JP6798456B2 - High frequency front end circuit and communication equipment - Google Patents

Description

The present invention relates to high frequency front end circuits and communication devices including multiplexers.

In recent years, communication devices such as mobile phones are required to have multi-bands corresponding to a plurality of frequency bands (bands) with one terminal. Along with this, high-frequency front-end circuits such as front-end modules mounted on communication devices are also required to be multi-banded, and further, CA (Carrier Aggregation) that simultaneously transmits and receives high-frequency signals of multiple bands is used. Correspondence is required.

As such a high-frequency front-end circuit, a diversity module in which a diplexer, a switch IC (Integrated Circuit), a plurality of BPFs (bandpass filters) and an LNA (low noise amplifier) are connected in this order is disclosed (for example, Patent Documents). 1). According to this high-frequency front-end circuit, CA can be supported by selecting two or more of the plurality of BPFs by the switch IC.

U.S. Patent Application Publication No. 2016/0127015

However, in the above-mentioned conventional configuration, when transmitting and receiving high-frequency signals of a plurality of bands at the same time as in CA, the high-frequency signal of one band leaks not only to a filter having the one band as a pass band but also to another filter. It ends up. Therefore, for other filters, the amount of attenuation outside the pass band becomes small due to leakage of high-frequency signals outside the pass band. Therefore, the damping characteristics deteriorate. Further, with respect to one filter, the loss in the pass band becomes large due to the leakage of the high frequency signal in the pass band. Therefore, the passing characteristics are deteriorated. As a result, in the conventional configuration, there is a problem that it is difficult to secure the attenuation characteristic and the passage characteristic of the entire high frequency front end circuit.

Therefore, an object of the present invention is to provide a high-frequency front-end circuit and a communication device capable of improving attenuation characteristics and passage characteristics.

In order to achieve the above object, the high frequency front end circuit according to one aspect of the present invention is a high frequency front end circuit applicable to a communication method for transmitting, receiving, or transmitting and receiving a plurality of frequency bands at the same time. A plurality of filters having terminals commonly connected and having different pass bands, the multiplexer composed of a plurality of filters including the first elastic wave filter, and the pass band within the pass band of the first elastic wave filter. A switch having a second elastic wave filter, a common terminal connected to the other terminal of the first elastic wave filter, and a plurality of selection terminals including a selection terminal connected to the second elastic wave filter. The first elastic wave resonator arranged on the switch side most of the one or more elastic wave resonators constituting the first elastic wave filter, and one or more elastic wave resonators constituting the second elastic wave filter. Among the elastic wave resonators, the second elastic wave resonator arranged closest to the switch side is a series arm resonator.

As a result, when the first elastic wave filter is viewed from the switch side, the impedance outside the pass band of the first elastic wave filter shows a capacitance closer to OPEN on the Smith chart. Further, when the second elastic wave filter is viewed from the switch side, the impedance outside the pass band of the first elastic wave filter shows capacitance.

Therefore, when the first elastic wave filter and the second elastic wave filter are connected by the switch, the reflectance coefficient outside the pass band of the first elastic wave filter is obtained when viewed from the side in which the filters constituting the multiplexer are commonly connected. Can be enhanced. Therefore, the damping characteristics of the first elastic wave filter (specifically, the path provided with the first elastic wave filter) can be improved. Further, it is possible to improve the passing characteristics of the other filter (specifically, the path provided with the other filter) constituting the multiplexer together with the first elastic wave filter.

As described above, according to this aspect, it is possible to realize a high frequency front-end circuit capable of improving the attenuation characteristic and the passage characteristic.

Further, the impedance at the other terminal of the first elastic wave filter and the impedance at the terminal on the switch side of the second elastic wave filter are both on the Smith chart outside the pass band of the first elastic wave filter. It may be located in the right half area and have a capacitance.

As a result, when the first elastic wave filter and the second elastic wave filter are connected by the switch, the passage of the first elastic wave filter as seen from the other terminal of the first elastic wave filter on the second elastic wave filter side. Regarding the impedance outside the band, it is possible to suppress a shift to inductive due to the influence of the wiring and the switch connecting the first elastic wave filter and the second elastic wave filter. That is, the impedance can be easily accommodated in the capacitance. Similarly, the impedance outside the pass band of the first SAW filter when the first SAW filter side is viewed from the input terminal of the second SAW filter can also be suppressed from shifting to inductive.

Here, the impedance at the other terminal of the first elastic wave filter and the impedance at the terminal on the switch side of the second elastic wave filter both exhibit capacitance outside the pass band of the first elastic wave filter.

Therefore, the impedance of the second elastic wave filter side viewed from the other terminal of the first elastic wave filter and the impedance of the terminal on the switch side of the second elastic wave filter will eventually be the impedance outside the pass band of the first elastic wave filter. Will also show capacitance. Similarly, the impedance seen from the switch side terminal of the second elastic wave filter to the first elastic wave filter side and the output impedance of the first elastic wave filter are both capacitances outside the pass band of the first elastic wave filter. It will show the sex.

This makes it difficult for the impedance of one to be inductive and the impedance of the other to be capacitive, which is a factor that causes deterioration of the damping characteristics outside the pass band of the first elastic wave filter.

Therefore, according to the above aspect, the damping characteristic and the passing characteristic can be further improved.

Further, in the switch, when the common terminal is not connected to any of the plurality of selection terminals, the impedance seen from the first elastic wave filter side has a capacitive property, and the right half on the Smith chart. It may be located in the area.

As a result, even when the first elastic wave filter and the second elastic wave filter are not connected by the switch when they are not connected, the damping characteristics and the passing characteristics are improved in the same manner as when they are connected. Can be done.

Further, when the switch is not connected, the off capacitance value of the switch may be substantially the same as the capacitance value of the second elastic wave resonator.

As a result, even when not connected, the passing characteristics of other filters (specifically, paths provided with other filters) that constitute the multiplexer together with the first SAW filter are substantially the same as those when connected. Can be improved.

Further, the capacitance value of the first elastic wave resonator and the capacitance value of the second elastic wave resonator may be substantially equivalent.

As a result, the impedance seen from the switch side of the first elastic wave filter and the impedance seen from the switch side of the second elastic wave filter are in substantially the same region on the Smith chart outside the pass band of the first elastic wave filter. Can be located in. Therefore, when the first elastic wave filter and the second elastic wave filter are connected by the switch, the reflectance coefficient outside the pass band of the first elastic wave filter when viewed from the point side where the filters constituting the multiplexer are commonly connected. Can be further increased. Therefore, the damping characteristics and the passing characteristics can be further improved.

Further, the plurality of second elastic wave filters that are individually connected to the plurality of selection terminals and have different pass bands may be provided.

As a result, it is possible to cope with more bands while improving the damping characteristics and the passing characteristics.

Further, the high-frequency front-end circuit includes a plurality of sets including the first elastic wave filter, the switch, and the plurality of second elastic wave filters, and the plurality of first elastic wave filters have one terminal in common. The multiplexer may be configured because it is connected and has different pass bands from each other.

Further, at least one of the first elastic wave filter and the second elastic wave filter may be a BAW filter.

Further, the first elastic wave filter may be a hybrid filter.

The plurality of filters constituting the multiplexer include an MLB / LMB filter having a pass band of 1475.9-2025 MHz, an MB filter having a pass band of 2110-2200 MHz, and an MHB having a pass band of 2300-2400 MHz. A filter and an HB filter having a pass band of 2496-2690 MHz may be included.

Further, the high frequency front-end circuit includes a plurality of sets including the first elastic wave filter, the second elastic wave filter, and the switch, and one terminal of the plurality of first elastic wave filters is commonly connected. The multiplexer may be configured, and the high-frequency front-end circuit may further include another multiplexer connected in front of the multiplexer, which have different pass bands from each other.

Further, at least one of the filters constituting the other multiplexer may be a hybrid filter.

Further, the other multiplexer may be a diplexer.

Further, the other multiplexer may be a triplexer.

Further, the triplexer may be composed of an LB filter having a pass band of 699-960 MHz, an MB filter having a pass band of 1427-2200 MHz, and an HB filter having a pass band of 2300-2690 MHz. Good.

Further, the other multiplexer may be a quad plexer.

The quad plexer includes an LB filter having a pass band of 699-960 MHz, an MB filter having a pass band of 1427-2200 MHz, an HB1 filter having a pass band of 2300-2400 MHz, and a pass band of 2496-2690 MHz. The HB2 filter may be configured as the above.

Further, the communication device according to one aspect of the present invention includes an RF signal processing circuit that processes a high frequency signal transmitted, received, or transmitted and received by an antenna element, and the high frequency between the antenna element and the RF signal processing circuit. It comprises any of the above high frequency front end circuits that transmit signals.

As a result, it is possible to cope with more bands while improving the damping characteristics and the passing characteristics.

This makes it possible to provide a communication device capable of improving the attenuation characteristics and the passage characteristics.

According to the present invention, it is possible to provide a high frequency front-end circuit and a communication device capable of improving attenuation characteristics and passage characteristics.

