Filter and multiplexer
阅读说明:本技术 滤波器以及多路复用器 (Filter and multiplexer ) 是由 加藤雅则 岩永穰 松原裕 于 2019-06-24 设计创作,主要内容包括:本发明提供具有较宽的通过频带、较小的插入损耗以及通过频带端的陡峭的衰减特性的滤波器。滤波器(10)具备:谐振电路(11),其构成连接端子(P1、P2)的信号路径(R)的至少一部分;弹性波谐振器(17),其一端接地;电感器(15),其一端与谐振电路(11)的一端连接且另一端与弹性波谐振器(17)的另一端连接;以及电感器(16),其一端与谐振电路(11)的另一端连接且另一端与弹性波谐振器(17)的上述另一端连接,谐振电路(11)是串联连接了电感器(12)和电容器(13、14)的LC串联谐振电路。(The present invention provides a filter having a wide pass band, a small insertion loss, and a steep attenuation characteristic at the end of the pass band. A filter (10) is provided with: a resonance circuit (11) that constitutes at least a part of a signal path (R) connecting the terminals (P1, P2); an elastic wave resonator (17) having one end grounded; an inductor (15) having one end connected to one end of the resonance circuit (11) and the other end connected to the other end of the elastic wave resonator (17); and an inductor (16) having one end connected to the other end of the resonance circuit (11) and the other end connected to the other end of the elastic wave resonator (17), wherein the resonance circuit (11) is an LC series resonance circuit in which an inductor (12) and capacitors (13, 14) are connected in series.)
1. A filter is provided with:
a series arm resonant circuit that constitutes at least a part of a signal path connecting the first terminal and the second terminal;
a parallel arm resonator having one end grounded;
a first inductor having one end connected to one end of the series arm resonant circuit and the other end connected to the other end of the parallel arm resonator; and
a second inductor having one end connected to the other end of the series arm resonant circuit and the other end connected to the other end of the parallel arm resonator,
the series arm resonant circuit is an LC series resonant circuit in which a third inductor and a capacitor are connected in series.
2. The filter of claim 1, wherein,
the parallel arm resonator has a substrate made of a piezoelectric material containing lithium niobate, and transmits a signal by a rayleigh wave propagating through the substrate.
3. The filter of claim 1 or 2,
in the series arm resonant circuit, the third inductor is formed by a laminated chip inductor, and the capacitor is formed by a laminated chip capacitor.
4. The filter of claim 1 or 2,
the capacitor is constituted by a plurality of stacked chip capacitors connected in series.
5. The filter according to any one of claims 1 to 4,
the filter includes a fourth inductor for matching at least one of a portion connected between the series arm resonant circuit and the first terminal of the signal path and a portion connected between the series arm resonant circuit and the second terminal of the signal path,
in the pass band of the filter, the Q value of the first inductor and the Q value of the second inductor are both higher than the Q value of the fourth inductor.
6. The filter according to any one of claims 1 to 5,
the filter has a passband of 2300MHz to 2400MHz, a passband of 2496MHz to 2690MHz, and a stopband of 1427MHz to 2200 MHz.
7. A multiplexer, having:
the filter of claim 6, namely the first filter;
a second filter having a pass band of 1427MHz to 2200MHz inclusive; and
a third filter having a passband of 617MHz to 960MHz inclusive,
one end of the first filter, one end of the second filter, and one end of the third filter are connected to each other.
8. The multiplexer of claim 7,
the second filter is composed of an LC resonance circuit and an elastic wave resonator,
the third filter is constituted by an LC resonant circuit.
Technical Field
The invention relates to a filter and a multiplexer.
Background
There are communication devices corresponding to a plurality of frequency bands (multi-band) and a plurality of radio systems (multi-mode). The front-end circuit of such a communication device uses a multiplexer for demultiplexing and multiplexing signals of a plurality of frequency bands. The multiplexer is constituted by, for example, a plurality of filters having mutually different pass bands.
Fig. 14 is a circuit diagram showing an example of the high-frequency circuit disclosed in
The high-frequency circuit shown in fig. 14 includes an
Patent document 1: U.S. patent application publication No. 2016/0191014 specification
Recently, against the background of the opening of new frequency bands and narrow gaps between frequency bands, filters constituting multiplexers are required to have a wide pass band, a small insertion loss, and a steep attenuation characteristic at the pass band end.
