JP2014171210A - High frequency filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency filter that acquires a large amount of attenuation in a stopband.SOLUTION: A high frequency filter 101 having a filter section 106 that is connected between first and second signal ends 103, 104 and that has a passband and a stopband is provided with an additional circuit section 108 disposed between the first signal end 103 and the second signal end 104 so as to be connected in parallel with the filter section. The additional circuit section has a frequency range having a pass characteristic in the stopband, and in the frequency range, a signal passing through the additional circuit section and a signal passing through the filter section have phase components in opposite directions.

Description

  The present invention relates to a high-frequency filter used in various communication devices and electronic devices.

  FIG. 9 shows a conventional high-frequency filter used in an electronic device such as a wireless communication device. In FIG. 9, the conventional high frequency filter 301 has two input / output terminals 302 and 303, a signal line 304, a plurality of series arm resonators 305, a plurality of parallel arm resonators 306, an inductance 307, and a reference potential unit 308. . The signal line 304 connects between the two input / output terminals 302 and 303, the plurality of series arm resonators 305 are provided in series with the signal line 304, and the plurality of parallel arm resonators 306 are connected to the signal line 304 and the reference potential. Provided in a plurality of wirings connecting the portion 308. These constitute a ladder circuit, function as a band pass filter, and have a pass band and a stop band.

  As prior art document information relating to the invention of this application, for example, Patent Document 1 is known.

International Publication No. 2010/073377

  However, the conventional high-frequency filter 301 has a limit in the amount of attenuation in the stop band, and it is difficult to obtain a large amount of attenuation in a specific stop band.

  The present invention provides a high frequency filter capable of obtaining a large attenuation in a specific stop band.

  In order to solve the above-described problems, the present invention provides a high-frequency filter that is connected between the first and second signal ends and includes a filter unit having a pass band and a stop band, and is connected in parallel with the filter unit. An additional circuit portion is provided between the first signal end and the second signal end. The additional circuit unit has a frequency region having a pass characteristic in the stop band, and a signal passing through the additional circuit unit and a signal passing through the filter unit in the frequency region have phase components in opposite directions.

  With such a configuration, the present invention has an excellent effect that a high frequency filter having a large attenuation in the stop band can be obtained.

Circuit diagram of high-frequency filter according to Embodiment 1 of the present invention Characteristics of the high frequency filter Characteristics of the high frequency filter Characteristics of the high frequency filter Circuit diagram of high-frequency filter according to Embodiment 2 of the present invention The principal part enlarged view of the other high frequency filter in Embodiment 2 of this invention The principal part enlarged view of the other high frequency filter in Embodiment 2 of this invention Circuit diagram of another high-frequency filter according to Embodiment 2 of the present invention Circuit diagram of conventional high-frequency filter

(Embodiment 1)
Hereinafter, the high-frequency filter according to Embodiment 1 of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram of a high-frequency filter according to Embodiment 1 of the present invention.

  In FIG. 1, a high-frequency filter 101 includes a piezoelectric substrate 102, an input-side signal terminal 103, an output-side signal terminal 104, a reference potential unit 105, a filter unit 106, and an inductor 107, and an additional circuit unit 108 is provided thereon. It is a thing.

  The filter unit 106 includes a plurality of series arm resonators 109 connected in series to a signal line connecting the two signal ends 103 and 104, and a plurality of series arm resonators 109 connected between the signal line and the reference potential unit 105. A parallel arm resonator 110 is included. Here, the plurality of series arm resonators 109 and the plurality of parallel arm resonators 110 are surface acoustic wave resonators formed on the piezoelectric substrate 102, and they constitute a ladder circuit, and have a pass band and a stop band. It functions as a band pass filter. Here, the individual series arm resonators 109 and the individual parallel arm resonators 110 can take different design values in terms of circuit design.

  The additional circuit unit 108 is connected between the input-side signal terminal 103 and the output-side signal terminal 104 so as to be connected in parallel with the filter unit 106. The additional circuit unit 108 has a pass characteristic that approximates the pass characteristic of the filter unit 106 in the attenuation band in the stop band of the filter unit 106, particularly in the attenuation band, and is opposite to the phase of the filter unit 106. The phase is given.