It is a block diagram of the high frequency front end circuit which concerns on embodiment. It is a block diagram which shows the state at the time of CA in the high frequency front end circuit which concerns on embodiment. It is a block diagram which shows the state at the time of CA in the high frequency front end circuit which concerns on Comparative Example 1. FIG. It is a circuit diagram which shows the structure of the switch in embodiment. It is a circuit diagram which shows the structure of the switch in the comparative example 2. It is a block diagram which shows the state at the time of non-CA in the high frequency front-end circuit which concerns on embodiment. It is a block diagram which shows the state at the time of non-CA in the high frequency front end circuit which concerns on Comparative Example 2. It is a circuit block diagram of the communication device which concerns on embodiment. It is a Smith chart which shows the output impedance of the multiplexer in the Example. It is a Smith chart which shows the output impedance of the multiplexer in the comparative example of an Example. It is a Smith chart which shows the input impedance of the filter which constitutes the filter circuit in an Example. It is a Smith chart which shows the input impedance of the switch which constitutes a switch circuit. It is a Smith chart which shows the impedance when the switch side is seen from the output terminal of a multiplexer. It is a graph which shows the reflection characteristic of the input side of the multiplexer in the Example. It is a graph which shows the characteristic about the high frequency front-end circuit in the comparative example of an Example. It is a graph which shows the characteristic about the high frequency front end circuit in an Example. It is a table which shows the improvement effect of the passing characteristic of the high frequency front end circuit in an Example in comparison with the comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to examples and drawings. It should be noted that all of the embodiments described below are comprehensive or specific examples. Numerical values, shapes, materials, components, arrangement of components, connection modes, etc. shown in the following embodiments are examples, and are not intended to limit the present invention. Among the components in the following embodiments, the components not described in the independent claims are described as arbitrary components. Further, in each figure, substantially the same configuration is designated by the same reference numerals, and duplicate description may be omitted or simplified.

(Embodiment)
[1. Overview]
[1-1. Constitution]
FIG. 1 is a configuration diagram of a high-frequency front-end circuit 2X according to the present embodiment. In the figure, a partial configuration diagram of each of the first stage filter 11a (first elastic wave filter) and the latter stage filter 13a (second elastic wave filter), which will be described later, is also shown.

The high frequency front end circuit 2X is a circuit that transmits a high frequency signal between an antenna element (not shown) and an RFIC (Radio Frequency Integrated Circuit, not shown). For example, a front end of a multi-band compatible mobile phone. It is a high frequency module arranged in the section. This high-frequency front-end circuit 2X can be applied to a communication method such as CA that uses a plurality of frequency bands at the same time. A communication method such as CA is a communication method for simultaneously transmitting, receiving, or transmitting / receiving a plurality of frequency bands.

In the present embodiment, the high-frequency front-end circuit 2X corresponds to LTE (Long Term Evolution) and transmits a high-frequency signal of Band (frequency band) defined by 3GPP (Third Generation Partnership Project). Specifically, the high-frequency front-end circuit 2 is arranged in the receiving system, and filters the high-frequency signal (here, the high-frequency receiving signal) received by the antenna element and input to the INPUT terminal 101X in a predetermined frequency band. Outputs from a plurality of individual terminals (BandA1 terminal, BandA2 terminal, BandB1 terminal, BandB2 terminal, etc.) to an RFIC via an amplifier (for example, a low noise amplifier, not shown).

In the following, "Band defined by 3GPP" is simply referred to as "Band", and the reception band of each Band is, for example, "Band **" or "B **" for the reception band of Band **. In some cases, it is abbreviated.

Hereinafter, the outline of the high-frequency front-end circuit according to the present embodiment will be described with reference to comparative examples as appropriate. Specific examples of the filter according to the present embodiment will be described later with reference to the examples.

The high-frequency front-end circuit 2X shown in the figure includes a plurality of first-stage filters (first elastic wave filters) such as filters 11a and 11b, and a plurality of subsequent-stage filters (second elastic wave filters) such as filters 13a to 13d. , A plurality of switches such as switches 21a and 21b arranged between the first-stage filter and the second-stage filter are provided. That is, the high-frequency front-end circuit 2X includes a plurality of sets (for example, four sets) including a first-stage filter, a switch, and a plurality of second-stage filters. The number of the above sets is not particularly limited as long as it is 2 or more, and the number of filters in the subsequent stage is not particularly limited as long as it is 2 or more for each set. However, in the following, for the sake of simplicity, among the components constituting the high-frequency front-end circuit 2X, a set consisting of the filter 11a, the switch 21a, and the filters 13a, 13b, and the filter 11b, the switch 21b, the filters 13c, and 13d The explanation will focus on the group consisting of.

The plurality of first-stage filters such as the filters 11a and 11b are elastic wave filters in which one terminal (input terminal in the present embodiment) is commonly connected and has different pass bands. These plurality of first-stage filters constitute a multiplexer 14X that demultiplexes or combines high-frequency signals (demultiplexes in the present embodiment), for example, corresponding to CA frequency allocation. The plurality of first-stage filters are commonly connected at the common connection point N of the multiplexer 14X (for example, the common terminal of the multiplexer 14X), and are connected to the INPUT terminal of the high-frequency front-end circuit 2X via the common connection point N.

Specifically, the filter 11a has an input terminal connected to the INPUT terminal 101X via a common connection point N, an output terminal connected to the switch 21a, and BandA as a pass band. The filter 11b has an input terminal connected to the INPUT terminal 101X via a common connection point N, an output terminal connected to the switch 21b, and a BandB different from BandA as a pass band.

Here, the "passbands different from each other" include not only the passbands in which the frequency bands are completely separated, but also the passbands in which at least a part of the frequency bands overlap.

The plurality of first-stage filters may be commonly connected at the INPUT terminal. That is, the INPUT terminal may be the common connection point N.

Each of the plurality of subsequent filters such as the filters 13a to 13d is an elastic wave filter having a pass band within the pass band of the first filter. In the present embodiment, these plurality of subsequent-stage filters filter the high-frequency signal demultiplexed by the multiplexer 14X in a pass band narrower than the pass band of the first-stage filter constituting the multiplexer 14X. Such a subsequent filter constitutes, for example, a filter circuit 15X corresponding to the frequency allocation of each Band. Each of the plurality of subsequent-stage filters has a pass band within the pass band of the first-stage filter forming the same set as the subsequent-stage filter. That is, the pass band of the filter in the subsequent stage is included in the pass band of the filter in the first stage that can be connected to the filter in the subsequent stage by the switch. Further, the plurality of subsequent filters constituting the same set have different pass bands from each other.

Specifically, the filter 13a has a BandA1 in which the input terminal is connected to the filter 11a via the switch 21a, the output terminal is connected to the BandA1 terminal, and the pass band is included in the pass band BandA of the filter 11a. The filter 13b has a BandA2 (however, different from the BandA1) in which the input terminal is connected to the filter 11a via the switch 21a, the output terminal is connected to the BandA2 terminal, and the passband is included in the passband BandA of the filter 11a. .. The filter 13c has a BandB1 in which an input terminal is connected to the filter 11b via a switch 21b, an output terminal is connected to the BandB1 terminal, and the passband is included in the passband BandB of the filter 11b. The filter 13d has a BandB2 (however, different from the BandB1) whose output terminal is connected to the BandB2 terminal, the input terminal is connected to the filter 11b via the switch 21b, and is included in the filter 11b as a pass band.

Each of the first-stage filter and the second-stage filter is composed of one or more surface acoustic wave resonators, and is composed of, for example, a resonator using an elastic surface wave, a bulk wave, or an elastic boundary wave.

That is, the first-stage filter and the second-stage filter may be a SAW (Surface Acoustic Wave) filter or a BAW (Bulk Acoustic Wave) filter.

In the case of a SAW filter, the filter may be composed of a piezoelectric substrate and an IDT (Interdigital Transducer) electrode, or may be composed of a laminated substrate having at least a part of piezoelectricity and an IDT electrode. The laminated substrate having piezoelectricity in at least one part is laminated on a high sound velocity support substrate having a bulk wave sound velocity faster than the elastic wave sound velocity propagating in the piezoelectric thin film, and is piezoelectric. A substrate composed of a bass sound film whose bulk wave sound velocity is slower than the elastic wave sound velocity propagating in the thin film and a piezoelectric thin film laminated on the bass velocity film. Here, the hypersonic support substrate serves as both a hypersonic film and a support substrate, which will be described later.

In addition to the above, as a laminated substrate having piezoelectricity in at least one part, it is formed on the support substrate and the support substrate, and the bulk wave sound velocity propagating is faster than the elastic wave sound velocity propagating in the piezoelectric thin film. A low-speed film and a low-speed film that are laminated on a high-speed film and have a slower bulk wave sound velocity that propagates than an elastic bulk wave sound velocity that propagates through the piezoelectric thin film, and a piezoelectric thin film that is laminated on a low-pitched speed film. It may be a laminated body composed of and.

In addition to the above, as a laminated substrate having piezoelectricity in at least one part, it is formed on the support substrate and the support substrate, and the bulk wave sound velocity propagating is faster than the elastic wave sound velocity propagating in the piezoelectric thin film. A high-pitched sound film, a low-pitched sound film that is laminated on a high-pitched sound velocity film and has a low bulk wave sound velocity that propagates from an elastic wave sound velocity that propagates through a piezoelectric thin film, and a piezoelectric thin film that is laminated on a low-pitched sound velocity film. It may be a laminated body composed of.

The IDT electrode can be formed of an appropriate metal material such as Al, Cu, Pt, Au, Ag, Ti, Ni, Cr, Mo, W or an alloy mainly composed of any of these metals. Further, the IDT electrode may have a structure in which a plurality of metal films made of these metals or alloys are laminated.

