KR102867528B1 - Filter device and SAW filter - Google Patents

Abstract

Improves the attenuation characteristics of a filter device having multiple filters sharing a single antenna, such as a multiplexer.
A SAW filter (10) including a filter circuit (20, 30) comprising a piezoelectric substrate (100), signal terminals (ST1, ST2) formed on the piezoelectric substrate (100), a common terminal (CT), and a ladder-type filter including a plurality of surface elastic wave resonators (S1 to S3, P1, P2) respectively configured between the signal terminals (ST1, ST2) and the common terminal (CT), and a matching circuit (50) for phase matching that is connected to a wiring connecting an antenna port (AP) installed on the outside of the SAW filter (10) and the common terminal (CT), and that is commonly applied to the filter circuits (20, 30), wherein the matching circuit (50) has an inductor (L) and a capacitor (C) that are connected in series between the wiring (WR) and a ground potential.

Description

Filter device and SAW filter

The present invention relates to a filter device used in mobile communication and a SAW filter applied thereto.

Recently, in mobile communications, in order to perform large-capacity, high-speed communications, a filter device having multiple filters sharing a single antenna, such as a multiplexer including a duplexer or quadplexer, is used (see, for example, Patent Document 1).

[Patent Document 1] JP2009-033733A

In devices such as the above, due to the increase in the frequency bands used, it has become necessary to secure attenuation amounts for multiple frequency bands with a single filter.

In order to secure the attenuation of multiple frequency bands with a single filter, it was not easy to maintain the transmission characteristics of the filter and secure the attenuation by only designing the filter configuration.

One object of the present invention is to provide a filter device including a multiplexer that shares a single antenna with a plurality of filters, wherein the filter device can improve the attenuation characteristics of the plurality of filters in any frequency band, and a SAW filter applied thereto.

A filter device according to a first aspect of the present invention comprises a SAW filter including first and second filter circuits, each of which is connected to a piezoelectric substrate, first and second signal terminals formed on the piezoelectric substrate, a common terminal, and a ladder-type filter including a plurality of surface acoustic wave resonators each configured between the first and second signal terminals and the common terminal,

It is connected to a wiring that connects the connection point of the first and second filter circuits and the antenna port installed externally of the SAW filter through the common terminal, and has a matching circuit for phase matching that is commonly applied to the first and second filter circuits,

The above matching circuit has an inductor and a capacitor connected in series between the wiring and ground potential.

A filter device according to a second aspect of the present invention has a matching circuit having an elastic surface wave resonator instead of the capacitor.

Preferably, the inductor for the matching circuit is formed outside the SAW filter,

A capacitor or elastic surface wave resonator for the above matching circuit is formed on the piezoelectric substrate.

In this case, more preferably, a configuration may be adopted in which the capacitor or elastic surface wave resonator for the matching circuit is connected to the line, and the inductor for the matching circuit is connected to ground potential.

In general, a configuration in which the inductor for the matching circuit and the capacitor or the elastic surface wave resonator are installed outside the SAW filter can be adopted.

The above matching circuit may have a plurality of elastic surface wave resonators, and a configuration in which the plurality of elastic surface wave resonators are connected in parallel may be adopted.

A filter device according to a third aspect of the present invention comprises a SAW filter including first and second filter circuits, each of which is connected to a piezoelectric substrate, first and second signal terminals formed on the piezoelectric substrate, a common terminal, and a ladder-type filter including a plurality of surface acoustic wave resonators each configured between the first and second signal terminals and the common terminal,

A phase matching circuit is provided that is connected to a wiring connecting a first signal port installed outside the SAW filter and the first signal terminal or a wiring connecting a second signal port and the second signal terminal,

The above matching circuit has an inductor and an elastic surface wave resonator connected in series between the wiring and the ground potential.

A SAW filter according to a fourth aspect of the present invention is a SAW filter comprising first and second filter circuits, each of which is connected to a piezoelectric substrate, first and second signal terminals formed on the piezoelectric substrate, a common terminal, and a ladder-type filter including a plurality of surface acoustic wave resonators each configured between the first and second signal terminals and the common terminal,

On the piezoelectric substrate, a capacitor or surface elastic wave resonator used in a matching circuit for phase matching applied to the first and second filter circuits is additionally formed.

