JP6822444B2 - Composite filter device, high frequency front end circuit and communication device - Google Patents

Description

The present invention relates to a composite filter device including a plurality of filters, a high frequency front end circuit, and a communication device.

In recent mobile communication devices, so-called multi-banding, in which one terminal supports a plurality of frequency bands, is required. In order to meet such demands, a composite filter device has been developed in which a plurality of filters having different pass bands are connected to one antenna.

As an example of such a composite filter device, in Patent Document 1, a first filter and a second filter having a passing frequency band higher than the passing frequency band of the first filter are connected to the transmission / reception common terminal. The wave device is shown. The first filter and the second filter each include a series arm resonator and a parallel arm resonator arranged between the series arm resonator and the ground. Further, a phase shifter is connected between the transmission / reception common terminal and the first filter.

Japanese Unexamined Patent Publication No. 2008-294780

As described in Patent Document 1, when the second filter is connected to the common terminal together with the first filter, a part of the signal passing through the first filter may leak to the second filter side. This is because the induction component of the phase shifter becomes smaller in the pass band of the first filter, which is lower than the pass band of the second filter, so that the impedance of the second filter when the second filter is viewed from the common terminal side. This is because it tends to become smaller. If the impedance is low, a signal leaking to the second filter is generated in the pass band of the first filter.

In order to prevent signal leakage, the impedance of the second filter seen from the common terminal side should be sufficiently increased in the passing frequency band of the first filter by increasing the induction component of the phase shifter (open state, that is, normalization). At least one of the real and imaginary components of the impedance may be infinite (∞)). However, when the induction component of the phase shifter is increased, the insertion loss of the phase shifter increases, so that the loss of the pass band of the second filter may increase.

Therefore, the present invention has been made to solve the above problems, and provides a composite filter device, a high-frequency front-end circuit, and a communication device that can easily reduce the loss of the pass band of each filter. The purpose.

In order to achieve the above object, the composite filter device according to one aspect of the present invention is connected between the common terminal, the first terminal, the second terminal, and the common terminal and the first terminal, and is the first. The first filter having a pass band, the second filter connected between the common terminal and the second terminal and having the second pass band which is higher than the first pass band, and the common terminal and the second filter. A composite filter device including a first inductor provided between them, the second filter having one or more series arm circuits and two or more parallel arm resonators, and one or more series arm circuits. Are connected in series with each other on the path connecting the common terminal and the second terminal, and two or more parallel arm resonators connect the first series arm circuit and the first inductor closest to the common terminal among the series arm circuits. One or more connected to the first parallel arm resonator connected to the node on the connecting path and the reference terminal, and to the node and the reference terminal on the path connecting the first series arm circuit and the second terminal. The anti-resonance frequency of the first parallel arm resonator is located in the second pass band, including the other parallel arm resonators, and the resonance frequency of the first parallel arm resonator is high in the first pass band. It is lower than the edge frequency and lower than any resonance frequency of one or more other parallel arm resonators.

According to the above configuration, the impedance of the second filter seen from the common terminal side is both the inductive component of the first inductor, which is an element having a function of advancing the impedance phase, and the inductive component of the first parallel arm resonator. Can be adjusted to approach the open state using. Therefore, the induction component of the device can be reduced as compared with the case where the phase is adjusted by using only the induction component of the element having the function of advancing the phase. Therefore, the loss of the pass band of the first filter can be reduced without increasing the loss of the pass band of the second filter.

By providing an inductor that can be configured by wiring as an element having the function of advancing the phase, it is expected that the size of the composite filter device can be reduced as compared with the case where a phase shifter is provided.

Further, the second filter includes a first parallel arm resonator circuit, and the first parallel arm resonator circuit is connected to a first parallel arm resonator, a first parallel arm resonator, and a first parallel arm resonator. It is preferable to include a second inductor provided on the path connecting the reference terminal.

According to the above configuration, a first parallel arm resonance circuit having a resonance frequency lower than the resonance frequency of the first parallel arm resonator is formed in the second filter. The induction component of the first parallel arm resonator circuit is increased as compared with the first parallel arm resonator alone. Therefore, the impedance of the second filter seen from the common terminal side has a phase that is more advanced in the pass band of the first filter and approaches the open state, so that the loss of the pass band of the first filter can be further reduced.

Further, it is preferable that the second inductor is provided only on the path connecting the first parallel arm resonator and the reference terminal to which the first parallel arm resonator is connected.

According to the above configuration, the magnitude of the inductive component of the second inductor applied to the first parallel arm resonator is greater than when the inductor is connected to two or more parallel arm resonators of another parallel arm resonator. To increase. That is, in the above configuration, since the induction component of the first parallel arm resonance circuit is further increased, the impedance phase of the second filter advances more clockwise on the Smith chart. Therefore, since the impedance is closer to the open state in the pass band of the first filter, the loss in the pass band of the first filter can be further reduced.

Further, the resonance frequency of the first parallel arm resonance circuit is preferably lower than the low frequency of the first pass band.

According to the above configuration, the inductive component of the first parallel arm resonant circuit increases to the extent that the entire pass band of the first filter becomes inductive. Therefore, the impedance of the second filter seen from the common terminal side greatly advances the phase on the Smith chart in the pass band of the first filter. That is, since the impedance further approaches the open state in the pass band of the first filter, the loss in the pass band of the first filter can be further reduced.

Further, in the composite filter device, it is preferable that the impedance when the second filter alone is viewed from the common terminal side is at least partially open in the first pass band.

Further, the first filter includes a plurality of resonators, and among the plurality of resonators in the first filter, the resonator closest to the common terminal is preferably a series arm resonator.

Among the resonators included in the filter, the parallel arm resonator is a resonator that forms the pass characteristic (pass band and attenuation band) on the low frequency side of the filter. Assuming that such a resonator is the resonator closest to the common terminal in the first filter, the impedance of the first filter seen from the common terminal side in the pass band of the second filter, which is higher than the pass band of the first filter. Is lower than the open state. Since the loss of the second filter increases in such a configuration, an element having a function of advancing the phase of the impedance is provided between the common terminal and the first filter to increase the impedance and prevent the loss characteristics of the second filter from deteriorating. I'm out.