  The configuration of the additional circuit unit 108 is such that a capacitor 111, two IDT electrodes 113 and 114, and a capacitor 112 are connected on the piezoelectric substrate 102 between the signal terminal 103 on the input side and the signal terminal 104 on the output side in this order. It is. Here, the two IDT electrodes 113 and 114 are formed on the same elastic wave waveguide at a predetermined distance, and constitute a transversal filter. By design of this transversal type filter, the pass characteristic in the above attenuation band is formed, the phase characteristic is adjusted by setting the distance between the two IDT electrodes 113, 114, and the phase characteristic in the opposite direction to the filter unit is obtained. It is what you have.

  The capacitances of the capacitances 111 and 112 are set to capacitance values smaller than the capacitances of the IDT electrodes 113 and 114, and the capacitance 111 close to the input side signal end 103 is set to the capacitance 112 close to the output side signal end 104. It is set to a smaller capacity. Capacitors 111 and 112 are elements that shift the amplitude level of the pass characteristic of the additional circuit unit 108 in the attenuation band, and the filter unit is configured to change the amplitude level of the pass characteristic of the additional circuit unit 108 according to the design of the capacitor 111 and the capacitor 112. It is possible to approximate the amplitude level of 106 pass characteristics.

  Since the phase of the additional circuit unit 108 and the phase of the filter unit 106 in the attenuation band are opposite to each other, the amplitude of the filter unit 106 in the attenuation band can be canceled and the attenuation characteristic in the attenuation band can be improved. In addition, the phase of the additional circuit unit 108 can be finely adjusted by setting the distance between the two IDT electrodes 113 and 114. In addition, the capacitor 111 and the capacitor 112 also have a function of protecting the IDT electrodes 113 and 114 from destruction by suppressing a current flowing from the filter unit 106 to the additional circuit unit 108.

  2 to 4 are diagrams showing pass characteristics and phase characteristics of the high frequency filter 101 according to the first embodiment of the present invention.

  In FIG. 2, the broken line is the pass characteristic A of the filter unit 106. In FIG. 2, the solid line indicates the pass characteristic B of the additional circuit unit 108. A pass characteristic A of the filter unit 106 is a pass characteristic of the high-frequency filter 101 when the additional circuit unit 108 is not provided. The pass characteristic A of the filter unit 106 has a pass band at 880 to 915 MHz, and has a stop band at 880 or less and 915 MHz or more outside the pass band. The attenuation band is a frequency band in which the attenuation characteristics are particularly improved in the stop band. Here, the attenuation band is a band that requires attenuation on the system, such as a reception band for a transmission filter constituting a duplexer or a transmission band for a reception filter constituting a duplexer. Alternatively, a high frequency filter used in mobile communication is a band that requires attenuation on the system, such as a reception band for a transmission filter or a transmission band for a reception filter constituting a duplexer. The pass characteristic B of the additional circuit unit 108 is designed to approximate the pass characteristic A in this attenuation band.

  When the attenuation band is higher in frequency than the pass band, the electrode finger pitch of the two IDT electrodes 113 and 114 is smaller than the electrode finger pitch of the filter unit 106, and the attenuation band is larger than the pass band. When the frequency is low, the electrode finger pitch of the two IDT electrodes 113 and 114 is larger than the electrode finger pitch of the filter unit 106.

  In FIG. 3, the broken line is the phase C of the filter unit 106, and the solid line is the phase D of the additional circuit unit 108. As shown in FIG. 3, the phase D of the additional circuit unit 108 in the attenuation band is set to have a phase characteristic in the opposite direction to the phase C of the filter unit 106. The phase D of the additional circuit unit 108 can be adjusted by setting the distance between the two IDT electrodes 113 and 114 constituting the transversal filter. Here, the phase characteristic being in the reverse direction means that the absolute value of the phase difference is 90 degrees or more within a range of −180 degrees to 180 degrees and has a phase component in the reverse direction. In this way, by providing the phase D of the additional circuit unit 108 with a component in the opposite direction to the phase C of the filter unit 106, it is possible to cancel the amplitude of the additional circuit unit 108 from the amplitude of the filter unit 106 in the attenuation band. Thus, the attenuation amount of the high frequency filter 101 can be improved.