A SAW filter according to a fifth aspect of the present invention is a SAW filter comprising first and second filter circuits each having one end connected to the other, each of the first and second signal terminals formed on the piezoelectric substrate, a common terminal, and a ladder-type filter including a plurality of surface acoustic wave resonators each configured between the first and second signal terminals and the common terminal, wherein a surface acoustic wave resonator used in a phase matching matching circuit applied to the first or second filter circuit is additionally formed on the piezoelectric substrate.

According to the present invention, in addition to the phase matching function of the matching circuit, an attenuation pole can be formed in the filter, thereby improving the attenuation characteristics of the filter at any frequency. In particular, by installing a matching circuit including a capacitor or a surface acoustic wave resonator in the wiring connecting the antenna port and the common terminal, an attenuation pole of the same frequency can be provided to the first and second filters, thereby improving the attenuation characteristics of the two filters simultaneously. Furthermore, by utilizing a surface acoustic wave resonator as the capacitance of the matching circuit, a plurality of attenuation poles can be formed in the filter simultaneously, thereby efficiently improving the attenuation characteristics of the filter.

Fig. 1 is a circuit diagram schematically showing the circuit configuration of a filter device according to the first embodiment of the present invention.
Fig. 2 is a cross-sectional view showing an example of a chip structure in which a SAW filter is formed.
Figure 3 is a circuit diagram of a matching circuit according to a first embodiment of the present invention.
Fig. 4 is a graph showing an example of the pass characteristics of the matching circuit of Fig. 3.
Fig. 5 is a circuit diagram of a conventional matching circuit.
Fig. 6 is a graph showing an example of the pass characteristics of the matching circuit of Fig. 5.
Figure 7A is a graph showing an example of the pass characteristics of a transmission filter of a filter device.
Figure 7B is a graph showing an example of the pass characteristics of a receiving filter of a filter device.
Fig. 8 is a circuit diagram showing a modified example of the filter device of Fig. 1.
Fig. 9 is a circuit diagram schematically showing the circuit configuration of a filter device according to a second embodiment of the present invention.
Figure 10A is an equivalent circuit diagram of an elastic surface wave resonator.
Figure 10B is a circuit diagram of a matching circuit using an elastic surface wave resonator.
Fig. 11 is a graph showing an example of the pass characteristics of the matching circuit of Fig. 10B.
Fig. 12A is a graph showing an example of the pass characteristics of the transmission filter of the filter device of Fig. 9.
Figure 12B is a graph that enlarges the display band of the graph of Figure 12A.
Fig. 13A is a graph showing an example of the pass characteristics of the receiving filter of the filter device of Fig. 9.
Figure 13B is a graph that enlarges the display band of the graph of Figure 13A.
Fig. 14A is a circuit diagram showing a modified example of the filter device of Fig. 9.
Fig. 14B is a circuit diagram showing another modified example of the filter device of Fig. 9.
Fig. 14C is a circuit diagram showing another modified example of the filter device of Fig. 9.
Figure 15A is a circuit diagram schematically showing the circuit configuration of a filter device according to a third embodiment of the present invention.
Figure 15B is a circuit diagram schematically showing a modified example of a filter device according to a third embodiment of the present invention.

First embodiment

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 is a circuit diagram schematically showing the circuit configuration of a filter device according to the first embodiment of the present invention.

The filter device (1) of the present embodiment has a duplexer (10) as a SAW filter of the present invention, a phase matching matching circuit (50) connected between an antenna port (AP) and a common terminal of the duplexer (10), a phase matching matching circuit (150) connected between a transmission port (Tx) and a signal terminal (ST1), and a phase matching matching circuit (160) connected between a reception port (Rx) and a signal terminal (ST2).

The duplexer (10) has a filter circuit (20) for forming a transmission filter and a filter circuit (30) for forming a reception filter. The transmission filter passes a signal in a transmission band among high-frequency signals input from a transmission port (Tx) as a transmission signal to an antenna (ANT) and suppresses signals of other frequencies. The reception filter passes a signal in a reception band different from the transmission band among high-frequency signals input from an antenna (ANT) as a reception signal to a reception port (Rx) and suppresses signals of other frequencies.

The filter circuit (20, 30) is formed on a piezoelectric substrate (100) described later and is composed of a ladder-type filter circuit including a plurality of elastic surface wave resonators, and one end of which is connected to each other.