The piezoelectric thin film is made of any one of LiTaO3, LiNbO3, ZnO, AlN, and PZT.

The low sound velocity film is composed of silicon oxide, glass, silicon nitride, tantalum oxide, a compound obtained by adding fluorine, carbon or boron to silicon oxide, or a material containing each of the above materials as a main component.

High-pitched sound speed support substrates include piezoelectric materials such as aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon, sapphire, lithium tantalate, lithium niobate, and crystal, alumina, zirconia, cordierite, mulite, steatite, and fol. It is composed of various ceramics such as sterite, magnesia diamond, a material containing each of the above materials as a main component, and a material containing a mixture of the above materials as a main component.

The treble speed film includes DLC film, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon, sapphire, lithium tantalate, lithium niobate, piezoelectric material such as crystal, alumina, zirconia, cordierite, mulite, and steatite. , Various ceramics such as forsterite, magnesia diamond, or a material containing each of the above materials as a main component, or a material containing a mixture of the above materials as a main component.

Support substrates include piezoelectric materials such as sapphire, lithium tantalate, lithium niobate, and crystals, and various ceramics such as alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cozylite, mulite, steatite, and forsterite. , Dielectrics such as glass, semiconductors such as silicon and gallium nitride, and resin substrates can be used.

The film thickness of the piezoelectric thin film is preferably 3.5 λ or less, where λ is the wavelength of the elastic wave determined by the electrode period of the IDT electrode. This is because the Q value becomes high. Further, by setting the temperature to 2.5λ or less, the temperature characteristic (TCF) is improved. Further, by setting it to 1.5λ or less, the sound velocity can be easily adjusted.

The film thickness of the bass velocity film is preferably 2.0 λ or less, where λ is the wavelength of the elastic wave determined by the electrode finger period of the IDT electrode. By setting the film thickness of the low sound velocity film to 2.0λ or less, the film stress can be reduced, and as a result, the warpage of the wafer can be reduced, the non-defective rate can be improved, and the characteristics can be stabilized. It becomes. Further, if the film thickness of the low sound velocity film is within the range of 0.1λ to 0.5λ, there is an effect that the electromechanical coupling coefficient is almost the same regardless of the material of the high sound velocity film.

Regarding the film thickness of the high-pitched sound film, since the high-sound velocity film has a function of confining elastic waves in the piezoelectric thin film and the low-sound velocity film, it is desirable that the film thickness of the high-sound velocity film is thick. By setting the film thickness of the hypersonic film to 0.3λ or more, the energy concentration at the resonance point can be set to 100%. Further, by setting the value to 0.5λ or more, the energy concentration at the antiresonance point can be set to 100%, and even better device characteristics can be obtained.

In this regard, as shown in the upper part of FIG. 1, among one or more elastic wave resonators constituting the first stage filter (first elastic wave filter), the first elastic wave resonator arranged on the switch side and the first elastic wave resonator and Of the one or more elastic wave resonators constituting the subsequent filter (second elastic wave filter), the second elastic wave resonators arranged on the switch side are all series arm resonators.

For example, the filter 11a has a series arm resonator s11 as the first elastic wave resonator, and the filter 13a has a series arm resonator s13 as the second elastic wave resonator. That is, the series arm resonator s11 and the common terminal of the switch 21a are connected without interposing another elastic wave resonator. Further, one selection terminal of the switch 21a and the series arm resonator s13 are connected to each other without using another elastic wave resonator. Therefore, when the common terminal and the one selection terminal are connected by the switch 21a, that is, when the filter 13a is selected, the filter 11a and the filter 13a resonate in series without interposing another elastic wave resonator. The child s11 and the series arm resonator s13 are connected to each other.

As a result, according to the high-frequency front-end circuit 2X according to the present embodiment, when the filter 13a is selected, it is out of the pass band of the filter 11a when the filter 13a side selected from the INPUT terminal 101X is viewed (here). Then, the reflectance coefficient in (outside Band A) can be increased. That is, when the multiplexer 14X composed of a plurality of first-stage filters is viewed from the common connection point N, when a certain second-stage filter is selected, the reflection coefficient outside the pass band of the first-stage filter connected to the second-stage filter is increased. Can be done. The details of this will be described in Examples.

Further, the capacitance value of the elastic wave resonator (first elastic wave resonator) arranged on the switch side most in the first stage filter and the elastic wave resonator (second elastic wave filter) arranged on the switch side most in the second stage filter. ) Is substantially equivalent to the capacity value. For example, the capacitance value of the series arm resonator s11 of the filter 11a and the capacitance value of the series arm resonator s13 of the filter 13a are substantially equivalent.

Here, the capacitance value of the elastic wave resonator is a value of the capacitance value of the elastic wave resonator. That is, it is a capacitance value at a frequency sufficiently distant from the resonance point and the antiresonance point of the elastic wave resonator. The value of the capacitance of the elastic wave resonator can be adjusted by design parameters such as the logarithm and crossover width of the IDT (Interdigital Transducer) electrode in the case of an elastic wave resonator using an elastic surface wave, for example. .. Further, "substantially equivalent" includes not only exactly the same thing but also an error of about ± 10%.

Each of the plurality of switches such as the switches 21a and 21b includes a common terminal connected to the other terminal (output terminal in the present embodiment) of the first-stage filter and a selection terminal connected to the subsequent-stage filter. (In this embodiment, two selection terminals connected to two subsequent filters forming the same set) are provided. These plurality of switches constitute a switch circuit 21X which is a Band select switch for selecting a Band of a high frequency signal transmitted by the high frequency front end circuit 2X. The switch circuit 21X switches the Band of the high-frequency signal by switching the selection terminal connected to the common terminal according to the control signal from the control unit such as RFIC. In other words, the switch circuit 21X switches the transmission path of the high frequency signal in the high frequency front end circuit 2X.

In this embodiment, each of the switches 21a and 21b has one common terminal and two selection terminals. The number of selection terminals is not limited to this, and may be equal to or greater than the number of filters in the subsequent stage constituting the same set as described above.

Specifically, in the switch 21a, a common terminal is connected to the output terminal of the filter 11a, one selection terminal is connected to the input terminal of the filter 13a, and the other selection terminal is connected to the input terminal of the filter 13b. .. In the switch 21b, a common terminal is connected to the output terminal of the filter 11b, one selection terminal is connected to the input terminal of the filter 13c, and the other selection terminal is connected to the input terminal of the filter 13d.

Further, in each switch constituting the switch circuit 21X, the impedance seen from the filter side (first elastic wave filter side) of the first stage has a capacitance when the common terminal is not connected to any of the plurality of selection terminals. And it is located in the right half area on the Smith chart. The details of this will be described in Examples.

Specifically, at the time of the above disconnection, the impedance of the switch seen from the filter side of the first stage (first elastic wave filter side) is arranged on the most switch side of the filter of the latter stage connected to the switch. It is substantially equivalent to the capacitance value of the elastic wave resonator (second elastic wave resonator). For example, when the switch 21a is not connected, the impedance seen from the filter 11a is substantially the same as that of the subsequent filters 13a and 13b. In other words, the off capacitance value of the switch 21a when not connected is substantially the same as the capacitance value of the second elastic wave resonator. That is, when the switch 21a is not connected, the impedance of the switch 21a is Z, the resistance value is R and the off capacitance value is C in the equivalent circuit of the switch 21a, and Z can be expressed by the following equation using R and C. ..

Z = R + (1 / jωC)

At this time, since | R | << | 1 / jωC |, the impedance of the switch 21a is dominated by the off capacitance value. Therefore, for the switch 21a, the impedance and the off capacitance value seen from the filter 11a when not connected are the same.

Although the configuration of the high-frequency front-end circuit 2X has been described above, the configuration of the high-frequency front-end circuit 2X is not limited to this. For example, the high frequency front end circuit 2X may be provided in the transmission system. In this case, the INPUT terminal 101X is an OUTPUT terminal to which a high frequency signal (in this case, a high frequency transmission signal) is output. That is, the high-frequency front-end circuit 2X outputs a high-frequency signal output from the RFIC, amplified by an amplifier (for example, a power amplifier), and input to a plurality of individual terminals (BandA1 terminal, BandA2 terminal, BandB1 terminal, BandB2 terminal, etc.). , Filtering in a predetermined frequency band may be performed and output from the OUTPUT terminal to the antenna element.

[1-2. motion]
Next, the operation of the high-frequency front-end circuit 2X according to the present embodiment will be described including the detailed configuration of the switches constituting the switch circuit 21X.

The high-frequency front-end circuit 2X operates as follows according to a control signal from a control unit (not shown) such as an RFIC.

That is, the first connection form in which two or more rear-stage filters are selected from the plurality of rear-stage filters constituting the filter circuit 15X by the switch circuit 21X, and one rear-stage filter among the plurality of rear-stage filters constituting the filter circuit 15X. The second connection form in which only is selected is switched.

[1-2-1. CA operation]
In the present embodiment, the switch circuit 21X is included in the pass band of the Band included in the pass band of one first-stage filter and the pass band of the other first-stage filter among the plurality of first-stage filters constituting the multiplexer 14Y. When performing CA with Band, the above-mentioned first connection form is used. That is, at the time of CA, two or more subsequent filters are selected by connecting a common terminal to one of the selection terminals in two or more switches among the plurality of switches constituting the switch circuit 21X.