  In FIG. 4, the solid line is the pass characteristic E of the high frequency filter 101, and the broken line is the pass characteristic A of the filter unit 106. As can be seen from FIG. 4, the pass characteristic E of the high-frequency filter 101 can greatly improve the attenuation in the attenuation band as compared with the pass characteristic A of the filter unit 106.

  As described above, the high frequency filter according to the first exemplary embodiment of the present invention includes a filter unit that is connected between the first and second signal ends and includes a filter unit having a pass band and a stop band. An additional circuit portion is provided between the first signal end and the second signal end so as to be connected in parallel, and the additional circuit portion has a frequency region having a pass characteristic in the stop band, In the frequency domain, a signal passing through the additional circuit unit and a signal passing through the filter unit have phase components in opposite directions. As a result, the attenuation of the pass characteristic of the filter section in the frequency domain can be canceled and the attenuation can be increased, thereby greatly improving the attenuation characteristic in the frequency domain.

  Here, the absolute value of the phase difference between the filter section and the additional circuit section in this frequency domain is ideally 180 degrees within the range of 0 degrees to 180 degrees. However, if the absolute value of the phase difference is 90 degrees or more, it has an effect of canceling out the amplitude of the pass characteristic and improving the attenuation characteristic because it has a phase component in the reverse direction.

  In the high frequency filter according to the first embodiment of the present invention, two additional IDT electrodes formed at a predetermined distance on the same elastic wave waveguide are provided in the additional circuit section, so that a desired frequency region is obtained. The additional circuit unit having the phase component in the reverse direction and having the pass characteristic can be configured, and the attenuation characteristic of the high frequency filter can be improved.

  The high-frequency filter according to Embodiment 1 of the present invention is configured such that the signal passing through the filter unit and the additional circuit unit are set by setting the distance between two IDT electrodes formed on the same elastic wave waveguide. The signal passing through the circuit can be provided with means having a phase component in the reverse direction, and there is no need to add a separate phase inversion function, and the phase of the signal passing through the additional circuit section can be finely adjusted. It has the effect.

  In the high frequency filter according to the first embodiment of the present invention, the filter unit is configured using an acoustic wave element, so that both the filter unit and the additional circuit unit are configured using the acoustic wave element. The change in the frequency characteristic of the filter unit and the change in the frequency characteristic of the additional circuit unit when there is a temperature change can be approximated, and the deterioration of the attenuation characteristic with respect to the temperature change can be reduced.

  In addition, the high frequency filter according to the first embodiment of the present invention is provided with an element for shifting the amplitude level of the pass characteristic in the additional circuit unit, and thereby, in the frequency band for improving the attenuation characteristic, the additional circuit unit. Can be approximated to the amplitude of the filter section, and the attenuation characteristics of the high-frequency filter can be effectively improved.

  In particular, the capacitances of the capacitors 111 and 112 are set to capacitance values smaller than the capacitances of the IDT electrodes 113 and 114, and the capacitance 111 close to the signal end 103 is set to be smaller than the capacitance 112 close to the signal end 104. By doing so, it becomes possible to match the amplitude of the additional circuit section in the frequency band for improving the attenuation amount with the amplitude of the filter section, and the effect of improving the attenuation characteristic is enhanced.

  The high-frequency filter according to Embodiment 1 of the present invention includes a first acoustic wave element unit having an acoustic wave element and a first circuit terminal provided between the acoustic wave element unit and the first signal end in the additional circuit unit. By providing the capacitive element and the second capacitive element provided between the acoustic wave element unit and the second signal end, the acoustic wave element is protected from the current flowing into the additional circuit unit, and There is an effect that the destruction of the IDT electrodes 113 and 114 can be prevented.

  In the high frequency filter according to Embodiment 1 of the present invention, the filter unit and the additional circuit unit are formed on the same piezoelectric substrate, so that the change in frequency characteristics due to the temperature change is applied to both the filter unit and the additional circuit unit. Since it occurs in the same manner, the effect of the temperature change on the attenuation characteristic can be reduced, and an effect can be obtained that a high frequency filter with little deterioration of the attenuation characteristic with respect to the temperature change can be obtained. Further, by forming the filter portion and the additional circuit portion on the same piezoelectric substrate, a high-frequency filter with good attenuation characteristics can be obtained without increasing the size, and a small high-frequency filter can be realized.