On the other hand, according to the above configuration, the resonator closest to the common terminal is a series arm resonator that forms the pass characteristic (pass band and attenuation band) on the high frequency side of the filter. In this case, since the impedance of the first filter increases in the pass band of the second filter, the signal in the pass band of the second filter is attenuated even if the element is not provided between the common terminal and the first filter. Therefore, the size of the composite filter device can be reduced as compared with the case where the parallel arm resonator is provided at the position closest to the common terminal.

Further, the composite filter device is further shared with a third filter which is connected between the third terminal and the common terminal and the third terminal and has a third pass band which is higher than the second pass band. A third inductor provided between the terminal and the third filter, the third filter has one or more series arm circuits and two or more parallel arm resonators, and one or more in the third filter. The series arm circuits of are connected in series with each other on the path connecting the common terminal and the third terminal, and two or more parallel arm resonators in the third filter are common among one or more series arm circuits in the third filter. On the path connecting the second series arm circuit and the third terminal closest to the terminal, the second parallel arm resonator connected to the node and the reference terminal, and on the path connecting the second series arm circuit and the third terminal. Including one or more other parallel arm resonators connected to the node and the reference terminal, the path connecting the second parallel arm resonator and the reference terminal to which the second parallel arm resonator is connected is the fourth. An inductor is provided, and at least the second parallel arm resonator and the fourth inductor form a second parallel arm resonance circuit, and the anti-resonance frequency of the second parallel arm resonance circuit is located within the third pass band. The resonance frequency of the second parallel arm resonator circuit may be lower than the high frequency end frequency of the first pass band and lower than one or more other parallel arm resonators in the third filter.

In a composite filter device in which at least three filters are collectively connected to a common terminal, the third filter having the highest pass band among the three filters passes through the first filter and the second filter. There is a risk that each type of signal will wrap around. Here, if a second inductor is provided between the common terminal and the third filter, the impedance of the third filter seen from the common terminal side will be the pass band of the first filter and the pass band of the second filter. Rotate clockwise on the Smith chart to advance the phase.

At this time, according to the above configuration, both the induction component of the second inductor and the induction component of the second parallel arm resonator closest to the common terminal are used to advance the phase of the impedance of the third filter to the open state. Can be approached to.

Here, by connecting the fourth inductor to the second parallel arm resonator, it is possible to form a second parallel arm resonator circuit having an increased inductive component as compared with the second parallel arm resonator alone. At this time, if the inductive component increases to the extent that both the pass band of the second filter and the pass band of the first filter, which is lower than the pass band of the second filter, are inductive, the pass band of both passes The impedance phase can be advanced to bring it closer to the open state. Therefore, according to the above configuration, even in a composite filter device including three or more filters, the loss of the pass band of each filter can be reduced.

Further, the resonance frequency of the second parallel arm resonance circuit is preferably lower than the low frequency at the low end frequency of the first pass band.

According to the above configuration, the inductive component of the second parallel arm resonant circuit in the third filter is increased to the extent that the entire pass band of the first filter, which is lower than the pass band of the second filter, is inductive. .. Therefore, in the pass band of the first filter and the second filter, the impedance phase can be advanced to be closer to the open state, and the loss of the pass band of the third filter can be further reduced.

Further, the high-frequency front-end circuit according to one aspect of the present invention includes the composite filter device and an amplifier circuit connected to the composite filter device.

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

According to the composite filter device, the high-frequency front-end circuit, and the communication device according to the present invention, it is possible to easily reduce the loss of the pass band of each filter provided therein.

It is a circuit diagram which shows the circuit structure of the composite type filter apparatus which concerns on Example 1 of 1st Embodiment. It is a Smith chart which shows the impedance in the receiving filter seen from the common terminal side in the composite type filter apparatus which concerns on Comparative Example 1. It is a Smith chart which shows the impedance in the receiving filter seen from the common terminal side in the composite type filter apparatus which concerns on Example 1 of 1st Embodiment. It is a Smith chart which shows the impedance in the receiving filter seen from the common terminal side in the composite type filter apparatus which concerns on Comparative Example 2. It is a figure which shows the passing characteristic of the receiving filter in the composite type filter apparatus which concerns on Comparative Example 2 and the composite type filter apparatus which concerns on Example 1. FIG. It is a circuit diagram which shows the circuit structure of the receiving filter provided in the composite type filter apparatus which concerns on Example 2 of 1st Embodiment. It is a Smith chart which shows the impedance in the receiving filter seen from the common terminal side in the composite type filter apparatus which concerns on Example 2 of 1st Embodiment. It is a figure which shows the passing characteristic of the transmission filter in the composite type filter apparatus which concerns on Example 1 and Example 2 of Comparative Example 1, 1st Embodiment. It is a circuit diagram which shows the circuit structure of the 1st filter provided in the composite type filter apparatus which concerns on the modification of 1st Embodiment. It is a circuit diagram which shows the circuit structure of the composite type filter apparatus which concerns on 2nd Embodiment. It is a circuit diagram which shows the circuit structure of a high frequency front end circuit and a communication device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that all of the embodiments described below are comprehensive or specific examples. Numerical values, shapes, components, arrangement of components, connection forms, etc. shown in the following embodiments are examples, and are not intended to limit the present invention. Of the components in the following embodiments, components not described in the independent claims are described as optional components.

<< First Embodiment >>
Regarding the composite filter device according to the first embodiment of the present invention, refer to FIGS. 1 to 9 by taking a duplexer applied to Band 25 (transmission pass band: 1850-1915 MHz, reception pass band: 1930-11995 MHz) as an example. Will be explained.

<Example 1>
FIG. 1 is a circuit diagram showing a circuit configuration of the composite filter device 120 according to the first embodiment of the first embodiment of the present invention. As shown in the figure, the composite filter device 120 includes a common terminal 12, a transmitting side terminal 13, an inductor 14, a receiving side terminal 15, a transmitting filter 100, and a receiving filter 200. The composite filter device 120 is connected to an antenna element (not shown) or the like via a common terminal 12.

