JP7386741B2 - Filters, duplexers and communication equipment - Google Patents

Description

The present disclosure relates to a filter that filters a signal, a duplexer including the filter, and a communication device including the filter.

Ladder type filters are known as filters for filtering signals (for example, Patent Documents 1 and 2). A ladder filter includes, for example, one or more series resonators located in a signal path from an input terminal to an output terminal, and one or more parallel resonators located between the signal path and a reference potential. It is equipped with The resonator is, for example, an elastic wave resonator that uses elastic waves. Examples of elastic waves include SAW (Surface Acoustic Wave) and BAW (Bulk Acoustic Wave).

Japanese Patent Application Publication No. 2007-74698 International Publication No. 2016/031391

There is a need for filters, duplexers, and communication equipment that can reduce intermodulation distortion (IMD).

A filter according to an aspect of the present disclosure includes an input terminal into which a signal is input, an output terminal which outputs a signal, a first filter section located on a signal path from the input terminal to the output terminal, and a second filter section located in a signal path from the input terminal to the output terminal and connected in parallel to the first filter section, the first filter section and the second filter section being connected in parallel to the first filter section; Each section is a ladder type filter including two or more series resonators and one or more parallel resonators connected in a ladder type, and in each of the first filter section and the second filter section, the first The above parallel resonator includes a parallel resonator connected to a signal path from one of the two or more series resonators to another one, and includes the first filter section and the second filter section. In each filter section, the series resonator located closest to the output terminal side is called the last series resonator, and the passband is the sum of the passband of the first filter section and the passband of the second filter section. When referred to as a first pass band, the first filter section and the second filter section are such that a signal having a first frequency within the first pass band is simultaneously input to the first filter section and the second filter section. when the power of the signal applied to the last stage series resonator of the first filter section is greater than the power applied to the last stage series resonator of the second filter section, and within the first pass band. And when a signal having a second frequency higher than the first frequency is simultaneously input to the first filter section and the second filter section, the power applied to the last stage series resonator of the second filter section is: The power applied to the last stage series resonator of the first filter section is larger than the power applied to the last stage series resonator.

A duplexer according to an aspect of the present disclosure includes the filter described above and another filter connected to the output terminal.

A communication device according to one aspect of the present disclosure includes the filter, an antenna connected to the output terminal, and an integrated circuit element connected to the input terminal.

According to the above configuration, intermodulation distortion can be reduced.

FIG. 1 is a circuit diagram schematically showing the configuration of a filter according to an embodiment. FIG. 2 is a diagram for explaining the principle of a ladder filter. 2 is a diagram showing characteristics of the filter of FIG. 1. FIG. FIGS. 4(a) and 4(b) are diagrams showing one example and other examples of filter characteristics of a rear-stage filter section of the filter of FIG. 1. FIG. FIG. 2 is a plan view schematically showing the configuration of a SAW resonator. FIG. 2 is a circuit diagram illustrating an example of how filter characteristics are adjusted. FIG. 7 is a circuit diagram showing another example of how filter characteristics are adjusted. FIG. 7 is a circuit diagram showing still another example of how filter characteristics are adjusted. FIG. 2 is a block diagram showing main parts of a duplexer as an example of using the filter device of FIG. 1. FIG. 2 is a block diagram showing main parts of a communication device as an example of using the filter device of FIG. 1. FIG.

(Overall configuration of filter)
FIG. 1 is a circuit diagram schematically showing the electrical configuration of a filter 1 according to an embodiment. Note that the positional relationship explained with reference to a circuit diagram like FIG. 1 basically refers to the positional relationship from the viewpoint of electrical connection, and does not necessarily correspond to the spatial positional relationship.

The filter 1 has an input terminal 3, an output terminal 5, and a reference potential section 7. The filter 1 is configured as a bandpass filter that filters a signal input to an input terminal 3 and outputs the filtered signal from an output terminal 5. That is, the filter 1 removes the signal outside the passband from the signal input to the input terminal 3 (attenuates the signal outside the passband), and outputs the signal to the output terminal 5. Signals outside the passband are allowed to escape to the reference potential section 7.

Note that in FIG. 1, the reference potential portions 7 are shown at a plurality of positions for convenience of illustration. A part or all of the plurality of reference potential sections 7 may be separate parts or may be the same part in the actual filter 1. Furthermore, in the former case, the plurality of reference potential sections 7 formed from mutually separate parts may or may not be electrically connected to each other. The reference potential section 7 is, for example, a terminal to which a reference potential is applied.

The filter 1 includes two or more (three in the illustrated example) filter sections 11 located in a signal path from the input terminal 3 to the output terminal 5. The two or more filter sections 11 include, for example, a front-stage filter section 11A and two or more (two in the illustrated example) rear-stage filter sections 11B. The two or more post-filter sections 11B include, for example, a first post-filter section 11Ba and a second post-filter section 11Bb.

In this example, the front filter section 11A and the rear filter section 11B are connected in series, and two or more rear filter sections 11B (11Ba and 11Bb) are connected in parallel with each other. The front filter section 11A is connected in series to two or more rear filter sections 11B. Further, the front-stage filter section 11A is located on the input terminal 3 side with respect to the two or more rear-stage filter sections 11B. The two or more post-stage filter sections 11B may be considered to be a part of the filter 1 on the output terminal 5 side divided in parallel.

Although not particularly shown, there may be provided an electrical element (not shown) connected in series between the input terminal 3 and the pre-filter section 11A, and a signal path from the input terminal 3 to the pre-filter section 11A and a reference potential. An electrical element (not shown) may be provided to connect with the section 7. between the front-stage filter section 11A and two or more rear-stage filter sections 11B (all the rear-stage filter sections 11B or any one of the rear-stage filter sections 11B), and between the two or more rear-stage filter sections 11B (all the rear-stage filter sections 11B or one of the rear-stage filter sections 11B). The same applies between the rear filter section 11B) and the output terminal 5. Examples of electrical elements include resistors, capacitors, inductors, and filters. These may be considered as part of any filter section 11.

However, in this example, for any of the two or more post-filter sections 11B, there is an element connected in series between the post-filter section 11B and the output terminal 5 that causes relatively large intermodulation distortion. is not connected. For example, an elastic wave resonator (for example, a SAW resonator) and an elastic wave filter (for example, a SAW filter) connected in series to the rear-stage filter section 11B and the output terminal 5 are not provided. In other words, the elements most likely to cause intermodulation distortion for the same input signal between the last stage series resonators 9S4a and 9S4b (described later) included in two or more post-stage filter sections 11B and the output terminal 5. are the last stage series resonators 9S4a and 9S4b.

Each filter section 11 is configured, for example, by a ladder filter in which a plurality of resonators 9 are connected in a ladder shape. From another point of view, the entire filter 1 is constituted by a ladder type filter. Although not particularly illustrated, the pre-stage filter section 11A may be configured by a so-called multi-mode filter (in the present disclosure, a double-mode film is included).

The plurality of resonators 9 include, for example, a plurality of series resonators 9S connected in series between the input terminal 3 and the output terminal 5, a signal path from the input terminal 3 to the output terminal 5, and a reference potential section 7. It has a plurality of parallel resonators 9P connecting. More specifically, in the illustrated example, the series resonator 9S includes series resonators 9S1, 9S2, 9S3a, 9S3b, 9S4a, and 9S4b. Further, the plurality of parallel resonators 9P include parallel resonators 9P1, 9P2, 9P3a, and 9P3b.

From another perspective, the pre-filter section 11A includes series resonators 9S1 and 9S2 and parallel resonators 9P1 and 9P2. The first latter-stage filter section 11Ba includes series resonators 9S3a and 9S4a and a parallel resonator 9P3a. The second rear-stage filter section 11Bb includes series resonators 9S3b and 9S4b and a parallel resonator 9P3b.

As can be understood from the above description, the "S" attached to the resonator 9 corresponds to a series resonator, and the "P" attached to the resonator 9 corresponds to a parallel resonator. The numbers after "S" and "P" indicate the number of stages from the input terminal 3. For example, “1” indicates a first stage (initial stage) series resonator or parallel resonator closest to the input terminal 3. Furthermore, in the illustrated example, "4" after "S" indicates that it is the last stage series resonator closest to the output terminal 5. Further, "a" added after "S3", "P3", and "S4" indicates that the resonator 9 belongs to the first rear-stage filter section 11Ba. Similarly, "b" added after "S3", "P3", and "S4" indicates that the resonator 9 belongs to the second rear-stage filter section 11Bb.

When a plurality of resonators 9 are connected in a ladder shape, for example, as described above, one series resonator 9S or a plurality of series resonators 9S connected in series are connected between the input terminal 3 and the output terminal 5. A state in which the resonator 9S is electrically connected, and one or more parallel resonators 9P are electrically connected between the input side or output side of the one or more series resonators 9S and the reference potential section 7. Point. The signal path from the input terminal 3 to the output terminal 5, which includes one or more series resonators 9S, is sometimes called a series arm. Furthermore, each of the one or more signal paths from the series arm to the reference potential section, including one or more parallel resonators 9P, may also be referred to as a parallel arm.

