JPH09232906A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve attenuation characteristics toward lower frequencies by connecting an IDT SAW resonator as an attenuation improvement SAW resonator in parallel and in cascade connection with an n-stage ladder circuit configuration section so as to form a reflector type SAW resonator without generating spurious radiation. SOLUTION: An IDT SAW resonator 103 does not have a reflector at both ends of an IDT different from a reflector type SAW resonator, but the number of pairs of the IDTs 111 is selected to be a multiple structure of 200 pairs or over, then internal reflection in the inside of the IDTs to generate a standing wave on the IDTs thereby causing the resonance. The resonator type SAW filter of n-stage of a latter configuration of the reflector type SAW resonators is formed by connecting an IDT SAW resonator 103 as the attenuation improvement SAW resonator in parallel and in cascade with the n-stage latter type circuit configuration section 101. Thus even when an electrode finger film thickness H/λ of the SAW resonator is selected about 0.08 to 0.1, the attenuation characteristics toward lower frequencies is improved without causing spurious radiation in the pass band of the filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter, and more particularly to a resonator type surface acoustic wave filter using a surface acoustic wave resonator.

[0002]

2. Description of the Related Art Surface acoustic waves (SAW)
A wave (hereinafter, abbreviated as SAW) device is an interdigital transducer or a transducer (IDT: IDT) arranged on a piezoelectric substrate.
It is a device that performs electro-acoustic wave conversion by what is called an interdigital transducer. Among them, the SAW filter has features of small size, light weight, and no adjustment, and since the photolithography technique used for manufacturing a semiconductor device can be used in the manufacturing process, it is excellent in mass productivity. Since the SAW filter can arbitrarily and independently control the amplitude characteristic and the phase characteristic, a communication filter such as a PIF (video intermediate frequency) filter and a VSB (residual sideband) filter,
Applications are expanding more and more as filters for various digital signal processing.

Generally, a resonator type SAW filter has an ID
A filter is constructed by using a reflector type SAW resonator composed of T and a grating reflector arranged at both ends thereof. The structure of the resonator type SAW filter is shown in FIG.
As shown in FIG. 9, FIG. 7 is a diagram showing a configuration of a reflector type SAW resonator. The resonator type SAW filter can be classified into a ladder circuit configuration type shown in FIG. 8 and a dual mode type shown in FIG. Resonator type SA of ladder circuit configuration type
In principle, the W filter has the features of low loss, high attenuation, narrow band, and no matching circuit required.

In FIG. 7, 1 is an IDT of a reflector type SAW resonator, and 2 is a grating reflector of a reflector type SAW resonator. In FIG. 8, 3 is a reflector type SA
It is a W resonator, which is a simplified representation of the reflector SAW resonator 3 of FIG. 7. In the ladder circuit configuration described below, the SAW resonator is abbreviated as shown in FIG.

FIG. 10 is a diagram showing the structure of a reflector type SAW resonator 10, FIG. 11 is an equivalent circuit of the reflector type SAW resonator, and FIG. 12 is a reactance characteristic diagram thereof.

In FIG. 10, 11 is a piezoelectric substrate, 12 is an IDT, 13 and 14 are grating reflectors, 15 is an input terminal, 16 is an output terminal, and the arrow 17 indicates the propagation direction of the excited SAW. There is.

The electrode fingers of the IDT 12 of the reflector type SAW resonator 10 and the grating reflectors 13 and 14 are arranged at a λ / 2 pitch (λ: wavelength), respectively.
Similarly, the distance between the DT 12 and the grating reflectors 13 and 14 is also λ / 2 pitch. FIG.
As shown in 0, a normal reflector SAW resonator having a constant crossing length of each electrode finger of the IDT 12 is generally used.

The IDT 12 and the grating reflector 1
The patterning of 3, 14, the input terminal 15 and the output terminal 16 is made by a photolithography technique. ID
As the metal material of T12 and the grating reflectors 13 and 14, a metal material having a low specific gravity is used in order to reduce the load on the vibration of the SAW and reduce the propagation loss. Generally, aluminum, copper, or silicon is contained in several%. Aluminum alloy is used. Further, gold is often used for the metal material of the input terminal 15 and the output terminal 16 in order to facilitate bonding.

The operating principle of the reflector type SAW resonator will be described with reference to FIGS. 10 and 11.

When a high frequency electric signal is input to the input terminal 15 shown in FIG. 10, SAW is generated in the IDT 12, and
It propagates in both directions as indicated by the arrow 17 in 0. This excited SAW is reflected by the elastic and electrical perturbation effects on the grating reflectors 13 and 14 arranged at both ends of the IDT 12, and travels multiple times between the grating reflector 13 and the grating reflector 14. And I
On the DT 12, the transmitted wave and the reflected wave overlap with each other to generate a standing wave of SAW and a resonance phenomenon occurs.

FIG. 11 is an electrical equivalent circuit diagram of the SAW resonator. As shown in FIG. 11, the SAW resonator is connected in parallel with a series circuit of R, L and C and a parallel circuit like the crystal oscillator. It can be represented by the capacitance C0 of the IDT. The reactance characteristic of this electrically equivalent circuit is shown by the curve 18 in FIG.
, The resonance frequency fr and the anti-resonance frequency fa
Has double resonance characteristics. Therefore, SAW
A bandpass filter can be configured by forming the resonator in a ladder circuit configuration like a conventionally known LC filter.

Resonator type SAW of the above ladder type circuit configuration type
The principle of the filter will be described. 13 and 14 are diagrams showing the principle of a resonator type SAW filter of a ladder type circuit configuration, and FIG. 13 is a diagram showing a circuit configuration in which a SAW resonator is connected to a one-stage ladder type circuit.

