected to the unbalanced terminal 21. That is, one end 25a of the central IDT 25 and one end 28 of the central IDT 28
a, the other end 28b of the central IDT 28 is grounded to the ground circuit, and the other end 25b of the central IDT 25 is connected to the unbalanced terminal 21. In this series configuration, the IDT
If the termination resistance of each of 25 and IDT 28 is 50Ω, the termination resistance of the terminal 21 is 50Ω + 50Ω = 1.
It becomes 00Ω.

A pair of IDTs arranged in three rows (24 to 26 and 2)
7-29), the left IDTs 24 and 27 are connected in parallel and connected to one of the balanced terminals 22. That is, one end 24a of the left IDT 24 and one end 27a of the left IDT 27 are both connected to the balanced terminal 22, and the left ID
The other end 24b of T24 and the other end 27b of the left IDT 27
Are both grounded to the ground circuit. That is, IDT
24 and the IDT 27 are electrically connected in parallel. In this parallel configuration, if the termination resistance of each of the left IDT 24 and the IDT 27 is 100Ω, the termination resistance of the terminal 22 is 100Ω // 100Ω = 50Ω.

A pair of IDTs arranged in three rows (24 to 26 and 2)
7-29), the IDTs 26 and 29 on the right side are connected in parallel and connected to the other balanced terminal 23. That is, one end 26a of the right IDT 26 and one end 29a of the right IDT 29 are both connected to the balanced terminal 23, and the right ID
The other end 26b of T26 and the other end 29b of the right IDT 29
Are both grounded to the ground circuit. That is, IDT
26 and the IDT 29 are electrically connected in parallel. In this parallel configuration, the right IDT2 is the same as the left IDT described above.
6 and the IDT 29 each have a termination resistance of 100Ω, the termination resistance of the terminal 23 is 100Ω // 100Ω.
= 50Ω.

In the above structure, the central IDT 2
5, 28 from the center IDTs 25 and 28 to the right side IDT2.
Since the phases of the surface acoustic waves sent to the sensors 6 and 29 are opposite to each other, the signal phase of the one balanced terminal 22 (termination resistance 50Ω) is opposite to the signal phase of the other balanced terminal 23 (termination resistance 50Ω). . That is, with respect to the signal phase of the terminal 21,
An in-phase signal is obtained from the terminal 22, and an opposite-phase signal is obtained from the terminal 23. Therefore, the balanced terminals 22 to 23 can be directly connected to a balanced input circuit (or a balanced output circuit) having a circuit impedance of 100Ω (not shown).

Further, the unbalanced terminal 21 (terminating resistance 100Ω) connected to the central IDTs 25 and 28 can be directly connected to an unbalanced output circuit (or unbalanced input circuit) whose circuit impedance is not shown, and is 100Ω.

In the embodiment shown in FIG. 1, the surface acoustic wave filter device 100 that realizes the 100Ω unbalanced input (output) and the 100Ω balanced output (input) has been illustrated.
If the DT terminal resistance is designed to be 25Ω, 50
It is possible to obtain the surface acoustic wave filter device 100 having an Ω unbalanced input (output) and a 50 Ω balanced output (input).

The reflectors 12 to 15 shown in FIG.
It is provided in order to reduce the signal transmission loss from T to the left and right IDTs, etc. In order to equalize the terminating resistance of the unbalanced terminal and the terminating resistance between the balanced terminals, the reflectors 12 to
15 may be omitted.

In the IDT arrangement as in the embodiment of FIG. 1, the structural balance from the unbalanced input (output) to the balanced output (input) is made symmetrical, and both the amplification degree balance and the phase balance are balanced. It has a structure that makes it easy to obtain balanced output (input) with good frequency.