The filter circuit (20) is connected between the common terminal (CT) on the antenna port (AP) side and the signal terminal (ST1) on the transmission port (Tx) side. The filter circuit (30) is connected between the common terminal (CT) on the antenna port (AP) side and the signal terminal (ST2) on the reception port (Rx) side.

The filter circuit (20) includes series resonators (S1 to S3) and parallel resonators (P1, P2) as elastic surface wave resonators. A plurality of series resonators (S1 to S3) are connected in series between a signal terminal (ST1) and a common terminal (CT), and one end of the parallel resonators (P1, P2) is connected to a wiring connecting the series resonators (S1 to S3), and the other end is connected to a ground terminal (GT) connected to a ground potential.

The filter circuit (30) includes series resonators (S1 to S3) and parallel resonators (P1, P2) as elastic surface wave resonators. A plurality of series resonators (S1 to S3) are connected in series between a signal terminal (ST2) and a common terminal (CT), and one end of the parallel resonators (P1, P2) is connected to a wiring connecting the series resonators (S1 to S3), and the other end is connected to a ground terminal (GT) connected to a ground potential.

In addition, the configuration of the filter circuit (20, 30) is not limited, and the configurations of the filter circuit (20) and the filter circuit (30) may be different, and the number of surface elastic wave resonators is not limited. In addition, although a configuration is adopted in which a parallel resonator (P1) is installed between the series resonator (S1) and the series resonator (S2) on the common terminal (CT) side, it is also possible to install the parallel resonator (P1) on the common terminal (CT) side rather than the series resonator (S1).

The surface acoustic wave resonator formed on the piezoelectric substrate (100) has an Inter Digital Transducer (IDT) and reflectors positioned on both sides thereof, although not shown. The IDT and the reflector are patterned by a primary electrode (110), which is a metal film formed directly on the piezoelectric substrate (100) as shown in Fig. 2. The primary electrode (110) is formed of a thin film made of, for example, Cu. In addition, the surface acoustic wave resonator is covered with an insulating film (130).

The signal terminals (ST1, ST2), common terminal (CT), ground terminal (GT) and wiring are formed of a thick secondary electrode (120) made of, for example, Al.

Additionally, the duplexer (10) may be a SAW filter chip as shown in Fig. 2, or may be a SAW filter chip as shown in Fig. 2 mounted on a support substrate and packaged.

Returning to Fig. 1, the matching circuit (150) is a circuit for suppressing signal reflection by adjusting the phase (impedance adjustment) between the filter circuit (20) and the circuit connected to the transmission port (Tx), and is composed of an inductor (L) whose one end is connected to the wiring connecting the transmission port (Tx) and the signal terminal (ST1), and whose other end is connected to ground potential. The inductor (L) may be formed in the package of the duplexer (10) or may be installed outside the duplexer (10).

The matching circuit (160) is a circuit for suppressing signal reflection by adjusting the phase (impedance adjustment) between the filter circuit (30) and the circuit connected to the receiving port (Rx), and is composed of an inductor (L) whose one end is connected to the wiring connecting the receiving port (Rx) and the signal terminal (ST2), and whose other end is connected to ground potential. The inductor (L) may be formed in the package of the duplexer (10) or may be installed outside the duplexer (10).

The matching circuit (50) is connected to a common terminal (CT) on a piezoelectric substrate (100) and a wiring (WR) connecting an antenna port (AP) installed on the outside of the piezoelectric substrate (100), and has an inductor (L) and a capacitor (C) connected in series between the wiring (WR) and the ground potential, and is a phase matching circuit commonly applied to filter circuits (20, 30).

Fig. 3 shows an equivalent circuit of a matching circuit (50), and Fig. 4 shows an example of the pass characteristics of the matching circuit of Fig. 3.

The matching circuit (50) is a notch filter circuit using an inductor (L) and a capacitor (C). By adding a capacitor (C) in series to the matching circuit (50) in addition to the inductor (L) and adjusting the values of the inductor (L) and the capacitor (C), as shown in Fig. 4, an attenuation pole (AP0) is formed at a desired frequency (in this example, around 1500 MHz), and a large attenuation amount can be obtained.

As described above, since the matching circuit (50) is commonly applied to the filter circuits (20, 30), an attenuation pole (AP0) of the same frequency can be formed on both sides of the transmission filter including the filter circuit (20) and the reception filter including the filter circuit (30).