In FIG. 13, 21 is a series arm SAW resonator, 22 is a parallel arm SAW resonator, 23 is an input terminal, 24
Is an output terminal, and the SAW resonator is composed of a ladder circuit as shown in the figure.

FIG. 14 is a characteristic diagram showing a reactance characteristic and a transmission characteristic in the case where the SAW resonator has a one-stage ladder circuit configuration as shown in FIG. A curve 25 in FIG. 14 is the reactance characteristic of the series arm SAW resonator 21, and a curve 26 is the reactance characteristic of the parallel arm SAW resonator 22. Further, f1 and f2 are the resonance frequency and antiresonance frequency of the parallel arm SAW resonator 22, respectively, and f3 and f4 are the resonance frequency and antiresonance frequency of the series arm SAW resonator 21, respectively. When the series arm SAW resonator and the parallel arm SAW resonator are configured so that the anti-resonance frequency f2 of the parallel arm SAW resonator and the resonance frequency f3 of the series arm SAW resonator are substantially matched, a curve 27 in FIG. 14 is obtained. Transmission characteristics (S2
It is a well-known fact from the conventional network theory that a bandpass filter having 1) can be constructed.

Since a resonator type filter having a one-stage ladder circuit structure composed of one series arm SAW resonator 21 and parallel arm SAW resonator 22 as shown in FIG. 13 has a small attenuation amount, the attenuation amount is usually large. In order to achieve this, the SAW resonator has a multi-stage ladder circuit configuration.

Conventionally, when a normal type reflector SAW resonator 10 as shown in FIG. 10 is used to form a ladder circuit as shown in FIG. 13, the IDT 12 and the grating reflector 13 of the reflector SAW resonator 10 are arranged. , 14, the electrode finger film thickness H is set to be relatively thick and set so that H / λ ≧ 0.08 to 0.1. This H / λ ≧ 0.08 to 0.1 is a SAW whose pass band is 25 MHz and whose center frequency is 850 MHz band.
It is an example when it is used for a filter. Further, this film thickness condition is a condition when aluminum, copper, or an aluminum alloy containing several% of silicon is used as the metal material of the IDT and the grating reflector.

Hereinafter, a case of forming a ladder circuit using a normal type reflector SAW resonator will be described in detail with reference to FIGS.

15 to 18 show the case where the electrode finger film thickness H is thin in the conventional normal type reflector SAW resonator shown in FIG. 10 (for example, H / λ≤0.08 to 0.1). SA
3 is a circuit configuration and a transmission characteristic of a resonator-type SAW filter in which a W resonator and its SAW resonator are configured in a ladder circuit.

FIGS. 15 and 16 show the circuit configuration and the transmission characteristics thereof when the SAW resonators are connected in series.
In the characteristic diagram in FIG. 6, the vertical axis represents the insertion loss S21 and the horizontal axis represents the frequency. Reference numeral 31 in FIG. 15 is a reflector type SAW resonator, and FIG.
Reference numeral 32 is a transmission curve when the reflector type SAW resonator 31 is connected in series, 33 is an anti-resonance frequency, and 34 is a spurious (sub-resonance).

FIGS. 17 and 18 show the circuit configuration of a resonator type SAW filter in which SAW resonators are configured in n stages (n = 1, 2, 3, ...: Integer), and their transmission characteristics.
The vertical axis of the characteristic diagram in FIG. 18 represents the insertion loss S21, and the horizontal axis represents the frequency. In FIG. 17, 35 is a series arm SAW resonator for n-stage ladder circuit configuration, and 36 is a parallel arm S for n-stage ladder circuit configuration.
AW resonator, 37 in FIG. 18 is a transmission curve of a resonator type SAW filter having an n-stage ladder circuit configuration, and 38 is a parallel arm SA.
W resonator spurious, 39 series arm SAW resonator spurious, 40 pass band, 41 low-side attenuation band, 42
Is the attenuation range on the high frequency side.

As shown in FIG. 16, a conventional reflector type SA is used.
When the electrode finger thickness H of the W resonator 31 is thin (for example, H /
A large spurious characteristic occurs near the anti-resonance frequency for λ ≦ 0.08 to 0.1). When SAW resonators are connected in a ladder circuit in this film thickness range to form a filter, ripples are generated in the pass band 40 due to the spurious 38 of the parallel arm SAW resonator as shown in FIG.

On the other hand, FIGS. 19 to 22 show the normal reflector SAW resonator shown in FIG. 10 when the electrode finger thickness H is large (for example, H / λ ≧ 0.08 to 0.1). SA
7 is a transmission characteristic of a resonator type SAW filter in which a W resonator and its SAW resonator are configured in a ladder circuit.

FIG. 19 and FIG. 20 show the circuit configuration and its transmission characteristics when the SAW resonators are connected in series.
The vertical axis of the characteristic diagram in 0 is the insertion loss S21, and the vertical axis is frequency. Reference numeral 51 in FIG. 19 is a SAW resonator, and reference numeral 52 in FIG. 20 is a transmission curve when the SAW resonator 51 is connected in series.
3 is an anti-resonance frequency and 54 is a spurious.

21 and 21 show a resonator type S in which SAW resonators are configured in n stages (n = 1, 2, 3, ...: Integer).
FIG. 2 is a circuit configuration of the AW filter and its transmission characteristics.
55 in 1 is a series arm SAW resonator for n-stage ladder circuit configuration, 56 is a parallel arm SAW resonator for n-stage ladder circuit configuration,
Reference numeral 57 in FIG. 22 is a resonator type SA having an n-stage ladder type circuit configuration.
Transmission curve of W filter, 58 is spurious of parallel arm SAW resonator, 59 is spurious of series arm SAW resonator, 6
0 is a pass band, 61 is a low-side attenuation range, and 62 is a high-side attenuation range.

