JP2013115626A - Branching filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a branching filter capable of reducing transmission signals leaking from antenna terminal side to output side of a reception filter through the reception filter.SOLUTION: A branching filter 1 comprises: a transmission filter 5; a reception filter 9 including a plurality of series resonators 15A connected in series from an input side toward an output side; an antenna terminal 7 connected to an output side of the transmission filter 5 and the input side of the reception filter 9; and an adjustment circuit 13 that has one end connected to an input side of the transmission filter 5 and the other end connected between arbitrary two of the plurality of series resonators 15A of the reception filter 9, and that adjusts a phase of a signal flowing from the one end to the other end.

Description

  The present invention relates to a duplexer used for a communication device or the like.

  2. Description of the Related Art A duplexer (a duplexer) configured to improve isolation between a transmission path and a reception path is known. For example, the duplexer of Patent Document 1 has, as a basic configuration, a transmission filter that filters a transmission signal input to a transmission terminal and outputs the filtered signal to an antenna terminal, and a reception terminal that filters a reception signal input from the antenna terminal. And a reception filter for outputting to the receiver.

  In the duplexer disclosed in Patent Document 1, the reception filter has a balanced-unbalanced conversion function of converting an input unbalanced signal into a balanced signal and outputting the balanced signal to two reception terminals. In addition, the duplexer of Patent Document 1 allows an electrostatic coupling unit to flow power from a transmission terminal to two reception terminals and adjust the phase of the power so as to eliminate a phase difference between the two reception terminals. have.

  In Patent Document 1, the above-described configuration utilizes the balun in-phase removal principle, and as a result, it is possible to reduce the influence of the current flowing through the space from the transmission terminal to the reception terminal (improvement of isolation). Can do).

JP 2011-160203 A

  In the duplexer, the transmission signal that has passed through the transmission filter from the transmission terminal to the antenna terminal may also pass through the reception filter from the antenna terminal side and leak to the output side (reception terminal) of the reception filter. is there. In this case, the leaked transmission signal is mixed into the reception signal as noise, leading to a decrease in communication performance. With the technology of Patent Document 1, it is not possible to remove the influence of such a leaked signal on the received signal.

  An object of the present invention is to provide a duplexer that can reduce a transmission signal that leaks from an antenna terminal side to an output side of a reception filter via a reception filter.

  A duplexer according to an aspect of the present invention includes a transmission filter and a plurality of filter elements including a resonator or a filter, and at least some of the plurality of filter elements are connected in series from the input side to the output side. Receiving filters, antenna terminals connected to the output side of the transmission filter and the input side of the reception filter, the plurality of filters having one end connected to the input side of the transmission filter and the other end connected in series An adjustment circuit connected between any two of the elements and adjusting the phase of a signal flowing from the one end to the other end.

  Preferably, the reception filter is a ladder type reception filter including one or more parallel resonators and a plurality of series resonators as the plurality of filter elements, and the other end of the adjustment circuit is connected to the plurality of series resonances. Connected between any two of the children.

  Preferably, the reception filter includes, as the plurality of filter elements, a multimode filter and an auxiliary resonator connected in series to an input side or an output side of the multimode filter, and the adjustment circuit Is connected between the multimode filter and the auxiliary resonator.

  Preferably, the phase difference between the signal that the adjustment circuit sends to the other end and the signal that the filter element on the antenna terminal side of the two arbitrary filter elements sends to the output side is more than 160 ° and less than 200 ° It is.

  Preferably, the phase difference is not less than 170 ° and not more than 190 °.

  According to said structure, the transmission signal which passes a receiving filter and leaks to the output side of a receiving filter can be reduced.

The block diagram which shows the principal part of the utilization example of the duplexer which concerns on the 1st Embodiment of this invention. 1 is a circuit diagram showing a configuration of a duplexer according to a first embodiment of the present invention. FIG. 3 is a schematic plan view showing an example of a resonator included in the duplexer of FIG. 2. FIGS. 3A to 3C are circuit diagrams showing examples of the adjustment circuit of the duplexer in FIG. The circuit diagram which shows the structure of the duplexer which concerns on the 2nd Embodiment of this invention.

<First Embodiment>
FIG. 1 is a block diagram showing a main part of a usage example (communication module 101) of the duplexer 1 according to the first embodiment of the present invention. The communication module 101 performs wireless communication using radio waves. The duplexer 1 is used in the communication module 101 as a duplexer that demultiplexes a transmission frequency signal and a reception frequency signal.