One resonator 9 may be divided into two or more divided resonators in order to improve power durability and the like. In other words, one resonator 9 may be composed of two or more divided resonators connected in series. In such a divided resonator, the parallel resonator 9P is not connected between adjacent divided resonators. Therefore, for example, if two resonators are connected in series between the input terminal 3 and the output terminal 5, and the parallel resonator 9P is not connected between them, the two resonators Instead of the series resonator 9S, it may be specified as one series resonator 9S made up of two split resonators. In other words, when the filter section 11 has two series resonators 9S, the parallel resonator 9P is connected between the two series resonators 9S.

In the filter 1 and in each filter section 11, the number of series resonators 9S and the number of parallel resonators 9P may be set as appropriate. In principle, a ladder filter can be configured with one series resonator 9S and one parallel resonator 9P. Further, in the filter 1 or each filter section 11, the resonator 9 located closest to the input terminal 3 may be a series resonator 9S or a parallel resonator 9P. The same applies to the resonator 9 located closest to the output terminal 5 side.

In the illustrated example, the pre-stage filter section 11A includes two series resonators 9S and two parallel resonators 9P. Unlike the illustrated example, the pre-stage filter section 11A may include only one series resonator 9S and one parallel resonator 9P, or may include three or more series resonators 9S and/or three or more series resonators 9S and/or three or more series resonators 9S and/or The above parallel resonator 9P may be included. Instead of the pre-stage filter section 11A, only one of the plurality of series resonators 9S of the ladder-type filter as the entire filter 1 is provided at the position of the pre-stage filter section 11A, or the ladder-type filter as the entire filter 1 is provided. Only one of the plurality of parallel resonators 9P may be provided at the pre-stage filter section 11A.

As mentioned above, the ladder filter can be configured with one series resonator 9S and one parallel resonator 9P in principle. However, each post-stage filter section 11B has two or more (two in the illustrated example) series resonators 9S. As described above, parallel resonators 9P are connected between adjacent series resonators 9S. Unlike the illustrated example, each post-stage filter section 11B may include three or more series resonators 9S and/or three or more parallel resonators 9P. Further, the two or more post-stage filter sections 11B may have the same number of series resonators 9S (as shown in the figure), or may have different numbers of series resonators 9S. The same applies to the parallel resonator 9P.

(Principle of ladder filter)
FIG. 2 is a diagram for explaining the principle of a ladder type filter (filter 1 and filter section 11).

In the upper graph of FIG. 2, the horizontal axis shows the frequency f (Hz), and the vertical axis shows the absolute value of impedance |Z| (Ω). A line LS indicates the impedance of the series resonator 9S. Line LP indicates the impedance of parallel resonator 9P. In the graph at the bottom of FIG. 2, the horizontal axis represents the frequency f (Hz), and the vertical axis represents the attenuation amount A (dB). Line LF indicates the amount of attenuation of the ladder filter (filter 1 or each filter section 11). The horizontal axis of the upper graph in FIG. 2 and the horizontal axis of the lower graph in FIG. 2 match.

In the frequency characteristic of the impedance of the resonator 9 made of an elastic wave resonator, a resonance point where the impedance becomes a minimum value and an anti-resonance point where the impedance becomes a maximum value appear. The frequencies at which resonance points and anti-resonance points appear are defined as resonance frequencies (fsr, fpr) and anti-resonance frequencies (fsa, fpa). In the resonator 9, the anti-resonant frequency is, for example, higher than the resonant frequency.

The series resonator 9S and the parallel resonator 9P have a resonant frequency and an anti-resonant frequency such that the resonant frequency fsr of the series resonator 9S (line LS) and the anti-resonant frequency fpa of the parallel resonator 9P (line LP) approximately match. is set. As a result, the ladder filter (line LF) functions as a bandpass filter whose passband PB is slightly narrower than the frequency range from the resonant frequency fpr of the parallel resonator 9P to the anti-resonant frequency fsa of the series resonator 9S. do. The plurality of series resonators 9S basically have the same resonance frequency and the same anti-resonance frequency. The same applies to the plurality of parallel resonators 9P.

(Characteristics of filter and pre-filter section)
FIG. 3 is a diagram similar to the lower graph of FIG. 2, showing the characteristics of filter 1. Although FIG. 3 shows the characteristics of a duplexer, which will be described later, for convenience, the filter 1 is not intended to be used as a duplexer. Further, here, we mainly focus on only the band on the right side of the paper.

The symbols BT and BR represented by the three sides of the rectangle indicate the filter characteristics to be fulfilled. Such filter characteristics are, for example, defined by standards and/or by the specifications of the purchaser of the filter 1. The ladder type filter is configured, for example, so that the mountain drawn by the line LF (FIG. 2) indicating filter characteristics includes the symbol BT or BR and does not include other symbols.

In the illustrated example, line LF0 indicates the filter characteristic of filter 1. The mountain drawn by the line LF0 includes the symbol BT but does not include the symbol BR. The line LF0 may be considered to indicate the filter characteristics of the pre-stage filter section 11A.

(Characteristics of post-filter section)
FIG. 4A is a diagram corresponding to the area on the right side of the paper in FIG. 3, showing an example of the filter characteristics of the post-filter section 11B. In this figure, a line LF1 indicates the filter characteristic of the first rear-stage filter section 11Ba. In this figure, a line LF2 indicates the filter characteristic of the second post-stage filter section 11Bb.

As shown in this figure, the filter characteristics of the first post-filter section 11Ba satisfy the requirements on the low frequency side of the filter characteristics indicated by the symbol BT, but do not satisfy the requirements on the high frequency side. . Specifically, for example, in the first rear-stage filter section 11Ba, the required transmission characteristics are secured in a part of the band on the low frequency side of the band indicated by the symbol BT, but the required transmission characteristics are secured in other bands. (including outside the band indicated by symbol BT), the required transmission characteristics are not ensured.

Conversely, the filter characteristics of the second post-stage filter section 11Bb satisfy the requirements on the high frequency side of the filter characteristics indicated by the symbol BT, but do not satisfy the requirements on the low frequency side. Specifically, for example, in the second rear-stage filter section 11Bb, the required transmission characteristics are ensured in some bands on the high frequency side of the band indicated by the symbol BT, but the required transmission characteristics are secured in other bands. (including outside the band indicated by symbol BT), the required transmission characteristics are not ensured.

In addition, the band in which the required transmission characteristics are ensured in the first latter-stage filter section 11Ba and the band in which the required transmission characteristics are ensured in the second latter-stage filter section 11Bb are partially mutual. are overlapping with each other.

Although the above description has been made based on the band indicated by the symbol BT, the filter characteristics of the filter section 11 may be explained based on the pass band PB (see FIG. 2) of each filter section 11. Specifically, the lower boundary frequency (frequency at the end of the band) of the passband PB of the first latter-stage filter section 11Ba is lower than the lower-frequency boundary frequency of the passband PB of the second latter-stage filter section 11Bb. is also located on the low frequency side. Further, the boundary frequency on the high frequency side of the passband PB of the first post-filter section 11Ba is located on the lower frequency side than the boundary frequency on the high frequency side of the passband PB of the second post-filter section 11Bb. Further, a portion of the high frequency side of the passband PB of the first post-filter section 11Ba and a portion of the low frequency side of the passband PB of the second post-filter section 11Bb overlap with each other. The passband PB0, which is the sum of the passbands PB of two or more post-stage filter sections 11B, is the same as the passband PB of the entire filter 1 and/or the passband PB of the pre-stage filter section 11A.

Note that when the passband PB0 is the same as the passband PB of the filter 11 and/or the passband PB of the pre-filter section 11A, it goes without saying that there may be an error between the two. For example, if the difference between the boundary frequency on the low frequency side of passband PB0 and the boundary frequency on the low frequency side of another passband is 1/10 or less of passband PB0, it is assumed that they match. It's okay to be rejected. The same applies to the high frequency side. Then, if the difference between the boundary frequency of passband PB0 and the boundary frequency of other passbands is within the above error range on both the low frequency side and high frequency side, they are considered to match. good.

The pass band PB of the filter 1 that is actually in circulation may be specified with the accuracy necessary for determining whether it belongs to the technology according to the present disclosure, and does not necessarily need to be specified with high accuracy. Furthermore, the passband PB may be reasonably specified. For example, the passband PB may be specified based on specifications. Alternatively, the characteristics shown in the lower part of FIG. 2 may be measured, and the passband PB may be reasonably determined based on the measurement results and common technical knowledge. A band in which generally required transmission characteristics are ensured in the technical field in which the filter 1 is used may be specified as the pass band PB.

Furthermore, the filter characteristics of the filter section 11 may be explained from the relative relationship between the transmission characteristics of two or more post-stage filter sections 11B. For example, consider a passband PB0 obtained by adding the passbands PB of two or more post-filter sections 11B as described above. At this time, in a part of the low frequency side of the pass band PB0, the transmission characteristic of the first rear-stage filter section 11Ba is higher than the transmission characteristic of the second rear-stage filter section 11Bb. Conversely, in the other part of the passband PB0 (a part on the high frequency side), the transmission characteristic of the second post-filter section 11Bb is higher than the transmission characteristic of the first post-filter section 11Ba.

