JP5235004B2 - Filter, duplexer, communication module, communication device - Google Patents

Description

  The present disclosure relates to a filter, a duplexer, a communication module, and a communication device.

  In recent years, multiband / systemization of wireless communication devices represented by mobile phones has progressed, and a plurality of wireless devices are mounted on a single telephone. There is a concern that the size of wireless communication equipment will increase due to the installation of multiple wireless devices. However, by mounting a reception filter that eliminates the inter-reception stage filter and provides a balanced output, the wireless device can be downsized. There is a way to try. Patent Document 1 discloses a reception filter having a balanced output.

JP 2005-318308 A

  However, in the balanced filter, bridging capacitance may occur between the input terminal and one output terminal and between the input terminal and the other output terminal. When the bridging capacitance is generated, the signal input from the input terminal is bypassed by the bridging capacitance without passing through the filter. At this time, if the two bridging capacities are the same value, the influence of the bypass between the input and output terminals is in phase, so that it is canceled at the time of balance conversion. However, the two bridge capacities generally have different values in a balanced filter (such as a double mode elastic wave filter) using an actual elastic wave filter in order to perform balance conversion. As described above, when the value of the bridging capacitance is different (unbalanced), the influence of the bypass between the input and output terminals is not canceled out, so that there is a problem in that suppression degradation occurs in the reception filter.

  The object of the present application is to improve the degree of suppression of the balanced filter by eliminating the unbalance of the bridging capacitance existing between the input terminal and the two output terminals and removing unnecessary in-phase components.

  The filter disclosed in the present application includes an input terminal, a filter element that filters a signal input to the input terminal, and a first output terminal and a second output terminal that differentially output a signal from the filter element. A balanced filter having a capacitance connected between the input terminal and one of the first output terminal and the second output terminal. is there.

  According to the disclosure in the present application, it is possible to improve the degree of suppression of the balanced filter.

Block diagram of a radio unit corresponding to one frequency band of an FDD (Frequency Division Duplex) system mobile phone using an antenna duplexer Block diagram of a radio unit in which the reception interstage filter 104 and the transmission interstage filter 108 are deleted from the radio unit illustrated in FIG. Block diagram of balanced antenna duplexer The figure which showed the concept of bridging capacity C1 and C2 which generate | occur | produce between input-output of a receiving filter The figure which shows the concept of the filter concerning this Embodiment The schematic diagram of the receiving filter which is an example of the balance type filter concerning this Embodiment The characteristic diagram which shows the frequency characteristic of a reception filter in the case where the value of the bridge capacitance C1 is 0.03 pF and the value of the bridge capacitance C2 is 0.05 pF with and without the capacitance C3 added. Block diagram of balanced antenna duplexer Schematic diagram showing a specific configuration of the reception filter 32 in FIG. The characteristic diagram which shows the isolation characteristic between transmission / reception of a duplexer provided with the receiving filter with which the electrostatic capacitance was added, and the duplexer provided with the receiving filter without the electrostatic capacitance The schematic diagram which shows the wiring layout of the receiving filter concerning this Embodiment Diagram showing capacitance arrangement pattern Communication module block diagram Block diagram of communication device

  The filter is a balanced type including an input terminal, a filter element that filters a signal input to the input terminal, and a first output terminal and a second output terminal that differentially output a signal from the filter element. In the filter, a capacitance is connected between the input terminal and any one of the first output terminal and the second output terminal. In this configuration, it is possible to reduce the unbalance of the bridging capacitance existing between the input terminal and the two output terminals existing in the acoustic wave element, and to realize an improvement in the degree of suppression.

  In the filter, the filter element may be a double mode type acoustic wave filter, and the capacitance may be connected between an input terminal and an output terminal of the double mode type acoustic wave filter. .

  In the filter, a filter pass characteristic of a path from the input terminal to the first output terminal may be different from a filter pass characteristic of a path from the input terminal to the second output terminal. By adopting such a configuration, it is possible to simultaneously reduce the unbalance of the bridging capacitance existing between the input / output terminals and the unbalance of the in-phase component due to other influences, and the degree of suppression can be improved.