As is clear from a comparison between FIGS. 16 and 20, the antiresonance frequency is obtained when the electrode finger film thickness H is thin (H / λ ≦ 0.08 to 0.1) as shown in FIG. Although a large spurious characteristic is generated in the vicinity, it is experimentally known that the frequency film thickness deviation of the spurious is extremely smaller than the film thickness deviation of the anti-resonance frequency.

Therefore, as shown in FIGS. 19 and 20, the electrode film thickness H of the IDT is increased (H / λ ≧ 0.08-0.
1) Then, the spurious 4 is located at a frequency position greatly separated from the antiresonance frequency 53. If the SAW resonator is configured in a ladder circuit and a filter configuration in this film thickness range, it is possible to suppress ripple generation in the pass band due to spurious of the parallel arm SAW resonator as shown in FIG.

For the above reason, in the resonator type SAW filter having the ladder type circuit structure using the conventional normal type reflector type SAW resonator as shown in FIG. 10, the IDT of the SAW resonator and the electrode fingers of the grating reflector are used. The film thickness H is set to be relatively thick and set so that H / λ ≧ 0.08 to 0.1.

By the way, in addition to the multi-stage ladder circuit configuration described above as a method of improving the attenuation characteristic of the resonator type SAW filter of the ladder circuit configuration type, the transmission characteristic of the filter is newly attenuated at a frequency position outside the attenuation range. There is a method of providing a pole. The method will be described below with reference to FIGS. 23 to 28 show a method of improving the attenuation characteristic on the high frequency side, and FIGS. 29 to 34 show a method of improving the attenuation characteristic on the low frequency side.

23 and 24 show a conventional reflector type SAW.
1 is a circuit configuration of a resonator type SAW filter in which a resonator is configured in an n-stage ladder type circuit and its transmission characteristics. In FIG. 23, 71 is a series arm SAW resonator for a ladder circuit configuration, and 72 is a parallel arm SAW resonator for a ladder circuit configuration. Further, 73 in FIG. 24 is a transmission characteristic of a resonator type SAW filter having an n-stage ladder type circuit configuration, and f1 in the figure is a parallel arm SAW resonator 7.
At the same time as the resonance frequency of 2, the attenuation pole is on the low frequency side of the filter characteristic, and f3 is the anti-resonance frequency of the series arm SAW resonator 71 and at the same time is the attenuation pole on the high frequency side of the filter characteristic. Further, 74 is a pass band, and 75 is a high-side attenuation band.

25 and 26 show the circuit configuration of the SAW resonator for improving the attenuation characteristic on the high frequency side and its transmission characteristic. Reference numeral 76 in FIG. 25 is a SAW resonator for improving the attenuation characteristic on the high frequency side. Further, reference numeral 77 in FIG. 26 is a transmission characteristic when the high-frequency side attenuation characteristic improving SAW resonator 76 is connected in series, and f3 is an anti-resonance frequency of the SAW resonator 76.

Here, the structure of the SAW resonator 76 for improving the attenuation characteristic on the high frequency side is often the same as that of the conventional normal type reflector SAW resonator shown in FIG. 10, and its IDT and grating reflector. The electrode finger film thickness is also set relatively thick as described above, and is set so that H / λ ≧ 0.08 to 0.1. However, like the SAW resonators 71 and 72 for forming a ladder circuit, this film thickness condition is a condition when aluminum, copper, or an aluminum alloy containing several% of silicon is used as the metal material of the electrode fingers. In addition, the anti-resonance frequency f3 of the SAW resonator 76 for improving the damping characteristic on the high frequency side is as shown in FIG.
Since it is necessary to make the frequency higher than the anti-resonance frequency f2 of the series arm SAW resonator 71 for the ladder type circuit configuration in the middle, each electrode of the IDT and the grating reflector of the SAW resonator 76 for improving the attenuation characteristic on the high frequency side. The pitch between fingers is made shorter than the pitch of the series arm SAW resonator 71 for the ladder circuit configuration.

27 and 28 show the circuit configuration and the transmission characteristics thereof when the circuit configurations of FIG. 23 and FIG. 25 are cascade-connected. As shown in the transmission characteristic 78 of FIG. 28,
When the SAW resonators 76 for improving the attenuation characteristic on the high frequency side are connected in series in series in an n-stage ladder circuit as shown in FIG. 23, a new attenuation pole f3 is generated on the higher frequency side than the attenuation pole f2, and The attenuation amount in the attenuation region 75 on the region side becomes larger than the attenuation amount shown in FIG. 24, so that the characteristic can be improved.

29 and 30 show a conventional reflector type SAW.
1 is a circuit configuration of a resonator type SAW filter in which a resonator is configured in an n-stage ladder type circuit and its transmission characteristics. In FIG. 29, 81 is a series arm SAW resonator for a ladder circuit configuration, and 82 is a parallel arm SAW resonator for a ladder circuit configuration. Further, reference numeral 83 in FIG. 30 denotes a transmission characteristic of a resonator type SAW filter having an n-stage ladder circuit configuration, and f1 in the figure denotes a resonance frequency of the parallel arm SAW resonance pendulum 82 and at the same time, a low range of the filter characteristic. Is a side attenuation pole, and f2 is an anti-resonance frequency of the series arm SAW resonator 81 and at the same time is a high range side attenuation pole of the fill characteristic. Further, 84 is a pass band, and 85 is a low-side attenuation band.

31 and 32 show the circuit configuration of the SAW resonator for improving the attenuation characteristic on the low frequency side and its transmission characteristic. Reference numeral 86 in FIG. 31 is a SAW resonator for improving the attenuation characteristic on the low frequency side. Further, 87 in FIG. 32 is a transmission characteristic when the SAW resonator 86 for improving the attenuation characteristic on the low frequency side is connected in parallel arms, and f4 is a resonance frequency of the SAW resonator 86.