Further, the filter characteristics of the filter section 11 may be explained not based on a band but on a predetermined frequency. For example, consider a predetermined frequency f1 and a frequency f2 higher than the frequency f1. Both are included in the band indicated by the symbol BT and/or the already mentioned passband PB0.

At this time, for example, the first post-stage filter section 11Ba satisfies the required transmission characteristic condition at the frequency f1, but does not satisfy the required transmission characteristic condition at the frequency f2. On the other hand, the second post-stage filter section 11Bb does not satisfy the required transmission characteristic conditions at frequency f1, and satisfies the required transmission characteristic conditions at frequency f2.

Further, for example, the first latter-stage filter section 11Ba includes the frequency f1 in its passband, but does not include the frequency f2 in its passband. On the other hand, the second latter-stage filter section 11Bb does not include the frequency f1 in its passband, but includes the frequency f2 in its passband.

Further, for example, at the frequency f1, the transmission characteristic of the first rear-stage filter section 11Ba is higher than the transmission characteristic of the second rear-stage filter section 11Bb. Conversely, at frequency f2, the transmission characteristic of the second rear-stage filter section 11Bb is higher than the transmission characteristic of the first rear-stage filter section 11Ba.

FIG. 4(b) is a diagram similar to FIG. 4(a), showing another example of the filter characteristics of the post-stage filter section 11B.

In FIG. 4(b), compared to FIG. 4(a), the amount of overlap (frequency band) between the rear-stage filter sections 11B in the band in which the required transmission characteristics are ensured is larger. From another point of view, in FIG. 4(b), the amount of overlap between the passbands PB of two or more post-filter sections 11B is larger than in FIG. 4(a). However, the frequency f1 and the frequency f2 are not included in the above-mentioned overlapping band, for example, similarly to FIG. 4(a).

(Reduction of intermodulation distortion)
Two or more post-stage filter sections 11B are provided between the input terminal 3 and the output terminal 5, and constitute mutually parallel signal paths, and as described with reference to FIG. 4(a), the two or more post-stage filter sections 11B By setting the filter characteristics, for example, intermodulation distortion can be reduced. Specifically, it is as follows.

As shown by the arrow drawn near the input terminal 3 in FIG. 1, it is assumed that a signal with a frequency f1 and a signal with a frequency f2 are input to the input terminal 3 at the same time. The frequencies f1 and f2 are as described with reference to FIG. 4(a). The signal of frequency f1 and the signal of frequency f2 are mutually separate signals, and for example, contain mutually different information.

As shown in FIG. 3, the passband PB of the pre-filter section 11A includes frequencies f1 and f2. Therefore, near the input terminal 3, as shown by the lengths of the arrows labeled f1 and f2 being drawn equal to each other, the signals of frequencies f1 and f2 are both transmitted to the pre-stage filter. 11A (the amount of attenuation is relatively small).

On the other hand, as described with reference to FIG. 4(a), the passband PB of the first latter-stage filter section 11Ba includes the frequency f1, but does not include the frequency f2. Therefore, as shown by the arrow labeled f1 being drawn longer than the arrow labeled f2 near the first post-filter section 11Ba, the signal of frequency f1 is filtered by the filter. It passes through part 11A (the amount of attenuation is relatively small). On the other hand, the signal at frequency f2 is attenuated by a larger amount of attenuation than the signal at frequency f1.

Contrary to the above, the passband PB of the second post-stage filter section 11Bb includes the frequency f2, but does not include the frequency f1. Therefore, as shown by drawing the arrow labeled f2 longer than the arrow labeled f1 near the second post-filter section 11Bb, the signal of frequency f2 is It passes through the second post-stage filter section 11Bb (the amount of attenuation is relatively small). On the other hand, the signal at frequency f1 is attenuated with a larger amount of attenuation than the signal at frequency f2.

Further, when two signals having different frequencies are simultaneously input to one resonator 9, intermodulation distortion occurs. Here, the amplitude of the AC power applied to the resonator 9 (power passing through the resonator 9) due to the signal of the frequency f1 is set to P1, and the amplitude of the AC power applied to the resonator 9 due to the signal of the frequency f2 is set to P2. At this time, for example, the power of the second-order intermodulation distortion (for example, its amplitude) is proportional to P1×P2. Further, for example, the power of third-order intermodulation distortion (for example, its amplitude) is proportional to P1 ² ×P2 or P1 × P2 ² . Therefore, if the value of either P1 or P2 is reduced, intermodulation distortion is reduced. Note that in the description of the present disclosure, the amplitude of AC power may be simply referred to as power for convenience.

On the other hand, as described above, in the first post-filter section 11Ba, the signal of frequency f2 (power P2 from another point of view) is reduced. As a result, the power of intermodulation distortion in the first post-stage filter section 11Ba is reduced. Similarly, in the second post-filter section 11Bb, the signal of frequency f1 (power P1 from another point of view) is reduced. As a result, the power of intermodulation distortion in the second post-stage filter section 11Bb is reduced.

Although the above description has been made from the viewpoint of electric power, the description can also be made from the viewpoint of voltage. For example, the voltage applied to the resonator 9 by a signal of frequency f1 is set to V1, and the voltage applied to the resonator 9 by a signal of frequency f2 is set to V2. At this time, for example, the voltage of second-order intermodulation distortion is proportional to V1×V2. Further, for example, the voltage of third-order intermodulation distortion is proportional to V1 ² ×V2 or V1 × V2 ² .

Since the signal of frequency f2 is attenuated by the first post-stage filter section 11Ba, the voltage V2 applied to the last stage series resonator 9S4a is reduced. As a result, the voltage of intermodulation distortion in the first latter-stage filter section 11Ba is reduced. Similarly, since the signal of frequency f1 is attenuated by the second post-stage filter section 11Bb, the voltage V1 applied to the last stage series resonator 9S4b is reduced. As a result, the voltage of intermodulation distortion in the second post-stage filter section 11Bb is reduced.

Since the two post-filter sections 11B are connected in parallel between the input terminal 3 and the output terminal 5, the signal of frequency f1 that has passed through the first post-filter section 11Ba and the signal that has passed through the second post-filter section 11Bb. It is combined with the signal of frequency f2 and output from the output terminal 5. Therefore, in the filter 1, the function of passing both the signal of frequency f1 and the signal of frequency f2 is maintained.

The above principle may be applied to any of the resonators 9 from the input terminal 3 to the output terminal 5. However, intermodulation distortion that occurs closer to the input terminal 3 than the part that functions as a filter (for example, a combination of one series resonator 9S and one parallel resonator 9P) is attenuated by the part that functions as a filter. Cheap. In other words, the closer the resonator 9 is to the output terminal 5, the more likely the intermodulation distortion will affect the characteristics of the filter 1. In particular, in the last stage series resonator 9S, intermodulation distortion has a relatively large effect on the characteristics of the filter 1. Therefore, the filter 1 is configured such that the rear-stage filter sections 11B, which are connected in parallel with each other, include the last-stage series resonators 9S (9S4a and 9S4b) in the filter 1.

Since the two or more post-stage filter sections 11B are connected in parallel, the same voltage is applied to each of them. Therefore, for example, when each of the post-stage filter sections 11B is composed of only one series resonator 9S and one parallel resonator 9P, the last stage series resonator 9S in the two or more post-stage filter sections 11B The voltages applied to both are the same. In this embodiment, since each post-stage filter section 11B includes two or more series resonators 9S, different voltages can be applied to the series resonators 9S4a and 9S4b at the last stage. As a result, the above-described principle of reducing intermodulation distortion can be easily utilized.

As can be understood from the above description, in this embodiment, the power P2 at frequency f2 applied to the last stage series resonator 9S4a is reduced, and the power P1 at frequency f2 applied to the last stage series resonator 9S4b is reduced. By doing so, intermodulation distortion is reduced. Therefore, in the explanation so far, the explanation has been made on the premise that the filter characteristics appearing in the graph with the vertical axis representing the attenuation amount are different between the two post-stage filter sections 11B, but such a difference is an essential feature of the technology of the present disclosure. isn't it. For example, the above power reduction may be achieved as a result of adjusting various parameters. Therefore, the configuration of the filter 1 (two or more post-stage filter sections 11B) may be explained from the viewpoint of power.

For example, the filter 1 is configured such that when a signal having a frequency f1 within the passband PB0 is simultaneously input to the two subsequent filter sections 11B, the power applied to the series resonator 9S4a is greater than the power applied to the series resonator 9S4b. It can be said that it is composed of Furthermore, in the filter 1, when a signal having a frequency f2 within the passband PB0 and higher than the frequency f1 is simultaneously input to the two subsequent filter sections 11B, the power applied to the series resonator 9S4b is changed from the power applied to the series resonator 9S4a. It can be said that it is configured to be larger than the

Further, for example, assume a situation in which the power input to the input terminal 3 is the same for a signal of frequency f1 and a signal of frequency f2. In this case, it can be said that the filter 1 is configured such that the power P1 at the frequency f1 is greater than the power P2 at the frequency f2 regarding the power applied to the series resonator 9S4a. Similarly, it can be said that the filter 1 is configured such that the power P2 at the frequency f2 is greater than the power P1 at the frequency f1 regarding the power applied to the last stage series resonator 9S4b. However, the precondition that the input power (or voltage) is the same at frequency f1 and frequency f2 does not necessarily hold true in actual equipment.