In general, for phase adjustment between circuits, a matching circuit (300) composed only of an inductor (L) such as that shown in Fig. 5 is used. However, in a matching circuit (300) composed only of an inductor (L), as shown in Fig. 6, an attenuation pole cannot be formed around 1500 MHz, and the attenuation amount around 1500 MHz cannot be significantly controlled.

The matching circuit (300) without a capacitor (C) is a circuit for phase adjustment only. Meanwhile, the matching circuit (50) shown in Fig. 3, in addition to the phase adjustment function, also has the function of providing an attenuation pole (AP0) of the same frequency to both sides of the transmission filter including the filter circuit (20) and the reception filter including the filter circuit (30). This is an important point of the present invention.

Figures 7A and 7B illustrate examples of the pass characteristics of a transmitting filter and a receiving filter. From Figures 7A and 7B, it can be seen that an attenuation pole is formed at 1575.42 MHz by a matching circuit (50) in both filters.

According to this embodiment, the attenuation of an arbitrary but identical frequency band other than the passband of the transmission filter and the reception filter can be increased.

Fig. 8 is a modified example of the filter device (1) shown in Fig. 1, and the configuration of the matching circuit (50B) in the filter device (1') shown in Fig. 8 is different from the matching circuit (50) of the filter device (1) shown in Fig. 1, and the other configurations are the same.

The capacitor (C) of the matching circuit (50B) is connected in series with the inductor (L) installed on the outside of the piezoelectric substrate (100), but the capacitor (C) of the matching circuit (50B) is formed as the above-mentioned primary electrode on the piezoelectric substrate (100), one end is formed on the piezoelectric substrate (100) and is connected to a signal terminal (ST) that is also connected to the inductor (L), and the other end is formed on the piezoelectric substrate (100) and is connected to a ground terminal (GT) that is connected to a ground potential.

By configuring the matching circuit (50B) in this manner, the matching circuit (50) can be configured by adding only an inductor (L) to the outside of the duplexer (10) or to the package of the duplexer (10) without installing a capacitor (C) outside of the duplexer (10), thereby miniaturizing the device.

Second embodiment

Fig. 9 is a circuit diagram schematically showing the circuit configuration of a filter device (1B) according to a second embodiment of the present invention. Furthermore, in Fig. 9, descriptions of the same components as those of the filter device (1) according to the first embodiment are omitted.

The matching circuit (50C) of the filter device (1B) according to the second embodiment is a phase matching circuit connected between the antenna port (AP) and the common terminal (CT) of the duplexer (10), and includes an inductor (L) and a surface acoustic wave resonator (Re) that are connected in series. Specifically, one end of the inductor (L) is connected to a wiring connecting the common terminal (CT) formed on the piezoelectric substrate (100) and the antenna port (AP), and the other end is connected to a signal terminal (ST) formed on the piezoelectric substrate (100). The surface acoustic wave resonator (Re) has an IDT (Inter Digital Transducer) (not shown) and reflectors arranged on both sides thereof. The surface acoustic wave resonator (Re), like the series resonators (S1 to S3) and the parallel resonators (P1, P2), is formed by a primary electrode on the piezoelectric substrate (100). The elastic surface wave resonator (Re) has one end connected to a signal terminal (ST) formed on a piezoelectric substrate (100), and the other end connected to a ground terminal (GT) connected to a ground potential formed on the piezoelectric substrate (100).

By using a surface elastic wave resonator (Re) instead of a capacitor (C) in the matching circuit (50C), as described later, multiple (two) attenuation poles (AP1, AP2) with different frequencies can be formed. That is, since the matching circuit (50C) is commonly applied to the filter circuits (20, 30), multiple attenuation poles (AP1, AP2) with different frequencies can be formed on both sides of the transmission filter including the filter circuit (20) and the reception filter including the filter circuit (30).

Fig. 10A shows an equivalent circuit diagram of a surface elastic wave resonator (Re), and Fig. 10B shows a circuit diagram of a matching circuit (50C) to which the surface elastic wave resonator (Re) is applied.