Disclosure of Invention
Therefore, an object of the present invention is to provide a filter having a wide pass band, a small insertion loss, and a steep attenuation characteristic at a pass band end, and a multiplexer using such a filter.
In order to achieve the above object, a filter according to an aspect of the present invention includes: a series arm resonant circuit that constitutes at least a part of a signal path connecting the first terminal and the second terminal; a parallel arm resonator having one end grounded; a first inductor having one end connected to one end of the series arm resonant circuit and the other end connected to the other end of the parallel arm resonator; and a second inductor having one end connected to the other end of the series arm resonant circuit and the other end connected to the other end of the parallel arm resonator, wherein the series arm resonant circuit is an LC series resonant circuit in which a third inductor and a capacitor are connected in series.
According to the filter of the present invention, the LC series resonant circuit constituting the series arm resonant circuit does not have an antiresonant frequency and changes the resonance characteristics more slowly than the elastic wave resonator, so that matching in a wide pass band can be improved and the insertion loss of the filter can be reduced. In addition, a steep attenuation characteristic at the end of the pass band can be formed by utilizing the frequency characteristic of the parallel arm resonator in which the impedance sharply decreases in the vicinity of the resonance frequency. As a result, a filter having a wide passband, a small insertion loss, and a steep attenuation characteristic at the passband end can be obtained.
Drawings
Fig. 1 is a block diagram showing an example of a configuration of a multiplexer using the filter according to
Fig. 2 is a graph illustrating a pass characteristic required for the filter according to
Fig. 3 is a circuit diagram showing an example of the configuration of a filter according to a comparative example.
Fig. 4 is a graph showing an example of the pass characteristic of the filter according to the comparative example.
Fig. 5 is a graph showing an example of resonance characteristics of a partial circuit of the filter according to the comparative example.
Fig. 6A is a graph showing an example of the reflection characteristic and the pass characteristic of the partial circuit of the filter according to the comparative example.
Fig. 6B is a graph showing an example of the reflection characteristic and the pass characteristic of the partial circuit of the filter according to the comparative example.
Fig. 6C is a graph showing an example of the reflection characteristic and the pass characteristic of the entire filter according to the comparative example.
Fig. 7 is a circuit diagram showing an example of the configuration of the filter according to
Fig. 8 is a graph showing an example of the pass characteristic of the filter according to
Fig. 9 is a graph showing an example of resonance characteristics of a partial circuit of the filter according to
Fig. 10A is a graph showing an example of the reflection characteristic and the pass characteristic of the partial circuit of the filter according to
Fig. 10B is a graph showing an example of the reflection characteristic and the pass characteristic of the partial circuit of the filter according to
Fig. 10C is a graph showing an example of the reflection characteristic and the pass characteristic of the entire filter according to
Fig. 11 is a block diagram showing an example of the configuration of the multiplexer according to
Fig. 12 is a graph showing an example of the pass characteristics of the multiplexer according to
Fig. 13 is a graph showing an example of wide-area transmission characteristics of the filter according to
Fig. 14 is a circuit diagram showing an example of a conventional high-frequency circuit.
Description of the reference numerals
1. 2 … multiplexer, 10, 20, 30, 40, 90 … filter, 11 … resonant circuit, 13, 14 … capacitor, 17, 91, 97 … elastic wave resonator, 12, 15, 16, 18, 19, 95, 96, 98, 99 … inductor.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below are all general or specific examples. The numerical values, shapes, materials, constituent elements, arrangement of constituent elements, connection modes, and the like shown in the following embodiments are merely examples, and do not limit the present invention.
(embodiment mode 1)
The filter according to
Fig. 1 is a block diagram showing an example of a configuration of a multiplexer using the filter according to
In fig. 1, as an example, the first frequency band is set to 2300MHz to 2690MHz, and the second frequency band is set to 1427MHz to 2200 MHz. For reference, the band of 2300MHz to 2690MHz is referred to as a high band HB, and the band of 1427MHz to 2200MHz is referred to as a medium band MB.