(Specific example of resonator)
The resonator 9 constituting the filter 1 may have various configurations. For example, the resonator 9 may be a SAW resonator, a BAW resonator that uses BAW while having electrodes similar to the SAW resonator, or a piezoelectric thin film that vibrates on a cavity. It may be a piezoelectric thin film resonator (sometimes referred to as FBAR (Film Bulk Acoustic Resonator)). A SAW resonator will be described below as an example of the resonator 9.

FIG. 5 is a plan view schematically showing the configuration of a SAW resonator as the resonator 9. As shown in FIG.

For convenience, FIG. 5 shows an orthogonal coordinate system consisting of a D1 axis, a D2 axis, and a D3 axis. The resonator 9 may be directed either upward or downward. However, in the following description, for convenience, terms such as upper surface or lower surface may be used with the positive side of the D3 axis being the upper side. Note that the D1 axis is defined to be parallel to the propagation direction of elastic waves propagating along the upper surface 21a (described later). The D2 axis is defined to be parallel to the upper surface 21a and orthogonal to the D1 axis. The D3 axis is defined to be orthogonal to the upper surface 21a.

The resonator 9 is constituted by a so-called one-port acoustic wave resonator. For example, the resonator 9 outputs a signal input from one of the two wiring lines 23 shown on both sides of the paper from the other of the two wiring lines 23. At this time, the resonator 9 converts an electric signal into an elastic wave, and converts an elastic wave into an electric signal.

The resonator 9 includes, for example, a substrate 21 (at least a part of the upper surface 21a), an excitation electrode 25 located on the upper surface 21a, and a pair of reflectors 27 located on both sides of the excitation electrode 25. There is. A plurality of resonators 9 may be configured on one substrate 21. That is, the substrate 21 may be shared by a plurality of resonators 9. In the following description, in order to distinguish between a plurality of resonators 9 that share the same substrate 21, for convenience, the combination of the excitation electrode 25 and one reflector 27 (electrode portion of the resonator 9) is referred to as the resonator 9. (as if the resonator 9 does not include the substrate 21).

The substrate 21 has piezoelectricity at least in the region of the upper surface 21a where the resonator 9 is provided. An example of such a substrate 21 is one in which the entire substrate is made of a piezoelectric material (that is, a piezoelectric substrate). Further, for example, a so-called bonded substrate can be mentioned. The laminated substrate is a substrate made of a piezoelectric material having an upper surface 21a (piezoelectric substrate) and a surface of the piezoelectric substrate opposite to the upper surface 21a, which is directly attached with or without an adhesive. and a mated support substrate. Further, as the substrate 21 having piezoelectricity in the region where the resonator 9 is provided, for example, the support substrate and a part of the main surface on the +D3 side of the support substrate or the entire main surface are made of piezoelectric material. Examples include those in which a film (piezoelectric film) or a multilayer film including a piezoelectric film is formed.

The piezoelectric material constituting at least the region of the substrate 21 where the resonator 9 is provided is made of, for example, a piezoelectric single crystal. Examples of materials constituting such a single crystal include lithium tantalate (LiTaO ₃ ), lithium niobate (LiNbO ₃ ), and quartz (SiO ₂ ). The cut angle, planar shape, and various dimensions may be set appropriately.

The excitation electrode 25 and the reflector 27 are constituted by a layered conductor provided on the substrate 21. The excitation electrode 25 and the reflector 27 are, for example, made of the same material and the same thickness. The layered conductors constituting these are, for example, metal. The metal is, for example, Al or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an Al-Cu alloy. The layered conductor may be composed of multiple metal layers. The thickness of the layered conductor is appropriately set depending on the electrical characteristics required of the resonator 9 and the like. As an example, the thickness of the layered conductor is 50 nm or more and 600 nm or less.

The excitation electrode 25 has a pair of comb-teeth electrodes 29 (one is hatched for convenience to improve visibility). Each comb-teeth electrode 29 includes, for example, a busbar 31, a plurality of electrode fingers 33 extending in parallel from the busbar 31, and a plurality of dummy electrodes 35 protruding from the busbar 31 between the plurality of electrode fingers 33. There is. The pair of comb-teeth electrodes 29 are arranged so that the plurality of electrode fingers 33 interlock with each other (cross each other).

The bus bar 31 is, for example, formed in an elongated shape that has a substantially constant width and extends linearly in the propagation direction of the elastic wave (direction D1). The pair of bus bars 31 face each other in a direction (direction D2) orthogonal to the propagation direction of elastic waves. Note that the bus bar 31 may have a width that changes or may be inclined with respect to the propagation direction of the elastic wave.

Each electrode finger 33 is formed, for example, in an elongated shape that has a substantially constant width and extends linearly in a direction (D2 direction) orthogonal to the propagation direction of the elastic wave. In each comb-teeth electrode 29, the plurality of electrode fingers 33 are arranged in the propagation direction of the elastic wave. Further, the plurality of electrode fingers 33 of one comb-teeth electrode 29 and the plurality of electrode fingers 33 of the other comb-teeth electrode 29 are basically arranged alternately.

The pitch p of the plurality of electrode fingers 33 (for example, the distance between the centers of two adjacent electrode fingers 33) is basically constant within the excitation electrode 25. Note that the excitation electrode 25 may have a part that is unique with respect to the pitch p. Specific areas include, for example, a narrow pitch part where the pitch p is narrower than the majority (for example, 80% or more), a wide pitch part where the pitch p is wider than the majority, and a small number of electrode fingers 33 that are substantially spaced apart. An example is the thinned out part.

In the following, unless otherwise specified, pitch p refers to the pitch of a portion (most of the plurality of electrode fingers 33) excluding the peculiar portions as described above. In addition, if the pitch of most of the plurality of electrode fingers 33 excluding a peculiar part is changing, the average value of the pitch of most of the plurality of electrode fingers 33 is used as the value of pitch p. May be used.

The number of electrode fingers 33 may be appropriately set depending on the electrical characteristics required of the resonator 9 and the like. Since FIG. 5 is a schematic diagram, the number of electrode fingers 33 is shown to be small. In reality, more electrode fingers 33 than shown may be arranged. The same applies to the strip electrode 39 of the reflector 27, which will be described later.

The lengths of the plurality of electrode fingers 33 are, for example, equal to each other. Note that the excitation electrode 25 may be subjected to so-called apodization, in which the length of the plurality of electrode fingers 33 (from another point of view, the cross width W described later) changes depending on the position in the propagation direction. The length and width of the electrode fingers 33 may be set as appropriate depending on required electrical characteristics and the like.

For example, the dummy electrode 35 has a substantially constant width and protrudes in a direction perpendicular to the propagation direction of the elastic wave. Its width is, for example, equivalent to the width of the electrode finger 33. Further, the plurality of dummy electrodes 35 are arranged at the same pitch as the plurality of electrode fingers 33, and the tip of the dummy electrode 35 of one comb-teeth electrode 29 is the tip of the electrode finger 33 of the other comb-teeth electrode 29. and are facing each other through a gap. Note that the excitation electrode 25 may not include the dummy electrode 35.

The pair of reflectors 27 are located on both sides of the plurality of excitation electrodes 25 in the propagation direction of the elastic waves. For example, each reflector 27 may be electrically floating or may be provided with a reference potential. Each reflector 27 is formed, for example, in a lattice shape. That is, the reflector 27 includes a pair of bus bars 37 facing each other and a plurality of strip electrodes 39 extending between the pair of bus bars 37. The pitch between the plurality of strip electrodes 39 and the pitch between adjacent electrode fingers 33 and strip electrodes 39 are basically equivalent to the pitch between the plurality of electrode fingers 33.

When a voltage is applied to the pair of comb-teeth electrodes 29, the voltage is applied to the piezoelectric upper surface 21a by the plurality of electrode fingers 33, causing the upper surface 21a to vibrate. This excites elastic waves propagating in the D1 direction. The elastic waves are reflected by the plurality of electrode fingers 33. Then, a standing wave is created in which the pitch p of the plurality of electrode fingers 33 is approximately half a wavelength (λ/2). Electric signals generated in the piezoelectric film 57 by the standing waves are extracted by the plurality of electrode fingers 33. Based on this principle, the resonator 9 functions as a resonator whose resonant frequency is the frequency of an elastic wave whose pitch p is a half wavelength.

In the resonator 9, the anti-resonance frequency is basically defined by the resonance frequency defined by the pitch p and the capacitance ratio in the resonator 9. The capacitance ratio is the ratio between the capacitance of the resonator 9 (excitation electrode 25) and the capacitance (dynamic capacitance) of a series resonant circuit when the resonator 9 is represented by an equivalent circuit. On the other hand, as described above, in the ladder type filter, the anti-resonant frequencies of the plurality of series resonators 9S are basically the same, and the anti-resonant frequencies of the plurality of parallel resonators 9P are basically the same. Therefore, the capacitances (hereinafter sometimes simply referred to as capacitances) of the plurality of series resonators 9S may be equal to each other unless otherwise specified. The same applies to the plurality of parallel resonators 9P.