SAW resonator 86 for improving low-frequency side attenuation characteristics
The structure of the conventional normal type reflector SAW shown in FIG.
Many are similar to the resonator, and the electrode finger film thickness of the IDT and the grating reflector thereof are made relatively thick as described above, and are set so that H / λ ≧ 0.08 to 0.1.
However, similar to the above, this film thickness condition is a condition when the metal material of the electrode finger is aluminum or copper, or an aluminum alloy containing several% of silicon is used. Further, the resonance frequency f4 of the SAW resonator 86 for improving the attenuation characteristic on the low frequency side is shown in FIG.
Since it is necessary to make the frequency lower than the resonance frequency f1 of the parallel arm SAW resonator 82 for the ladder circuit configuration in 0, each electrode of the IDT and the grating reflector of the SAW resonator 86 for improving the attenuation characteristic on the low frequency side. The pitch between fingers is made longer than the pitch of the parallel arm SAW resonator 82 for the ladder type circuit configuration.

FIGS. 33 and 34 show the circuit configuration and the transmission characteristics thereof when the circuit configuration diagrams of FIG. 29 and FIG. 31 are cascade-connected. As in the transmission characteristic 88 shown in FIG.
When the parallel arms are connected in cascade to the n-stage ladder circuit, the new attenuation pole f4 is generated on the lower frequency side than the attenuation pole f1, and the attenuation amount in the low-side attenuation region 85 increases from the attenuation amount shown in FIG. Therefore, the characteristics can be improved.

[0037]

Therefore, as described above, the resonator type SA in which the SAW resonator has the n-stage ladder type circuit configuration.
In the W filter, as shown in FIGS. 29 to 34, in order to improve the attenuation characteristic on the low frequency side with respect to the pass band,
As a SAW resonator for improving the attenuation characteristic on the low frequency side, a conventional reflector SAW resonator is cascaded in parallel with the n-stage ladder circuit shown in FIG. 29, and the low-frequency side attenuation pole f1 by the n-stage ladder circuit is formed. An attenuation pole f4 is newly generated on the lower frequency side to improve the attenuation characteristic on the low frequency side. In this case, the electrode finger thickness of the IDT of the SAW resonator for improving the attenuation characteristic on the low frequency side and the grating reflector is set to H / similar to the electrode finger film thickness of the SAW resonator of the n-stage ladder structure shown in FIG. λ ≧ 0.08
However, when the electrode finger thickness H / λ is set to about 0.08 to 0.1, the resonator type S
The transmission characteristics of the AW filter are as shown in FIGS. However, this film thickness condition is a condition when the metal material of the electrode finger is aluminum or an aluminum alloy containing copper or silicon by several%.

In FIG. 35, 81 is a series arm SAW resonator for n-stage ladder type circuit configuration, 82 is a parallel arm SAW resonator for n-stage ladder type circuit configuration, and 93 is a SAW for improving attenuation characteristics on the low frequency side. A resonator, and 94 in FIG. 36, the transmission characteristics of the resonator type SAW filter when the electrode finger thickness H / λ of the SAW resonator is set to about 0.08 to 0.1, and 95 is the low frequency side. Of the SAW resonator 93 for improving the attenuation characteristics of the above, 96 is a spurious due to the parallel arm SAW resonator for the ladder circuit configuration,
Reference numeral 97 is a spurious due to a series arm SAW resonator for a ladder circuit configuration, 98 is a pass band, and 99 is an attenuation band on the low band side.
Further, in FIG. 36, f4 is an attenuation pole by the reflector SAW resonator 86 for improving the attenuation characteristic on the low frequency side, f1 is an attenuation pole by the parallel arm resonator 82 for the ladder circuit configuration, and f2 is a ladder circuit. It is an attenuation pole by the series arm resonator 81 for composition.

As is apparent from FIG. 36, the electrode finger film thickness H / λ of the SAW resonator 93 for improving the attenuation characteristic on the low frequency side and the SAW resonators 81, 82 for forming a ladder circuit is 0.08 to 0.1.
When set to the vicinity, there arises a problem that spurious 95 of the SAW resonator 93 for improving the attenuation characteristic on the low frequency side occurs in the pass band 98 of the filter.

In order to improve this, when the electrode finger film thickness H / λ of the SAW resonator is made thicker than 0.1, the mass load of the electrode fingers and the acoustics of the regions where the electrode fingers exist and where they do not exist. Since the amount of impedance discontinuity increases, surface acoustic wave scattering and mode conversion into bulk waves occur.
The Q value of the resonator becomes low, which causes a problem that the characteristics of the filter deteriorate.

In the present invention, the electrode finger thickness H / H of the SAW resonator is
Even if λ is set in the vicinity of 0.08 to 0.1, spurious is not generated in the pass band of the filter, the attenuation characteristic on the low frequency side can be improved, and the Q value of the SAW resonator is not deteriorated. An object of the present invention is to provide a surface acoustic wave filter capable of improving only the attenuation characteristic.

[0042]

A surface acoustic wave filter according to the present invention comprises a surface acoustic wave resonator using interdigital transducers for converting an electric signal into a surface acoustic wave or a surface acoustic wave into an electric signal. A surface acoustic wave resonator having a resonance frequency lower than that of the parallel arm surface acoustic wave resonator for the ladder circuit configuration is further used as a surface acoustic wave resonator for improving the attenuation characteristic on the low frequency side. In a surface acoustic wave filter in which parallel arms are connected in cascade and the attenuation characteristic on the low frequency side is improved with respect to the pass band of the filter, the surface acoustic wave resonator for improving the attenuation characteristic is composed of an IDT surface acoustic wave resonator. There is.