FIG. 2 is a diagram illustrating the configuration of a balanced operation type surface acoustic wave filter device 100 according to another embodiment of the present invention. The device 100 of FIG. 2 has a balanced output terminal 23.
Arrangement direction and terminals 2 of IDTs 26 and 29 connected to
3 and the IDTs 26 and 29 are wired in the device 100 of FIG.
Different from In FIG. 2, the electrode arrangement method of the IDTs 26 and 29 is upside down from that of FIG. 1, but the wiring method to the terminal 23 is also changed to correspond to this electrode upside down, so the signal phase of the terminal 21 and the terminal 23 The relationship with the signal phase is the same as in the case of FIG. That is, with respect to the signal phase of the terminal 21,
For example, the in-phase signal is obtained from the terminal 22, and the anti-phase signal is obtained from the terminal 23.

The IDTs 24 to 24 having the same termination resistance as in the case of FIG.
When 29 is used, the surface acoustic wave filter device 100 realizing the 100Ω unbalanced input (output) and the 100Ω balanced output (input) can be obtained even with the configuration of FIG. Also, FIG.
Even in the IDT arrangement as in the embodiment of the present invention, the structural balance from the unbalanced input (output) to the balanced output (input) is symmetrical, and the balanced output with a good balanced degree for both the amplification degree balance and the phase balance. It has a structure that makes it easy to obtain (input).

In the structure shown in FIG. 2, one end (24a + 27a) of the one parallel electrode structure (24, 27) is located at a position where the first surface acoustic wave element 1 and the second surface acoustic wave element 2 face each other. However, the other end (26b + 29b) of the other parallel electrode structure (26, 29) is arranged so that the first surface acoustic wave element 1 and the second surface acoustic wave element 2 do not face each other. . Comparing this with FIG. 1, in FIG.
2 may look more disadvantageous than FIG. 1 with respect to the gain balance / phase balance because it is different from the routing of wiring to, but this is not always the case. For example, when each of the terminals 21 to 23 on the substrate 10 of FIG. 2 is connected to an external terminal (not shown) provided in the package of the surface acoustic wave filter device 100, an actual connection from the external terminal to the terminals 22 and 23 is performed. There is a possibility that the wiring routing pattern of the terminal 22 and the terminal 23 may be different. In consideration of this "slightly collapse of amplification degree balance / phase balance due to difference in actual wiring layout pattern", it may be better to adopt the structure of FIG. 2 than that of FIG.

FIG. 3 is a diagram for explaining the structure of a balanced operation type surface acoustic wave filter device 200 according to still another embodiment of the present invention.

The surface acoustic wave filter device 200 shown in FIG.
A plurality of (here, two) surface acoustic wave devices 3 and 4 are provided on the piezoelectric substrate 10, and at least one unbalanced terminal (signal port) 31 and at least one pair of balanced terminals (signal port) 32 and 33 are provided. It is configured to include. In this balanced operation type surface acoustic wave filter device 200, the piezoelectric substrate 10 can be made of lithium tetraborate, lithium tantalate, or the like, as in the embodiment of FIG. 1 or 2. Comb-shaped electrodes 34 to 43 made of an aluminum alloy or a copper alloy are formed on the substrate 10.

The first surface acoustic wave element 3 includes a first comb tooth-shaped electrode group (34 to 38), and the second surface acoustic wave element 4 includes a second comb tooth shaped electrode group (39 to 43). Is included. In this embodiment, the first comb tooth-shaped electrode group (34 to 38) includes five IDTs 34 to 38 and two reflectors 16 and 17.
The second comb tooth-shaped electrode group (39 to 43) is composed of five IDTs 39 to 43 and two reflectors 18 and 19.

A pair of IDTs arranged in five rows (34 to 38 and 3)
9 to 43), the central IDTs 36 and 41 are connected in series and connected to the unbalanced terminal 31, and the leftmost IDT 3 is connected.
4 and 39 are connected in series and connected to the unbalanced terminal 31, and the right end IDTs 38 and 43 are connected in series and connected to the unbalanced terminal 31. These three serially connected IDTs
(34 + 39; 36 + 41; 38 + 43) are connected in parallel, one end of which is connected to the unbalanced terminal 31 and the other end is grounded to the ground circuit.