Although not particularly shown, the resonator 9 may have a protective film (not shown) that covers the upper surface 21a of the substrate 21 from above the excitation electrode 25 and the reflector 27. Such a protective film is made of an insulating material such as SiO ₂ , for example, and reduces the possibility that the excitation electrode 25 etc. will corrode, and/or compensates for changes in characteristics due to temperature changes in the resonator 9. Contribute to things. Furthermore, the resonator 9 may have an additional film that overlaps the upper surface or the lower surface of the excitation electrode 25 and the reflector 27 and has a shape that basically fits within the excitation electrode 25 and the reflector 27 in a plan view. good. Such an additional film is made of, for example, an insulating material or a metal material that has different acoustic characteristics from the material of the excitation electrode 25, etc., and contributes to improving the reflection coefficient of the SAW.

The filter 1 has all the resonators 9 on the same substrate 21, for example. The input terminal 3, the output terminal 5, and the reference potential section 7 (reference potential terminal) are constituted by a conductor layer located on the substrate 21, for example. However, the filter 1 may include a plurality of substrates 21. The plurality of resonators 9 of the filter 1 may be distributed and arranged on the plurality of substrates 21.

(Specific method to vary power)
As described above, in this embodiment, regarding the power applied to the resonator 9, the power at the frequency f1 is made different between the series resonators 9S4a and 9S4b at the last stage, and the power at the frequency f2 is made different between the series resonators 9S4a and 9S4b. The power of the frequency f1 is made to differ in magnitude relationship opposite to that of the power of the frequency f1. Various methods are possible for making the power applied to the series resonators 9S4a and 9S4b different in this way. In the above explanation, the explanation has been made from the perspective of the passband with reference to the graph (FIG. 4(a)) in which the vertical axis is the attenuation amount A, but the passband explained with reference to FIG. 4(a) etc. No need to be realized. Below, some examples will be shown about methods of varying the power applied to the series resonators 9S4a and 9S4b.

(Difference in capacity)
The difference in power applied to the last-stage series resonators 9S4a and 9S4b is, for example, between the first rear-stage filter section 11Ba (all or a part thereof) and the second rear-stage filter section 11Bb (all or a part thereof). This may be realized by a difference in capacity. As is clear from the formula for the impedance of the capacitor, the larger the capacitance of the filter section 11 and/or the resonator 9, the easier it is to pass signals on the high frequency side. This property may be utilized.

In the resonator 9 configured as a SAW resonator, parameters that define the capacitance include, for example, the intersection width W of the electrode fingers 33 and the number of the electrode fingers 33. For example, as shown in FIG. 5, the intersection width W is defined by the length in the D2 direction from the tip of one electrode finger 33 to the tip of the other electrode finger 33 in two adjacent electrode fingers 33. Ru. In the illustrated example, the intersection width W is the same at any position in the D1 direction. The larger the crossing width W, the larger the capacitance of the resonator 9. Furthermore, the larger the number of electrode fingers 33, the larger the capacitance of the resonator 9.

(Difference in crossover width in parallel resonators)
FIG. 6 is a circuit diagram schematically showing a part of the filter 1. In this figure, a part of the filter 1 on the output terminal 5 side is shown. More specifically, parallel resonators 9P3a and 9P3b, series resonators 9S4a and 9S4b, and output terminal 5 are shown. Further, in this figure, only the excitation electrode 25 of the resonator 9 is shown.

The parallel resonator 9P3a is a parallel resonator connected between the last-stage series resonator 9S4a and the immediately previous series resonator 9S3a (FIG. 1) in the first rear-stage filter section 11Ba. Similarly, the parallel resonator 9P3b is a parallel resonator connected between the last stage series resonator 9S4b and the previous series resonator 9S3b (FIG. 1) in the second rear-stage filter section 11Bb. It is.

The crossing width of the electrode fingers 33 of the parallel resonator 9P3a is made longer than the crossing width of the electrode fingers 33 of the parallel resonator 9P3b, so that the capacitance of the parallel resonator 9P3a is greater than the capacitance of the parallel resonator 9P3b. May be made larger. In this way, the parallel resonator 9P3a can more easily release high-frequency signals to the reference potential section 7 than the parallel resonator 9P3b. As a result, at a relatively low frequency f1, the power applied to the series resonator 9S4a becomes larger than the power applied to the series resonator 9S4b, and at a relatively high frequency f2, the power applied to the series resonator 9S4b becomes larger than the power applied to the series resonator 9S4b. The power is larger than the power applied to the resonator 9S4a.

The difference in capacitance between the parallel resonators 9P3a and 9P3b may be set as appropriate. In a typical ladder filter, parallel resonators may have different capacitances in order to fine-tune their characteristics. The difference in capacitance between parallel resonators 9P3a and 9P3b may be made larger than the difference in capacitance for such fine adjustment, for example. For example, the difference in capacity between the two may be 5% or more, 10% or more, 20% or more, or 30% or more of the average value of both capacities.

The capacitances of the parallel resonators 9P3a and 9P3b may both be different from the capacitance of the parallel resonator 9P of the pre-stage filter section 11A, or only one of them may be different from the capacitance of the parallel resonator 9P of the pre-stage filter section 11A. good. As for the former, for example, the capacitance of the parallel resonator 9P3a is made larger than the capacitance of the parallel resonator 9P of the pre-stage filter section 11A, and the capacitance of the parallel resonator 9P3b is made smaller than the capacitance of the parallel resonator 9P of the pre-stage filter section 11A. Here are some examples of how this can be done.

Conditions other than the intersection width (for example, pitch p) are the same for parallel resonator 9P3a and parallel resonator 9P3b, for example. However, conditions other than the crossing width may also be different between the two. Further, the conditions other than the crossing width (capacitance) of the parallel resonators 9P3a and 9P3b (for example, the pitch p) may be the same as the conditions other than the crossing width of the parallel resonator 9P of the pre-stage filter section 11A, or may be different. You can.

(Difference in crossover width in series resonators)
As shown in FIG. 6, the crossing width of the electrode fingers 33 of the last stage series resonator 9S4b is made longer than the crossing width of the electrode fingers 33 of the last stage series resonator 9S4a. The capacitance may be made larger than the capacitance of the electrode finger 33 of the series resonator 9S4a. In this way, the series resonator 9S4b allows signals on the high frequency side to flow more easily to the output terminal 5 than the series resonator 9S4a. As a result, at a relatively low frequency f1, the power applied to the series resonator 9S4a becomes larger than the power applied to the series resonator 9S4b, and at a relatively high frequency f2, the power applied to the series resonator 9S4b becomes larger than the power applied to the series resonator 9S4b. The power is larger than the power applied to the resonator 9S4a.

The difference in capacitance between the series resonators 9S4a and 9S4b may be set as appropriate. In a typical ladder filter, the series resonators may have different capacitances in order to fine-tune their characteristics. The difference in capacitance between the series resonators 9S4a and 9S4b may be made larger than the difference in capacitance for such fine adjustment, for example. For example, the difference in capacity between the two may be 5% or more, 10% or more, 20% or more, or 30% or more of the average value of both capacities.

The capacitances of the series resonators 9S4a and 9S4b may both be different from the capacitance of the series resonator 9S of the pre-stage filter section 11A, or only one of them may be different from the capacitance of the series resonator 9S of the pre-stage filter section 11A. good. As for the former, for example, the capacitance of the series resonator 9S4a is made smaller than the capacitance of the series resonator 9S of the pre-stage filter section 11A, and the capacitance of the series resonator 9S4b is made larger than the capacitance of the series resonator 9S of the pre-stage filter section 11A. Here are some examples of how this can be done.

Conditions other than the intersection width (for example, pitch p) are the same for the series resonator 9S4a and the series resonator 9S4b, for example. However, conditions other than the crossing width may also be different between the two. Further, conditions other than the crossing width (capacitance) of the series resonators 9S4a and 9S4b (for example, pitch p) may be the same as or different from the conditions other than the crossing width of the series resonator 9S of the pre-stage filter section 11A. You can.

(Difference in the number of electrode fingers in parallel resonators)
FIG. 7 is a circuit diagram similar to FIG. 6, schematically showing a part of the filter 1.

Also in the example of FIG. 7, similarly to the example of FIG. 6, the capacitance of the parallel resonator 9P3a is made larger than the capacitance of the parallel resonator 9P3b. However, in the example of FIG. 7, the number of electrode fingers 33 of the parallel resonator 9P3a is greater than the number of electrode fingers 33 of the parallel resonator 9P3b, thereby achieving a difference in capacitance.

The parallel resonators 9P3a and 9P3b in FIG. 7 may be the same as the parallel resonators 9P3a and 9P3b in FIG. 6, except that the method of realizing the difference in capacitance is different. The description of the parallel resonators 9P3a and 9P3b in FIG. 6 may be used as appropriate by replacing the intersection width with the number of electrode fingers.