In the filter, the filter element includes a first double mode type acoustic wave filter connected between the input terminal and the first output terminal, and between the input terminal and the second output terminal. And a second double mode type elastic wave filter and an input interdigital transducer and an output interdigital transducer, respectively. The electrostatic capacitance includes a potential difference between nearest electrode fingers between the input interdigital transducer and the output interdigital transducer in the first double-mode acoustic wave filter, and the second double-mode acoustic wave. Input interdigital transducer and output interface in filter Among the potential difference between the nearest electrode fingers each other between the digital transducer may be a configuration that is connected to a path towards a potential difference is small.
As a result, capacitance is added to the double mode SAW filter of the path with the smaller bridging capacity, and the imbalance of the bridging capacity that originally exists can be reduced, and the degree of suppression can be improved. It becomes possible.

  In the filter, the capacitance may be formed on the filter element. With such a configuration, capacitance can be added without increasing the size of the filter, the degree of suppression can be improved while maintaining a small size, and a more desirable structure can be obtained.

(Embodiment)
[1. Filter configuration
In recent years, multiband / systemization of wireless communication devices represented by mobile phones has progressed, and a plurality of wireless devices are mounted on a single telephone. For this reason, the complexity of the circuit in the radio section and the increase in the number of used parts are serious problems.

  FIG. 1 shows a radio unit corresponding to one frequency band of an FDD (Frequency Division Duplex) mobile phone using an antenna duplexer. The radio unit shown in FIG. 1 includes an antenna 101, a duplexer 102, an LNA (Low Noise Amplifier) 103, a reception interstage filter 104, an LNA 105, a reception circuit 106, a transmission circuit 107, a transmission interstage filter 108, and a power amplifier 109. Yes. In a multi-band mobile phone, for example, the radio unit shown in FIG. 1 is mounted for the frequency band, and there is a problem that the size of the device is increased.

  FIG. 2 shows a radio unit in which the reception interstage filter 104 and the transmission interstage filter 108 are deleted from the radio unit shown in FIG. As shown in FIG. 2, when the inter-reception stage filter 104 is deleted from the radio unit, the reception port 102a of the duplexer 102 must be a balanced output. Also, the duplexer 102 takes charge of the function of suppressing unnecessary waves in the inter-reception stage filter 104. That is, a high attenuation characteristic (transmission band) between the antenna and the receiving terminal is required. Furthermore, considering that the largest unwanted wave to be attenuated is leakage of the transmission signal to the reception side, it is important for the duplexer 102 to improve isolation between the transmission and reception terminals (transmission band). It becomes.

  As described above, in the duplexer 102 in the system in which the reception interstage filter 104 is deleted, the reception port 102a is required to have a balanced output and have high attenuation and high isolation characteristics. .

  FIG. 3 is a block diagram of a balanced antenna duplexer. As shown in FIG. 3, the balanced antenna duplexer includes a single-ended transmission filter 1, a single-ended-balance conversion reception filter 2, and a matching circuit 3. The transmission filter 1 is connected to one transmission terminal 1a (single input). Two reception terminals 2a and 2b (balance output) are connected to the reception filter 2. An antenna terminal 4 connected to the antenna is connected to the matching circuit 3.

  Here, in order to achieve the above-described improvement in the attenuation characteristic of the transmission band between the antenna and the reception terminal and the improvement in the transmission-reception isolation in the transmission band, it is essential to improve the suppression degree of the reception filter 2 that is a balanced filter. Become. Therefore, factors that hinder the improvement of the suppression degree of the balanced filter are considered. One factor is the influence of the bridging capacitance (C1, C2 in FIG. 4) between the input and output terminals present in the filter. FIG. 4 is a diagram showing the concept of the bridging capacitances C1 and C2 generated between the input and output of the reception filter 2. As shown in FIG. 4, if the bridging capacitors C1 and C2 exist in the reception filter 2, the signal input to the input terminal 2c of the reception filter 2 does not pass through the filter element 5, and the bridging capacitances C1 and C2 To the output terminals 2a and 2b. That is, the signal input to the input terminal 2 c bypasses the reception filter 2. Therefore, the degree of suppression in the reception filter 2 is degraded.