  In the communication module 101, an information signal TIS including information to be transmitted is modulated by a modulator 103, the frequency is raised by a mixer 105 (a high-frequency signal having a carrier frequency), and a transmission passband is transmitted by a bandpass filter 107. Unnecessary components other than are removed, amplified by the amplifier 109, and input to the duplexer 1. Then, the duplexer 1 removes unnecessary components other than the transmission passband from the input signal and outputs the result to the antenna 111. The antenna 111 converts the input electric signal into a radio signal TRS (radio wave) and transmits the radio signal TRS.

  In the communication module 101, a radio signal RRS (radio wave) received by the antenna 111 is converted into an electric signal by the antenna 111 and input to the duplexer 1. The duplexer 1 removes unnecessary components other than the reception passband from the input signal and outputs the result to the amplifier 113. The output signal is amplified by the amplifier 113, unnecessary components other than the pass band for reception are removed by the band pass filter 115, the frequency is lowered by the mixer 117, demodulated by the demodulator 119, and information to be received is received. It is output as an information signal RIS containing.

  The information signals TIS and RIS may be low-frequency signals (baseband signals) including appropriate information, and are, for example, analog audio signals or digitized audio signals. The passbands of the radio signals TRS and RRS may conform to various standards such as UMTS (Universal Mobile Telecommunications System). The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more thereof. The circuit system may be appropriate, for example, a direct conversion system or a double superheterodyne system. FIG. 1 schematically shows only the main part, and a low-pass filter, an isolator or the like may be added at an appropriate position, and the position of an amplifier or the like may be changed.

  FIG. 2 is a circuit diagram showing the configuration of the duplexer 1.

  The duplexer 1 includes a transmission terminal 3 to which a transmission signal from the amplifier 109 is input, and a transmission filter 5 that removes unnecessary components other than the transmission passband from the signal input to the transmission terminal 3 and outputs the result. And an antenna terminal 7 to which a signal from the transmission filter 5 is input. The antenna terminal 7 is connected to the antenna 111.

  Further, the duplexer 1 removes unnecessary components other than the reception passband from the signal input from the antenna 111 via the antenna terminal 7 and outputs the received signal, and the signal from the reception filter 9 is input. The receiving terminal 11 is provided. The reception terminal 11 is connected to the amplifier 113.

  Further, the duplexer 1 is connected to the adjustment circuit 13 in order to prevent the signal input to the transmission terminal 3 and output from the transmission filter 5 from leaking to the reception terminal 11 through the reception filter 9. have.

  The transmission filter 5 is configured by, for example, a ladder type filter. That is, the transmission filter 5 includes one or more (3 in the present embodiment) series resonators 15A connected in series between the input side and the output side, and between the series line and the reference potential unit. One or more (2 in this embodiment) parallel resonators 15B are provided (hereinafter simply referred to as “resonator 15”, which may not be distinguished). Note that the parallel resonator 15B has at least one series resonator 15A closer to the transmission terminal 3 side so that the signal strength in the reception filter 9 of the reception signal input from the antenna terminal 7 to the reception filter 9 does not decrease. It is preferable that it is connected to.

  The reception filter 9 is constituted by a ladder type filter, for example, like the transmission filter 5. However, in the present embodiment, the reception filter 9 needs to have a plurality of series resonators 15A. Note that the parallel resonator 15B is located closer to the receiving terminal 11 than at least one series resonator 15A so that the signal strength at the antenna terminal 7 of the transmission signal output from the transmission filter 5 to the antenna terminal 7 does not decrease. It is preferable that it is connected to.

  The adjustment circuit 13 has one end (transmission side line 17) connected to the input side of the transmission filter 5 (between the transmission filter 5 and the transmission terminal 3), and the other end (reception side line 19) of the reception filter 9. It is connected between two series resonators 15A (connection point Pt1). Then, the adjustment circuit 13 adjusts the phase of the signal input to the transmission terminal 3 and sends it to the reception filter 9.

  Therefore, at least part of the signal output from the transmission terminal 3 and output from the transmission terminal 3 via the adjustment circuit 13 and leaked to the reception terminal 11 via the transmission filter 5 and the reception filter 9 is canceled. The influence of the leakage signal on the received signal can be reduced.

  The adjustment circuit 13 most preferably has a phase difference α of 180 ° with respect to a leakage signal (transmission signal) flowing from the antenna terminal 7 side to the connection point Pt1 via one or more series resonators 15A of the reception filter 9. A signal (in reverse phase) is sent to the connection point Pt1. In this case, it is expected that the leakage signal is almost completely removed.