The transmission filter 100 is a bandpass filter that filters the transmission signal generated by the transmission circuit (RFIC or the like) in the transmission pass band (1850-1915 MHz) of the Band 25. The transmission signal is input to the transmission filter 100 via the transmission side terminal 13 and output to the common terminal 12.

As shown in the figure, the transmission filter 100 includes series arm resonators 101 to 105, parallel arm resonators 106 to 109, and inductors 116 to 119. The series arm resonators 101 to 105 are provided on a path connecting the common terminal 12 and the transmitting side terminal 13. The parallel arm resonators 106 to 109 are provided on the path connecting the node on the path connecting the common terminal 12 and the transmitting side terminal 13 and the reference terminal (ground). Of these plurality of resonators 101 to 109, the resonator closest to the common terminal 12 is the series arm resonator 101. In addition, in this specification, "closest to a common terminal" means "closest to a common terminal in terms of an electric circuit". Further, the inductors 116 to 119 are connected to the parallel arm resonators 106 to 109 and the reference terminal, respectively, and together with the parallel arm resonators 106 to 109, form the parallel arm resonator circuits 16 to 19.

The reception filter 200 filters the reception signal received from the antenna element (not shown) or the like in the reception pass band (1930-11995 MHz) of the Band 25, which is higher than the transmission pass band of the Band 25 (high frequency range). It is a path filter. At this time, the received signal is input from the common terminal 12 to the receiving filter 200 and output to the receiving terminal 15. An inductor 14 is provided between the common terminal 12 and the receiving filter 200 on the path connecting the common terminal 12 and the receiving terminal 15.

As shown in the figure, the receiving filter 200 includes series arm resonators 201 to 204 and parallel arm resonators 206 to 209. In this figure, all the series arm circuits are series arm resonators, but for example, a vertically coupled filter unit may be used. The series arm resonators 201 to 204 are provided on the path connecting the common terminal 12 and the receiving side terminal 15 . The parallel arm resonators 206 to 209 are provided on the path connecting the node on the path connecting the common terminal 12 and the receiving side terminal 15 and the reference terminal (ground). The parallel arm resonator 206 is provided on the path connecting the reference terminal and the node on the path connecting the series arm resonator 201 closest to the common terminal and the inductor 14 among the series arm resonators 201 to 204. .. The parallel arm resonators 207 to 209 are provided on a node on the path connecting the series arm resonator 201 and the receiving terminal 15 and on a path connecting the reference terminal, respectively. That is, among the plurality of resonators 201 to 204 and 206 to 209 included in the receiving filter 200, the resonator closest to the common terminal 12 is the parallel arm resonator 206.

In the composite filter device 120 according to the present embodiment, regarding the receiving filter 200, (1) an inductor 14 is provided between the common terminal 12 and the receiving filter 200, and (2) the parallel arm resonator 206. The resonance frequency is lower than the high frequency end frequency in the pass band of the transmission filter 100, and (3) the resonance frequency of the parallel arm resonator 206 is lower than the resonance frequency of any of the other parallel arm resonators 207 to 209.

In the composite filter device 120 having the above configuration, it is possible to reduce the loss of the pass band of the transmission filter 100 without deteriorating the loss of the pass band of the reception filter 200.

In a composite filter device in which a plurality of filters having different pass bands are collectively connected to a common terminal as in the present embodiment, the filters affect each other and the pass characteristics deteriorate. In particular, among a plurality of filters, a part of the signal passing through the filter having a pass band which is a relatively low frequency band (hereinafter referred to as a low frequency filter) has a pass band which is a relatively high frequency band. Leakage to the filter (hereinafter referred to as a high frequency filter) tends to cause a problem that the loss of the pass band of the low frequency filter is deteriorated.

This problem occurs because the impedance of the high-frequency filter seen from the common terminal side does not become sufficiently high (not in the open state) in the pass band of the low-frequency filter. If the impedance is low, a signal leaking to the high frequency filter is generated in the pass band of the low frequency filter.

The reason why the impedance of the high-frequency filter is low in the pass band of the low-frequency filter is that it is the resonance frequency, not the anti-resonance frequency of the resonator, that forms the attenuation band on the low-frequency side of the filter. ..

In a filter provided with a resonator, the attenuation band on the high frequency side of the pass band is formed by using the anti-resonance frequency of the resonator, while the attenuation band on the low frequency side of the pass band is formed by using the resonance frequency of the resonator. .. A filter provided with such a resonator is a filter that is affected by the capacitance component and the induction component of the resonator in its pass band and attenuation band. Specifically, the frequency band lower than the resonance frequency of the resonator and the frequency band higher than the antiresonance frequency of the resonator become capacitive bands under the influence of the capacitive component. On the other hand, the frequency band between the resonance frequency and the antiresonance frequency becomes an inductive band under the influence of the inductive component.

At this time, in the inductive band, the closer to the anti-resonance frequency, the greater the influence of the inductive component and the stronger the inducibility, and the closer to the resonance frequency, the smaller the influence of the inductive component and the weaker the inducibility. Therefore, in the composite filter device provided with a plurality of the above filters, the impedance of each filter seen from the common terminal side tends to be high (near the open state) in the attenuation band on the high frequency side of the pass band where the inductive property is relatively strong. .. On the other hand, it tends to be low (near the short state) in the attenuation band on the low frequency side of the pass band where the inductive property is relatively weak. Therefore, the impedance of the high frequency filter tends to be low in the pass band of the low frequency filter.

In order to solve this problem, in a composite filter device in which a plurality of filters are connected, an element having a function of advancing the impedance phase may be connected between the common terminal and the high frequency filter. By connecting such elements, the impedance of the high-frequency filter seen from the common terminal side rotates clockwise on the Smith chart in the pass band of the low-frequency filter, and the phase advances. If the impedance of the high frequency filter is advanced to the open state by using this, it is possible to suppress the wraparound of the signal from the low frequency filter. Therefore, according to the composite filter device having the above configuration (1), the loss of the pass band of the low frequency filter can be improved. At this time, if the element is an inductor that can be configured by wiring, the size of the composite filter device can be expected to be smaller than that in the case of providing a phase shifter.