  In the case of a balanced filter such as the reception filter 2, if the bridging capacitors C1 and C2 have the same size, the influence of the bypass between the input and output terminals via the bridging capacitors C1 and C2 is in-phase. Therefore, it is canceled out by balance conversion. However, in a balanced filter (such as a double mode SAW filter) using an actual acoustic wave filter, C1 ≠ C2 in general in order to perform balance conversion, and the bridging capacitances C1 and C2 are unbalanced. It did not escape the suppression deterioration due to the influence of.

  Japanese Patent Application Laid-Open No. 2005-318308 discloses that there is a bridging capacity in each of the paths between the two input / output terminals in the balanced filter, but the bridging capacity between the two input / output terminals is Cc. And are considered identical. That is, the unbalance of the bridging capacity is not disclosed, and only when the same bridging capacity exists ideally is shown. Furthermore, Japanese Patent Laid-Open No. 2005-318308 discloses a common GND inductance Lg3 as another factor that hinders the balance, but as a solution to this, only reducing the common GND inductance Lg3 is disclosed. There is no mention of other correction methods.

  FIG. 5 is a diagram showing the concept of the filter according to the present embodiment. As shown in FIG. 5, the reception filter 2, which is a balanced filter using an acoustic wave filter, has an input terminal 2c and one of the two output terminals 2a and 2b (in the example shown in FIG. 5). A capacitance C3 is connected between the output terminal 2a). In this way, by connecting the capacitance C3, the unbalance of the bridging capacitance existing in the respective paths between the input terminal 2c and the two output terminals 2a and 2b is reduced, and the suppression is improved. be able to. 5 is a case where the values of the bridging capacitances C1 and C2 are in a relationship of C1 <C2, and the capacitance C3 is connected in parallel to the bridging capacitance C1, and the input terminal 2c and the output terminal. The combined capacity with 2a is increased to ensure a balance with the bridging capacity C2. When the bridge capacities C1 and C2 are in the relationship of C1> C2, the balance between the two bridge capacities between the input and output of the reception filter 2 is secured by connecting the capacitance C3 in parallel to the bridge capacity C2. can do. That is, the input / output of the reception filter 2 is connected by connecting an electrostatic capacitance of an arbitrary value to at least one of the path of the input terminal 2c-output terminal 2a and the path of the input terminal 2c-output terminal 2b. A balance between the two bridging capacities in between can be ensured. Hereinafter, a specific configuration of the filter according to the present embodiment of the above concept will be described.

  FIG. 6 is a schematic diagram of a reception filter which is an example of a balanced filter according to the present embodiment. The reception filter shown in FIG. 6 includes a double-mode SAW filter designed with a pass band of 2110 to 2170 MHz and a stop band of 1920 to 1980 MHz. The reception filter shown in FIG. 6 is a filter in which two double-mode SAW filters 21 and 22 having anti-phase and in-phase outputs are connected.

  The double mode SAW filter 21 includes an input IDT electrode 21a and output IDT electrodes 21b and 21c. The input IDT electrode 21a is connected to the input terminal 2c. The output IDT electrodes 21b and 21c are connected to the output terminal 2a. The input IDT electrode 21a is provided with a grounded IDT electrode 21h that is grounded at an opposing position. The output IDT electrode 21b is provided with a grounded IDT electrode 21i that is grounded at an opposing position. The output IDT electrode 21c is provided with a grounded IDT electrode 21j that is grounded at an opposing position. Reflectors 21k are disposed at both ends of the input IDT electrode 21a and the output IDT electrodes 21b and 21c in the arrangement direction.

  The double mode SAW filter 22 includes an input IDT electrode 22a and output IDT electrodes 22b and 22c. The input IDT electrode 22a is connected to the input terminal 2c. The output IDT electrodes 22b and 22c are connected to the output terminal 2b. The input IDT electrode 22a is provided with a grounded IDT electrode 22h that is grounded at an opposing position. The output IDT electrode 22b is provided with a grounded IDT electrode 22i that is grounded at an opposing position. The output IDT electrode 22c is provided with a grounded IDT electrode 22j that is grounded at an opposing position. Reflectors 22k are disposed at both ends of the input IDT electrode 22a and the output IDT electrodes 22b and 22c in the arrangement direction.