  However, in consideration of an error of the adjustment circuit 13 and the like, the phase difference α may be 170 ° or more and 190 ° or less.

  Further, if the leakage signal is considered as a sine wave (sin θ) and the signal from the adjustment circuit 13 is considered as a sine wave (sin (θ + α)) having a phase difference α with respect to the leakage signal, 160 ° <α <200 °, The amplitude of the sum (sinθ + sin (θ + α)) of both signals is less than 0.35, and the leakage signal is reduced to less than half the amplitude. Therefore, it is preferable that the adjustment circuit causes the signal that is different in phase from over 160 ° to less than 200 ° with respect to the leakage signal flowing at the connection point Pt1 to flow to the connection point Pt1.

  Note that the phase of the transmission signal input to the transmission terminal 3 is shifted in the process of passing through a part of the transmission filter 5 and the reception filter 9. As a result, the phase of the leakage signal (transmission signal) flowing to the connection point Pt1 is different from the phase of the transmission signal input to the transmission terminal 3 (transmission signal immediately after being input).

  Therefore, for example, when the output of the adjustment circuit 13 having a phase difference of 180 ° is desired to collide with the leakage signal, the output of the adjustment circuit 13 is simply shifted by 180 ° from the signal input to the input side of the transmission filter 5. It is necessary to take into account the phase shifted by passing through the transmission filter 5 instead of the phase.

  For example, when the leakage signal is shifted by 90 ° compared to the signal input to the input side of the transmission filter 5, the output of the adjustment circuit 13 is compared with the signal input to the input side of the transmission filter 5. Must be shifted by -90 °. As a result, the phase difference between the leakage signal and the output of the adjustment circuit 13 is 180 °.

  FIG. 3 is a schematic plan view showing the configuration of the resonator 15.

  The resonator 15 is constituted by, for example, a 1-port SAW resonator. Although not particularly illustrated, the resonator 15 has one IDT (Interdigital Transducer) 23 formed on the piezoelectric substrate 21 and a SAW propagation direction with respect to the IDT 23. And reflectors 25 arranged on both sides. The IDT 23 has a pair of comb-like electrodes 27 arranged so as to cross (mesh) each other, one of which is connected to the input side line and the other is connected to the output side line.

  In FIG. 2, the IDT 23 and the reflector 25 are symbolized so as to be denoted by reference numerals 23 and 25 in the series resonator 15 </ b> A closest to the transmission terminal 3 of the transmission filter 5.

  FIG. 4A to FIG. 4C are circuit diagrams illustrating examples of the adjustment circuit 13.

  In the example of FIG. 4A, the adjustment circuit 13 is configured by a capacitor 31 (capacitance: C) provided in series between the transmission side line 17 and the reception side line 19. The transmission side line 17 and the reception side line 19 can function as an inductor (inductance: L) or a resistance (resistance value: R).

  Accordingly, tan β = (ωL−1 / ωC) / R, where β is the phase difference of the current flowing through the adjustment circuit 13 with respect to the voltage (angular velocity: ω) applied to the adjustment circuit 13. Then, by setting the capacitance C to an appropriate value, the phase of the signal output to the connection point Pt1 can be adjusted.

  However, in general, the inductance L and the resistance value R are relatively small, and the example of FIG. 4A is used for phase adjustment with a phase difference β of about 90 °. Then, the impedance can be adjusted by setting the capacitance C to an appropriate size, and as a result, the size of the signal output from the adjustment circuit 13 can be set to a size that can cancel out the leakage signal without excess or deficiency.

  In the example of FIG. 4B, the adjustment circuit 13 includes an inductor 33 connected in series to the capacitor 31 in addition to the configuration of FIG. Therefore, the phase can be adjusted by setting the capacitance C and / or the inductance L to appropriate values based on the same principle as in the example of FIG. In the example of FIG. 4B, not only the capacitance C but also the inductance L can be set, so that the phase can be adjusted in a wider range than the example of FIG. In addition, the inductor 33 of FIG.4 (b) may be formed with the transmission line by a wiring pattern.

  In the example of FIG. 4C, the adjustment circuit 13 is provided between the serial line from the transmission side line 17 to the reception side line 19 and the reference potential unit in addition to the configuration of FIG. 4B. A resistor 35 is included. In the example of FIG. 4C, the magnitude of the signal flowing through the connection point Pt1 can be easily adjusted by appropriately setting the resistance value R of the resistor 35.