FIG. 2A is a configuration diagram showing a state at the time of CA in the high frequency front-end circuit 2X according to the embodiment. In the figure, the high frequency signal of BandB2 in the CA of BandA1 and BandB2 (“BandB2 signal” in the figure) is also schematically shown. The same applies to FIG. 2B.

As shown in the figure, at this time, the filter 13a is selected by the switch 21a, and the filter 13d is selected by the switch 21b.

As described above, in the present embodiment, the series arm resonator s11 is arranged on the most switch 21a side of the filter 11a, and the series arm resonator s13 is arranged on the most switch 21a side of the filter 13a. Therefore, when the filter 13a is selected, the reflection coefficient outside the pass band (here, outside BandA) of the filter 11a when the filter 13a side selected from the INPUT terminal 101X is viewed is high. Therefore, the high-frequency signal of Band B2 input to the INPUT terminal 101X is less likely to leak to the filter 11a side and mainly passes through the filter 11b.

FIG. 2B is a configuration diagram showing a state at the time of CA in the high frequency front-end circuit 2Y according to Comparative Example 1.

The high-frequency front-end circuit 2Y according to Comparative Example 1 includes filters 11y and 13y instead of the filters 11a and 13a as compared with the high-frequency front-end circuit 2X according to the embodiment. At least one of the filters 11y and 13y has a parallel arm resonator arranged closest to the switch 21a.

On the other hand, in the configuration of Comparative Example 1 in which the reflection coefficient is low, the high frequency signal of Band B2 input to the INPUT terminal 101X leaks to the filter 11a side.

In such a configuration, the reflection coefficient outside the pass band of the filter 11a (here, outside the Band A) when the filter 13a side selected from the INPUT terminal 101X is viewed is low, so that the high frequency of the Band B2 input to the INPUT terminal 101X is high. The signal leaks to the filter 11a side.

Therefore, in the high-frequency front-end circuit 2Y according to Comparative Example 1, the attenuation characteristic of the filter 13y is reduced because the high-frequency signal of the Band B2 outside the pass band leaks and the attenuation amount outside the pass band (outside the Band A1) becomes small. It will deteriorate. Further, with respect to the filter 13d, the high frequency signal of the Band B2 in the pass band leaks, so that the loss in the pass band (in the Band B2) becomes large, so that the pass characteristics deteriorate. As a result, in the high-frequency front-end circuit 2Y according to Comparative Example 1, it is difficult to secure the attenuation characteristics and the passage characteristics of the entire high-frequency front-end circuit 2Y at the time of CA.

On the other hand, according to the high-frequency front-end circuit 2X according to the present embodiment, the filter 13a is out of the passband (outside the bandA1) by suppressing leakage of the high-frequency signal of the BandB2 outside the passband. The amount of attenuation can be improved (increased). Further, with respect to the filter 13d, the loss in the pass band (in the Band B2) can be improved (suppressed) by suppressing the leakage of the high frequency signal of the Band B2 in the pass band. Therefore, according to the high-frequency front-end circuit 2X according to the present embodiment, the attenuation characteristic and the passage characteristic at the time of CA can be improved as compared with the high-frequency front-end circuit 2Y according to Comparative Example 1.

[1-2-2. Non-CA operation]
Further, in the present embodiment, the switch circuit 21X becomes the above-mentioned second connection mode when CA is not performed. That is, at the time of non-CA, the common terminal is connected to one of the selection terminals in only one of the plurality of filters constituting the switch circuit 21X, and the common terminal is not connected to any of the selection terminals in the other filters. Therefore, only one post-stage filter is selected.

Here, the configuration of each switch constituting the switch circuit 21X in the embodiment will be described by taking the switch 21a as an example. Since the other switches have the same configuration as the switch 21a except that the number of selection terminals may be different, the description thereof will be omitted.

FIG. 3A is a circuit diagram showing the configuration of the switch 21a according to the embodiment, and in FIG. 3A of the figure, the common terminal 21ac is connected to either the selection terminal 211s or 212s (here, the selection terminal 211s). The state at the time of connection is shown, and (b) of the figure shows the state at the time of non-connection in which the common terminal 21ac is not connected to either of the selection terminals 211s and 212s.

As shown in the figure, the switch 21a is an SPST (Single-Pole, Single-Throw) type switch that switches between connection (conduction) and non-connection (non-conduction) between the common terminal 21ac and the selection terminal 211s by turning it on and off. It has a main switch 211. Further, the switch 21a has an SPST type sub switch 211g that switches the connection and non-connection between the selection terminal 211s and the ground by exclusively turning on and off with the main switch 211. Further, the switch 21a has an SPST type main switch 212 that switches between connection and non-connection between the common terminal 21ac and the selection terminal 212s by turning on and off without being restricted by the on and off of the main switch 211. Further, the switch 21a has an SPST type sub switch 212g that switches the connection and non-connection between the selection terminal 212s and the ground by exclusively turning on and off with the main switch 212SW2.

Examples of the switches (main switches 211 and 212, sub-switches 211g and 212g) constituting such a switch 21a include FET (Field Effect Transistor) switches and diode switches. Further, the switch 21a may be configured as a switch IC (Integrated Circuit) having a plurality of switches. Further, each switch is not limited to the semiconductor switch formed on the semiconductor substrate, and may be a mechanical switch composed of MEMS (Micro Electro Mechanical Systems).

According to the switch 21a configured in this way, when the connection shown in (a) of the figure, that is, when the main switch 211 is on, the sub switch 211g is turned off, so that the common terminal 21ac and the selection terminal 211s Get a connection between. On the other hand, when the main switch 211 is off, the sub switch 211g is turned on, so that the common terminal 21ac and the selection terminal 211s are not connected, and the isolation between the common terminal 21ac and the selection terminal 211s is established. To get. These matters are not limited to the main switch 211 and the sub switch 211g connected to the selection terminal 211s, but the same applies to the main switch 212 and the sub switch 212g connected to the selection terminal 212s.

Further, at the time of connection shown in (b) of the figure, that is, when both the main switches 211 and 212 are off, both the sub switches 211g and 212g are turned on, so that the common terminal 21ac is selected from the selection terminals 211s and 212s. Both are disconnected, and isolation between the common terminal 21ac and the selection terminals 211s and 212s is obtained.

At this time, the common terminal 21ac is in an OPEN state in which it is not connected to the ground. That is, the potential of the common terminal 21ac is a float potential floating from the ground. As a result, the switch 21a in the present embodiment has a capacitive property when viewed from the filter side (that is, the multiplexer 14X side) of the first stage.

On the other hand, FIG. 3B shows the switch 21z of Comparative Example 2 in which the common terminal 21ac is connected to the ground in the SHORT state when not connected.

FIG. 3B is a circuit diagram showing the configuration of the switch 21z in Comparative Example 2. In FIG. 3A, the common terminal 21ac is connected to either the selection terminal 211s or 212s (here, the selection terminal 211s). The state at the time of connection is shown, and (b) of the figure shows the state at the time of non-connection in which the common terminal 21ac is not connected to either of the selection terminals 211s and 212s.

Compared to the switch 21a in the embodiment, the switch 21z in Comparative Example 2 shown in the figure is provided with an SPST type sub-switch 213g that switches between connection and non-connection between the common terminal 21ac and the ground by turning on and off. ing. The sub switch 213g is provided outside the switch 21z.

According to such a switch 21z, the sub switch 213g is turned off at the time of the connection shown in (a) of the figure, that is, when the main switch 211 is on. On the other hand, at the time of connection shown in (b) of the figure, that is, when both the main switches 211 and 212 are off, the sub switch 213g is turned on to bring the common terminal 21ac into a SHORT state connected to the ground.

Hereinafter, the operation during non-CA will be described by comparing the high frequency front-end circuit 2X according to the embodiment including the switch 21a and the high-frequency front-end circuit 2Z according to the comparative example 2 including the switch 21z.

FIG. 4A is a configuration diagram showing a non-CA state in the high frequency front-end circuit 2X according to the embodiment. FIG. 4B is a configuration diagram showing a non-CA state in the high frequency front-end circuit 2Z according to Comparative Example 2. In these figures, the high frequency signal of BandB2 in the non-CA of BandB2 (“BandB2 signal” in the figure) is also schematically shown. That is, here, the switches 21a and 21z are not connected, and the filter 13d is selected by the switch 21b.

As shown in FIG. 4A, in the embodiment, the common terminal 21ac of the switch 21a is in the OPEN state (see FIG. 3A), so that the filter 11a when the filter 13a side selected from the INPUT terminal 101X is viewed. The reflectance coefficient outside the pass band (here, outside BandA) is high. Therefore, the high-frequency signal of Band B2 input to the INPUT terminal 101X is less likely to leak to the filter 11a side and mainly passes through the filter 11b.

On the other hand, as shown in FIG. 4B, in Comparative Example 2, since the common terminal 21ac of the switch 21z is in the SHORT state (see FIG. 3B), the high frequency signal of BandB2 input to the INPUT terminal 101X is the common terminal 21ac. Leaks out to the ground. In other words, in the comparative example, since the common terminal 21ac is in the SHORT state, the reflectance coefficient outside the pass band (here, outside BandA) of the filter 11a when the filter 13a side selected from the INPUT terminal 101X is viewed. Will be low.

Therefore, in the high-frequency front-end circuit 2Z according to Comparative Example 2, the loss in the pass band (in the Band B2) increases due to the leakage of the high-frequency signal of the Band B2 in the pass band for the filter 13d, so that the pass characteristics deteriorate. It ends up. As a result, in the high-frequency front-end circuit 2Z according to Comparative Example 2, it is difficult to secure the passage characteristics of the entire high-frequency front-end circuit 2Y during non-CA.