(Difference in the number of electrode fingers in series resonators)
Similar to the parallel resonators 9P3a and 9P3b, the series resonators 9S4a and 9S4b shown in FIG. 7 differ from the series resonators 9S4a and 9S4b shown in FIG. 6 in that a difference in capacitance is realized depending on the number of electrode fingers 33. Other than this point, the series resonators 9S4a and 9S4b in FIG. 7 may be the same as the series resonators 9S4a and 9S4b in FIG. 6. The description of the series resonators 9S4a and 9S4b in FIG. 6 may be used as appropriate by replacing the intersection width with the number of electrode fingers.

(difference in pitch)
The difference in power applied to the last-stage series resonators 9S4a and 9S4b may be realized in a form similar to the concept described with reference to FIGS. 2, 3, and 4(a). That is, the pass band may be adjusted by adjusting the pitch p (FIG. 5) of the electrode fingers 33, thereby realizing a difference in power. Specifically, it is as follows.

FIG. 8 is a circuit diagram similar to FIG. 6, schematically showing a part of the filter 1.

In the example shown in FIG. 8, the pitch p of the parallel resonators 9P3a is larger than the pitch p of the parallel resonators 9P3b. Therefore, the resonant frequency fpr (FIG. 2) of the parallel resonator 9P3a is lower than the resonant frequency fpr of the parallel resonator 9P3b. Further, the anti-resonance frequency fpa (FIG. 2) of the parallel resonator 9P3a is lower than the anti-resonance frequency fpa of the parallel resonator 9P3b.

Moreover, in the example shown in FIG. 8, the pitch p of the series resonators 9P4a is made larger than the pitch p of the series resonators 9P4b. Therefore, the resonant frequency fsr (FIG. 2) of the series resonator 9P4a is lower than the resonant frequency fsr of the series resonator 9P4b. Further, the anti-resonant frequency fsa (FIG. 2) of the series resonator 9P4a is lower than the anti-resonant frequency fsa of the series resonator 9P4b.

Therefore, the passband PB (FIG. 2) of the first post-filter section 11Ba is compared with the passband PB of the second post-filter section 11Bb, as explained with reference to FIGS. 4(a) and 4(b). It is located on the low frequency side.

The passband PB of each post-filter section 11B is narrower than the passband PB of the pre-filter section 11A (eg, the same as the passband PB0 obtained by adding the passbands PB of the two post-filter sections 11B). From another perspective, the frequency difference between the resonant frequency and the anti-resonant frequency in each resonator 9 of the post-stage filter section 11B is smaller than the frequency difference between the resonant frequency and the anti-resonant frequency in each resonator 9 of the pre-stage filter section 11A. . Such frequency difference adjustment may be realized, for example, by various known methods.

For example, by increasing the ratio of the capacitance of the resonator 9 to the capacitance (dynamic capacitance) of the series resonant circuit when the resonator 9 is expressed as an equivalent circuit, the anti-resonant frequency can be adjusted to the lower frequency side (resonant frequency side), thereby reducing the frequency difference. The method of adjusting this capacitance ratio may also be realized by various known methods. For example, various parameters of the resonator 9 may themselves be adjusted. Further, for example, a capacitor may be connected in parallel to the resonator 9. In this case, the combination of the resonator 9 and the added capacitor may be regarded as a resonator.

(other adjustment parameters)
Although not particularly shown, various methods for varying the power applied to the series resonators 9S4a and 9S4b at the last stage are possible in addition to adjusting the capacitance of the resonators 9 and varying the pitch.

Further, for example, the duty ratio of the resonator 9 may be adjusted. The duty ratio is expressed, for example, by w0/p, where the width of the electrode finger 33 is w0 (FIG. 5). The larger the duty ratio, the lower the resonant frequency and anti-resonant frequency of the resonator 9. Therefore, for example, the duty ratio of the parallel resonator 9P3a may be made larger than the duty ratio of the parallel resonator 9P3b, and/or the duty ratio of the series resonator 9S4a may be made larger than the duty ratio of the series resonator 9S4b. You may do so.

Further, for example, the thickness of the excitation electrode 25 of the resonator 9 may be adjusted. The thicker the excitation electrode 25, the lower the resonant frequency and anti-resonant frequency of the resonator 9. Therefore, for example, the excitation electrode 25 of the parallel resonator 9P3a may be made thicker than the excitation electrode 25 of the parallel resonator 9P3b, and/or the excitation electrode 25 of the series resonator 9S4a may be made thicker than the excitation electrode 25 of the series resonator 9S4b. It may also be made thicker.

Further, for example, in an embodiment in which the excitation electrode 25 is covered with a protective film (not shown), the thickness of the protective film may be adjusted. The thicker the protective film, the lower the resonant frequency and anti-resonant frequency of the resonator 9. Therefore, for example, the protective film covering the excitation electrode 25 of the parallel resonator 9P3a may be made thicker than the protective film covering the excitation electrode 25 of the parallel resonator 9P3b, and/or the protection film covering the excitation electrode 25 of the series resonator 9S4a. The film may be thicker than the protective film covering the excitation electrode 25 of the series resonator 9S4b.

Further, for example, in a mode in which an additional film (not shown) is superimposed on the excitation electrode 25, the thickness of the additional film may be adjusted. The thicker the additional film, the lower the resonant frequency and anti-resonant frequency of the resonator 9. Therefore, for example, the additional film of the parallel resonator 9P3a may be made thicker than the additional film of the parallel resonator 9P3b, and/or the additional film of the series resonator 9S4a may be made thicker than the additional film of the series resonator 9S4b. You may do so. However, the additional film may be considered as part of the excitation electrode 25. Further, for example, an additional film may be provided only for the former of the parallel resonators 9P3a and 9P3b, and/or an additional film may be provided only for the former of the series resonators 9S4a and 9S4b.

Further, for example, a resistor, an inductor, and/or a capacitor may be connected to the resonator 9 in series and/or in parallel. For example, as described above, when a capacitor is connected in parallel to the resonator 9, the anti-resonance frequency shifts to the lower frequency side. Furthermore, when an inductor is connected in series with the resonator 9, the resonant frequency is shifted to the lower frequency side. Therefore, for example, a capacitor may be connected in parallel and an inductor may be connected in series only to the former of the parallel resonators 9P3a and 9P3b, and/or a capacitor may be connected only to the former of the series resonators 9S4a and 9S4b. Inductors may be connected in series as well as in parallel. Alternatively, capacitors are connected in parallel to both parallel resonators 9P3a and 9P3b, and inductors are connected in series, and the capacitance and inductance added to the parallel resonator 9P3a are made larger than the capacitance and inductance added to the parallel resonator 9P3b. You may. The same applies to series resonators 9S4a and 9S4b. Note that the combination of the resonator 9 and the above electronic element connected to the resonator 9 may be regarded as a resonator.

As understood from the above description, the object to be adjusted in order to vary the power may be the resonator 9 itself (in a narrow sense), or components other than the resonator 9 (for example, capacitors and inductors). ).

The methods of varying power described above may be combined as appropriate. For example, adjusting the crossing width, adjusting the number of electrode fingers 33, adjusting the pitch, adjusting the thickness of the excitation electrode 25, adjusting the thickness of the protective film, adjusting the thickness of the additional film, and connecting other electronic elements. Two or more of them may be combined and applied to realize the difference between the parallel resonators 9P3a and 9P3b, or applied to realize the difference between the series resonators 9S4a and 9S4b. Further, for example, the method applied to the parallel resonators 9P3a and 9P3b may be different from the method applied to the series resonators 9S4a and 9S4b.

(Adjustment in other resonators)
In FIGS. 6 to 8, the configurations of the series resonators 4Sa and 4Sb at the last stage are different, and the configurations of the parallel resonators 9P3a and 9P3b immediately before them are different, so that the power applied to the series resonators 4Sa and 4Sb at the last stage is were made different from each other. In other words, it was assumed that the other configurations (for example, other resonators 9) of the two post-stage filter sections 11B were the same. Further, the other resonators 9 (in the example of FIG. 1, series resonators 9S3a and 9S3b) of the two rear-stage filter sections 11B are similar to the resonators 9 of the front-stage filter section 11A. However, although not particularly illustrated, instead of or in addition to adjusting the configurations of the series resonators 4Sa and 4Sb and the parallel resonators 9P3a and 9P3b, the configurations of other resonators 9 included in the post-stage filter section 11B may be adjusted. Accordingly, the power applied to the last stage series resonators 4Sa and 4Sb may be made different.

For example, the various adjustments to the series resonators 4Sa and 4Sb described above can be made by adjusting the other series resonators 9S (in the example of FIG. 9S3a and 9S3b). Moreover, unlike the example of FIG. 1, in a case where any of the post-stage filter sections 11B has three or more series resonators 9S and two or more parallel resonators 9P, the above-mentioned parallel resonators 9P3a and Adjustments similar to the various adjustments made to 9P3b may be made to other parallel resonators 9P of the post-filter section 11B instead of or in addition to the parallel resonators 9P3a and 9P3b.

Furthermore, although the explanation has focused on the individual resonators 9, for example, when viewed from the input side, at the frequency f1, the impedance of the entire first rear-stage filter section 11Ba is smaller than the impedance of the entire second rear-stage filter section 11Bb. Therefore, at frequency f2, the impedance of the entire first filter section 11Ba may be designed to be larger than the impedance of the entire second filter section 11Bb. And/or, when viewed from the input side, in the first post-stage filter section 11Ba, the impedance at the frequency f1 becomes smaller than the impedance at the frequency f2, and in the second post-stage filter section 11Bb, the impedance at the frequency f1 becomes smaller than the impedance at the frequency f2. The design may be such that it is larger than the impedance. In addition, the partial pressure within each post-filter section 11B may be adjusted as appropriate.