In the surface acoustic wave filter according to the present invention, surface acoustic wave resonators using interdigital transducers for converting an electric signal into a surface acoustic wave or a surface acoustic wave into an electric signal are connected in a ladder shape. A surface acoustic wave resonator having a filter configuration and a resonance frequency lower than that of the parallel arm surface acoustic wave resonator for the ladder circuit configuration is further connected in parallel as a surface acoustic wave resonator for improving the damping characteristic on the low frequency side. However, in a surface acoustic wave filter having improved attenuation characteristics on the low frequency side with respect to the pass band of the filter, the surface acoustic wave resonator for improving attenuation characteristics has a spacing between the interdigital electrode and the grating reflector of 0.56λ.
.About.0.63.lamda. (.Lamda. Is the wavelength of the surface wave).

[0044]

BEST MODE FOR CARRYING OUT THE INVENTION The surface acoustic wave filter according to the present invention can be applied to a communication filter such as a PIF filter and a VSB filter, and a surface acoustic wave filter for digital signal processing.

FIG. 1 is a circuit configuration diagram of a resonator type SAW filter according to a first embodiment of the present invention, which is an example applied to a circuit configuration for improving attenuation characteristics on the low frequency side with respect to the pass band of the filter. is there. 2 is a diagram showing the transmission characteristics of the resonator type SAW filter. In FIGS. 1 and 2, the same or corresponding elements as those in FIGS. 35 and 36 are designated by the same reference numerals.

The resonator type SAW filter 100 shown in FIG.
In the figure, the part 101 is n having the same configuration as the conventional example.
Reference numeral 81 denotes a stepped ladder circuit configuration unit, 81 is a series arm SAW resonator for a ladder circuit configuration, and 82 is a parallel arm SAW for a ladder circuit configuration.
It is a resonator. Reference numeral 102 is a circuit component for improving the attenuation characteristic on the low frequency side, and 103 is an IDT SAW resonator (a surface acoustic wave resonator for improving the attenuation characteristic) installed as a SAW resonator for improving the attenuation characteristic. ).

Further, in FIG. 2, 104 is the transmission characteristic of the resonator type SAW filter in the circuit configuration method of the first embodiment, 105 is the spurious due to the parallel arm SAW resonator for the ladder type circuit configuration, and 106 is the ladder type circuit. Series arm SA for configuration
Spurious due to the W resonator, 107 is a pass band, and 108 is a low-side attenuation band. Further, in FIG. 2, f4 is an attenuation pole by the reflector SAW resonator 82 for improving the attenuation characteristic on the low frequency side, f1 is an attenuation pole by the parallel arm resonator 81 for the ladder circuit configuration, and f2 is a ladder type. It is an attenuation pole by the series arm resonator for circuit configuration (n-stage ladder type circuit configuration section 101).

The circuit configuration method is the same as that of the conventional circuit configuration shown in FIGS. 33 and 35, but in the resonator type SAW filter 100 according to the first embodiment, the SAW resonance for improving the attenuation characteristic on the low frequency side is obtained. IDT type SAW resonator 103 as a child
Have cascaded parallel arms.

FIG. 3 is a schematic diagram showing the IDT SAW resonator 103. In FIG. 3, 111 is IDT, 1
Reference numeral 12 is an input terminal, 113 is an output terminal, and 114 is a piezoelectric substrate. The electrode fingers of the IDT are arranged at a λ / 2 pitch. The IDT SAW resonator 103 has an ID
By making the logarithm of T more than 200 pairs,
It is a resonator that utilizes internal reflection in the IDT to generate a standing wave on the IDT to cause a resonance phenomenon.

The operation of the surface acoustic wave filter 100 configured as described above will be described below. First, the IDT SA
The W resonator 103 will be described. As shown in FIG.
The IDT SAW resonator 103 includes an IDT 111, an input terminal 112, an output terminal 113, and a piezoelectric substrate 114,
The electrode fingers of the IDT 111 are arranged at a λ / 2 pitch.

The IDT-type SAW resonator 103 is similar to that shown in FIG.
Unlike the reflector type SAW resonator shown in FIG. 3, there is no reflector at both ends of the IDT, but by making the number of pairs of the IDT 111 more than 200 pairs, the internal reflection inside the IDT is utilized to make use of the IDT. It is a resonator that generates a standing wave on top and causes a resonance phenomenon. It is experimentally known that the transmission characteristics of the IDT-type SAW resonator 103 do not cause spurious characteristics regardless of the size of the electrode finger film thickness of the IDT.

Therefore, as shown in FIG. 2, the n-stage ladder circuit component 101 is provided with an IW as a SAW resonator for improving the attenuation characteristic.
By connecting the DT-type SAW resonators 103 in parallel in cascade, even if the electrode film thickness H / λ of the IDT is set to about 0.08 to 0.1, the pass band 10 of the transmission characteristic 104 of the filter is reduced.
It is possible to improve the attenuation characteristic on the low frequency side without generating spurious in 7.

As described above, the resonator-type SAW filter 100 in which the reflector-type SAW resonator has an n-stage ladder structure.
Is an IDT-type SAW resonator 103 as a SAW resonator 102 for improving the attenuation characteristic in the n-stage ladder type circuit configuration section 101.
By connecting in parallel with each other in parallel, even if the electrode finger film thickness H / λ of the SAW resonator is set to about 0.08 to 0.1, spurious is not generated in the pass band of the filter and Attenuation characteristics can be improved, and the Q of SAW resonator can be improved.
Only the damping characteristic can be improved without deteriorating the value.