One end of the
When the
In order to realize such carrier aggregation, the following pass characteristics are required for the
Fig. 2 is a graph for explaining an example of the pass characteristic required for the filter 10 (more precisely, between the antenna terminal and the high-band terminal of the multiplexer 1). As shown in fig. 2, the
The present inventors have studied a case where a filter having such a passband is realized using a conventional high-frequency circuit. The results of this study are described below as comparative examples.
Fig. 3 is a circuit diagram showing an example of the configuration of a filter 90 according to a comparative example. As shown in fig. 3, filter 90 is configured by adding matching inductors 98 and 99 to the high-frequency circuit of fig. 14 including
Fig. 4 is a graph showing an example of the passing characteristic between the terminals P1 and P2 of the filter 90. The pass band of the filter 90 is set as a portion where the communication band actually used in the high band HB is located, by being divided into a first portion between 2300MHz and 2400MHz inclusive and a second portion between 2496MHz and 2690MHz inclusive (shown in gray in fig. 4). For the portion of the high band HB, an amplified waveform is shown.
As shown by the broken line along the amplified waveform in fig. 4, the pass characteristic of the filter 90 is a waveform largely recessed in the high band HB, and the insertion loss increases at the middle of the high band HB. The gap between the first portion and the second portion is intentionally arranged outside the passband due to unnecessary waves of
Fig. 5 is a graph showing an example of resonance characteristics of a partial circuit of the filter 90. Fig. 5 shows frequency characteristics of impedances of a partial circuit B including
The pass characteristic of fig. 4 is analyzed in more detail.
Fig. 6A is a graph showing an example of reflection characteristics and pass characteristics of partial circuit B (that is, elastic wave resonator 97) of filter 90, where fig. 6A (a) shows the reflection characteristics and fig. 6A (B) shows the pass characteristics. The passing signal forms the reflection characteristic and the passing characteristic of fig. 6A through the ground according to the impedance of the partial circuit B shown in fig. 5.
Reference numerals fr and fa in fig. 6A denote the resonance frequency and the antiresonance frequency of the
The specific frequency band of the elastic wave resonator is generally narrow. For example, there is a substrate made of a piezoelectric material containing lithium niobate, and the specific frequency band of an elastic wave resonator (hereinafter, abbreviated as LN rayleigh) that transmits a signal by a rayleigh wave propagating through the substrate is several percent. Here, the specific frequency band of the elastic wave resonator is a ratio of a difference between an anti-resonance frequency and a resonance frequency of the elastic wave resonator with respect to a center frequency.
For example, by configuring
Fig. 6B is a graph showing an example of the reflection characteristic and the pass characteristic of the partial circuit C of the filter 90, and fig. 6B (a) shows the reflection characteristic and fig. 6B (B) shows the pass characteristic. The reflection characteristic and the pass characteristic of fig. 6B are formed by suppressing the pass of the signal by the impedance of the partial circuit C according to fig. 5.
Reference numerals fr and fa in fig. 6B denote the resonance frequency and the antiresonance frequency of the partial circuit C, respectively. The antiresonant frequency of the partial circuit C is arranged outside the band on the high-frequency side of the high-band HB.
The specific frequency band of the partial circuit C is slightly enlarged by the
Fig. 6C is a graph showing an example of the reflection characteristic and the pass characteristic of the entire filter 90 a, and fig. 6C (a) shows the reflection characteristic and fig. 6C (b) shows the pass characteristic. The reflection characteristic and the pass characteristic of fig. 6C are formed by further adding matching based on the inductors 98, 99 to the combination of the characteristics of the partial circuit B, C of fig. 6A, 6B.
As seen within the dotted circle of fig. 6C (a), the reflection loss of the entire a of the filter 90 is smaller at the middle of the band than at both ends of the high band HB. In other words, the reflection of the signal at the input of the filter 90 is greater in the middle of the high band HB the more. This is because the reflection characteristic of the partial circuit C is too steep, and therefore sufficient reflection loss cannot be secured at the center of the high frequency band.
As a result, as seen in the dotted circle in fig. 6C (b), the insertion loss of the entire filter 90 a has a waveform that is largely concave in the high band HB, and the insertion loss increases (deteriorates) at the middle of the high band HB.