On the other hand, according to the high-frequency front-end circuit 2X according to the present embodiment, the filter 13d has a loss in the pass band (in the Band B2) due to the suppression of leakage of the high-frequency signal of the Band B2 in the pass band. Can be improved (suppressed). Therefore, according to the high-frequency front-end circuit 2X according to the present embodiment, the passing characteristics at the time of non-CA can be improved as compared with the high-frequency front-end circuit 2Z according to Comparative Example 2.

It should be noted that a sub switch 213g may be provided outside the switch 21a as in the switch 21z of the comparative example. Even with such a configuration, the same effect as described above can be obtained by turning off the sub switch 213g during non-CA.

[2. Example]
[2-1. Constitution]
Next, a specific configuration example of the high-frequency front-end circuit 2X according to the present embodiment described above will be described with reference to examples.

FIG. 5 is a circuit configuration diagram of the communication device 3 according to the embodiment of the embodiment. The communication device 3 shown in the figure is composed of a high frequency front end circuit 2 according to an embodiment and a high frequency signal processing circuit (RFIC) 40.

The high-frequency front-end circuit 2 includes an antenna common terminal 101, a diplexer 10, a multiplexer 14, switch circuits 21 and 22, a filter circuit 15, and an amplifier circuit 30.

The diplexer 10 is an example of a multiplexer provided in front of the multiplexer 14, and has two filters in which one terminal is commonly connected and has different pass bands. The pass band of each of the two filters includes the pass band of a plurality of filters constituting the multiplexer or the like provided in the subsequent stage. Specifically, the diplexer 10 is connected to the antenna common terminal 101 of the high-frequency front-end circuit 2 and is composed of a low-pass filter 10A (passband: 699-960 MHz) and a high-pass filter 10B (passband: 1475.9-2690 MHz). Has been done.

The multiplexer provided in front of the multiplexer 14 is not limited to the diplexer 10, and may be a triplexer, a quadplexer, or a multiplexer of a pentaplexer or higher. In the case of a triplexer, it is composed of an LB filter having a pass band of 699-960 MHz, an MB filter having a pass band of 1427-2200 MHz, and an HB filter having a pass band of 2300-2690 MHz. In the case of a quad plexer, from an LB filter with a pass band of 699-960 MHz, an MB filter with a pass band of 1427-2200 MHz, an HB1 filter with a pass band of 2300-2400 MHz, and an HB2 filter with a pass band of 2496-2690 MHz. It is composed. The filter constituting the multiplexer A may be an LC filter, an elastic wave filter, a hybrid filter composed of an elastic wave resonator and / or L, C, or both.

The multiplexer 14 is connected to the high-pass filter 10B and is connected to the MLB / LMB filter 11A (1475.9-2025 MHz), the MB filter 11B (2110-2200 MHz), the MHB filter 11C (2300-2400 MHz), and the HB filter 11D (2496-2690 MHz). ).

The switch circuit 21 is composed of switches 21A, 21C, and 21D. The switch circuit 22 is composed of switches 22A, 22B, 22C, and 22D.

The filter circuit 15 is composed of filters 13A, 13B, 13C, 13D, 13E, 13F, 13G, 13H, 13J, and 13K.

The amplifier circuit is composed of LNA 31, 32, 33, 34, 35, and 36.

The multiplexer 14 divides the frequency band of the high frequency signal into four frequency band groups. More specifically, the MLB / LMB filter 11A passes the signals of Ba (band a), Bb (band b), Bc (band c), Bd (band d), and Be (band e) to pass the MB filter. 11B passes the signal of Bp (band p), MHB filter 11C passes the signal of Bf (band f) and Bg (band g), and HB filter 11D passes the signal of Bh (band h), Bj (band j), And Bk (band k) signals are passed. Here, Ba corresponds to B3 (Band3), Bc corresponds to B25 (Band25), and Bj corresponds to B7 (Band7).

The common terminal of the switch 21A is connected to the MLB / LMB filter 11A, and each selection terminal is connected to the filters 13A (Ba), 13B (Bb), 13C (Bc), 13D / 13E (Bd / Be). ..

The common terminal of the switch 21C is connected to the MHB filter 11C, and each selection terminal is connected to the filters 13F (Bf) and 13G (Bg).

The switch 21D has a common terminal connected to the HB filter 11D, and each selection terminal connected to the filters 13H (Bh), 13J (Bj), and 13k (Bk).

A common terminal of the switch 22B is connected to the LNA 31, and each selection terminal is connected to the MB filter 11B and the filter 13d.

The switch 22A has a common terminal connected to the LNA 32, and each selection terminal connected to the filters 13c, 13b, and 13e.

The switch 22D has a common terminal connected to the LNA 33, and each selection terminal connected to the filters 13K, 13H, and 13J.

In the switch 22C, a common terminal is connected to the LNA34, and each selection terminal is connected to the filters 13f and 13g.

Here, the pass band (1475.9-2025 MHz) of the MLB / LMB filter 11A is larger than the pass band of each of the filters 13A (Ba), 13B (Bb), 13C (Bc), and 13D / 13E (Bd / Be). It broadly covers each pass band. The MB filter 11B (2110-2200 MHz) includes each pass band of Bp. The MHB filter 11C (2300-2400 MHz) is wider than each pass band of the filters 13F (Bf) and 13G (Bg) and includes each pass band. The HB filter 11D (2496-2690 MHz) is wider than the pass bands of the filters 13H (Bh), 13J (Bj), and 13K (Bk) and includes the pass bands.

The high-frequency signal processing circuit (RFIC) 40 is connected to the output terminals of the LNA 31 to 36, processes the high-frequency received signal input from the antenna element via the received signal path of each band, and performs signal processing by down-conversion or the like. The received signal generated by processing is output to the base band signal processing circuit in the subsequent stage. The RF signal processing circuit 40 is, for example, an RFIC. Further, the high frequency signal processing circuit (RFIC) 40 outputs control signals S1A, S1C, S1D, S2A, S2B, S2C, and S2D to switches 21A, 21C, 21D, 22A, and 22B, respectively, according to the band used. , 22C, and 22D. As a result, each switch switches the connection of the signal path.

In the communication device 3 having the above configuration, for example, by switching the switches 21A, 21C and 21D, MLB / LMB (1475.9-2025 MHz), MB (2110-2200 MHz), MHB (2300-2400 MHz), and HB ( CA operation is possible by selecting one band from each of 2496-2690 MHz).

Here, the configuration of the high-frequency front-end circuit 2X according to the embodiment can be applied to the high-frequency front-end circuit 2 according to the present embodiment. That is, each filter (MLB / LMB filter 11A, MB filter 11B, MHB filter 11C, and HB filter 11D) constituting the multiplexer 14 in this embodiment is elastic in which the series arm resonator is arranged most on the switch circuit 21 side. It is a wave filter. Further, each filter (filters 13A to 13H, 13J and 13K) constituting the filter circuit 15 is an elastic wave filter in which a series arm resonator is arranged most on the switch circuit 21 side. Further, each switch (switches 21A, 21B, 21D) constituting the switch circuit 21 has a capacitive impedance as seen from the filter side (that is, the multiplexer 14 side) of the first stage when not connected.

Thereby, for example, at the time of CA between Band 3 and Band 7, the reflection coefficient of the MLB / LMB filter 11A at 2496-2690 MHz (pass band of the HB filter 11D) can be increased. Specifically, the reflection coefficient can be made higher than the reflection coefficient of the HB filter 11D at 2496-2690 MHz (pass band of the HB filter 11D).

Further, for example, when the Band 3 is not CA, the reflectance coefficient at 1475.9-2025 MHz (pass band of the MLB / LMB filter 11A) can be increased for each of the MB filter 11B, the MHB filter 11C, and the HB filter 11D. Specifically, the reflection coefficient can be made higher than the reflection coefficient of the MLB / LMB filter 11A at 1475.9-2025 MHz (pass band of the MLB / LMB filter 11A).

According to the above configuration, even if the number of bands to be CA is increased, it is possible to correspond to all CA combinations specified in the 3GPP standard, for example. Further, the band corresponding to the filter circuit 15 can be easily changed. Therefore, it is possible to provide a module having an optimum band configuration for each destination with a simplified circuit design.

[2-2. Characteristic]
Hereinafter, the characteristics of the high-frequency front-end circuit 2 according to the embodiment configured in this way will be described while comparing with the comparative example of the embodiment.

FIG. 6A is a Smith chart showing the output impedance of the multiplexer 14 in this embodiment. Specifically, the figure shows the output impedance of the MLB / LMB filter 11A. FIG. 6B is a Smith chart showing the output impedance of the multiplexer in the comparative example of the example. Here, the multiplexer in the comparative example is a parallel arm resonator as compared with the multiplexer 14 in the embodiment which ends with the series arm resonator (that is, the series arm resonator is arranged on the most switch circuit 21 side of each filter). The only difference is that it ends (that is, the parallel arm resonator is placed closest to the switch circuit 21 side). Therefore, a detailed description of the multiplexer in the comparative example will be omitted.

In addition, markers are added to these figures in the Smith chart. Further, on the right side of the Smith chart, the frequencies of the markers in the Smith chart (here, markers m * and * are numerical values following m in the graph) are shown. This also applies to the subsequent Smith charts.