  In the duplexer 1, the transmission filter 5 and the reception filter 9 are formed together on, for example, one piezoelectric substrate 21. Furthermore, the transmission terminal 3, the antenna terminal 7, the reception terminal 11 and the wiring connecting them may be formed on the piezoelectric substrate 21 together with the transmission filter 5 and the reception filter 9.

  The adjustment circuit 13 is configured as a component different from the component including the piezoelectric substrate 21 as described above, and may be connected to the transmission filter 5 and the reception filter 9 through an appropriate circuit substrate. Even if it is connected to the transmission filter 5 and the reception filter 9 via the wiring on the piezoelectric substrate 21, the electrode constituting the capacitor 31 is formed on the piezoelectric substrate 21 on which the reception filter 9 and the like are formed. Good.

  As described above, in the present embodiment, the duplexer 1 includes the transmission filter 5, the reception filter 9 including the plurality of series resonators 15A connected in series from the input side to the output side, and the output side of the transmission filter 5. And the antenna terminal 7 connected to the input side of the reception filter 9, one end connected to the input side of the transmission filter 5, and the other end connected between any two of the plurality of series resonators 15 </ b> A of the reception filter 9. And an adjustment circuit 13 for adjusting the phase of the signal flowing from one end to the other end.

  Therefore, as described above, the leaked signal that attempts to pass through the reception filter 9 by the signal that has passed through the adjustment circuit 13 can be canceled, and the influence of the leaked signal can be reduced.

  Here, when the signal of the adjustment circuit 13 is sent to the output side (reception terminal 11) of the reception filter 9, the leakage signal is attenuated by the reception filter 9, and thus the adjustment circuit for removing the signal. The signal from 13 must be adjusted in a very small amount, which makes adjustment difficult. For example, in the example of FIG. 4A, the capacitance C must be adjusted in a minute size, and high accuracy is required for manufacturing the capacitor 31.

  However, in the present embodiment, the signal of the adjustment circuit 13 is sent not in the output side of the reception filter 9 but in the middle of the reception filter 9. In other words, the leakage signal is canceled by the signal from the adjustment circuit 13 before the filter function of the reception filter 9 completely acts on the leakage signal. Therefore, the influence of the leakage signal can be suitably reduced while relaxing the manufacturing conditions of the adjustment circuit 13.

<Second Embodiment>
FIG. 5 is a circuit diagram showing a duplexer 201 according to the second embodiment. Similar to the duplexer 1 of the first embodiment, the duplexer 201 is used in a communication module or the like.

  In the duplexer 201, the same reference numerals as those in the first embodiment are assigned to the same configurations as those in the duplexer 1 of the first embodiment, and the description thereof is omitted.

  The second embodiment is different from the first embodiment in the configuration of the reception filter 209 and is different from the first embodiment in that two reception terminals 11 are provided. Other configurations are the same as those of the first embodiment.

  The reception filter 209 includes a multimode filter 215 and an auxiliary resonator 15C connected in series on the input side thereof. In the present embodiment, the multiplex mode includes a double mode.

  The multimode filter 215 is, for example, a vertically coupled filter, and includes a plurality (three in this embodiment) of IDTs 23 arranged in the SAW propagation direction, and reflectors 25 arranged on both sides thereof. doing.

  The multimode filter 215 is, for example, an unbalanced input-balanced output type that converts an input unbalanced signal into a balanced signal and outputs the balanced signal. Note that the unbalanced signal is a signal whose signal level is a potential with respect to a reference potential (not limited to 0 V), and the balanced signal is a signal composed of two signals and having a potential difference between the two signals as a signal level. Specifically, the two receiving terminals 11 output signals having a phase difference of 180 ° and the same amplitude.

  As with the resonator 15 of the first embodiment, the auxiliary resonator 15C is configured by, for example, a one-port SAW resonator, and has a resonance frequency and anti-resonance so as to form an attenuation pole outside the band of the multimode filter 215. The resonance frequency is set.

  The adjustment circuit 13 has one end connected to the input side of the transmission filter 5 and the other end connected between the auxiliary resonator 15 </ b> C and the multimode filter 215. Then, similarly to the first embodiment, the phase of the signal flowing from one end to the other end is adjusted.