Based on such a study, a filter in which deterioration of the insertion loss is improved by alleviating the steepness of the frequency characteristic of
Fig. 7 is a circuit diagram showing an example of the configuration of the filter according to
The
One end of
One end of
One end of
One end of the
One end of
Fig. 8 is a graph showing an example of the passing characteristic between the terminals P1 and P2 of the
As shown by the broken line along the enlarged waveform of fig. 8, the pass characteristic of the
Fig. 9 is a graph showing an example of resonance characteristics of a partial circuit of the
The pass characteristic of fig. 8 is analyzed in more detail.
Fig. 10A is a graph showing an example of reflection characteristics and pass characteristics of partial circuit B (that is, elastic wave resonator 17) of
As described with reference to fig. 6A, by configuring
Fig. 10B is a graph showing an example of the reflection characteristic and the pass characteristic of the partial circuit C of the
Therefore, unlike the partial circuit C of the filter 90, the anti-resonance frequency fa does not need to be arranged outside the band of the high band HB, and the arrangement of the resonance frequency fr is not restricted. For example, as shown in fig. 10B (a), the resonance frequency fr can be arranged outside the band of the high band HB, and a region in which the variation in reflection loss is small can be arranged within the band of the high band HB.
The LC resonance circuit is suitable for arranging a region in which the variation in the reflection loss is small in the frequency band of the high band HB even if the variation in the frequency characteristic is slower than that of the elastic wave resonator.
Fig. 10C is a graph showing an example of the reflection characteristic and the pass characteristic of the entire filter 10a, and fig. 10C (a) shows the reflection characteristic and fig. 10C (b) shows the pass characteristic.
As seen within the dotted circle of (a) of fig. 10C, the reflection loss is maintained more favorably at the middle of the high frequency band HB. This is because the steepness of the reflection characteristic of the partial circuit C is reduced, and a sufficient reflection loss is secured at the center of the high frequency band, so that good matching can be obtained over the entire region of the high frequency band HB by the
As a result, as seen in the dotted circle in fig. 10C (b), the insertion loss of the entire filter 10a has a waveform without large notches in the high band HB, and the insertion loss decreases (improves) at the middle of the high band HB.
As described above, according to
This makes it possible to obtain a filter having a wide passband, a small insertion loss, and a steep attenuation characteristic at the passband end.
The above-described configuration of the
For example, in the example of fig. 7,
In the
Further, the Q value of each of the
According to this configuration, since the
In the above description, the high band HB (or the first portion and the second portion included in the high band HB) is described as an example of the passband of the
(embodiment mode 2)
A multiplexer according to
Fig. 11 is a block diagram showing an example of the configuration of the multiplexer according to
In fig. 11, as an example, the pass band of the
The passband of the
One end of the
The
Fig. 12 is a graph showing an example of the pass characteristic of the
In the above, the high band HB, the middle band MB, and the low band LB are exemplified as frequency bands, but recently, frequency bands higher than the high band HB are also allocated. As a frequency band higher than the high band HB, for example, a 5G band of 5150MHz to 5925 inclusive can be cited.
The
Fig. 13 is a graph showing an example of wide-area pass characteristics of the
As seen in fig. 13, the pass characteristic of the filter 90 has almost no attenuation in the 5G band. Therefore, when the filter 90 is used for the filter for the high band HB of the multiplexer for demultiplexing and multiplexing the high band HB and the 5G band, an attenuation circuit for the 5G band is additionally required. In this regard, since there is attenuation in the 5G band in the
The filter and the multiplexer according to the embodiments of the present invention have been described above, but the present invention is not limited to the respective embodiments. As long as the present invention is not limited to the above-described embodiments, it is possible to configure the present embodiment by combining constituent elements of different embodiments and various modifications of the present embodiment that may occur to those skilled in the art, without departing from the spirit of the present invention.
(conclusion)
A filter according to an aspect of the present invention includes: a series arm resonant circuit that constitutes at least a part of a signal path connecting the first terminal and the second terminal; a parallel arm resonator having one end grounded; a first inductor having one end connected to one end of the series arm resonant circuit and the other end connected to the other end of the parallel arm resonator; and a second inductor having one end connected to the other end of the series arm resonant circuit and the other end connected to the other end of the parallel arm resonator, wherein the series arm resonant circuit is an LC series resonant circuit in which a third inductor and a capacitor are connected in series.