As shown in FIG. 6A, in the embodiment, the output impedance outside the pass band (1475.9-2025 MHz) of the MLB / LMB filter 11A is generally capacitive because the MLB / LMB filter 11A is an elastic wave filter. Shown. Further, the output impedance is located closer to OPEN because the series arm resonator is arranged on the most switch circuit 21 side of the MLB / LMB filter 11A. Here, closer to OPEN means that it is located in the right half area on the Smith chart.

In general, the input impedance of an elastic wave filter has a frequency characteristic that depends on the frequency. Therefore, when the characteristics are explained for a certain frequency range such as within the pass band or outside the pass band, the characteristics are not always satisfied over the entire frequency range. Therefore, for example, the fact that the output impedance of the MLB / LMB filter 11A is located near the OPEN outside the passband is not only when the output impedance is located near the OPEN over the entire passband, but also at least a part of the outside of the passband. In the case where the output impedance is located closer to OPEN.

Specifically, in FIG. 6A, the output impedance of the MLB / LMB filter 11A is closer to OPEN in the pass band of any filter other than the MLB / LMB filter 11A (MHB filter 11C in the figure) constituting the multiplexer 14. Indicates capacitance.

On the other hand, as shown in FIG. 6B, in the comparative example, the output impedance outside the pass band of the MLB / LMB filter generally shows capacitance as in the embodiment. However, the output impedance is located closer to SHORT because the parallel arm resonator is arranged on the most switch circuit 21 side of the MLB / LMB filter. Here, closer to SHORT means that it is located in the left half area on the Smith chart.

Specifically, in FIG. 6B, the output impedance of the MLB / LMB filter is the capacitance closer to SHORT in the pass band of any filter other than the MLB / LMB filter constituting the multiplexer in the comparative example (MHB filter in the figure). Show sex.

FIG. 7 is a Smith chart showing the input impedance of the filter constituting the filter circuit 15 in this embodiment (that is, the filter in the subsequent stage starting with the series arm resonator). Specifically, the figure shows the input impedance of the filter 13C (Bc, that is, B25).

As shown in the figure, the input impedance outside the pass band (1850-1915 MHz) of the filter 13C generally exhibits capacitance because the filter 13C is an elastic wave filter. That is, the input impedance of the filter 13C exhibits capacitance outside the pass band of the first-stage filter (here, MLB / LMB filter 11A) connected to the filter 13C by the switch circuit 21, and specifically, is closer to OPEN. Located in capacitive. In other words, in this embodiment, the impedance at the output terminal of the first stage filter (the other terminal of the first elastic wave filter) and the impedance at the input terminal of the latter stage filter (the terminal on the switch side of the second elastic wave filter). Are located in the right half region on the Smith chart outside the pass band of the first-stage filter, and have capacitance.

Here, when the first-stage filter (that is, the filter that constitutes the multiplexer) and the second-stage filter (that is, the filter that constitutes the filter circuit 15) are connected by the switch circuit 21, the first-stage filter is transferred from the input side of the second-stage filter. The impedance seen was shifted clockwise on the Smith chart from the output impedance of the first-stage filter due to the influence of the wiring in the high-frequency front-end circuit connecting the first-stage filter and the second-stage filter and the switch circuit 21. It becomes impedance.

In the comparative example, the output impedance of the first-stage filter is located in the capacitive region closer to SHORT on the Smith chart outside the pass band of the first-stage filter. Therefore, when the first-stage filter and the second-stage filter are connected by the switch circuit 21, the passband impedance of the first-stage filter when the first-stage filter is viewed from the input side of the second-stage filter is induced by wiring or the like. Can be located in sex. Here, as shown in FIG. 7, the input impedance of the filter in the subsequent stage exhibits capacitance outside the pass band of the filter in the first stage. Therefore, if the pass-band impedance of the first-stage filter when the first-stage filter is viewed from the input side of the second-stage filter is located inductively, it has an inversion relationship with the input impedance of the second-stage filter outside the pass band. Therefore, in the configuration of the comparative example, the attenuation characteristics of the filter in the latter stage outside the pass band of the filter in the first stage may deteriorate.

On the other hand, in the embodiment, the output impedance of the first-stage filter is located in the capacitive region closer to OPEN on the Smith chart outside the pass band of the first-stage filter. Therefore, even if the first-stage filter and the second-stage filter are connected by the switch circuit 21, the passband impedance of the first-stage filter when the first-stage filter is viewed from the input side of the second-stage filter is likely to be located in the capacitance. .. Therefore, in the configuration of the embodiment, the attenuation characteristic outside the pass band of the first-stage filter can be improved as compared with the comparative example.

In other words, in the embodiment, as compared with the comparative example, when the first-stage filter and the second-stage filter are connected by the switch circuit 21, the first-stage filter is viewed from the input side (that is, the first-stage filter is a common connection point). It is possible to increase the reflectance coefficient outside the pass band of the first-stage filter (as seen from the side). As a result, at the time of CA, it is possible to improve the pass characteristics of the paths of the other first-stage filters while improving the attenuation characteristics of the paths of the first-stage filter.

FIG. 8A is a Smith chart showing the input impedance of the switches constituting the switch circuit 21. Specifically, the figure shows the input impedance of the switch 21A when the common terminal of the switch 21A is in the OPEN state, that is, when the switch 21A is not connected.

As shown in the figure, the input impedance of the switch 21A at this time indicates the capacitance closer to OPEN because the common terminal of the switch 21A is in the OPEN state. That is, the input impedance of the switch 21A outside the pass band (1475.9-2025 MHz) of the MLB / LMB filter 11A to which the switch 21A is connected shows a capacitance closer to OPEN.

Therefore, the impedance (switch input impedance @ MPX in FIG. 5) of the switch 21A having such an input impedance seen from the output terminal of the multiplexer 14 is as shown in FIG. 8B.

FIG. 8B is a Smith chart showing the impedance when the switch 21A side is viewed from the output terminal of the multiplexer 14.

As shown in the figure, the impedance of the switch 21A seen from the output terminal of the multiplexer 14 is phase-shifted from the impedance shown in FIG. 8A by the wiring connecting the multiplexer 14 and the switch 21A. Specifically, it shifts clockwise on the Smith chart. In this embodiment, since the impedance before the shift has a capacitance close to OPEN, there is a sufficient margin for the impedance after the shift to change to the inductive region on the Smith chart. Therefore, the impedance after shifting shows capacitance. That is, the impedance when the switch 21A side is seen from the output terminal of the MLB / LMB filter 11A exhibits capacitance outside the pass band (1475.9-2025 MHz) of the MLB / LMB filter 11A.

As described above, when the switch constituting the switch circuit 21 is not connected, the impedance seen from the output terminal of the first-stage filter constituting the multiplexer 14 to the switch side has a capacitance outside the pass band of the first-stage filter. Shown.

Here, as shown in FIG. 6A, the output impedance of the first-stage filter constituting the multiplexer 14 exhibits capacitance outside the pass band of the first-stage filter. Therefore, according to the embodiment, it is possible to suppress leakage of high-frequency signals outside the pass band of the first-stage filter, as compared with the configuration in which the common terminal is in the SHORT state when not connected.

In other words, in the embodiment, as compared with the comparative example, when the switches constituting the switch circuit 21 are not connected, the first stage filter is viewed from the input side (that is, the first stage filter is viewed from the common connection point side). The reflectance coefficient outside the pass band of the filter can be increased. This makes it possible to improve the passage characteristics of the paths of other first-stage filters during non-CA.

Hereinafter, the effect of improving the passing characteristics produced by the high-frequency front-end circuit 2 according to the embodiment will be described with reference to specific numerical examples.

FIG. 9 is a graph showing the reflection characteristics on the input side of the multiplexer 14 in the embodiment. Specifically, the figure shows the reflectance coefficient at the input terminal of the multiplexer 14 when the output side of the multiplexer 14 is the following (i) to (iii).

(I) Termination with 50Ω (ii) Connect the post-stage filter (here, filter 13J (B7)) (iii) Connect the switch 21D with the common terminal in the OPEN state

Here, in the cases of (ii) and (iii) above, only the point where the subsequent filter or the switch 21D is connected to the HB filter 11D constituting the multiplexer 14 as compared with the case of (i) above. different.

A marker is added to the figure. Further, below the graph, a table showing the frequency and the reflectance coefficient of the markers in the graph (here, markers M * and * are numerical values following M in the graph) is shown.

As shown in the figure, both when (ii) the subsequent filter is connected to the output side of the multiplexer 14 and (iii) when the switch 21D whose common terminal is in the OPEN state is connected, the output side of the multiplexer 14 (I) The reflectance coefficient outside the pass band (2496-2690 MHz) of the HB filter 11D is higher than that in the case of terminating with 50Ω. This is particularly remarkable in the pass band (1475.9-2025 MHz) of the MLB / LMB filter 11A.

Therefore, when the filter 13A whose pass band is included in the pass band of the MLB / LMB filter 11A (that is, the filter whose pass band is Band 3) is connected to such a multiplexer 14, the following characteristics are obtained.

FIG. 10 is a graph showing the characteristics of the high frequency front end circuit in the comparative example of the example. Specifically, in the figure, in order from the top, the configuration diagram of the high-frequency front-end circuit when this passing characteristic is obtained, the passing characteristic of the multiplexer 14 alone (specifically, the passing characteristic of the MLB / LMB filter 11A). ), The passing characteristics of the filter 13A (Band3 filter) alone, and the passing characteristics of the entire high-frequency front-end circuit in the comparative example are shown.