As shown in Fig. 10A, the equivalent circuit (ReC) of the elastic surface wave resonator (Re) includes an inductor (L1), a capacitor (C1), and a resistor (R1) connected in series between the input port (IN) and the output port (OUT), and a capacitor (C0) connected in parallel with the inductor (L1), the capacitor (C1), and the resistor (R1). When this elastic surface wave resonator (Re) is applied to a matching circuit (50C), the matching circuit (50C) is divided into a filter element (ATP1) composed of an inductor (L) and a capacitor (C0) connected in series between a line between an input port (IN) and an output port (OUT) and a ground potential, as shown in FIG. 10B, and a filter element (ATP2) composed of an inductor (L), an inductor (L1), and a capacitor (C1) connected in series between a line between an input port (IN) and an output port (OUT) and a ground potential.

Fig. 11 shows an example of the pass characteristics of a single matching circuit (50C).

As can be seen in Fig. 11, by applying a surface elastic wave resonator (Re) to a matching circuit (50C), attenuation poles (AP1, AP2) can be formed at two different frequencies. The attenuation pole (AP1) is formed by a filter element (ATP1), and the attenuation pole (AP2) is formed by a filter element (ATP2).

In this way, by applying a single elastic surface wave resonator (Re) to the matching circuit (50C) instead of a single capacitor (C), two different attenuation poles (AP1, AP2) can be formed.

The pass characteristics of the transmission filter of the filter device (1B) to which the matching circuit (50C) is applied are shown in Figs. 12A and 12B, and the pass characteristics of the reception filter of the filter device (1B) to which the matching circuit (50C) is applied are shown in Figs. 13A and 13B.

In FIGS. 12A, 12B and 13A, 13B, the dotted lines represent the pass characteristics of the filter device (1B), and the comparative example represented by the solid lines, although not shown, represents the pass characteristics of a filter device that is not equipped with a capacitance or a surface elastic wave resonator in the matching circuit on the antenna port side, and is equipped only with an inductor (L).

In Figs. 12A, 12B and 13A, 13B, it can be seen that a large attenuation amount can be obtained by multiple attenuation poles at frequencies of 881.5 MHz and 1176.45 MHz.

According to this embodiment, by using a single elastic surface wave resonator (Re) instead of a single capacitor (C), it is possible to secure a large amount of attenuation at multiple (two) different frequencies outside the passbands of the transmission filter and the reception filter.

Fig. 14A shows a modified example of the filter device (1B) of Fig. 9. In addition, in Fig. 14A, descriptions of the same components as the filter device (1) according to the first embodiment and the filter device (1B) according to the second embodiment are omitted.

In the filter device (1B') shown in Fig. 14A, one end of a surface elastic wave resonator (Re) of a matching circuit (50D) installed on the antenna port (AP) side is connected to a wiring connecting a connection point (CP) of the filter circuit (20) and the filter circuit (30) and a common terminal (CT), and the other end of the surface elastic wave resonator (Re) and one end of an inductor (L) are connected via a signal terminal (ST) formed on a piezoelectric substrate (100), and the other end of the inductor (L) is connected to ground potential. That is, the order of the inductor (L) and the surface elastic wave resonator (Re) connected in series is inverse to that of the matching circuit (50C) of the filter device (1B) described above.

According to this configuration, a matching circuit (50D) can be formed simply by connecting an inductor (L) as an external component to the signal terminal (ST) of the duplexer (10).

Additionally, in the first embodiment described above, it is also possible to reverse the connection relationship between the inductor (L) and capacitor (C) used in the matching circuit (50).

Fig. 14B shows another modified example of the filter device (1B) of Fig. 9. In addition, in Fig. 14B, descriptions of the same components as the filter device (1) according to the first embodiment and the filter device (1B) according to the second embodiment are omitted.

The elastic surface wave resonator (Re) applied to the matching circuit (50E) of the filter device (1B'') shown in Fig. 14B is not formed on the piezoelectric substrate (100) of the duplexer (10), but is formed on another SAW filter (500).

In addition, it is not limited to the SAW filter (500), and an elastic surface wave resonator (Re) additionally formed in another SAW device, such as another duplexer or multiplexer, can be used.

In addition, it is also possible to use a capacitor (C) additionally formed in another SAW device, such as another duplexer or multiplexer, as the capacitor (C) applied to the matching circuit (50) of the first embodiment.

Fig. 14C shows another modified example of the filter device (1B) of Fig. 9. In addition, in Fig. 14C, descriptions of the same components as the filter device (1) according to the first embodiment and the filter devices (1B, 1B', 1B'') according to the second embodiment are omitted.