  The high-frequency filter according to the first embodiment of the present invention includes at least the electrode finger of the IDT electrode 113 closest to the IDT electrode 114 and the electrode finger of the IDT electrode 114 closest to the IDT electrode 113 in the additional circuit unit 108. By using one of the electrode fingers connected to the reference potential section, the attenuation in the pass band of the pass characteristic of the additional circuit section 108 can be improved, and the insertion loss in the pass band of the high frequency filter 101 can be reduced. it can.

  In the high frequency filter according to the first embodiment of the present invention, no other electrode is disposed between the two IDT electrodes 113 and 114 of the additional circuit unit 108. However, the two IDT electrodes 113 and 114 are not provided. Between them, a shield electrode connected to the reference potential portion may be provided. By providing such a shield electrode, the attenuation amount in the pass band of the pass characteristic of the additional circuit unit 108 can be improved, and the insertion loss in the pass band of the high frequency filter 101 can be reduced.

  In the high frequency filter according to Embodiment 1 of the present invention, the number of electrode fingers of the IDT electrode 113 and the number of electrode fingers of the IDT electrode 114 are the same in FIG. The number of pairs and the number of pairs of electrode fingers of the IDT electrode 114 are not necessarily the same. By making the number of pairs of electrode fingers of the IDT electrode 113 different from the number of pairs of electrode fingers of the IDT electrode 114, it is possible to improve the attenuation in the pass band of the pass characteristic of the additional circuit unit 108, and pass through the high frequency filter 101. It makes it possible to reduce the insertion loss in the band.

(Embodiment 2)
FIG. 5 is a circuit diagram of the high frequency filter according to Embodiment 2 of the present invention.

  In FIG. 5, the high frequency filter 201 according to the second embodiment of the present invention includes a piezoelectric substrate 202, an antenna terminal 203, a transmission terminal 204, a pair of reception terminals 205, a transmission filter 206, a reception filter 207, and a phase. It has a circuit 208 and a ground terminal 209 and functions as a duplexer.

  The transmission filter 206 is provided on the piezoelectric substrate 202 between the series arm elastic wave resonators S1 to S5 provided in series with the signal line connecting the antenna terminal 203 and the transmission terminal 204, and between the signal line and the ground terminal 209. Has a ladder circuit composed of parallel arm elastic wave resonators P1 to P5.

  The reception filter 207 is connected between the antenna terminal 203, the pair of reception terminals 205, and the ground terminal 209 on the piezoelectric substrate 202, and is connected to the one-terminal elastic wave resonator R1 and the longitudinally coupled elastic wave resonators R2, R3. Have

  The phase circuit 208 is connected between the antenna terminal 203, the transmission terminal 204, and the ground terminal 209 on the piezoelectric substrate 202, and includes two IDT electrodes 210 and two capacitive elements 211 that constitute a transversal filter. Have

  The phase circuit 208 has pass characteristics in the attenuation band of the transmission filter 206 due to the design of the two IDT electrodes 210, and adjusts the phase characteristics by setting the distance between the two IDT electrodes 210. A high-frequency filter having phase characteristics in the opposite direction to that of the transmission filter 206 and having a large attenuation in the attenuation band can be obtained. In particular, by setting this attenuation band within the reception band of the reception filter 207, the isolation of the reception band can be improved, and a decrease in reception sensitivity due to noise of a power amplifier connected to the duplexer in a communication device can be prevented. And a duplexer having excellent characteristics can be obtained.

  The IDT electrode 210 of the phase circuit 208 and the serial arm elastic wave resonator S5 of the transmission filter 206 have regions overlapping in the propagation direction of the elastic wave propagating through the piezoelectric substrate 202, and the IDT electrode 210 in the propagation direction of the elastic wave An absorber 212 that absorbs elastic waves is provided between the series arm elastic wave resonator S5. The absorber 212 can suppress the interference between the elastic wave excited by the IDT electrode 210 and the elastic wave excited by the series arm elastic wave resonator S5, and can prevent the attenuation characteristic and isolation characteristic of the high frequency filter 201 from deteriorating. And good filter characteristics can be obtained.