In this serial-parallel configuration, the IDTs 36, 4
1 Each terminating resistance is 50Ω, IDT34, 3
It is assumed that the terminating resistance of each of 8, 39 and 43 is 100Ω. In this case, the termination resistances of the central IDTs 36 and 41 are 50Ω + 50Ω = 100Ω, the termination resistances of the right end IDTs 38 and 43 are 100Ω + 100Ω = 200Ω, and the termination resistances of the left end IDTs 34 and 39 are 100Ω.
+ 100Ω = 200Ω. Since the termination resistance at the terminal 31 has parallel resistance values of 100Ω, 200Ω, and 200Ω, the termination resistance at the terminal 31 is 50Ω.

A pair of IDTs arranged in five rows (34 to 38 and 3)
9-43), the central IDTs 36 and 41 and the leftmost ID
IDT 35 and 4 on the left side sandwiched between T34 and 39
0s are connected in parallel and connected to one balanced terminal 32.
That is, one end 35a of the IDT 35 and one end 40a of the IDT 40 are both connected to the balanced terminal 32.
The other end 35b of the IDT 40 and the other end 40b of the IDT 40 are both grounded to the ground circuit. That is, IDT35 and IDT
40 is electrically connected in parallel. In this parallel configuration, I
If the termination resistance of each of DT35 and IDT40 is 50Ω, the termination resistance of the terminal 32 is 50Ω // 50Ω = 2.
It becomes 5Ω.

A pair of IDTs arranged in five rows (34 to 38 and 3)
9-43), the central IDTs 36 and 41 and the rightmost ID
IDT 37 and 4 on the right side sandwiched between T38 and T43
2 are connected in parallel and connected to the other balanced terminal 33.
That is, one end 37a of the IDT 37 and one end 42a of the IDT 42 are both connected to the balanced terminal 33.
The other end 37b of the IDT 42 and the other end 42b of the IDT 42 are both grounded to the ground circuit. That is, IDT37 and IDT
42 is electrically connected in parallel. In this parallel configuration, I
If the termination resistance of each of DT37 and IDT42 is 50Ω, the termination resistance of the terminal 33 is 50Ω // 50Ω = 2.
It becomes 5Ω.

In the embodiment of FIG. 3, the terminating resistance of the unbalanced terminal 31 is 50Ω, and the terminating resistances of the balanced terminal 32 and the balanced terminal 33 are the same 25Ω, so that the balanced terminal 32 and the balanced terminal are Termination resistance between 33 and 2
5Ω + 25Ω = 50Ω. That is, also in the embodiment of FIG. 3, the terminating resistance (50Ω) of the unbalanced terminal and the terminating resistance (50Ω) between the balanced terminals are the same.

Even in the IDT arrangement as in the embodiment of FIG. 3, the structural balance from the unbalanced input (output) to the balanced output (input) is symmetric, and both the amplification degree balance and the phase balance are balanced. It has a structure that makes it easy to obtain balanced output (input) with good frequency.

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 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.

[0038]

As described above, according to the balanced operation type surface acoustic wave filter device of the present invention, a plurality of combinations of interdigital converters (comb-shaped electrodes) having the same structure are used to realize the unbalanced terminals. The terminating resistance and the terminating resistance between the balanced terminals can be the same.

[Brief description of drawings]

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

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

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

[Explanation of symbols]

10 ... Piezoelectric substrate; 1-4 ... Surface acoustic wave element; 24-2
9, 34 to 43 ... Comb-shaped electrodes (interdigital converter / IDT); 21, 31 ... Unbalanced terminals; 22, 32 ... One balanced terminal; 23, 33 ... Other balanced terminal; 100,
200 ... Balanced operation type surface acoustic wave filter device.