The matching circuit (50F) installed on the antenna port (AP) side of the filter device (1B''') shown in Fig. 14C is equipped with two surface elastic wave resonators (Re1, Re2), and the surface elastic wave resonators (Re1, Re2) are formed on a piezoelectric substrate (100) and are connected in parallel. The surface elastic wave resonators (Re1, Re2) have the same configuration as the above-described surface elastic wave resonator (Re), but the values of the inductor and capacitor are each different according to the frequency of the attenuation pole to be formed.

By adopting this configuration, it is possible to additionally provide a plurality of attenuation poles of arbitrary frequencies to the receiving filter and the transmitting filter configured in the filter circuit (20) and the filter circuit (30), respectively, and as a result, it becomes possible to secure a large attenuation amount in a wide frequency band.

In addition, although this example exemplifies a case in which multiple surface elastic wave resonators (Re1, Re2) are connected in parallel and used, it is also possible to connect multiple capacitors in parallel and use them. Furthermore, although the surface elastic wave resonators (Re1, Re2) are connected to the wiring (WR) side and the inductor (L) is connected to the ground potential side, the inverse relationship is also possible.

Third embodiment

Fig. 15A is a circuit diagram schematically showing the circuit configuration of a filter device (2) according to a third embodiment of the present invention. Furthermore, in Fig. 15A, descriptions of the same components as those in the first and second embodiments are omitted.

The filter device (2) has a duplexer (10B) as a SAW filter of the present invention, a phase matching matching circuit (60) connected between an antenna port (AP) and a common terminal (CT) of the duplexer (10B), a phase matching matching circuit (200) connected between a transmission port (Tx) and a signal terminal (ST1), and a phase matching matching circuit (160) connected between a reception port (Rx) and a signal terminal (ST2).

The matching circuit (60 and 160) consists only of an inductor (L), and a detailed description is omitted.

A feature of the filter device (2) according to the present embodiment is that a matching circuit (200) is connected to a wiring (WR1) connecting a signal terminal (ST1) formed on a piezoelectric substrate (100) and a transmission port (Tx), and this matching circuit (200) has an inductor (L) and a surface elastic wave resonator (Re) connected in series between the wiring (WR1) and a ground potential.

The elastic surface wave resonator (Re) is formed on a piezoelectric substrate (100), has one end connected to a signal terminal (ST3) formed on the piezoelectric substrate (100), and has the other end connected to a ground terminal (GT) formed on the piezoelectric substrate (100).

In addition to the phase adjustment function between the filter circuit (20) and the circuit connected to the transmission port (Tx), the matching circuit (200) can provide a plurality of attenuation poles to the transmission filter including the filter circuit (20) according to the same principle as described in the second embodiment. As a result, a large attenuation amount can be secured in a wide band of the transmission filter including the filter circuit (20).

In addition, in this embodiment, the surface elastic wave resonator (Re) is formed on the piezoelectric substrate (100), but as described in the above embodiment, it may be formed on the outside of the piezoelectric substrate (100). In addition, it is also possible to use multiple surface elastic wave resonators (Re), and it is also possible to reverse the connection order of the inductor (L) and the surface elastic wave resonator (Re).

Fig. 15B illustrates a modified example of a filter device (2) according to a third embodiment of the present invention. Furthermore, in Fig. 15B, descriptions of the same components as those in the first to third embodiments are omitted.

A feature of the filter device (2B) according to the present embodiment is that a matching circuit (210) is connected to a wiring (WR2) connecting a signal terminal (ST2) formed on a piezoelectric substrate (100) and a receiving port (Rx), and this matching circuit (210) has an inductor (L) and a surface elastic wave resonator (Re) connected in series between the wiring (WR2) and a ground potential.

The elastic surface wave resonator (Re) is formed on a piezoelectric substrate (100), has one end connected to a signal terminal (ST4) formed on the piezoelectric substrate (100), and has the other end connected to a ground terminal (GT) formed on the piezoelectric substrate (100).

In addition to the phase adjustment function between the filter circuit (30) and the circuit connected to the transmission port (Tx), the matching circuit (210) can provide a plurality of attenuation poles to the transmission filter including the filter circuit (30) according to the same principle as described in the second embodiment. As a result, a large attenuation amount can be secured in a wide band of the transmission filter including the filter circuit (30).

Although the surface elastic wave resonator (Re) is formed on the piezoelectric substrate (100), as described in the above embodiment, it may be formed on the outside of the piezoelectric substrate (100). In addition, it is also possible to use multiple surface elastic wave resonators (Re), and it is also possible to reverse the connection order of the inductor (L) and the surface elastic wave resonator (Re).

