JP7208828B2 - Filters and multiplexers - Google Patents

Description

The present invention relates to filters and multiplexers, and to filters and multiplexers having resonant circuits and acoustic wave resonators.

A filter is known in which an acoustic wave resonator is provided in a resonance circuit formed by a capacitor and an inductor (for example, Patent Documents 1 and 2).

JP 2018-129680 A JP 2018-129683 A

By providing the elastic wave resonator in the resonance circuit, the sharpness between the passband and the stopband can be enhanced. However, the temperature characteristics may deteriorate.

The present invention has been made in view of the above problems, and an object of the present invention is to improve temperature characteristics.

The present invention comprises an input terminal, an output terminal, an LC resonance circuit connected between the input terminal and the output terminal and forming a first attenuation pole, and a circuit connected between the input terminal and the output terminal. and an acoustic wave resonator forming a second attenuation pole between the passband and the first attenuation pole, the direction of movement of the frequency of the attenuation pole due to temperature change being the same as the direction of movement of the first attenuation pole is a filter with .

In the above configuration, the LC resonant circuit includes a capacitor and an inductor connected in parallel between the input terminal and the output terminal, and one end of the elastic wave resonator is connected to one end of the capacitor or the inductor. The other end of the elastic wave resonator is grounded, and the sign of the temperature coefficient of the resonance frequency of the LC resonant circuit and the sign of the temperature coefficient of the elastic wave resonator can be the same.

In the above configuration, the temperature coefficient of the resonance frequency of the elastic wave resonator may be negative, and the frequency of the first attenuation pole may be lower than the passband.

In the above structure, the capacitor may have a dielectric layer and a pair of electrodes sandwiching the dielectric layer, and the temperature coefficient of the dielectric constant of the dielectric layer may be positive.

In the above configuration, the capacitor may be two capacitors connected in parallel with the inductor, and one end of the elastic wave resonator may be connected to a node between the two capacitors.

In the above configuration, the LC resonant circuit includes a plurality of laminated dielectric layers including the dielectric layer and a plurality of wiring patterns provided on at least one dielectric layer of the plurality of dielectric layers, The plurality of wiring patterns may include the pair of electrodes and the inductor.

The present invention is a multiplexer including the above filters.

According to the present invention, temperature characteristics can be improved.

FIG. 1 is a circuit diagram of a filter according to Example 1. FIG. 2(a) is a plan view of an elastic wave resonator in Example 1, and FIG. 2(b) is a cross-sectional view of another elastic wave resonator in Example 1. FIG. FIG. 3 is a cross-sectional view of an LC component according to Example 1. FIG. FIG. 4 is a circuit diagram showing a multiplexer used in experiments. FIG. 5 is a circuit diagram of the filter 22 used in the experiment. 6A and 6B are diagrams showing pass characteristics of the filter 22 in Comparative Example 1. FIG. FIG. 7 is a diagram showing pass characteristics of filters 42 and 44 in the multiplexer of Comparative Example 1. FIG. FIG. 8 is a diagram showing the temperature dependence of the pass characteristics of the filter 44 in the multiplexer of Comparative Example 1. FIG. FIG. 9(a) is a diagram showing the temperature dependence of the pass characteristics of the component 24 in Comparative Example 1, and FIG. 9(b) is an enlarged view of the range A in FIG. 9(a). FIG. 10(a) is a diagram showing the temperature dependence of the pass characteristic of the acoustic wave resonator R31 in Comparative Example 1, and FIG. 10(b) is an enlarged view of range A in FIG. 10(a). FIG. 11(a) is a diagram showing the temperature dependence of the pass characteristic of the component 24 in the simulation of Example 1, and FIG. 11(b) is an enlarged view of range A in FIG. 11(a). FIG. 12(a) is a diagram showing the temperature dependence of the pass characteristic of the component 24 in the experiment of Comparative Example 1, and FIG. 12(b) is an enlarged view of the range A of FIG. 12(a). FIG. 13(a) is a diagram showing the temperature dependence of the pass characteristics of the component 24 in the simulation of Example 1, and FIG. 13(b) is an enlarged view of range A in FIG. 13(a).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a filter according to Example 1. FIG. As shown in FIG. 1, in the filter according to the first embodiment, a resonant circuit 20 is connected between the input terminal Tin and the output terminal Tout. The resonance circuit 20 comprises capacitors C1, C2 and an inductor L1. Capacitors C1 and C2 are connected in series between input terminal Tin and output terminal Tout. Inductor L1 is connected in parallel with capacitors C1 and C2 between node N1 between input terminal Tin and capacitor C1 and node N2 between output terminal Tout and capacitor C2. One end of the acoustic wave resonator R1 is connected to a node N3 between the capacitors C1 and C2, and the other end is connected to the ground terminal.