  Therefore, also in the second embodiment, the same effect as in the first embodiment is achieved. That is, the leaked signal that attempts to pass through the reception filter 209 can be canceled by the signal that has passed through the adjustment circuit 13 to reduce the influence of the leaked signal, and the manufacturing conditions of the adjustment circuit 13 for that purpose are relaxed.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The duplexer is not limited to that used for wireless communication, and may be used for wired communication via an electric wire or an optical transmission line, for example. The duplexer may have another transmission or reception filter in addition to one transmission filter and one reception filter.

  The transmission filter and the reception filter are not limited to those using an elastic wave, and may be, for example, a series resonance circuit or a double resonance circuit including a capacitor, an inductor, and a resistor.

  The filter using the elastic wave is not limited to the SAW filter, and is, for example, a piezoelectric thin film resonator (FBAR: Film Bulk Acoustic Resonator) or a boundary acoustic wave filter (however, included in the broad sense SAW filter). May be.

  The SAW filter is not limited to a resonator type, and may be a transversal type, for example. The resonator type SAW filter is not limited to the ladder type and the multimode type, and may be, for example, a lattice type. The multi-mode SAW filter is not limited to a longitudinally coupled type, and may be a laterally coupled type in which resonators are arranged in a direction orthogonal to the SAW propagation direction. The SAW resonator is not limited to a one-port resonator, and may be a two-port resonator, for example.

  Note that the ladder filter can also be configured by a resonator other than a resonator using an elastic wave, and the multimode filter can also be configured by an IDT using a boundary acoustic wave.

  In the reception filter, two filter elements connected in series from the input side to the output side and connected to the adjustment circuit therebetween are a resonator-resonator (first embodiment) and a resonator-filter (second filter). It is not limited to the combination of the embodiment. For example, the two filter elements may be a multimode filter and a resonator (filter-resonator) provided on the output side thereof, or two multimode filters that are cascaded in two stages. It may be a filter (filter-filter).

  In the reception filter, the line connecting two filter elements connected in series from the input side to the output side and connected to the adjustment circuit therebetween is not limited to one line, and may be two or more lines. . For example, the above-described two multi-mode filters connected in two stages may be connected to each other by two lines. Note that the two lines may be the same signal flowing, or may be different signals (balanced signals).

  In the case where there are such a plurality of lines, the adjustment circuit may be connected to only some of the plurality of lines or may be connected to all of them. For example, the output side of the adjustment circuit may be branched into two and connected to two lines through which the same signal flows. Also, for example, the output side of the adjustment circuit branches into two, and the signal flowing through one of them is 180 ° phase-shifted with respect to the signal flowing through the other, and is connected to two lines through which balanced signals flow. Also good.

  The adjustment circuit may be appropriately configured in addition to the configuration illustrated in FIG. For example, as described above, since the signal is shifted in phase even when passing through the SAW resonator, the adjustment circuit may be configured including the SAW resonator.

  The adjustment circuit may have a function of not only adjusting the phase but also filtering a signal that flows from the input side of the transmission filter to the middle of the reception filter. For example, the adjustment circuit may have a function of attenuating a signal outside the pass band of the transmission filter.

  DESCRIPTION OF SYMBOLS 1 ... Splitter, 5 ... Transmission filter, 7 ... Antenna terminal, 9 ... Reception filter, 15A ... Series resonator (filter element), 13 ... Adjustment circuit.

Claims (5)

A send filter,
A reception filter including a plurality of filter elements each including a resonator or a filter, wherein at least some of the plurality of filter elements are connected in series from the input side to the output side;
An antenna terminal connected to the output side of the transmission filter and the input side of the reception filter;
One end is connected to the input side of the transmission filter, the other end is connected between any two of the plurality of filter elements connected in series, and the phase of the signal flowing from the one end to the other end is adjusted. An adjustment circuit;
A duplexer with The reception filter is a ladder type reception filter including one or more parallel resonators and a plurality of series resonators as the plurality of filter elements,
The duplexer according to claim 1, wherein the other end of the adjustment circuit is connected between any two of the plurality of series resonators. The reception filter, as the plurality of filter elements,
A multimode filter;
An auxiliary resonator connected in series to the input side or output side of the multimode filter;
Including
The duplexer according to claim 1, wherein the other end of the adjustment circuit is connected between the multimode filter and the auxiliary resonator. The phase difference between a signal that the adjustment circuit flows to the other end and a signal that the filter element on the antenna terminal side of the arbitrary two filter elements flows to the output side is more than 160 ° and less than 200 °. The duplexer of any one of 1-3. The duplexer according to claim 4, wherein the phase difference is not less than 170 ° and not more than 190 °.

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