Furthermore, the present invention is not limited to the embodiments described above. Those skilled in the art can make various additions and modifications within the scope of the present invention.

In each of the above embodiments, the SAW filter of the present invention has been described as an example of applying it to a duplexer, but it is not limited thereto and may be applied to a multiplexer having three or more different filter circuits.

In each of the above embodiments, two filter circuits (20, 30) are used for the receiving circuit and the transmitting circuit, but it is also possible to use the filter circuits (20, 30) only for the receiving circuit or only for the transmitting circuit.

In the above embodiment, the arrangement of the common terminal (CT) and the connection point (CP) is different, but it is also possible to make them the same position.

1, 1', 1B, 1B', 1B'', 1B''', 2, 2B: Filter device
10, 10B: Duplexer (SAW filter)
20: Filter circuit (first filter circuit)
30: Filter circuit (second filter circuit)
50, 50B, 50C, 50D, 50E, 50F: Matching circuit
60: Matching circuit
100: Piezoelectric substrate
110: Primary electrode
120: Secondary electrode
130: Insulating film
150: Matching circuit
160: Matching circuit
200: Matching circuit
210: Matching circuit
300: Matching circuit
500: SAW filter
ANT: Antenna
AP0, AP1, AP2: Attenuation poles
AP: Antenna port
ATP1: filter element
ATP2: filter element
C, C0, C1: Capacitors
CP: Junction Point
CT: Common terminal
GT: Ground terminal
IN: Input port
L: Inductor
L1: Inductor
IN: Input port
OUT: Output port
P1, P2: Parallel resonators
Re, Re1, Re2: surface elastic wave resonators
ReC: Equivalent circuit
R1: Resistance
Tx: Transmitting port
Rx: receiving port
S1~S3: Series resonators (surface elastic wave resonators)
ST, ST1, ST2, ST3, ST4: signal terminals
WR, WR1, WR2: Wiring

Claims (12)

A SAW filter comprising first and second filter circuits each having one end connected to the other, the first and second signal terminals formed on the piezoelectric substrate, a common terminal, and a ladder-type filter including a plurality of surface elastic wave resonators each configured between the first and second signal terminals and the common terminal,
It is connected to a wiring that connects the connection point of the first and second filter circuits and the antenna port installed externally of the SAW filter through the common terminal, and has a matching circuit for phase matching that is commonly applied to the first and second filter circuits,
The above matching circuit is a filter device having an inductor and an elastic surface wave resonator connected in series between the wiring and the ground potential. delete In the first paragraph,
The inductor of the above matching circuit is formed outside the SAW filter,
A filter device, wherein the elastic surface wave resonator of the above matching circuit is formed on the piezoelectric substrate. In the third paragraph,
A filter device in which the elastic surface wave resonator of the above matching circuit is connected to a wiring connecting the connection point and the common terminal, and the inductor of the above matching circuit is connected to ground potential. In the first paragraph,
A filter device in which the inductor of the above matching circuit and the surface elastic wave resonator are installed outside the SAW filter. In the first paragraph,
A filter device in which the above matching circuit has a plurality of the above surface elastic wave resonators, and the plurality of the above surface elastic wave resonators are connected in parallel. In any one of the first and third to sixth clauses,
The above first filter circuit is used for a transmission filter,
The above second filter circuit is a filter device used in a receiving filter. delete A SAW filter comprising first and second filter circuits each having one end connected to the other, the first and second signal terminals formed on the piezoelectric substrate, a common terminal, and a ladder-type filter including a plurality of surface elastic wave resonators each configured between the first and second signal terminals and the common terminal,
A phase matching circuit is provided that is connected to a wiring connecting a first signal port installed outside the SAW filter and the first signal terminal or a wiring connecting a second signal port and the second signal terminal,
The above matching circuit is a filter device having an inductor and an elastic surface wave resonator connected in series between the wiring and the ground potential. In paragraph 9,
The inductor for the above matching circuit is formed outside the SAW filter,
A filter device in which an elastic surface wave resonator for the above matching circuit is formed on the piezoelectric substrate. In claim 9 or 10,
The above first filter circuit is used for a transmission filter,
The above second filter circuit is a filter device used in a receiving filter. delete