  In the reception filter shown in FIG. 6, a signal input via the input terminal 2 c is input to the double mode SAW filters 21 and 22. In the double mode SAW filter 21, the electrode finger 21d at the end of the input IDT electrode 21a and the electrode finger 21e at the end of the output IDT electrode 21b have the same potential, and the electrode finger 21d at the end of the input IDT electrode 21a The electrode finger 21e at the end of the output IDT electrode 21b has the same potential. Therefore, the surface acoustic wave excited by the input IDT electrode 21a is received in the opposite phase (phase inverted by 180 °) at the output IDT electrodes 21b and 21c. Therefore, the signal output from the output terminal 2a is inverted in phase (phase difference 180 degrees) with respect to the signal input to the input terminal 2c.

  On the other hand, the double mode SAW filter 22 has a potential difference between the electrode finger 22d at the end of the input IDT electrode 22a and the electrode finger 22e at the end of the output IDT electrode 22b, and the electrode finger 22d at the end of the input IDT electrode 22a. And the electrode finger 22e at the end of the output IDT electrode 22b has a potential difference. Therefore, the surface acoustic wave excited by the input IDT electrode 22a is received in the same phase by the output IDT electrodes 22b and 22c. Therefore, the signal output from the output terminal 2b is in phase with the signal input to the input terminal 2c. As described above, the reception filter 2 that is a balanced filter can output a signal having a reverse phase from the output terminal 2a and a signal having the same phase from the output terminal 2b based on the signal input to the input terminal 2c. .

  Here, in the reception filter shown in FIG. 6, bridging capacitances C1 and C2 exist between the input terminal 2c and the output terminals 2a and 2b, respectively. Note that the bridging capacitances C1 and C2 in FIG. 6 are equivalently showing the bridging capacitances present in the reception filter 2, and are not actually connected with capacitors or the like. The bridging capacitances C1 and C2 are unbalanced in value due to the structure of the double mode SAW filters 21 and 22. The bridging capacitances C1 and C2 are generated based on a potential difference between adjacent electrode fingers in the double mode SAW filters 21 and 22. For example, the electrode finger 21d at the end of the output IDT electrode 21b and the electrode finger 21e at the end of the input IDT electrode 21a (electrode finger adjacent to the electrode finger 21d) in the double mode SAW filter 21 are both signal potentials. Therefore, the potential is the same, and the bridging capacity between the electrode finger 21d and the electrode finger 21e becomes a small value. Similarly, the electrode finger 21f at the end of the ground IDT electrode facing the input IDT electrode 21a, and the electrode finger 21g (the electrode finger adjacent to the electrode finger 21f) at the end of the ground IDT electrode facing the output IDT electrode 21c Since both are ground potentials, they are the same potential, and the bridging capacity between the electrode finger 21f and the electrode finger 21g is a small value. Thus, in the double mode type SAW filter 21, since the adjacent electrode fingers have the same potential, the bridging capacitance C1 has a small value. On the other hand, the electrode finger 22d at the end of the output IDT electrode 22b in the double mode SAW filter 22 and the electrode finger 22e at the end of the input IDT electrode 22a (electrode finger adjacent to the electrode finger 22d) Since the electrode finger 22e is a ground potential at the signal potential, the potential is different, and the bridging capacity between the electrode finger 22d and the electrode finger 22e is a large value. Similarly, an electrode finger 22f at the end of the ground IDT electrode facing the input IDT electrode 22a, and an electrode finger 22g (an electrode finger adjacent to the electrode finger 22f) at the end of the ground IDT electrode facing the output IDT electrode 22c Are different potentials because the electrode finger 22f is a signal potential and the electrode finger 22g is a ground potential, and the bridging capacity between the electrode finger 22f and the electrode finger 22g is a large value. Thus, in the double mode type SAW filter 22, since the potential difference between adjacent electrode fingers is large, the bridging capacitance C2 has a large value.

  In the filter shown in FIG. 6, it is assumed that the value of the bridging capacitance C1 is 0.03 pF and the value of the bridging capacitance C2 is 0.05 pF. In order to eliminate such an imbalance between the values of the bridging capacitances C1 and C2, consider a case where an electrostatic capacitance C3 having a capacitance of 0.02 pF is added to the bridging capacitance C1 side.