Continued front page    (72) Inventor Yasuo Ebata             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office (72) Inventor Koji Kanazaki             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office (72) Inventor Naoki Akahori             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office F-term (reference) 5J097 AA11 BB17 CC04

Claims (3)

[Claims] 1. A balanced circuit comprising a piezoelectric substrate and a plurality of surface acoustic wave elements formed on the piezoelectric substrate, the balanced circuit including at least one unbalanced terminal and at least one pair of one and the other balanced terminal. In the operational surface acoustic wave filter device, the plurality of surface acoustic wave elements are at least first and second.
A surface acoustic wave element, the first surface acoustic wave element includes a first comb tooth-shaped electrode group, and the second surface acoustic wave element includes a second comb tooth-shaped electrode group; The balanced terminal is connected to one end of a series electrode structure in which a part of the first comb-shaped electrode group and a part of the second comb-shaped electrode group are connected in series, and the one balanced terminal is the The first other portion of the first comb-teeth electrode group and the first other portion of the second comb-teeth electrode group are connected in parallel and are connected to one end of one parallel electrode structure, and the other balanced terminal is , The second other portion of the first comb-teeth electrode group and the second other portion of the second comb-teeth electrode group are connected in parallel, and are connected to one end of the other parallel electrode structure. Balanced surface acoustic wave filter device. 2. A balance comprising a piezoelectric substrate and a plurality of surface acoustic wave elements formed on the piezoelectric substrate, the balance comprising at least one unbalanced terminal and at least one pair of one and the other balanced terminals. In the operation type surface acoustic wave filter device, the plurality of surface acoustic wave elements are arranged at least in a row in a direction substantially orthogonal to a main propagation direction of a surface wave of the piezoelectric substrate.
And a second surface acoustic wave element, wherein the first surface acoustic wave element includes a first comb tooth-shaped electrode group arranged in a row along the main propagation direction of the surface wave of the piezoelectric substrate. The surface acoustic wave device of No. 2 includes a second comb tooth-shaped electrode group arranged in a row along the main propagation direction of the surface wave of the piezoelectric substrate; and the unbalanced terminal is the first comb tooth-shaped electrode group. Is connected to one end of a series electrode structure in which a part of the first comb-shaped electrode group is connected in series, and the one balanced terminal is a first other part of the first comb-shaped electrode group. And a first other part of the second comb-teeth electrode group are connected in parallel, and are connected to one end of one parallel electrode structure, and the other balanced terminal is the second electrode of the first comb-teeth electrode group. The other part and the second other part of the second comb-shaped electrode group are connected in parallel, and are connected to the other end of the other parallel electrode structure. The end is located at a location where the first surface acoustic wave element and the second surface acoustic wave element face each other, and the other end of the other parallel electrode structure has the first surface acoustic wave element and the second surface acoustic wave element. A balanced operation type surface acoustic wave filter device, characterized in that it is arranged so as not to face the surface acoustic wave element. 3. A balanced substrate comprising a piezoelectric substrate and a plurality of surface acoustic wave elements formed on the piezoelectric substrate, the balanced substrate including at least one unbalanced terminal and at least one pair of one and the other balanced terminal. In the operational surface acoustic wave filter device, the plurality of surface acoustic wave elements are at least first and second.
The surface acoustic wave element, the first surface acoustic wave element includes a first comb tooth-shaped electrode group, and the second surface acoustic wave element includes a second comb tooth-shaped electrode group; The unbalanced terminal has a first series electrode structure in which a part of the first comb-teeth electrode group and a part of the second comb-teeth electrode group are connected in series, and
Of the second comb-teeth electrode group and another part of the second comb-teeth electrode group connected in series, and another part of the first comb-teeth electrode group A part of the second comb-teeth-shaped electrode group and another part of the second comb-shaped electrode group connected in series to each other, and the third series electrode structure is connected in parallel. The first other portion of the first comb-teeth electrode group and the first other portion of the second comb-teeth electrode group are connected in parallel and are connected to one end of one parallel electrode structure, and the other balanced terminal is , The second other portion of the first comb-teeth electrode group and the second other portion of the second comb-teeth electrode group are connected in parallel, and are connected to one end of the other parallel electrode structure. Balanced surface acoustic wave filter device.