Here, the first embodiment is an example in which it is applied to the circuit configuration for improving the attenuation characteristic on the low frequency side with respect to the pass band of the filter. However, when improving the attenuation characteristic on the high frequency side, Can be similarly applied. For example, in FIG.
When the IDT SAW resonator 103 is connected in series with the n-stage ladder circuit shown in FIG. 23 in series, instead of the high-frequency side attenuation characteristic improving SAW resonator 76 shown in FIG. An attenuation pole f3 is newly generated on the higher frequency side,
The attenuation amount in the high-side attenuation region 75 becomes larger than the attenuation amount shown in FIG. 24, so that the characteristic can be improved. In this case, the electrode finger film thickness H / λ of the SAW resonator is 0.08 to. 0.
Even if it is set near 1, it is possible to improve the attenuation characteristic on the high frequency side without generating spurious in the pass band of the filter, and improve only the attenuation characteristic without deteriorating the Q value of the SAW resonator. be able to.

FIG. 4 is a circuit configuration diagram of a resonator type SAW filter according to a second embodiment of the present invention, and FIG. 5 is a diagram showing a transmission characteristic of the resonator type SAW filter. Second
Similarly to the first embodiment, the resonator type SAW filter according to the second embodiment is also an example applied to the attenuation characteristic improving circuit configuration on the low frequency side with respect to the pass band of the filter. Note that FIG.
In FIG. 5, elements that are the same as or correspond to those in FIGS. 1 and 2 are given the same reference numerals.

The resonator type SAW filter 120 shown in FIG.
In the figure, the part 101 is n having the same configuration as the conventional example.
Reference numeral 81 denotes a stepped ladder circuit configuration unit, 81 is a series arm SAW resonator for a ladder circuit configuration, and 82 is a parallel arm SAW for a ladder circuit configuration.
It is a resonator. Reference numeral 102 denotes a circuit component for improving the attenuation characteristic on the low frequency side, and reference numeral 121 denotes a pitch between the IDT and the grating reflector installed as a SAW resonator for improving the attenuation characteristic of 0.625λ (λ: It is a reflector type SAW resonator (a surface acoustic wave resonator for improving attenuation characteristics) having a wavelength corresponding to the resonance frequency.

Further, in FIG. 5, 122 is the transmission characteristic of the resonator type SAW filter in the circuit configuration method of the second embodiment, 123 is the spurious due to the parallel arm SAW resonator for the ladder type circuit configuration, and 124 is the ladder type circuit. Series arm SA for configuration
Spurious by the W resonator, 125 is a pass band, and 126 is a low-side attenuation band. Further, in FIG. 2, f4 is an attenuation pole by the reflector SAW resonator 82 for improving the attenuation characteristic on the low frequency side, f1 is an attenuation pole by the parallel arm resonator 81 for the ladder circuit configuration, and f2 is a ladder type. It is an attenuation pole by the series arm resonator for circuit configuration (n-stage ladder type circuit configuration section 101).

The circuit configuration method is the same as that of the conventional circuit configuration shown in FIGS. 33 and 35. However, in the resonator type SAW filter 120 according to the second embodiment, the SAW resonance for improving the attenuation characteristic on the low frequency side is obtained. As a child, a reflector type SAW resonator 121 (a surface acoustic wave resonator for improving the attenuation characteristic) having a pitch between the IDT and the grating reflector of 0.625λ is connected in parallel in a cascade.

FIG. 6 shows a reflector type SAW resonator 12 in which the pitch between the IDT and the grating reflector is 0.625λ.
It is a block diagram which shows the outline of 1. In FIG. 6, 131 is I
DT, 132, 133 are grating reflectors, 134
Is an input terminal, 135 is an output terminal, and 136 is a piezoelectric substrate. The electrode fingers of the IDT 131 are arranged at a λ / 2 pitch. As shown in the enlarged view of FIG. 6, the pitch between the IDT 131 and the grating reflectors 132 and 133 is 0.625λ.

The operation of the surface acoustic wave filter 120 configured as described above will be described below. First, the reflector type SAW resonator 121 in which the pitch between the IDT and the grating reflector is 0.625λ will be described. As shown in FIG. 6, the reflector type SAW resonator 121 has the IDT1.
31, the grating reflectors 132 and 133, the input terminal 134, the output terminal 135, and the piezoelectric substrate 136.
The electrode fingers of the DT 131 are arranged at a λ / 2 pitch, and the pitch between the IDT 131 and the grating reflectors 132 and 133 is 0.625λ.

The transmission characteristics of the reflector type SAW resonator 121 in which the pitch between the IDT and the grating reflector is 0.56λ to 0.63λ is similar to that of the IDT type SAW resonator 103 of the first embodiment. It is experimentally known that spurious characteristics do not occur regardless of the electrode film thickness.

Therefore, as shown in FIG. 4, as the attenuation characteristic improving SAW resonator 102, the pitch between the IDT and the grating reflector is 0.
By connecting the reflector type SAW resonators 121 having a wavelength of 625λ in parallel and in parallel, the pass band of the transmission characteristic 122 of the filter is set even if the electrode film thickness H / λ of the IDT is set to about 0.08 to 0.1. It is possible to improve the attenuation characteristic on the low frequency side without generating spurious at 125.

As described above, in the resonator type SAW filter 120 in which the reflector type SAW resonator is constructed in the n-stage ladder type, the n-stage ladder type circuit constituting section 101 is further provided with the IDT and the grating as the SAW resonator 102 for improving the attenuation characteristic. By connecting the reflector type SAW resonators 121 having a pitch between the reflectors of 0.625λ in parallel and in parallel, the electrode finger film thickness H / λ of the SAW resonator is set to about 0.08 to 0.1. However, it is possible to improve the attenuation characteristic on the low frequency side without generating spurious in the pass band of the filter, and to improve only the attenuation characteristic without deteriorating the Q value of the SAW resonator.

Here, in the second embodiment, an example in which the SAW resonator for improving the attenuation characteristic on the low frequency side is applied to a reflector type SAW resonator in which the pitch between the IDT and the grating reflector is 0.625λ. However, a similar effect can be obtained with a reflector SAW resonator having a pitch between the IDT and the grating reflector of 0.56λ to 0.63λ, for example, a reflector SAW resonance of 0.5625λ. A child may be used.