  Here, by making the cross width of the IDT electrode 210 of the phase circuit 208 smaller than the cross width of the series arm elastic wave resonator S5 of the transmission filter 206, interference between the IDT electrode 210 and the series arm elastic wave resonator S5 is reduced. It can be further reduced.

  The absorber 212 is made of a polyimide-based photocurable resin material, and is a support column support that seals the acoustic wave elements constituting the transmission filter 206, the reception filter 207, and the phase circuit 208 through the excitation space. The mechanical strength of the excitation space can be ensured, and the excitation space can be prevented from being crushed when the high frequency filter is resin-molded.

  An electrode 213 is provided between the IDT electrode 210 and the series arm elastic wave resonator S5 in the elastic wave propagation direction, and the end of the electrode 213 on the IDT electrode 210 side or the electrode 213 on the series arm elastic wave resonator S5 side. Is made non-perpendicular to the propagation direction of the elastic wave propagating through the piezoelectric substrate 202. Thereby, the elastic wave propagating between the IDT electrode 210 and the series arm elastic wave resonator S5 can be scattered on the surface of the piezoelectric substrate 202, and the elastic wave excited by the IDT electrode 210 and the series arm elastic wave resonator can be scattered. Since the interference of the elastic wave excited by S5 can be suppressed, deterioration of the attenuation characteristic and isolation characteristic of the high frequency filter 201 can be prevented, and a good filter characteristic can be obtained. By providing the absorber 212 on the electrode 213, the isolation characteristics can be further improved, and the area occupied by the piezoelectric substrate 202 can be reduced, so that the high-frequency filter can be reduced in size.

  The IDT electrode having a region overlapping with the IDT electrode 210 of the phase circuit 208 in the propagation direction of the elastic wave may be an IDT electrode constituting the reception filter 207.

  The IDT electrode of the transmission filter 206 or the reception filter 207 having a region overlapping with the IDT electrode 210 of the phase circuit 208 in the propagation direction of the elastic wave may be an elastic wave resonator having a reflector.

  Further, the phase circuit 208 may be connected between the antenna terminal 203 and the reception terminal 205, or may be connected between the transmission terminal 204 and the reception terminal 205, which is effective in improving the isolation of the duplexer. Have.

  In the high-frequency filter 201 shown in FIG. 5, the electrode 213 that is non-perpendicular to the elastic wave propagation direction is a wiring electrode that connects the antenna terminal 203 and the phase circuit 208. The shape of the non-vertical electrode is not limited to this. 6 and 7 are enlarged views of the main part of the phase circuit 208 in the high-frequency filter 201, and show other configurations of electrodes that are non-perpendicular to the propagation direction of the elastic wave. In FIG. 6, an electrode 213a that is non-perpendicular to the propagation direction of the elastic wave is a reflector electrode pattern. In FIG. 7, an electrode 213b that is non-perpendicular to the propagation direction of the elastic wave is a triangular floating electrode pattern. Also in the electrodes 213a and 213b as shown in FIGS. 6 and 7, the elastic wave propagating between the IDT electrode 210 and the series arm elastic wave resonator S5 can be scattered, and the elastic wave excited by the IDT electrode 210 Since the interference of the elastic wave excited by the series arm elastic wave resonator S5 can be suppressed, the attenuation characteristic and the isolation characteristic of the high-frequency filter 201 can be improved.

  Moreover, the absorber 212 is not restricted to the shape of FIG. FIG. 8 shows another high frequency filter 301. The other high-frequency filter 301 is different from the high-frequency filter 201 in the second embodiment in that one side of the absorber 212a provided on the electrode 213 is non-perpendicular to the propagation direction of the elastic wave. The IDT electrode 210 of the phase circuit 208 and the serial arm elastic wave resonator S5 of the transmission filter 206 have regions overlapping in the propagation direction of the elastic wave propagating through the piezoelectric substrate 202, and the IDT electrode 210 in the propagation direction of the elastic wave Between the serial arm elastic wave resonator S5, an absorber 212a that absorbs an elastic wave is provided, and the IDT electrode 210 is excited by making one side of the absorber 212a non-perpendicular to the propagation direction of the elastic wave. Interference between the elastic wave to be excited and the elastic wave excited by the series arm elastic wave resonator S5 can be suppressed, the deterioration of the attenuation characteristic and the isolation characteristic of the high-frequency filter 201 can be prevented, and good filter characteristics can be obtained. .