At this time, as the induction component of the element increases, the impedance phase also advances significantly. However, increasing the inductive component of the device increases the insertion loss of the device. Since the element is provided on the path connecting the common terminal and the input / output terminal to which the high frequency filter is connected, if the insertion loss of the element increases, the loss of the signal passing through the path increases, and the high frequency band becomes large. Increased filter passband loss.

On the other hand, in the composite filter device according to the present invention, in addition to the induction component of the above element, the induction component of the parallel arm resonator closest to the common terminal is used to advance the impedance phase. This makes it possible to reduce the loss of the pass band of the high frequency filter.

In a filter having a plurality of parallel arm resonators, the pass band and the attenuation band of the filter are set as the capacitive band or the inductive band because the parallel arm resonance closest to the common terminal among the plurality of parallel arm resonators. It is a capacity component or an induction component of the vessel. That is, the inductive band is the frequency band between the resonance frequency and the antiresonance frequency of the parallel arm resonator closest to the common terminal.

Therefore, if the resonance frequency of the parallel arm resonator closest to the common terminal is lower than the high frequency end frequency, which is the highest frequency of the pass bands in the pass band of the low frequency filter, the pass band of the low frequency filter. Part of is the inductive band. Then, the impedance of the high-frequency filter seen from the common terminal side rotates clockwise on the Smith chart in the pass band of the low-frequency filter, and the phase advances. At this time, as the inductive band in the pass band of the low frequency filter increases, that is, as the inductive component of the parallel arm resonator increases, the phase also advances significantly.

In this way, since the phase of the impedance of the high frequency filter can be advanced by using the induction component of the parallel arm resonator at the same time as the induction component of the element, the impedance can be increased without increasing the induction component of the element. It can be raised to an open state. Therefore, according to the composite filter device having (2) in addition to the above configuration (1), it is possible to reduce the loss of the pass band of the high frequency filter in addition to the loss of the pass band of the low frequency filter.

Further, since the inductive band is the frequency band between the resonance frequency and the anti-resonance frequency of the parallel arm resonator closest to the common terminal, the resonance frequency of the parallel arm resonator closest to the common terminal is The lower the value, the wider the inductive band and the larger the inducing component. That is, when the resonance frequency of the parallel arm resonator closest to the common terminal is lower than the resonance frequency of the other parallel arm resonator, the resonance frequency of the other parallel arm resonator is higher than that of the parallel arm resonator closest to the common terminal. The phase of the impedance can be advanced more than when it is low. Therefore, according to the composite filter device having (3) in addition to the above configurations (1) and (2), it is possible to further improve the passing characteristics of the composite filter device.

Here, the effect of the above configuration (3) will be described in comparison with Comparative Examples 1 and 2.
First, the composite filter device according to Comparative Example 1 will be described. The composite filter device according to Comparative Example 1 is different from the composite filter device 120 in that it does not have the above configuration (3).

Table 1 shows the numerical values of the resonance frequency and the anti-resonance frequency of the parallel arm resonator provided in the receiving filter of the composite filter device according to each of the above examples. In Table 1, the parallel arm resonator closest to the common terminal (parallel arm resonator 206 in FIG. 1) is P1, and the parallel arm resonator closest to the second (parallel arm resonator 207 in FIG. 1) is P2. The third closest parallel arm resonator (parallel arm resonator 208 in FIG. 1) is P3, and the fourth closest parallel arm resonator (parallel arm resonator 209 in FIG. 1) is P4.

As shown in Table 1, in the composite filter device according to Comparative Example 1, the resonance frequency of the parallel arm resonator P1 is lower than the high frequency end frequency (1915 MHz) of the transmission filter, but the parallel arm resonator P1. It is higher than the resonator P4. That is, the composite filter device according to Comparative Example 1 does not have the above configuration (3).

On the other hand, in the composite filter device according to the first embodiment, the resonance frequency of the parallel arm resonator P1 is lower than the high frequency end frequency of the transmission filter, and among the parallel arm resonators P1 to P4. It is the lowest. That is, the composite filter device according to the first embodiment has the above configuration (3).

The anti-resonance frequency of the parallel arm resonator P1 is located within the pass band (1930-11995 MHz) of the receiving filter in the composite filter device according to either Example 1 or Comparative Example 1. There is. This is because the anti-resonance frequency of the parallel arm resonator P1 forms a pass band of the receiving filter.

Here, in the composite filter apparatus according to Example 1 and Comparative Example 1, the reflection characteristic (impedance) and the pass characteristic are compared. In the Smith chart used in the following description, 50Ω is used as the characteristic impedance. At this time, the left end where the normalized impedance normalized by the characteristic impedance is 0 + 0j indicates a short state (short). Further, the central portion where the normalized impedance is approximately 1 + 0j indicates an impedance matching state. Further, the right end where at least one of the real number component and the imaginary number component of the normalized impedance is infinite (∞) indicates an open state (open).

FIG. 2 is a Smith chart showing the impedance when the receiving filter alone is viewed from the common terminal in the composite filter device according to Comparative Example 1. The figure is a diagram when the inductor value of the series inductor (inductor 14 in FIG. 1) provided between the common terminal and the receiving filter is 4.7 nH.

In the figure, the impedance of the reception filter applied to the reception pass band of the Band 25 is largely deviated from the open in the entire transmission pass band of the Band 25 to which the transmission filter is applied.

On the other hand, FIG. 3 is a Smith chart showing the impedance of the composite filter device according to the first embodiment when the receiving filter alone is viewed from the common terminal. Also in this figure, the inductor value of the series inductor is 4.7 nH.

In the figure, the impedance of the reception filter is rotated significantly clockwise as compared with Comparative Example 1 in the transmission pass band of Band 25 to which the transmission filter is applied. That is, the impedance of the reception filter is open especially in the vicinity of the high frequency end frequency (1915 MHz) of the band 25 transmission pass band. This is because the composite filter device according to the first embodiment includes (3) in addition to the above configurations (1) and (2), so that the inductive band among the transmission pass bands of the Band 25 is compared with that of the comparative example 1. This is because it has increased. If the above configuration (3) is provided when the inductor value of the series inductor is fixed in this way, the impedance phase can be made closer to open.