Further, the second embodiment is an example in which it is applied to the attenuation characteristic improving circuit configuration on the low frequency side with respect to the pass band of the filter, but it is also applied to the case where the attenuation characteristic on the high frequency side is improved. It can be applied similarly. For example, instead of the SAW resonator 76 for improving the attenuation characteristic on the high frequency side shown in FIG. 27, a reflector type SAW resonator 121 having a pitch between the IDT and the grating reflector of 0.625λ is used in FIG. When the series arms are connected in cascade to the n-stage ladder circuit as shown in Fig. 24, a new attenuation pole f3 is generated on the higher frequency side than the attenuation pole f2, and the attenuation amount in the high-side attenuation region 75 is the attenuation amount shown in Fig. 24. The characteristics can be improved by further increasing the value. In this case, the electrode finger film thickness H / λ of the SAW resonator is set to 0.
Even if it is set near 08 to 0.1, the attenuation characteristic on the high frequency side can be improved without generating spurious in the pass band of the filter, and the attenuation characteristic can be achieved without deteriorating the Q value of the SAW resonator. Only can be improved.

In each of the above embodiments, the example is applied to the circuit configuration for improving the attenuation characteristic on the low frequency side with respect to the pass band of the filter, but the same applies to the case where the attenuation characteristic on the high frequency side is improved. It can be applied as described above, and needless to say, the same can be applied to the case where both the low-frequency side and high-frequency side attenuation characteristics are simultaneously improved by a similar method.

Further, in each of the above-described embodiments, in the resonator type SAW filter having the n-stage ladder structure, the structure of the SAW resonator as the constituent element is described as a normal type reflector SAW resonator. The present invention is not limited to the normal type reflector SAW resonator, but may be a normal type IDT type SAW resonator, a weighted IDT type SAW resonator, a weighted reflector type SAW resonator, or a combination thereof. The same effect can be obtained by applying a resonator type SAW filter having an n-stage ladder structure.

In each of the above embodiments, the SAW resonator for the ladder circuit configuration is applied to the reflector type SAW resonator in which the grating reflectors are provided at both ends of the IDT, but the IDT has a multi-pair structure. The present invention is also applicable to a resonator type SAW filter of a ladder circuit configuration type using an IDT type SAW resonator that causes a resonance phenomenon by utilizing internal reflection inside the IDT, and similar effects can be obtained. .

Further, in each of the above-mentioned embodiments, the case where aluminum or copper, or an aluminum alloy containing several% of silicon is used as the metal material of the IDT of the SAW resonator and the grating reflector has been described. Resonator type S using SAW resonator composed of
Also in the AW filter, the condition of the electrode film thickness H / λ of the filter IDT and the spurious can be applied in the same manner, although the conditions are slightly changed, and the configuration method described in each of the embodiments can be applied as it is. The effect of can be obtained.

Further, in the surface acoustic wave filter according to each of the above embodiments, the IDT SAW resonator or the pitch between the IDT and the grating reflector is set to 0. Any structure may be used as long as it uses a reflector type SAW resonator having a wavelength of 56λ to 0.63λ, such as a pattern structure of a ladder circuit, the number of stages of the ladder circuit, and a wiring pattern shape of an input / output ground terminal. Further, the type and number of the interdigital electrodes, the connection state, etc. are not limited to those in the above embodiments.

[0071]

According to the surface acoustic wave filter of the present invention, a surface acoustic wave resonator having a resonance frequency lower than that of a parallel arm surface acoustic wave resonator for a ladder circuit configuration is used as an elastic material for improving attenuation characteristics on the low frequency side. In a surface acoustic wave filter in which parallel arms are connected in cascade as surface acoustic wave resonators to improve the attenuation characteristic on the low frequency side of the pass band of the filter, the surface acoustic wave resonator for improving the attenuation characteristic is an IDT surface acoustic wave. Since the resonator is composed of a resonator, the film thickness H / λ of the electrode finger of the surface acoustic wave resonator is 0.0
Even if it is set in the vicinity of 8 to 0.1, it is possible to improve the damping characteristic on the low frequency side without generating spurious in the pass band of the filter, and without deteriorating the Q value of the surface acoustic wave resonator. Only the damping characteristic can be improved.

In the surface acoustic wave filter according to the present invention, a surface acoustic wave resonator having a lower resonance frequency than that of the parallel arm surface acoustic wave resonator for the ladder circuit configuration is used for improving the damping characteristic on the low frequency side. In a surface acoustic wave filter in which parallel arms are connected in cascade as a surface acoustic wave resonator to improve the attenuation characteristics on the low frequency side of the filter passband, the surface acoustic wave resonator for improving the attenuation characteristics has a comb-shaped electrode and a grating. Since the reflector-type surface acoustic wave resonator is arranged at a distance of 0.56λ to 0.63λ from the reflector, the electrode finger thickness H / λ of the surface acoustic wave resonator is 0.08 to 0. Even if it is set near 1, it is possible to improve the attenuation characteristic on the low frequency side without generating spurious in the pass band of the filter, and to improve only the attenuation characteristic without deteriorating the Q value of the surface acoustic wave resonator. Can be improved.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a surface acoustic wave filter according to a first embodiment of the present invention.

FIG. 2 is a transmission characteristic diagram of the surface acoustic wave filter.

FIG. 3 is a configuration diagram of an IDT-type SAW resonator of the surface acoustic wave filter.

FIG. 4 is a circuit configuration diagram of a surface acoustic wave filter according to a second embodiment of the present invention.

FIG. 5 is a transmission characteristic diagram of the surface acoustic wave filter.

FIG. 6 is a reflector type S in which the pitch between the IDT and the grating reflector of the surface acoustic wave filter is 0.625λ.
It is a block diagram of an AW resonator.