A marker is added to the graph showing the passage characteristics. In addition, on the right side of the graph, the frequency and insertion loss (IL) at the marker in the graph (here, the marker M * or m *, * is the numerical value following M or m in the graph) are shown. .. This also applies to FIG.

FIG. 11 is a graph showing the characteristics of the high frequency front end circuit 2 in the embodiment. Specifically, the figure shows, in order from the top, a configuration diagram of the high-frequency front-end circuit 2 when this pass characteristic is obtained, and a pass characteristic of the entire high-frequency front-end circuit 2 as a whole.

In the graph of passing characteristics, in addition to the passing characteristics in the examples shown by the solid line, the passing characteristics of the comparative example shown in FIG. 10 shown by the broken line are also shown. Further, in the configuration diagram of the figure, the post-stage filters other than the filter 13A are shown as Band ** filters, but these post-stage filters are elastic wave filters starting with a series arm resonator, and specifically, the filter 13F. ~ 13H, 13J and 13K are supported as appropriate.

Here, the high-frequency front-end circuit 2 in the embodiment differs from the high-frequency front-end circuit in the comparative example only in the configuration on the output side of the multiplexer 14. Therefore, the characteristics of the multiplexer 14 alone and the characteristics of the filter 13A alone in the examples are the same as those of the comparative example.

FIG. 12 is a table showing the effect of improving the passing characteristics of the high-frequency front-end circuit 2 in the examples in comparison with the comparative examples. Specifically, this table shows the loss (insertion loss) of the multiplexer 14 alone, the loss of the filter 13A (Band 3 filter) alone, and the entire high-frequency front-end circuit at the frequencies marked with markers in FIGS. 11 and 12. And the improvement of the loss of the entire high frequency front end circuit of the embodiment as compared with the comparative example is shown.

As is clear from FIGS. 10 to 12, according to the high-frequency front-end circuit 2 in this embodiment, the loss in the path of the high-frequency signal passing through the multiplexer 14 and the filter 13A is the loss of the multiplexer 14 alone and the filter 13A alone. It can be improved (suppressed) more than the total with the loss (comparative example in FIG. 12).

That is, in the comparative example, among the plurality of filters (MLB / LMB filter 11A, MB filter 11B, MHB filter 11C, HB filter 11D) constituting the multiplexer 14, other than the MLB / LMB filter 11A connected to the filter 13A. The output side of the filter is terminated with 50Ω. Therefore, the reflection coefficient in the pass band (1475.9-2025 MHz) of the MLB / LMB filter 11A when the other filter is viewed from the input side of the multiplexer 14 is low.

On the other hand, in this embodiment, among the plurality of filters constituting the multiplexer 14, the output side of the filter other than the MLB / LMB filter 11A other than the filter 11A connected to the filter 13A starts with a series arm resonator. An elastic wave filter is connected. Therefore, the reflection coefficient in the pass band of the MLB / LMB filter 11A when the other filter is viewed from the input side of the multiplexer 14 can be increased as compared with the comparative example. Therefore, it is possible to suppress leakage of the MLB / LMB band high frequency signal input to the multiplexer 14 to filters other than the MLB / LMB filter 11A. In other words, the pass characteristics of the MLB / LMB filter 11A can be improved by improving the attenuation characteristics of the other filters. Therefore, in the entire high-frequency front-end circuit 2, the pass characteristics of the Band 3 included in the pass band (1475.9-2025 MHz) of the MLB / LMB filter 11A can be improved.

[3. Summary]
The high-frequency front-end circuit 2X according to the embodiment has been described above using the high-frequency front-end circuit 2 according to the embodiment. Hereinafter, the effects produced by the high-frequency front-end circuit 2X will be described with reference to FIG. Here, the high-frequency front-end circuit 2X includes a plurality of sets including a first-stage filter (first elastic wave filter), a switch, and a plurality of subsequent-stage filters (second elastic wave filter), and each set includes a corresponding pass. It has a similar configuration except for the fact that the bands are different. Therefore, for the sake of simplicity, the effects produced by the set consisting of the filter 11a (first stage filter), the switch 21a (switch) and the two filters 13a and 13b (second stage filter) will be described below, and the effects produced by the other sets will be described. The description of the similar effect produced will be omitted.

As described above, according to the present embodiment, the elastic wave resonator (first elastic wave resonator) arranged on the most switch 21a side of the filter 11a (first elastic wave filter) constituting the multiplexer 14X, and , The elastic wave resonators (second elastic wave resonators) arranged on the most switch 21a (switch) side of the filters 13a and 13b (second elastic wave filters) are all series arm resonators.

As a result, when the filter 11a is viewed from the switch 21a side, the impedance outside the pass band of the filter 11a shows a capacitance closer to OPEN on the Smith chart. Further, when the filters 13a and 13b are viewed from the switch 21a side, the impedance outside the pass band of the filter 11a shows capacitance.

Therefore, when the filter 11a and the filters 13a and 13b are connected by the switch 21a, the filter 11a is viewed from the point where the filters constituting the multiplexer 14X are commonly connected (common connection point N in the present embodiment). The reflectance coefficient outside the pass band can be increased. Therefore, the attenuation characteristics of the filter 11a (specifically, the path provided with the filter 11a) can be improved. Further, the passage characteristics of the other filter 11b (specifically, the path provided with the other filter 11b) constituting the multiplexer 14X together with the filter 11a can be improved.

Therefore, it is possible to realize a high frequency front-end circuit 2X that can improve the attenuation characteristics and the passage characteristics.

Further, according to the present embodiment, the impedance at the output terminal of the filter 11a (the other terminal of the first elastic wave filter) and the input terminals of the filters 13a and 13b (the terminal on the switch side of the second elastic wave filter). The impedances in the above are all located in the right half region on the Smith chart outside the pass band of the filter 11a.

As a result, when the filter 11a and the filters 13a and 13b are connected by the switch 21a, the impedance outside the pass band of the filter 11a viewed from the output terminal of the filter 11a on the filter 13a and 13b side is the impedance of the filter 11a and the filter 13a. , The shift to inductive due to the influence of the wiring connecting 13b and the switch 21a can be suppressed. That is, the impedance can be easily accommodated in the capacitance. Similarly, the impedance outside the pass band of the filter 11a viewed from the input terminals of the filters 13a and 13b on the filter 11a side can also suppress the shift to inductive.

Here, in the elastic wave filter, both the input impedance and the output impedance show capacitance. Therefore, the output impedance of the filter 11a (impedance at the other terminal of the first elastic wave filter) and the input impedance of the filters 13a and 13b (impedance at the terminal on the switch side of the second elastic wave filter) are the impedance of the filter 11a. Both show capacitance outside the passband.

Therefore, according to the above configuration, the impedance of the filters 13a and 13b viewed from the output terminal of the filter 11a (the other terminal of the first SAW filter) and the input impedance of the filters 13a and 13b are outside the pass band of the filter 11a. In each case, the capacitance is shown. Similarly, the impedance when the filter 11a side is viewed from the input terminal of the filters 13a and 13b (the terminal on the switch side of the second elastic wave filter) and the output impedance of the filter 11a are both capacitances outside the pass band of the filter 11a. It will show the sex.

That is, with the above configuration, it is difficult to have an inversion relationship in which one impedance indicates inductive and the other impedance indicates capacitance, which is a factor that causes deterioration of the attenuation characteristic outside the pass band of the filter 11a.

Therefore, according to the above configuration, it is possible to further improve the damping characteristics and the passing characteristics.

Further, according to the present embodiment, the switch 21a has a capacitive impedance when viewed from the filter 11a (first elastic wave filter) side when not connected.

As a result, even when the filters 11a and the filters 13a and 13b are not connected by the switch 21a (non-CA in the embodiment), they are connected (CA in the embodiment) when they are not connected. ), The damping characteristics and the passing characteristics can be improved.

When the switch 21a is not connected, the impedance seen from the filter 11a (first elastic wave filter) side may be inductive. Even with such a configuration, the damping characteristic and the passing characteristic can be improved at the time of connection.

Further, according to the present embodiment, the off capacitance value of the switch 21a is the capacitance of the elastic wave resonator (second elastic wave resonator) arranged on the most switch 21a side of the filters 13a and 13b when not connected. It is almost equivalent to the value.

As a result, even when not connected, the passing characteristics of the other filter 11b (specifically, the path provided with the other filter 11b) constituting the multiplexer 14X together with the filter 11a are substantially the same as those at the time of connection. Can be improved.

When not connected, the impedance of the switch 21a seen from the filter 11a side is different from the capacitance value of the elastic wave resonator (second elastic wave resonator) arranged on the most switch 21a side of the filters 13a and 13b. It doesn't matter. Even with such a configuration, the damping characteristic and the passing characteristic can be improved at the time of connection.

Further, according to the present embodiment, the capacitance value of the elastic wave resonator (first elastic wave resonator, in this case, the series arm resonator s11) arranged closest to the switch 21a in the filter 11a and the filters 13a and 13b. The capacitance value of the elastic wave resonator (second elastic wave filter, in this case, the series arm resonator s13) arranged most on the switch 21a side is substantially the same.