It is possible to advance the phase of the impedance of the receiving filter by increasing the inductive component of the series inductor without providing the above configuration (3), but in this case, the loss of the pass band of the receiving filter is lost. Getting worse. Next, this problem will be described with reference to Example 1 in comparison with Comparative Example 2.

The composite filter device according to Comparative Example 2 is different from Comparative Example 1 in that it includes a series inductor having an inductor value of 6.2 nH, which is larger than that of Comparative Example 1.

FIG. 4 is a Smith chart showing the impedance when the receiving filter alone is viewed from the common terminal in the composite filter device according to Comparative Example 2. Also in the figure, the impedance of the receiving filter is in phase with that of FIG. 3 in the transmission pass band of the Band 25 to which the transmitting filter is applied.

However, in the composite filter device of Comparative Example 2, the induction component of the series inductor is larger than that of the composite filter device according to the first embodiment. Therefore, the pass characteristics in the pass band of the reception filter are deteriorated from the pass characteristics in the pass band of the reception filter of the composite filter device according to the first embodiment.

FIG. 5 is a diagram showing the passing characteristics (chain line) of the composite filter device according to the first embodiment and the passing characteristics (dotted line) of the composite filter device according to Comparative Example 2. Specifically, the passage characteristics of the path passing through the reception filter are shown, and the insertion loss is the absolute value of the intensity ratio (S21) of the signal output from the receiving terminal to the signal input from the common terminal. It is shown.

Focusing on the composite filter device according to Comparative Example 2 in the pass band of the reception filter in the figure (the reception pass band of Band 25), the loss is significantly deteriorated particularly in the vicinity of the center frequency thereof. On the other hand, the composite filter device according to the first embodiment can realize a lower loss than the composite filter device according to the second comparative example. That is, according to the composite filter device provided with (3) in addition to the above configurations (1) and (2), the size of the inductive component of the series inductor can be reduced when the impedance phase is advanced by a certain amount. The loss in the pass band of the receiving filter can also be further reduced.

As described above, according to the composite filter apparatus having the above configurations (1), (2), and (3) according to the present embodiment, the loss of the pass band of each filter included in the composite filter apparatus is reduced, and the composite is combined. It is possible to greatly improve the passing characteristics of the type filter device.

Hereinafter, other effects produced by the composite filter device 120 according to the first embodiment of the first embodiment will be described.

In the transmission filter 100 of the composite filter device 120, the resonator closest to the common terminal 12 is the series arm resonator 101.

Among the resonators included in the filter, the parallel arm cavity is a resonator that forms an attenuation band on the low frequency side of the filter. If such a resonator is used as the resonator closest to the common terminal 12 in the transmission filter 100, the attenuation characteristic of the attenuation band on the high frequency side of the transmission filter 100 deteriorates. That is, in the pass band of the reception filter 200, which is higher than the transmission filter 100, the impedance of the transmission filter 100 seen from the common terminal 12 side deviates more than open, so that the pass band loss of the reception filter 200 is lost. Getting worse. In order to improve the loss, it is conceivable to provide an element having a function of advancing the impedance phase between the common terminal 12 and the transmission filter 100 to increase the impedance.

On the other hand, in the transmission filter 100 of the composite filter device 120 according to the present embodiment, the series arm resonator forming the attenuation band on the high frequency side of the filter is the resonator closest to the common terminal 12. Therefore, even if the above elements are not connected, the impedance in the frequency band higher than the pass band of the transmission filter 100 increases. That is, the impedance in the pass band of the reception filter 200, which is higher than the pass band of the transmission filter 100, also increases. Therefore, the wraparound of the leaked signal from the receiving filter 200 side is suppressed, and the loss of the receiving filter 200 is reduced. Therefore, according to the composite filter device 120 according to the present embodiment, the size of the composite filter device 120 can be reduced.

<Example 2>
FIG. 6 is a circuit diagram showing a circuit configuration of a receiving filter 220 provided in a path connecting the inductor 14 and the receiving terminal 15 in the composite filter device according to the second embodiment of the first embodiment of the present invention. is there. As shown in the figure, the receiving filter 220 includes a parallel arm resonator circuit 26 including a parallel arm resonator 206 closest to the common terminal 12 and an inductor 216 connected to the parallel arm resonator 206. The circuit configuration other than the reception filter 220 is the same as the circuit configuration of the composite filter device 120 according to the first embodiment.

By forming the parallel arm resonance circuit 26 including the inductor 216, in the composite filter device according to the second embodiment, the resonance frequency of the parallel arm resonator P1 included in the parallel arm resonance circuit 26 is the composite according to the first embodiment. It is shifted to the low frequency side from the type filter device. For example, in Table 1, the resonance frequency of the parallel arm resonance circuit 26 including the parallel arm resonator P1 (parallel arm resonator 206 in FIG. 6) closest to the common terminal 12 is among the frequencies used as the pass band of the transmission filter 100. It is lower than the lowest frequency, the low frequency (1850 MHz). As a result, the induction component of the parallel arm resonance circuit 26 becomes larger than that of the composite filter device according to the first embodiment, and the impedance phase of the high frequency filter seen from the common terminal side can be advanced closer to open.

FIG. 7 is a Smith chart showing the impedance of the composite filter device according to the second embodiment when the receiving filter alone is viewed from the common terminal. In this figure, the inductor value of the series inductor provided between the common terminal and the receiving filter is 4.7 nH, which is the same as in the first embodiment. In the figure, the impedance of the receiving filter rotates to near open not only at the high frequency end of the transmission pass band of Band 25 but also at the low frequency end. This is because, in addition to the above configurations (1) to (3), the resonance frequency of the parallel arm resonator P1 is lower than the low frequency of the transmission pass band of the Band 25, so that the transmission pass of the Band 25 is provided. This is because the entire band is inductive.