FIG. 7 is a diagram showing a configuration of a conventional surface acoustic wave filter.

FIG. 8 is a circuit configuration diagram of a conventional surface acoustic wave filter.

FIG. 9 is a diagram showing a configuration of a conventional surface acoustic wave filter.

FIG. 10: Reflector type SAW of conventional surface acoustic wave filter
It is a figure which shows the structure of a resonator.

FIG. 11: Reflector type SAW of conventional surface acoustic wave filter
It is an equivalent circuit diagram of a resonator.

FIG. 12: Reflector type SAW of conventional surface acoustic wave filter
It is a figure which shows the reactance characteristic of a resonator.

FIG. 13 is a circuit configuration diagram of a conventional surface acoustic wave filter.

FIG. 14 is a diagram showing reactance characteristics and transmission characteristics of a conventional surface acoustic wave filter.

FIG. 15 is a circuit configuration diagram when a SAW resonator of a conventional surface acoustic wave filter is connected in series.

FIG. 16 is a transmission characteristic diagram when the SAW resonator of the conventional surface acoustic wave filter is connected in series.

FIG. 17 is a circuit configuration diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 18 is a transmission characteristic diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 19 is a circuit configuration diagram when a SAW resonator of a conventional surface acoustic wave filter is connected in series.

FIG. 20 is a transmission characteristic diagram when a SAW resonator of a conventional surface acoustic wave filter is connected in series.

FIG. 21 is a circuit configuration diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 22 is a transmission characteristic diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 23 is a circuit configuration diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 24 is a transmission characteristic diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 25 is a circuit configuration diagram of a SAW resonator for improving attenuation characteristics on the high frequency side of a conventional surface acoustic wave filter.

FIG. 26 is a transmission characteristic diagram of the SAW resonator for improving the attenuation characteristic on the high frequency side of the conventional surface acoustic wave filter.

FIG. 27 is a circuit configuration diagram of an n-stage ladder circuit in which a SAW resonator for improving attenuation characteristics on the high frequency side of a conventional surface acoustic wave filter is connected.

FIG. 28 is a transmission characteristic diagram of an n-stage ladder circuit in which a SAW resonator for improving the attenuation characteristic on the high frequency side of the conventional surface acoustic wave filter is connected.

FIG. 29 is a circuit configuration diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 30 is a transmission characteristic diagram of an n-stage ladder circuit of a SAW resonator of a conventional surface acoustic wave filter.

FIG. 31 is a circuit configuration diagram of a SAW resonator for improving attenuation characteristics on the low frequency side of a conventional surface acoustic wave filter.

FIG. 32 is a transmission characteristic diagram of the SAW resonator for improving the attenuation characteristic on the low frequency side of the conventional surface acoustic wave filter.

FIG. 33 is a circuit configuration diagram of an n-stage ladder circuit in which a SAW resonator for improving the attenuation characteristic on the low frequency side of the conventional surface acoustic wave filter is connected.

FIG. 34 is a transmission characteristic diagram of an n-stage ladder circuit in which a SAW resonator for improving the attenuation characteristic on the low frequency side of the conventional surface acoustic wave filter is connected.

FIG. 35 is a circuit configuration diagram of an n-stage ladder circuit in which a SAW resonator for improving the attenuation characteristic on the low frequency side of the conventional surface acoustic wave filter is connected.

FIG. 36 is a transmission characteristic diagram of an n-stage ladder circuit in which a SAW resonator for improving the attenuation characteristic on the low frequency side of the conventional surface acoustic wave filter is connected.

[Explanation of symbols]

81 series arm SAW resonator for ladder type circuit configuration, 82 parallel arm SAW resonator for ladder type circuit configuration, 100, 120
Resonator type SAW filter, 101 n-stage ladder type circuit configuration section, 102 Circuit configuration section for improving attenuation characteristics on low frequency side, 1
03 IDT type SAW resonator (surface acoustic wave resonator for improving attenuation characteristics), 111, 131 IDT, 112, 134
Input terminal, 113,135 Output terminal, 114,13
6 Piezoelectric substrate, 121 Reflector type SAW resonator having a pitch between the IDT and the grating reflector of 0.625λ (surface acoustic wave resonator for improving attenuation characteristics), 132, 133
Grating reflector

Claims (2)

[Claims] 1. A surface acoustic wave resonator using interdigital transducers for converting an electric signal into a surface acoustic wave or converting a surface acoustic wave into an electric signal in a ladder connection to form a filter, which is used for the ladder circuit configuration. The parallel arm surface acoustic wave resonator having a lower resonance frequency than that of the parallel arm surface acoustic wave resonator is connected in parallel with the parallel arm as a surface acoustic wave resonator for improving the damping characteristic on the low frequency side, and the A surface acoustic wave filter with improved attenuation characteristics on the band side, wherein the attenuation characteristic improving surface acoustic wave resonator is constituted by an IDT type surface acoustic wave resonator. 2. A surface acoustic wave resonator using a comb-shaped electrode for converting an electric signal into a surface acoustic wave or a surface acoustic wave into an electric signal, which is connected in a ladder shape to form a filter, which is used for the ladder circuit configuration. The parallel arm surface acoustic wave resonator having a lower resonance frequency than that of the parallel arm surface acoustic wave resonator is connected in parallel with the parallel arm as a surface acoustic wave resonator for improving the damping characteristic on the low frequency side, and the In a surface acoustic wave filter having improved attenuation characteristics on the band side, in the surface acoustic wave resonator for improving attenuation characteristics, the interval between the interdigital electrode and the grating reflector is 0.56λ to 0.6.
A surface acoustic wave filter comprising a reflector type surface acoustic wave resonator having 3λ (where λ is a surface wave wavelength).