As described above, in this embodiment, the filter 1 includes an input terminal 3 to which a signal is input, an output terminal 5 to which a signal is output, and a first terminal located on the signal path from the input terminal 3 to the output terminal 5. It has a filter section (first rear filter section 11Ba) and a second filter section (second rear filter section 11Bb). The two post-stage filter sections 11B are connected in parallel. Each of the two post-stage filter sections 11B includes two or more (two in this embodiment) series resonators 9S and one or more (one in this embodiment) parallel resonators 9P connected in a ladder shape. It is a ladder type filter. In each of the two post-stage filter sections 11B, one or more parallel resonators 9P connect a parallel resonator 9P3a or 9P3b connected to a signal path from one to the other of the two or more series resonators 9S. Contains. Focusing on the first frequency (frequency f1) and the second frequency (frequency f2) higher than frequency f1 within the first passband (passband PB0) that is the sum of the passbands PB of the two post-filter sections 11B. . At this time, the two post-stage filter sections 11B are configured so that the following relationship is satisfied. When signals having the frequency f1 are simultaneously input to the two post-stage filter sections 11B, the power of the signal applied to the series resonator 9S4a becomes larger than the power applied to the series resonator 9S4b. When signals having the frequency f2 are simultaneously input to the two post-stage filter sections 11B, the power applied to the series resonator 9S4b becomes larger than the power applied to the series resonator 9S4a.

Thus, for example, as already mentioned, intermodulation distortion is reduced. By reducing intermodulation distortion, for example, signals of two or more frequencies can be used simultaneously within one standardized passband (passband PB0). As a result, for example, by using filter 1 as a transmission filter for a base station, it becomes easier for a plurality of carriers to use one base station at the same time. Until now, countermeasures against intermodulation distortion of weak received signals input to antennas have been studied, but countermeasures that can cope with intermodulation distortion of high-power transmission signals as in this embodiment have not been considered. do not have.

The inventor of the present application has confirmed the effect of reducing intermodulation distortion through simulation calculations. Specifically, in the configuration shown in FIG. 1, a configuration in which parallel resonators 9P3a and 9P3b have the same configuration and series resonators 9S4a and 9S4b have the same configuration was used as a comparative example. From another point of view, an aspect in which the configurations of all the series resonators 9S and parallel resonators 9P of the post-stage filter section 11B are the same as the configurations of the series resonators 9S and parallel resonators 9P of the pre-stage filter section 11A is taken as a comparative example. . Furthermore, in the comparative example, the ratio of the capacitances of the parallel resonators 9P3a and 9P3b was changed to 3:2, and the ratio of the capacitances of the series resonators 9S4a and 9S4b was changed to 3:4. In the example, intermodulation distortion was reduced compared to the comparative example, and the difference was about 0.05 dB.

In this embodiment, at least a part of the pass band PB of the first post-filter section 11Ba includes a boundary frequency on the high frequency side, and a low frequency of the pass band PB of the second post-filter section 11Bb. At least a part of the band including the boundary frequency on the side overlaps.

In this case, for example, the probability that a frequency band in which a signal is attenuated will occur between the passbands PB of the two post-filter sections 11B is reduced. Furthermore, the filter 1 including the two post-stage filter sections 11B can function as a filter having one passband PB0.

In this embodiment, the filter 1 further includes a third filter section (pre-stage filter section 11A). The front-stage filter section 11A is located in the signal path from the input terminal 3 to the two rear-stage filter sections 11B, and has a passband including frequencies f1 and f2 (for example, the sum of the passbands of the two rear-stage filter sections 11B). It has a passband PB0).

In this case, for example, the effect of passing the signal in the passband PB0 and attenuating the signal outside the passband PB0 is improved. That is, the original function of the filter 1 having the passband PB0 is improved.

In this embodiment, the capacitance of the last-stage series resonator 9S4a of the first rear-stage filter section 11Ba is smaller than the capacitance of the last-stage series resonator 9S4b of the second rear-stage filter section 11Bb.

In this case, as already stated, the higher the frequency of the signal, the easier it is to pass through the latter of the series resonators 9S4a and 9S4b. Thereby, the powers applied to the series resonators 9S4a and 9S4b can be made different from each other, and intermodulation distortion can be reduced. Furthermore, the occurrence of ripples is reduced compared to an embodiment in which the pitch p of the series resonators 9S4a and the pitch p of the series resonators 9S4b are made different. This has been confirmed by the inventor's simulation calculations. For example, if the pitch p of the series resonator 9S4a and the pitch p of the series resonator 9S4b differ by an amount corresponding to a width of 1/4 or more of the pass band PB0, ripples occur. However, in an embodiment in which the powers applied to the series resonators 9S4a and 9S4b are made to differ from each other due to the difference in capacitance, such probability is reduced.

In this embodiment, the capacitance of the last-stage parallel resonator 9P3a of the first rear-stage filter section 11Ba is larger than the capacitance of the last-stage parallel resonator 9P3b of the second rear-stage filter section 11Bb.

In this case, as already mentioned, the higher the frequency of the signal, the easier it is to pass through the former of the parallel resonators 9P3a and 9P3b. Thereby, the powers applied to the series resonators 9S4a and 9S4b can be made different from each other, and intermodulation distortion can be reduced. Furthermore, as described with respect to the series resonators 9S4a and 9S4b, the probability that ripples occur can be reduced compared to the case where the pitches p are different.

In this embodiment, the two or more series resonators 9S and the one or more parallel resonators 9P included in the two post-filter sections 11B are elastic wave resonators (for example, SAW resonators) each having an excitation electrode 25. The excitation electrode 25 has a plurality of electrode fingers 33 arranged in the propagation direction of the elastic wave.

In such a configuration, for example, the power applied to the last stage series resonators 9S4a and 9S4b can be adjusted using various methods. Further, for example, the capacitance can be easily adjusted by adjusting the crossing width and/or the number of electrode fingers 33.

In the present embodiment, the pitch p of the plurality of electrode fingers 33 in the last stage series resonator 9S4a of the first rear filter section 11Ba is the same as the pitch p of the plurality of electrode fingers 33 in the last stage series resonator 9S4b of the second rear filter section 11Bb. is larger than the pitch p.

In this case, for example, since the principle of attenuating the signal of frequency f2 in the first post-filter section 11Ba is based on the principle of a ladder filter using an elastic wave resonator, the frequency f2 applied to the series resonator 9S4a is more noticeable. power can be reduced. Similarly, in the second post-stage filter section 11Bb, the power at the frequency f1 applied to the series resonator 9S4b can be reduced more significantly.

In this embodiment, the pitch p of the plurality of electrode fingers 33 in the last-stage parallel resonator 9P3a of the first rear-stage filter section 11Ba is the same as the pitch p of the plurality of electrode fingers 33 in the last-stage parallel resonator 9P3b of the second rear-stage filter section 11Bb. is larger than the pitch p.

In this case, for example, similar to the case where the pitches of the series resonators 9S are different, the power at the frequency f2 applied to the series resonator 9S4a and the power at the frequency f1 applied to the series resonator 9S4b are more significantly reduced. can do.

(Example of filter usage)
Hereinafter, electronic components and electronic equipment including the filter 1 described above will be illustrated.

(branching filter)
FIG. 9 is a circuit diagram schematically showing the configuration of a duplexer 101 as an example of how the filter 1 is used.

More specifically, the branching filter 101 is configured as a duplexer. The duplexer 101 includes, for example, a transmission filter 109 that filters the transmission signal from the transmission terminal 103 and outputs it to the antenna terminal 105, and a transmission filter 109 that filters the reception signal from the antenna terminal 105 and outputs it to a pair of reception terminals 107. It has a reception filter 111.

In the illustrated example, filter 1 is used as transmit filter 109. The transmission terminal 103 corresponds to the input terminal 3 of the filter 1. Antenna terminal 105 corresponds to output terminal 5. For convenience, unlike FIG. 1, the transmission terminal 103 and antenna terminal 105 are illustrated as external components of the transmission filter 109 (filter 1).

In the illustrated example, the reception filter 111 is configured by a ladder filter like the transmission filter 109 (filter 1). However, the reception filter 111 may be configured by other types of filters. For example, the reception filter 111 may be configured as a multimode filter. Although not particularly illustrated, the multimode filter includes, for example, two or more excitation electrodes 25 arranged in the propagation direction of elastic waves and a pair of reflectors 27 located on both sides of the excitation electrodes 25.

Unlike the illustrated example, filter 1 may be applied to reception filter 111 in addition to or instead of transmission filter 109. In this case, the antenna terminal 105 corresponds to the input terminal 3 and the receiving terminal 107 corresponds to the output terminal 5. The transmission filter 109 and the reception filter 111 may be provided on the same substrate 21 or may be provided on different substrates 21.