  The high frequency filter according to the present invention is useful in configuring various electronic devices.

101, 201, 301 High-frequency filter 102, 202 Piezoelectric substrate 103, 104 Signal end 105 Reference potential section 106 Filter section 107 Inductor 108 Additional circuit section 109 Series arm resonator 110 Parallel arm resonator 111, 112 Capacitance 113, 114, 210 IDT Electrode 203 Antenna terminal 204 Transmission terminal 205 Reception terminal 206 Transmission filter 207 Reception filter 208 Phase circuit 212, 212a Absorber 213, 213a, 213b Electrode

Claims (15)

In a high-frequency filter having a filter portion connected between the first and second signal ends and having a pass band and a stop band,
An additional circuit portion is provided between the first signal end and the second signal end so as to be connected in parallel with the filter portion,
The additional circuit section has a frequency region having a pass characteristic in the stop band,
A high frequency filter in which a signal passing through the additional circuit section and a signal passing through the filter section in the frequency domain have phase components in opposite directions. The high frequency filter according to claim 1, wherein the additional circuit section includes two IDT electrodes formed at a predetermined distance on the same elastic wave waveguide. The high frequency filter according to claim 2, wherein the phase component in the reverse direction is provided by setting the predetermined distance. The high-frequency filter according to claim 1, wherein the filter unit is configured using an acoustic wave element. The high frequency filter according to claim 1, wherein an element for shifting an amplitude level of a pass characteristic in the frequency domain is provided in the additional circuit section. The additional circuit unit includes an elastic wave element unit having an elastic wave element;
A first capacitive element provided between the acoustic wave element unit and the first signal end;
The high frequency filter according to claim 2, further comprising: a second capacitive element provided between the acoustic wave element unit and the second signal end. The high-frequency filter according to claim 1, wherein the filter unit and the additional circuit unit are formed on the same piezoelectric substrate. A piezoelectric substrate, an antenna terminal, a transmission terminal, a reception terminal,
A transmission filter connected between the antenna terminal and the transmission terminal;
A reception filter connected between the antenna terminal and the reception terminal,
The transmission filter or the reception filter has a first IDT electrode provided on the piezoelectric substrate,
A phase circuit connected between at least two of the antenna terminal, the transmission terminal and the reception terminal;
The phase circuit has a second IDT electrode provided on the piezoelectric substrate,
The first IDT electrode and the second IDT electrode have regions that overlap in the propagation direction of elastic waves propagating through the piezoelectric substrate,
A high-frequency filter in which an absorber for absorbing the elastic wave is provided between the first IDT electrode and the second IDT electrode on the piezoelectric substrate. The high frequency filter according to claim 8, wherein the absorber is made of a resin material. The high frequency filter according to claim 8, wherein an electrode is provided between the absorber and the piezoelectric substrate. A cover body for sealing the first IDT electrode and the second IDT electrode;
The high frequency filter according to claim 8, wherein the absorber constitutes a part of the cover body. A piezoelectric substrate, an antenna terminal, a transmission terminal, a reception terminal,
A transmission filter connected between the antenna terminal and the transmission terminal;
A reception filter connected between the antenna terminal and the reception terminal,
The transmission filter or the reception filter has a first IDT electrode provided on the piezoelectric substrate,
A phase circuit connected between at least two of the antenna terminal, the transmission terminal and the reception terminal;
The phase circuit has a second IDT electrode provided on the piezoelectric substrate,
The first IDT electrode and the second IDT electrode have regions that overlap in the propagation direction of elastic waves propagating through the piezoelectric substrate,
On the piezoelectric substrate, an electrode is provided between the first IDT electrode and the second IDT electrode,
A high frequency filter in which an end side of the electrode on the first IDT electrode side or an end side on the second IDT electrode side is made non-perpendicular to the propagation direction. The high frequency filter according to claim 8 or 12, wherein a cross width of the first IDT electrode is larger than a cross width of the second IDT electrode. The high-frequency filter according to claim 8 or 12, wherein the phase circuit is a transversal filter having two IDT electrodes. The high-frequency filter according to claim 8 or 12, wherein the phase circuit is connected between the antenna terminal and the transmission terminal.