  FIG. 7 shows the frequency characteristics of the reception filter when the capacitance C3 is added to the filter having the bridge capacitance C1 of 0.03 pF and the value of the bridge capacitance C2 of 0.05 pF. . In FIG. 7, the characteristic indicated by the solid line is the frequency characteristic of the reception filter 2 to which the capacitance C3 is added as shown in FIG. The characteristic indicated by the broken line is, for example, the frequency characteristic of the reception filter 2 to which the capacitance C3 is not added as shown in FIG. As shown in FIG. 7, by adding the capacitance C3 to the reception filter 2, the attenuation in the stop band (about 1920 to 1980 MHz) can be increased, and the degree of suppression can be improved.

[2. (Duplexer configuration)
FIG. 8 is a block diagram of a balanced antenna duplexer. The balanced antenna duplexer includes a transmission filter 31, a reception filter 32, an inductor 33, and an antenna terminal 34. The transmission filter 31 includes a ladder type SAW filter in which a plurality of resonators are connected in a ladder type. In the present embodiment, a seven-stage single-end (single input-single output) type ladder-type SAW filter is provided. The transmission filter 31 is connected to a transmission terminal 31a. The reception filter 32 includes a double mode type SAW filter. The reception filter 32 is a single input-balance output type filter, and is connected to reception terminals 32a and 32b. The inductor 33 is an inductor for phase matching between the transmission filter 31 and the reception filter 32. The antenna terminal 34 is connected to an antenna (not shown). The duplexer shown in FIG. 8 can be mounted on a W-CDMA (Wideband Code Division Multiple Access) system Band_I mobile phone. The transmission band is, for example, 1920 to 1980 MHz, and the reception band is, for example, 2110 to 2170 MHz.

  FIG. 9 is a schematic diagram showing a specific configuration of the reception filter 32 in FIG. The reception filter 32 shown in FIG. 9 includes double mode SAW filters 41 and 42, SAW filters 43 to 46, an input terminal 47, output terminals 48a and 48b, and a capacitance C40. SAW filters 43 and 44 are connected in series to the input terminal 47. The SAW filter 44 is connected to the input IDT electrode 41 a of the double mode SAW filter 41 and the input IDT electrode 42 a of the double mode SAW filter 42. The output IDT electrodes 41 b and 41 c of the double mode SAW filter 41 are connected to the SAW filter 45. The output IDT electrodes 42 b and 42 c of the double mode SAW filter 42 are connected to the SAW filter 46. An output terminal 48 a is connected to the SAW filter 45. An output terminal 48 b is connected to the SAW filter 46. The electrostatic capacitance C40 is connected to the input side of the SAW filter 43 and the output side of the SAW filter 45.

  As shown in FIG. 9, in the double mode type SAW filter 41 arranged between the input terminal 47 and the output terminal 48a, the nearest electrode fingers of the input IDT electrode 41a and the two output IDT electrodes 41b and 41c ( The electrode finger 41d and the electrode finger 41e, and the electrode finger 41f and the electrode finger 41g) have the same potential. In this structure, the surface acoustic wave excited by the input IDT electrode 41a is received in the opposite phase (phase inverted by 180 °) at the output IDT electrodes 41b and 41c. On the other hand, in the double mode type SAW filter 42 arranged between the input terminal 47 and the output terminal 48b, the closest electrode fingers (electrode fingers) of the input IDT electrode 42a and the two output IDT electrodes 42b and 42c. 42d and electrode finger 42e, and electrode finger 42f and electrode finger 42g) have different potentials. In this case, the surface acoustic wave excited by the input IDT electrode 42a is received in the same phase by the output IDT electrodes 42b and 42c. Based on such a principle, signals having a phase difference of 180 ° can be output from the output terminal 48a and the output terminal 48b.