As described above, as the impedance of the receiving filter approaches open in the pass band of the transmitting filter, the wraparound of the signal leaking from the transmitting filter side is suppressed, and the passing characteristics in the pass band of the transmitting filter can be improved.

FIG. 8 shows the pass characteristics (chain line) of the composite filter device according to the first embodiment, the pass characteristics (solid line) of the composite filter device according to the second embodiment, and the pass characteristics of the composite filter device according to the comparative example 1. It is a figure which showed (dotted line). Specifically, the passage characteristics of the path passing through the transmission filter are shown, and the insertion loss is the absolute value of the intensity ratio (S12) of the signal output from the common terminal to the signal input from the transmission side terminal. It is shown.

As shown in the figure, the composite filter device according to the second embodiment has better pass characteristics than the composite filter device according to the first embodiment in the pass band of the transmission filter (transmission pass band of Band 25). Shown. Further, in the composite filter device according to the first and second embodiments, as shown in FIGS. 3 and 7, the impedance of the reception filter seen from the common terminal side is open in at least a part of the transmission pass band. , It is possible to realize lower loss passing characteristics than the composite filter device according to Comparative Example 1.

As described above, according to the composite filter device according to the present embodiment, it is possible to further reduce the loss in the pass band of the filter included in the composite filter device and further improve the pass characteristics of the composite filter device. Become.

Further, in the composite filter device according to the second embodiment, the inductor 216 included in the parallel arm resonance circuit 26 of the reception filter 220 connects the parallel arm resonator 206 and the reference terminal to which the parallel arm resonator 206 is connected. It is provided only on the route. That is, the inductor 216 is attached to any of the other parallel arm resonators 207 to 209 connected to the node on the path connecting the series arm circuit (series arm resonator) 201 closest to the common terminal and the receiving side terminal 15. Not connected.

When the inductor 216 of the parallel arm resonator circuit 26 closest to the common terminal 12 is connected not only to the parallel arm resonator 206 but also to any of the other parallel arm resonators 207 to 209, the inductor 216 is connected to each resonator. The inductive component of the inductor 216 to be added is reduced as compared with the case where the inductor 216 is connected to only one resonator at a specific position on the electric circuit.

On the other hand, according to the above configuration, since the induction component of the inductor 216 is added only to the parallel arm resonator 206 provided in the parallel arm resonance circuit 26 closest to the common terminal 12, the induction component applied to the parallel arm resonator 206 is large. can do. Therefore, the impedance of the receiving filter 220 advances in a larger phase on the Smith chart in the pass band of the transmitting filter 100 and approaches open, so that the loss of the pass band of the transmitting filter 100 can be further reduced.

[Modification example]
Hereinafter, the composite filter device according to the modified example of this embodiment will be described with reference to FIG. The circuit configuration of the receiving filter is different from that of the composite filter device according to the present embodiment in each of the composite filter devices according to the modified example as follows.

(Modification example 1)
FIG. 9A is a circuit diagram showing a circuit configuration of a receiving filter 230 of the composite filter device 120 according to the first modification of this embodiment. In the figure, the parallel arm resonator 206 is composed of two parallel arm resonators 206A and 206B. As described above, the resonator included in the composite filter device according to the present invention is composed of a plurality of resonators connected to a path connecting the node to which the resonator is connected and the reference terminal to which the resonator is connected. It may be configured.

When the parallel arm resonator 206 closest to the common terminal 12 is composed of a plurality of resonators as shown in the figure, the resonance frequency of at least one of the plurality of resonators is the other. It should be lower than the parallel arm resonator.

(Modification 2)
FIG. 9B is a circuit diagram showing a circuit configuration of a receiving filter 240 of the composite filter device 120 according to the second modification of the present embodiment. In the figure, the parallel arm resonator 206 closest to the common terminal 12 and the inductor 216 constituting the parallel arm resonance circuit 26 are also connected to the parallel arm resonator 207 second closest to the common terminal 12.

As in this modification, the inductor 216 may also be connected to the second and subsequent parallel arm resonators 207 to 209 to the common terminal 12. According to such a composite filter device 120, the induction component added to the parallel arm resonator 206 from the inductor 216 is reduced, but the effect of the present invention is sufficiently exhibited.

<< Second Embodiment >>
The composite filter device according to the second embodiment of the present invention will be described with reference to FIG. 10 by taking a triplexer applied to Band 25 and Band 1 (reception pass band: 2110 MHz-2170 MHz) as an example.

FIG. 10 is a circuit diagram showing a circuit configuration of the composite filter device 130 according to the second embodiment of the present invention. The composite filter device 130 shown in the figure further includes an inductor 34, a receiving terminal 35, and a receiving filter 300 as compared with the composite filter device 120 according to the second embodiment of the first embodiment.

The reception filter 300 is a bandpass filter that filters the received signal received from the antenna element (not shown) or the like in the pass band (2110 MHz-2170 MHz) of Band 1 higher than the pass band (1930-11995 MHz) of Band 25. At this time, the received signal is input from the common terminal 12 to the receiving filter 300 and output to the receiving terminal 35. An inductor 34 is provided between the receiving filter 300 and the common terminal 12 on the path connecting the common terminal 12 and the receiving terminal 35.

Similar to the receiving filter 220, the receiving filter 300 includes series arm resonators 301 to 304 and parallel arm resonators 306 to 309. In this figure, all the series arm circuits are series arm resonators, but for example, a vertically coupled filter unit may be used.

The series arm resonators 301 to 304 are provided on a path connecting the common terminal 12 and the receiving side terminal 35. The parallel arm resonators 306 to 309 are provided on the path connecting the node on the path connecting the common terminal 12 and the receiving side terminal 35 and the reference terminal.

The parallel arm resonator 306 is provided on the path connecting the node and the reference terminal on the path connecting the series arm resonator 301 and the inductor 34 closest to the common terminal 12 among the series arm resonators 301 to 304. .. The parallel arm resonators 307 to 309 are provided on the path connecting the node and the reference terminal on the path connecting the series arm resonator 301 and the receiving side terminal 35, respectively. That is, among the plurality of resonators included in the receiving filter 300, the resonator closest to the common terminal 12 is the parallel arm resonator 306. The parallel arm resonator 306, the parallel arm resonator 306, and the inductor 316 connected to the reference terminal form the parallel arm resonator circuit 36.