With such a configuration, the LC series resonant circuit constituting the series arm resonant circuit does not have an antiresonant frequency and changes the resonance characteristics more slowly than the elastic wave resonator, and thus matching in a wider pass band can be improved and the insertion loss of the filter can be reduced. In addition, a steep attenuation characteristic at the end of the pass band can be formed by utilizing the frequency characteristic of the parallel arm resonator in which the impedance sharply decreases in the vicinity of the resonance frequency. As a result, a filter having a wide passband, a small insertion loss, and a steep attenuation characteristic at the passband end can be obtained.
In addition, the parallel arm resonator may have a substrate made of a piezoelectric material containing lithium niobate, and transmit a signal by a rayleigh wave propagating through the substrate.
In such a configuration, it is known that an elastic wave resonator (abbreviated as LN rayleigh) having a substrate made of a piezoelectric material containing lithium niobate and transmitting a signal by a rayleigh wave propagating through the substrate has particularly high steepness in frequency characteristics. Therefore, by configuring the parallel arm resonators with LN rayls, steeper attenuation characteristics can be formed at the low frequency end of the filter passband.
In the series arm resonant circuit, the third inductor may be formed by a stacked chip inductor, and the capacitor may be formed by a stacked chip capacitor.
With this configuration, the third inductor and the capacitor are formed by the laminated chip components. Thus, the Q value of the third inductor can be increased as compared with the case where the third inductor and the capacitor are formed by a patterned conductor in the substrate, and unnecessary coupling between the capacitor and the ground or the like can be suppressed. As a result, the insertion loss of the filter can be further reduced.
The capacitor may be formed by a plurality of stacked chip capacitors connected in series.
With this configuration, by using a plurality of stacked chip capacitors each having a large capacitance value, variation in capacitance value of the entire capacitor can be suppressed, and thus a filter having small characteristic variation can be realized.
In addition, the filter may include a fourth inductor for matching at least one of a portion connected between the series arm resonant circuit and the first terminal of the signal path and a portion connected between the series arm resonant circuit and the second terminal of the signal path, and the Q value of the first inductor and the Q value of the second inductor may be higher than the Q value of the fourth inductor in a pass band of the filter.
According to this configuration, since the first inductor and the second inductor are configured by the inductors having a high Q value, the steepness of the attenuation characteristic at the low frequency side of the passband can be improved, and the insertion loss can be reduced in a wide passband.
The filter may have a passband of 2300MHz to 2400MHz, a passband of 2496MHz to 2690MHz, and a stopband of 1427MHz to 2200 MHz.
With such a configuration, specifically, a filter having the high band and the middle band referred to in the present specification as a pass band and a stop band can be obtained. Such a filter is suitable as a filter for a high band in a multiplexer for demultiplexing and multiplexing a high band and a medium band.
A multiplexer according to an aspect of the present invention includes: a first filter as the above-mentioned filter; a second filter having a pass band of 1427MHz to 2200MHz inclusive; and a third filter having a passband of 617MHz to 960MHz, wherein one end of the first filter, one end of the second filter, and one end of the third filter are connected to each other.
With this configuration, a multiplexer for demultiplexing and multiplexing signals of the three frequency bands of the high band and the middle band to which the low band mentioned in the present specification is added can be obtained.
The second filter may be constituted by an LC resonance circuit and an elastic wave resonator, and the third filter may be constituted by an LC resonance circuit.
With this configuration, in the second filter for the intermediate band, a steep attenuation characteristic at the high frequency end of the passband can be formed by utilizing a steep frequency characteristic of the elastic wave resonator. By using the first filter and the second filter, it is possible to completely separate the frequency of the signal for the high frequency band and the frequency of the signal for the medium frequency band, and it is possible to simultaneously transmit and receive both signals by a single antenna. Thus, carrier aggregation communication based on a combination of a communication band included in the high band and a communication band included in the intermediate band can be performed with a single antenna.
The present invention can be widely used as a filter and a multiplexer in communication devices such as mobile phones.
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