  Here, the bridging capacity existing in the path connecting the input terminal 47 and the output terminal 48a and the path connecting the input terminal 47 and the output terminal 48b will be described. One cause of the bridging capacitance is the capacitance generated between the nearest electrode fingers between the input IDT electrode and the output IDT electrode. As shown in FIG. 9, the potentials of the closest electrode fingers of the double mode type SAW filter 41 and the double mode type SAW filter 42 are different in order to realize unbalance-balance conversion. Specifically, a pair of nearest electrode fingers in the double mode type SAW filter 41 is grounded, and the generated capacitance is not regarded as a bridging capacitance. As a result, it is considered that the bridging capacity existing between the input terminal 47 and the output terminal 48a is smaller than the bridging capacity existing between the input terminal 47 and the output terminal 48b. Will exist. In order to eliminate such imbalance of the bridging capacitance, it is preferable to connect a capacitance C40 between the input terminal 47 and the output terminal 48a as shown in FIG. The value of the capacitance C40 is, for example, 3 fF.

FIG. 10 shows isolation characteristics between transmission and reception of a duplexer including a reception filter to which a capacitance having a value of 3 fF is added and a duplexer including a reception filter to which no capacitance is added. In FIG. 10, a solid line characteristic indicates an isolation characteristic in a duplexer including a reception filter to which a capacitance of 3 fF is added. The broken line characteristic indicates the isolation characteristic in a duplexer including a reception filter to which no capacitance is added. In the duplexer used to obtain the characteristic result shown by the solid line in FIG. 10, the transmission filter and the reception filter are formed on a 42 ° rotated Y-cut lithium tantalate (LiTaO ₃ ) substrate, and are mainly composed of aluminum (Al). It was produced using an electrode material. As shown in FIG. 10, the isolation improvement of 10 dB or more at the maximum was observed by connecting a capacitance C40 of 3 fF between the input and output of the reception filter.

FIG. 11 is a schematic diagram illustrating a wiring layout of the reception filter according to the present embodiment. As shown in FIG. 11, the reception filter was formed on a 42 ° rotated Y-cut LiTaO ₃ substrate 50. On the substrate 50, wiring patterns such as double-mode SAW filters 51 and 52, SAW resonators 53 to 56, and an input terminal 57 are formed. The wiring pattern shown in FIG. 11 shows an example of a specific wiring pattern of the reception filter shown in FIG.

  As described above, in the present embodiment, a path for adding capacitance is determined by paying attention to the potential difference between the nearest electrode fingers between the input IDT electrode and the output IDT electrode. This is because, as shown in FIG. 11, the wiring layout of the reception filter manufactured in this embodiment is almost the same as the path of the input terminal 57-output terminal 58a and the path of the input terminal 57-output terminal 58b. This is because the location where the imbalance of the bridging capacitance exists is considered to be between the nearest electrode fingers between the input IDT electrode and the output IDT electrode in the double mode SAW filters 51 and 52. In order to reduce such an unbalance of the bridging capacitance, a capacitance 59 was connected between the input terminal 57 and the output terminal 58a. The electrostatic capacitance 59 is drawn from the input terminal 57 and includes a wiring pattern 59a mainly containing Al, a wiring pattern 59b drawn mainly from the output terminal 58a and mainly containing Al, and between the wiring pattern 59a and the wiring pattern 59b. The gap 59c is formed. The dimensions of the wiring patterns 59a and 59b (the length dimension from the input terminal 57 and the output terminal 58a, the dimension L of the air gap 59c, etc.) can be determined by experiments so as to achieve a desired improvement in isolation. For example, since the value of the capacitance 59 is inversely proportional to the width dimension L of the gap 59c, the length of the wiring pattern 59a and 59b is adjusted to adjust the width dimension L of the gap 59c. The value can be adjusted arbitrarily.

  In the present embodiment, as shown in FIG. 11, the wiring 59 is drawn out from the input terminal 57 and the output terminal 58a and the capacitance 59 is added. However, the location where the bridging capacitance imbalance occurs is a double mode. Since it is the type SAW filters 51 and 52, the same effect can be obtained regardless of the arrangement as long as the double mode type SAW filters 51 and 52 are sandwiched.

  For example, when an imbalance exists in the wiring layout of the surface acoustic wave filter, a capacitance may be added to the path on the input terminal 57-output terminal 58b side. In other words, in consideration of the wiring layout and the capacitance between the nearest electrode fingers, if the capacitance is added to the path having the larger bridging capacitance, the effect of improving the suppression can be further obtained.