The resonance frequency of the parallel arm resonance circuit 36 is shifted to a lower frequency side than the resonance frequency of the parallel arm resonator 306 alone by the inductor 316. As a result, the resonance frequency of the parallel arm resonance circuit 36 is located lower than the high frequency end frequency (1915 MHz) of the pass band of the transmission filter 100, which is the lowest of the three filters, and the parallel arm resonator 307 It is lower than ~ 309. The anti-resonance frequency of the parallel arm resonance circuit 36 is located within the pass band (2110 MHz-2170 MHz) of the reception filter 300.

In the reception filter 300 including the parallel arm resonance circuit 36, at least a part of the pass band of the transmission filter 100 and the entire pass band of the reception filter 200 in a frequency band higher than that of the transmission filter 100. However, it becomes an inductive band. Therefore, using the parallel arm resonance circuit 36, the impedance of the reception filter 300 seen from the common terminal 12 is largely rotated clockwise on the Smith chart in the pass band of the transmission filter 100 and the reception filter 220. It is possible to advance the phase. That is, it is possible to reduce the loss of the pass band of the transmission filter 100 and the reception filter 220 without significantly deteriorating the loss of the reception filter 300.

Further, at this time, if the resonance frequency of the parallel arm resonance circuit 36 is lower than the low frequency ( 1850 MHz) of the pass band of the transmission filter 100, the transmission is added to the entire pass band of the reception filter 220. The entire pass band of the credit filter 100 is also an inductive band. As a result, the impedance of the reception filter 300 as seen from the common terminal 12 can be made larger in the pass band of the transmission filter 100, so that the loss of the pass band of the transmission filter 100 and the reception filter 220 is further reduced. can do.

In the triplexer as described above, if the configuration of the present invention is applied to the filter having the highest pass band among the three filters, the signal from a plurality of filters having a lower pass band than the filter can be used. It can suppress dust. That is, according to the above configuration, even when the composite filter device includes three or more filters, the low loss property of the composite filter device can be realized.

The composite filter devices 120 and 130 described in the first embodiment and the second embodiment can be applied to a high frequency front-end circuit and a communication device including the composite filter devices 120 and 130. Therefore, hereinafter, such a high-frequency front-end circuit and a communication device will be described by taking as an example a configuration including a composite filter device according to the second embodiment.

FIG. 11 is a configuration diagram showing a configuration of a high-frequency front-end circuit 10 including the composite filter device 130 and a communication device 1 including the high-frequency front-end circuit 10. In the figure, a high frequency front-end circuit 10 composed of a composite filter device 130 and an amplifier circuit 4, an antenna element 2, and an RF signal processing circuit (RFIC) 3 are shown. The high frequency front-end circuit 10 and the RFIC 3 constitute the communication device 1. The antenna element 2, the high-frequency front-end circuit 10, and the RFIC 3 are arranged, for example, in the front-end portion of a multi-mode / multi-band compatible mobile phone.

The antenna element 2 is a multi-band compatible antenna that transmits and receives high-frequency signals and conforms to communication standards such as LTE. The antenna element 2 does not have to correspond to all the bands of the communication device 1, for example, and may correspond only to the low frequency band group or the high frequency band group. Further, the antenna element 2 may be built in the communication device 1.

The RFIC 3 is an RF signal processing circuit that processes high frequency signals transmitted and received by the antenna element 2. Specifically, the RFIC 3 processes a high frequency signal input from the antenna element 2 via the receiving side signal path and the transmitting side signal path of the high frequency front end circuit 10 by down-conversion or the like, and performs the signal processing. The generated received signal is output to a baseband signal processing circuit (not shown). Further, the RFIC 3 processes the transmission signal input from the baseband signal processing circuit by up-conversion or the like, and outputs the high frequency signal generated by the signal processing to the transmission side signal path of the high frequency front end circuit 10.

The high frequency front end circuit 10 is a circuit that transmits a high frequency signal between the antenna element 2 and the RFIC 3. Specifically, the high-frequency front-end circuit 10 transmits the high-frequency signal output from the RFIC 3 to the antenna element 2 via the transmission side signal path. Further, the high frequency front end circuit 10 transmits the high frequency signal received by the antenna element 2 to the RFIC 3 via the receiving side signal path.

The high-frequency front-end circuit 10 includes a composite filter device 130 and an amplifier circuit 4 in this order from the antenna element 2 side.

The amplifier circuit 4 is composed of amplifiers 43, 45, 55 that power-amplify the high-frequency signal input from the composite filter device 130 or the RFIC 3. In the present embodiment, the amplifier 43 connected to the transmitting side terminal 13 is a power amplifier, and the amplifiers 45 and 55 connected to the receiving side terminals 15 and 35 are low noise amplifiers.

The high-frequency front-end circuit 10 may include, for example, a switch for switching between transmission and reception, or a switch for sharing a low-noise amplifier among a plurality of filters constituting the composite filter device.

The high-frequency front-end circuit 10 configured in this way filters the high-frequency signal input from the antenna element 2 by the receiving filter 220 or 300, amplifies it by the amplifiers 45 and 55, and outputs it to the RFIC 3. Alternatively, the high-frequency signal input from the RFIC 3 is amplified by the amplifier 43, filtered by the transmission filter 100, and output to the antenna element 2. The RFIC corresponding to the low frequency band (Band 25 in this case) and the RFIC corresponding to the high frequency band (Band 1 in this case) may be provided separately.

As described above, the high-frequency front-end circuit 10 is provided with the composite filter device 130 according to the second embodiment, so that good electrical characteristics can be obtained (loss can be suppressed) and a multi-band compatible high-frequency front end can be obtained. The circuit can be realized.