As a result, the impedance of the filter 11a seen from the switch 21a side and the impedance of the filters 13a and 13b seen from the switch 21a side can be positioned in substantially the same region on the Smith chart outside the pass band of the filter 11a. it can. Therefore, when the filter 11a and the filters 13a and 13b are connected by the switch 21a, the filter 11a is viewed from the point where the filters constituting the multiplexer 14X are commonly connected (common connection point N in the present embodiment). It is possible to further increase the reflection coefficient outside the pass band. Therefore, the damping characteristics and the passing characteristics can be further improved.

The capacitance value of the series arm resonator s11 and the capacitance value of the series arm resonator s13 may be different. According to such a configuration, although the effect of improving the damping characteristic and the passing characteristic is slightly inferior to the case where these capacitance values are the same, a parallel arm resonator is provided instead of at least one of the series arm resonators s11 and s13. The damping characteristics and the passing characteristics can be improved as compared with the configured configuration.

Further, according to the present embodiment, a plurality of filters 13a and 13b (a plurality of second elastic wave filters) connected to the switch 21a are provided. As a result, it is possible to cope with more bands while improving the damping characteristics and the passing characteristics.

Further, according to the present embodiment, a plurality of sets including a filter constituting the multiplexer 14X, a switch connected to the filter, and a plurality of filters connected to the switch are provided. As a result, it is possible to cope with more bands while improving the damping characteristics and the passing characteristics.

(Modification example)
The high-frequency front-end circuit according to the embodiment of the present invention has been described above with reference to the embodiments and examples, but the present invention does not deviate from the gist of the present invention with respect to the above-described embodiments and examples. The present invention also includes various modifications obtained by performing various modifications that can be conceived by those skilled in the art within the range, and various devices such as a communication device incorporating a high-frequency front-end circuit according to the present invention.

According to such a communication device, the attenuation characteristic and the pass characteristic can be improved by incorporating the high frequency front end circuit.

Further, for example, at least one of the plurality of filters (first-stage filters) constituting the multiplexer may not be an elastic wave filter, and may be, for example, a dielectric filter or an LC filter. Similarly, at least one of the subsequent filters does not have to be an elastic wave filter.

Further, the switch and the filter may not be connected to at least one output side of the plurality of filters constituting the multiplexer.

Further, for example, in the first elastic wave filter and the second elastic wave filter, an inductor or a capacitor may be connected between each terminal such as an input / output terminal and a ground terminal, or an inductor such as a resistance element. And a circuit element other than the capacitor may be added.

Further, for example, a hybrid filter in which at least one elastic wave resonator among one or more elastic wave resonators constituting the first elastic wave filter and the second elastic wave filter is replaced with a capacitance is used as a first elastic wave filter. It may be used as a second elastic wave filter or both. Alternatively, for example, as the first elastic wave filter and the second elastic wave filter, a hybrid filter in which one or more elastic wave resonators are combined with an LC filter composed of an inductor, a capacitor, or both may be used. When such a filter is used, it is possible to achieve both a wide band and steep attenuation.

The present invention can be widely used in communication devices such as mobile phones as a high-frequency front-end circuit and communication device having good attenuation characteristics and pass characteristics that can be applied to a multi-band frequency standard.

2, 2X, 2Y, 2Z high frequency front end circuit 3 Communication device 10 Diplexer 10A Low pass filter 10B High pass filter 11A MLB / LMB filter 11B MB filter 11C MHB filter 11D HB filter 11a, 11b filter (1st elastic wave filter)
11y filter 13a to 13d, 13A to 13H, 13J, 13K filter (second elastic wave filter)
14, 14X, 14Y multiplexer 15, 15X Filter circuit 21, 21X, 22 Switch circuit 21A, 21C, 21D, 21a, 21b, 21z, 22A-22D Switch 21ac Common terminal 30 Amplifier circuit 31-34 LNA
101 Antenna common terminal 101X INPUT terminal 211s, 212s selection terminal

Claims (16)

A high-frequency front-end circuit that can be applied to communication methods that transmit, receive, or transmit and receive multiple frequency bands at the same time.
A multiplexer in which one terminal is commonly connected and has different pass bands and is composed of a plurality of filters including a first elastic wave filter.
A second elastic wave filter having a pass band within the pass band of the first elastic wave filter,
A switch having a common terminal connected to the other terminal of the first elastic wave filter and a plurality of selection terminals including a selection terminal connected to the second elastic wave filter is provided.
Of the one or more elastic wave resonators constituting the first elastic wave filter, the first elastic wave resonator arranged on the switch side most, and one or more elastic wave resonances constituting the second elastic wave filter. The second elastic wave resonators most arranged on the switch side among the children are series arm resonators .
The impedance at the other terminal of the first elastic wave filter and the impedance at the terminal on the switch side of the second elastic wave filter are capacitive and both are outside the pass band of the first elastic wave filter. Located in the right half area on the Smith chart in
When the common terminal is not connected to any of the plurality of selection terminals, the impedance of the switch as seen from the first SAW filter side is determined by the off capacitance of the switch, and is capacitive on the Smith chart. Located in the area of and the right half area ,
High frequency front end circuit. A high-frequency front-end circuit that can be applied to communication methods that transmit, receive, or transmit and receive multiple frequency bands at the same time.
A multiplexer in which one terminal is commonly connected and has different pass bands and is composed of a plurality of filters including a first elastic wave filter.
A second elastic wave filter having a pass band within the pass band of the first elastic wave filter,
A switch having a common terminal connected to the other terminal of the first elastic wave filter and a plurality of selection terminals including a selection terminal connected to the second elastic wave filter is provided.
Of the one or more elastic wave resonators constituting the first elastic wave filter, the first elastic wave resonator arranged on the switch side most, and one or more elastic wave resonances constituting the second elastic wave filter. The second elastic wave resonators most arranged on the switch side among the children are series arm resonators.
In the switch, when the common terminal is not connected to any of the plurality of selection terminals, the impedance seen from the first elastic wave filter side has a capacitive property, and the switch is in the right half region on the Smith chart. Position to,
At the time of disconnection, the off capacitance value of the switch is substantially equivalent to the capacitance value of the second elastic wave resonator .
High-frequency front-end circuit. A high-frequency front-end circuit that can be applied to communication methods that transmit, receive, or transmit and receive multiple frequency bands at the same time.
A multiplexer in which one terminal is commonly connected and has different pass bands and is composed of a plurality of filters including a first elastic wave filter.
A second elastic wave filter having a pass band within the pass band of the first elastic wave filter,
A switch having a common terminal connected to the other terminal of the first elastic wave filter and a plurality of selection terminals including a selection terminal connected to the second elastic wave filter is provided.
Of the one or more elastic wave resonators constituting the first elastic wave filter, the first elastic wave resonator arranged on the switch side most, and one or more elastic wave resonances constituting the second elastic wave filter. The second elastic wave resonators most arranged on the switch side among the children are series arm resonators.
The capacitance value of the first elastic wave resonator and the capacitance value of the second elastic wave resonator are substantially equivalent .
High-frequency front-end circuit. The second elastic wave filter is provided, which is individually connected to the plurality of selection terminals and has different pass bands.
The high-frequency front-end circuit according to any one of claims 1 to 3 . The high-frequency front-end circuit includes a plurality of sets including the first elastic wave filter, the switch, and the plurality of second elastic wave filters.
The plurality of first elastic wave filters have one terminal connected in common and have different pass bands from each other, and constitute the multiplexer.
The high frequency front end circuit according to claim 4 . At least one of the first elastic wave filter and the second elastic wave filter is a BAW filter.
The high frequency front end circuit according to claim 5 . The first elastic wave filter is a hybrid filter.
The high frequency front end circuit according to claim 5 or 6 . The plurality of filters constituting the multiplexer
An MLB / LMB filter with a pass band of 1475.9-2025 MHz and
An MB filter with a pass band of 2110-2200 MHz and
An MHB filter with a pass band of 2300-2400 MHz and
Includes an HB filter with a pass band of 2496-2690 MHz.
The high-frequency front-end circuit according to any one of claims 1 to 7 . The high-frequency front-end circuit includes a plurality of sets including the first elastic wave filter, the second elastic wave filter, and the switch.
The plurality of first elastic wave filters have one terminal connected in common and have different pass bands from each other to form the multiplexer.
The high frequency front-end circuit further comprises another multiplexer connected in front of the multiplexer.
The high frequency front end circuit according to any one of claims 1 to 8 . At least one of the filters constituting the other multiplexer is a hybrid filter.
The high frequency front end circuit according to claim 9 . The other multiplexer is a diplexer.
The high frequency front end circuit according to claim 9 or 10 . The other multiplexer is a triplexer,
The high frequency front end circuit according to claim 9 or 10 . The triplexa
An LB filter with a pass band of 699-960 MHz and
An MB filter with a pass band of 1427-2200 MHz and
It is composed of an HB filter having a pass band of 2300-2690 MHz.
The high frequency front end circuit according to claim 12 . The other multiplexer is a quad plexer,
The high frequency front end circuit according to claim 9 or 10 . The quad plexa is
An LB filter with a pass band of 699-960 MHz and
An MB filter with a pass band of 1427-2200 MHz and
An HB1 filter with a pass band of 2300-2400 MHz and
It is composed of an HB2 filter having a pass band of 2496-2690 MHz.
The high frequency front end circuit according to claim 14 . An RF signal processing circuit that processes high-frequency signals transmitted, received, or transmitted / received by the antenna element,
The high-frequency front-end circuit according to any one of claims 1 to 15 for transmitting the high-frequency signal between the antenna element and the RF signal processing circuit.
Communication device.

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