  Moreover, you may connect an electrostatic capacitance as shown in any one among code | symbol C41-C47 shown in FIG. The capacitances C40 to C43 are examples connected to the path on the input terminal 47-output terminal 48a side, and are examples in which the capacitances C40 to C43 are connected in parallel between the input and output of the double mode SAW filter 41. The capacitances C44 to C47 are examples connected to the path on the input terminal 47-output terminal 48b side, and are examples in which the capacitances C44 to C47 are connected in parallel between the input and output of the double mode SAW filter 42.

[3. (Configuration of communication module)
FIG. 13 shows an example of a communication module including the filter according to the present embodiment. As shown in FIG. 13, the duplexer 62 includes a reception filter 62a and a transmission filter 62b. The reception filter 62a is connected to reception terminals 63a and 63b corresponding to, for example, balanced output. The transmission filter 62b is connected to the transmission terminal 65 via the power amplifier 64. Here, the reception filter 62a includes the filter according to the present embodiment.

  When performing a reception operation, the reception filter 62a passes only a signal in a predetermined frequency band among reception signals input via the antenna terminal 61, and outputs the signal from the reception terminals 63a and 63b to the outside. Further, when performing a transmission operation, the transmission filter 62b passes only a signal in a predetermined frequency band among transmission signals input from the transmission terminal 65 and amplified by the power amplifier 64, and outputs the signal from the antenna terminal 61 to the outside. To do.

  By providing the communication module with the filter according to the present embodiment, it is possible to improve the degree of suppression in the reception filter 62a. Further, the isolation between the reception filter 62a and the transmission filter 62b can be improved.

  Further, in the communication module of FIG. 13, by connecting an electrostatic capacity between the antenna terminal 61 and the receiving terminal 63a or between the antenna terminal 61 and the receiving terminal 63b, the bridging capacity between both terminals is obtained. Can be further corrected.

  Note that the configuration of the communication module shown in FIG. 13 is an example, and the same effect can be obtained even if the filter according to the present embodiment is mounted on a communication module of another form.

[4. Configuration of communication device]
FIG. 14 shows an RF block of a mobile phone terminal as an example of a communication apparatus including the filter according to the present embodiment or the communication module described above. Further, the communication apparatus shown in FIG. 14 shows a configuration of a mobile phone terminal that supports a GSM (Global System for Mobile Communications) communication system and a W-CDMA (Wideband Code Division Multiple Access) communication system. Further, the GSM communication system in the present embodiment corresponds to the 850 MHz band, 950 MHz band, 1.8 GHz band, and 1.9 GHz band. In addition to the configuration shown in FIG. 14, the mobile phone terminal includes a microphone, a speaker, a liquid crystal display, and the like. However, illustration is omitted because they are unnecessary in the description of the present embodiment. Here, the reception filters 73a and 77 to 80 include the filters according to the present embodiment.

  First, the received signal input via the antenna 71 selects an LSI to be operated by the antenna switch circuit 72 depending on whether the communication method is W-CDMA or GSM. When the input received signal is compatible with the W-CDMA communication system, switching is performed so that the received signal is output to the duplexer 73. The reception signal input to the duplexer 73 is limited to a predetermined frequency band by the reception filter 73 a, and a balanced reception signal is output to the LNA 74. The LNA 74 amplifies the input received signal and outputs it to the LSI 76. The LSI 76 performs a demodulation process on the audio signal based on the input received signal, and controls the operation of each unit in the mobile phone terminal.

  On the other hand, when transmitting a signal, the LSI 76 generates a transmission signal. The generated transmission signal is amplified by the power amplifier 75 and input to the transmission filter 73b. The transmission filter 73b passes only a signal in a predetermined frequency band among input transmission signals. The transmission signal output from the transmission filter 73 b is output from the antenna 71 to the outside via the antenna switch circuit 72.

  In addition, when the received signal to be input is a signal corresponding to the GSM communication system, the antenna switch circuit 72 selects any one of the reception filters 77 to 80 according to the frequency band and outputs the received signal. To do. A reception signal whose band is limited by any one of the reception filters 77 to 80 is input to the LSI 83. The LSI 83 performs a demodulation process on the audio signal based on the input received signal, and controls the operation of each unit in the mobile phone terminal. On the other hand, when transmitting a signal, the LSI 83 generates a transmission signal. The generated transmission signal is amplified by the power amplifier 81 or 82 and output from the antenna 71 to the outside via the antenna switch circuit 72.