The high-frequency front-end circuit may be configured to include the composite filter device according to the first and second embodiments of the first embodiment and the first and second modifications of the second embodiment. Further, in the present embodiment, a configuration in which a composite filter device connected to both a transmitting side signal path and a receiving side signal path is provided has been described. However, the configuration of the high-frequency front-end circuit is not limited to this, and a composite filter device may be connected to either the receiving side signal path or the transmitting side signal path.

It is also planned that the embodiments disclosed this time will be appropriately combined and implemented within a consistent range. It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

12 Common terminal, 13 Transmitter terminal, 14 Inductor, 15 Receiver terminal, 16-19 Parallel arm resonator circuit, 100 Transmitter filter, 101-105, 201-204 Series arm resonator, 106-109, 206-209 Parallel Arm resonator, 120 composite filter device, 200 reception filter.

Claims (11)

With common terminals
1st terminal and
2nd terminal and
A first filter connected between the common terminal and the first terminal and having a first pass band,
A second filter connected between the common terminal and the second terminal and having a second pass band higher than the first pass band,
A first inductor provided between the common terminal and the second filter,
It is a composite type filter device equipped with
The second filter has one or more series arm circuits, two or more parallel arm resonators, and a second inductor .
The one or more series arm circuits are connected in series with each other on a path connecting the common terminal and the second terminal.
The two or more parallel arm resonators
A first parallel arm resonator connected to a node on the path connecting the first series arm circuit closest to the common terminal and the first inductor among the one or more series arm circuits, and a reference terminal.
A node on the path connecting the first series arm circuit and the second terminal, and one or more other parallel arm resonators connected to the reference terminal.
Including
The anti-resonance frequency of the first parallel arm resonator is located within the second pass band.
The resonant frequency of the first parallel arm resonator is lower than the high-frequency end frequency of the first pass band, and, rather lower than any of the resonant frequencies of the one or more other parallel arm resonators,
The second inductor is provided only on the path connecting the first parallel arm resonator and the reference terminal to which the first parallel arm resonator is connected .
Combined filter device. The first parallel arm resonator contains a plurality of resonators and contains a plurality of resonators.
The composite filter device according to claim 1, wherein the resonance frequency of at least one resonator of the plurality of resonators is lower than the resonance frequency of any of the one or more other parallel arm resonators. The second filter includes a first parallel arm resonant circuit.
The first parallel arm resonant circuit
Wherein the first parallel arm resonator, and a second inductor, the composite filter device of claim 1 or 2. The composite filter device according to claim 3 , wherein the resonance frequency of the first parallel arm resonance circuit is lower than the low frequency of the first pass band. In the composite filter device
The composite filter device according to any one of claims 1 to 4, wherein the impedance of the second filter unit as seen from the common terminal side is at least partially open in the first pass band. The first filter includes a plurality of resonators and has a plurality of resonators.
The composite filter device according to any one of claims 1 to 5, wherein the resonator closest to the common terminal among the plurality of resonators in the first filter is a series arm resonator. The composite filter device further
With the 3rd terminal
A third filter connected between the common terminal and the third terminal and having a third pass band higher than the second pass band,
A third inductor provided between the common terminal and the third filter,
With
The third filter has one or more series arm circuits and two or more parallel arm resonators.
The one or more series arm circuits in the third filter are connected in series with each other on a path connecting the common terminal and the third terminal.
The two or more parallel arm resonators in the third filter are
A second parallel connected to a node on the path connecting the second series arm circuit closest to the common terminal and the third inductor among the one or more series arm circuits in the third filter, and a reference terminal. With the arm resonator,
One or more other parallel arm resonators connected to a node on the path connecting the second series arm circuit and the third terminal, and a reference terminal.
Including
A fourth inductor is provided on the path connecting the second parallel arm resonator and the reference terminal to which the second parallel arm resonator is connected.
A second parallel arm resonator circuit is formed by at least the second parallel arm resonator and the fourth inductor.
The anti-resonance frequency of the second parallel arm resonance circuit is located within the third pass band.
The resonance frequency of the second parallel arm resonator circuit is lower than the high frequency end frequency of the first pass band and lower than the resonance frequency of the one or more other parallel arm resonators in the third filter. The composite filter device according to any one of claims 1 to 6. The composite filter device according to claim 7, wherein the resonance frequency of the second parallel arm resonance circuit is lower than the low frequency at the low frequency end of the first pass band. The composite filter device according to any one of claims 1 to 8.
An amplifier circuit connected to the composite filter device and
High frequency front end circuit. An RF signal processing circuit that processes high-frequency signals transmitted and received by the antenna element,
The high-frequency front-end circuit according to claim 9, which transmits the high-frequency signal between the antenna element and the RF signal processing circuit.
Communication device. With common terminals
1st terminal and
2nd terminal and
A first filter connected between the common terminal and the first terminal and having a first pass band,
A second filter connected between the common terminal and the second terminal and having a second pass band higher than the first pass band,
A first inductor provided between the common terminal and the second filter,
It is a composite type filter device equipped with
The second filter has one or more series arm circuits, two or more parallel arm resonators, and a second inductor.
The one or more series arm circuits are connected in series with each other on a path connecting the common terminal and the second terminal.
The two or more parallel arm resonators
A first parallel arm resonator connected to a node on the path connecting the first series arm circuit closest to the common terminal and the first inductor among the one or more series arm circuits, and a reference terminal.
A node on the path connecting the first series arm circuit and the second terminal, and one or more other parallel arm resonators connected to the reference terminal.
Including
The anti-resonance frequency of the first parallel arm resonator is located within the second pass band.
The resonance frequency of the first parallel arm resonator is lower than the high frequency of the first pass band and lower than the resonance frequency of any of the other parallel arm resonators of 1 or more.
The one or more other parallel arm resonators include a node on the path connecting the second series arm circuit second closest to the common terminal and the first series arm circuit among the one or more series arm circuits. Includes a reference terminal and a second parallel arm resonator connected to
The second inductor connects the first parallel arm resonator and the reference terminal to which the first parallel arm resonator is connected, and connects the second parallel arm resonator and the first parallel arm resonator. It is provided only on the path connecting the reference terminal.
Combined filter device.