(Communication device)
FIG. 10 is a block diagram showing main parts of a communication device 151 as an example of how the filter 1 is used. The communication device 151 performs wireless communication using radio waves, and includes, for example, the duplexer 101 described above.

In the communication device 151, a transmission information signal TIS containing information to be transmitted is modulated and frequency raised (converted to a high frequency signal having a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 153 to become a transmission signal TS. It is said that The transmission signal TS has unnecessary components outside the transmission passband removed by a bandpass filter 155, is amplified by an amplifier 157, and is input to the duplexer 101 (transmission terminal 103). Then, the duplexer 101 (transmission filter 109) removes unnecessary components other than the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS from the antenna terminal 105 to the antenna 159. . The antenna 159 converts the input electric signal (transmission signal TS) into a wireless signal (radio wave) and transmits the signal.

Further, in the communication device 151, a radio signal (radio wave) received by the antenna 159 is converted into an electric signal (received signal RS) by the antenna 159, and input to the duplexer 101 (antenna terminal 105). The duplexer 101 (reception filter 111) removes unnecessary components outside the reception passband from the input reception signal RS, and outputs the result from the reception terminal 107 to the amplifier 161. The output reception signal RS is amplified by an amplifier 161, and a bandpass filter 163 removes unnecessary components outside the reception passband. Then, the received signal RS is frequency lowered and demodulated by the RF-IC 153 to become a received information signal RIS.

Note that the transmission information signal TIS and the reception information signal RIS may be low frequency signals (baseband signals) containing appropriate information, such as analog audio signals or digitized signals. The passband of the wireless signal may be set as appropriate, and may be a relatively high frequency passband (for example, 5 GHz or higher). The modulation method may be phase modulation, amplitude modulation, frequency modulation, or a combination of two or more of these. As for the circuit system, although a direct conversion system is illustrated in FIG. 10, any other appropriate circuit system may be used, for example, a double superheterodyne system may be used. Further, FIG. 10 schematically shows only the main parts, and a low-pass filter, an isolator, etc. may be added at an appropriate position, or the position of an amplifier, etc. may be changed.

In FIG. 3, when the filter 1 is used in the duplexer 101, the reception band is indicated by the symbol BR, and the transmission band is indicated by the symbol BT. Frequency f3 is an example of a frequency of intermodulation distortion caused by signals of frequencies f1 and f2, and is located within the reception band. Even when the frequency f3 is located within the reception band in this way, in this embodiment, since intermodulation distortion is reduced, the probability that reception accuracy will decrease is reduced.

In FIG. 3, it is assumed that the duplexer 101 (communication device 151) is used in a base station, and the reception band is located on the lower frequency side than the transmission band. When the angular velocities of signals with frequencies f1 and f2 are ω1 and ω2, the angular velocities of third-order intermodulation distortion are 2×ω1+ω2, 2×ω1−ω2, ω1+2×ω2, or ω1−2×ω2. When the reception band and transmission band are set as shown in FIG. 3, intermodulation distortion having an angular velocity of 2×ω1−ω2 is likely to occur in the reception band. The power of this intermodulation distortion is proportional to P1 ² ×P2. Therefore, the reduction in the power P1 applied to the second post-filter section 11Bb may be prioritized over the reduction in the power P2 applied to the first post-filter section 11Ba.

In the above embodiment, the first post-filter section 11Ba is an example of a first filter. The second post-stage filter section 11Bb is an example of a second filter. The pre-filter section 11A is an example of a third filter. The series resonator 9P4a is an example of the last stage series resonator of the first filter. The series resonator 9P4b is an example of the last stage series resonator of the second filter.

The technology according to the present disclosure is not limited to the above embodiments, and may be implemented in various ways.

In the embodiment, two filter sections (post-stage filter sections 11B) are connected in parallel with each other. However, three or more filter sections connected in parallel to each other may be provided. In this case, the passbands of any two filter sections do not have to overlap with each other, unlike in FIGS. 4(a) and 4(b).

Further, two (or three or more) filter sections connected in parallel to each other do not need to constitute a filter having one passband. Also in this case, the passbands of the two filter sections do not have to overlap with each other, unlike in FIGS. 4(a) and 4(b).

No other filter section may be provided before the filter sections connected in parallel to each other. Furthermore, in the case where another filter section is provided, the pass band of this filter section may be different from the pass band obtained by adding up the pass bands of two or more filter sections connected in parallel. For example, the former may be a wider band than the latter, encompassing the latter, or conversely, may be narrower than the latter, encompassing only a portion of the latter.

1...Filter, 3...Input terminal, 5...Output terminal, 9S...Series resonator, 9P...Parallel resonator, 9S3a...Series resonator (first stage series resonator of the first filter section), 9S3b...Series resonator ( 9P3a... Parallel resonator (Parallel resonator of the first filter section), 9P3b... Parallel resonator (Parallel resonator of the second filter section), 9S4a... Series resonator ( 9S4b... series resonator (last stage series resonator of the second filter section), 11Ba... first rear stage filter section (first filter section), 11Bb... second Post-stage filter section (second filter section).

Claims (9)

An input terminal into which a signal is input,
An output terminal that outputs a signal,
a first filter section located in a signal path from the input terminal to the output terminal;
a second filter section located in a signal path from the input terminal to the output terminal and connected in parallel with the first filter section;
It has
Each of the first filter section and the second filter section is a ladder type filter including two or more series resonators and one or more parallel resonators connected in a ladder type,
In each of the first filter section and the second filter section, the one or more parallel resonators are connected to a signal path from one of the two or more series resonators to the other one. Contains a resonator,
In each of the first filter section and the second filter section, the series resonator located closest to the output terminal is referred to as the last stage series resonator, and the pass band of the first filter section and the pass band of the second filter section are When the passband obtained by adding the bands together is referred to as a first passband, the first filter section and the second filter section are
When a signal having a first frequency within the first passband is simultaneously input to the first filter section and the second filter section, the power of the signal applied to the last stage series resonator of the first filter section is , a signal having a second frequency greater than the power applied to the last stage series resonator of the second filter section and within the first passband and higher than the first frequency is transmitted to the first filter section and the second filter section. When simultaneously input to the second filter section, the power applied to the last stage series resonator of the second filter section is larger than the power applied to the last stage series resonator of the first filter section. It is configured,
The capacitance of the last stage series resonator of the first filter section is smaller than the capacitance of the last stage series resonator of the second filter section.
filter. An input terminal into which a signal is input,
An output terminal that outputs a signal,
a first filter section located in a signal path from the input terminal to the output terminal;
a second filter section located in a signal path from the input terminal to the output terminal and connected in parallel with the first filter section;
It has
Each of the first filter section and the second filter section is a ladder type filter including two or more series resonators and one or more parallel resonators connected in a ladder type,
In each of the first filter section and the second filter section, the one or more parallel resonators are connected to a signal path from one of the two or more series resonators to the other one. Contains a resonator,
In each of the first filter section and the second filter section, the series resonator located closest to the output terminal is referred to as the last stage series resonator, and the pass band of the first filter section and the pass band of the second filter section are When the passband obtained by adding the bands together is referred to as a first passband, the first filter section and the second filter section are
When a signal having a first frequency within the first passband is simultaneously input to the first filter section and the second filter section, the power of the signal applied to the last stage series resonator of the first filter section is , a signal having a second frequency greater than the power applied to the last stage series resonator of the second filter section and within the first passband and higher than the first frequency is transmitted to the first filter section and the second filter section. When simultaneously input to the second filter section, the power applied to the last stage series resonator of the second filter section is larger than the power applied to the last stage series resonator of the first filter section. It is configured,
In each of the first filter section and the second filter section, a parallel resonator connected between the last stage series resonator and the previous series resonator is the last stage parallel resonator. When called, the capacitance of the last stage parallel resonator of the first filter section is larger than the capacitance of the last stage parallel resonator of the second filter section.
filter. At least a part of the pass band of the first filter section that includes a boundary frequency on the high frequency side; and at least a part of the pass band of the second filter section that includes the boundary frequency on the low frequency side. The filter according to claim 1 or 2, wherein the bands overlap. The third filter section further includes a third filter section located in a signal path from the input terminal to the first filter section and the second filter section, and having a passband including the first frequency and the second frequency. The filter according to any one of claims 1 to 3, wherein : The two or more series resonators and the one or more parallel resonators are elastic wave resonators each having an excitation electrode,
The filter according to any one of claims 1 to 4 , wherein the excitation electrode has a plurality of electrode fingers arranged in the propagation direction of elastic waves. The pitch of the plurality of electrode fingers in the last stage series resonator of the first filter section is larger than the pitch of the plurality of electrode fingers in the last stage series resonator of the second filter section. filter. In each of the first filter section and the second filter section, a parallel resonator connected between the last stage series resonator and the previous series resonator is the last stage parallel resonator. When calling
The pitch of the plurality of electrode fingers in the last stage parallel resonator of the first filter section is larger than the pitch of the plurality of electrode fingers in the last stage parallel resonator of the second filter section . Filters listed in. The filter according to any one of claims 1 to 7 ,
another filter connected to the output terminal;
A duplexer that has a The filter according to any one of claims 1 to 7 ,
an antenna connected to the output terminal;
an integrated circuit element connected to the input terminal;
A communication device that has

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