  By providing the communication apparatus with the filter or communication module according to the present embodiment, the degree of suppression in the reception filter 62a can be improved. Further, the isolation in the reception filters 73a and 77-80 can be improved.

[5. Effects of the embodiment, etc.]
According to the present embodiment, an electrostatic capacitance having an arbitrary value is connected to at least one of the plurality of double mode SAW filters included in the balanced filter, and thus occurs in the plurality of double mode filters. The imbalance of the bridge capacity can be suppressed. Therefore, the degree of suppression of the filter can be improved. Further, the isolation of the filter can be improved.

  In this embodiment, a capacitance is connected to one of the two double mode SAW filters. However, an unbalance of bridging capacitance that occurs in the two double mode SAW filters is suppressed. If possible, a capacitance may be connected to each of the two double mode SAW filters.

  With respect to the present embodiment, the following supplementary notes are disclosed.

(Appendix 1)
A balanced filter comprising an input terminal, a filter element for filtering a signal input to the input terminal, and a first output terminal and a second output terminal for differentially outputting a signal from the filter element. And
A filter in which a capacitance is connected between the input terminal and any one of the first output terminal and the second output terminal.

(Appendix 2)
The electrostatic capacitance eliminates an unbalance of bridging capacitance existing between the input terminal and the first output terminal and between the input terminal and the second output terminal, and an unnecessary in-phase component The filter according to appendix 1, which has a value capable of removing.

(Appendix 3)
The filter according to appendix 1 or 2, wherein a filter pass characteristic of a path from the input terminal to the first output terminal is different from a filter pass characteristic of a path from the input terminal to the second output terminal.

(Appendix 4)
The filter element is connected between a first double mode type acoustic wave filter connected between the input terminal and the first output terminal, and between the input terminal and the second output terminal. A second double mode type elastic wave filter;
The first double-mode acoustic wave filter and the second double-mode acoustic wave filter each include an input interdigital transducer and an output interdigital transducer,
The capacitance includes a potential difference between nearest electrode fingers between an input interdigital transducer and an output interdigital transducer in the first double-mode acoustic wave filter, and the second double-mode acoustic wave filter. The filter according to claim 1, wherein the filter is connected to a path having a smaller potential difference among potential differences between nearest electrode fingers between the input interdigital transducer and the output interdigital transducer.

(Appendix 5)
The filter according to appendix 1, wherein the capacitance is formed on the filter element.

(Appendix 6)
A duplexer comprising a transmission filter that outputs a transmission signal and a reception filter that filters a signal input from an antenna,
The said reception filter is a duplexer provided with the filter as described in any one of Additional remarks 1-5.

(Appendix 7)
The communication module provided with the filter as described in any one of Additional remarks 1-5.

(Appendix 8)
The communication apparatus provided with the filter as described in any one of Additional remarks 1-5.

  The disclosure in the present application is useful for a filter, a duplexer, a communication module, and a communication device.

2 Reception filter 21, 22 Double mode type SAW filter C3, C40 Capacitance

Claims (3)

A balanced filter comprising an input terminal, a filter element for filtering a signal input to the input terminal, and a first output terminal and a second output terminal for differentially outputting a signal from the filter element. And
A capacitance is connected between the input terminal and any one of the first output terminal and the second output terminal ,
The filter element is connected between a first double mode type acoustic wave filter connected between the input terminal and the first output terminal, and between the input terminal and the second output terminal. A second double mode type elastic wave filter;
The first double-mode acoustic wave filter and the second double-mode acoustic wave filter each include an input interdigital transducer and an output interdigital transducer,
The capacitance includes a potential difference between nearest electrode fingers between an input interdigital transducer and an output interdigital transducer in the first double-mode acoustic wave filter, and the second double-mode acoustic wave filter. A filter connected to a path having a smaller potential difference among potential differences between nearest electrode fingers between the input interdigital transducer and the output interdigital transducer in FIG . Wherein the input terminal and the filter pass characteristic of the path toward the first output terminal, a filter pass characteristic of the path toward the second output terminal from said input terminal are different, the filter of claim 1. The capacitance is the formed on the filter element, the filter of claim 1.

Images