The resonance circuit 20 forms an attenuation pole in the pass characteristic between the input terminal Tin and the output terminal Tout. The acoustic wave resonator R1 forms an attenuation pole between the attenuation pole formed by the resonance circuit 20 and the passband. This makes it possible to increase the sharpness between the passband and the stopband.

2(a) is a plan view of an elastic wave resonator in Example 1, and FIG. 2(b) is a cross-sectional view of another elastic wave resonator in Example 1. FIG. In the example of FIG. 2A, the acoustic wave resonator R1 is a surface acoustic wave resonator. An IDT (Interdigital Transducer) 12 and a reflector 13 are provided on the upper surface of the substrate 10 . The IDT 12 has a pair of comb electrodes 12a facing each other. The comb-shaped electrode 12a has a plurality of electrode fingers 12b and a bus bar 12c connecting the plurality of electrode fingers 12b. Reflectors 13 are provided on both sides of the IDT 12 . The IDT 12 excites surface acoustic waves on the substrate 10 . The substrate 10 is, for example, a piezoelectric substrate such as a lithium tantalate substrate, a lithium niobate substrate, or a quartz substrate. The substrate 10 may be a composite substrate in which a piezoelectric substrate is bonded to a support substrate such as a sapphire substrate, spinel substrate, alumina substrate, quartz substrate, or silicon substrate. An insulating film such as a silicon oxide film or an aluminum nitride film may be provided between the supporting substrate and the piezoelectric substrate. The IDT 12 and reflector 13 are made of, for example, an aluminum film or a copper film. A protective film or temperature compensation film may be provided on the substrate 10 to cover the IDT 12 and the reflector 13 .

In the example of FIG. 2B, the elastic wave resonator R1 is a piezoelectric thin film resonator. A piezoelectric film 16 is provided on the substrate 10 . A lower electrode 14 and an upper electrode 18 are provided so as to sandwich the piezoelectric film 16 . A gap 15 is formed between the lower electrode 14 and the substrate 10 . An acoustic reflection film that reflects elastic waves may be provided instead of the air gap 15 . A resonance region 17 is a region where the lower electrode 14 and the upper electrode 18 face each other with at least part of the piezoelectric film 16 interposed therebetween. The lower electrode 14 and the upper electrode 18 in the resonance region 17 excite an elastic wave in the thickness longitudinal vibration mode in the piezoelectric film 16 . The substrate 10 is, for example, a sapphire substrate, a spinel substrate, an alumina substrate, a glass substrate, a crystal substrate, or a silicon substrate. The lower electrode 14 and the upper electrode 18 are metal films such as ruthenium films. The piezoelectric film 16 is, for example, an aluminum nitride film.

When a surface acoustic wave resonator or a piezoelectric thin film resonator is used as the acoustic wave resonator R1, the temperature coefficients of the resonant frequency and the antiresonant frequency are negative. As a result, the temperature coefficient of the attenuation pole formed by the elastic wave resonator R1 becomes negative. For example, the temperature coefficient of the resonant frequency of a surface acoustic wave resonator using a 42° Y-cut X-propagating lithium tantalate substrate for the substrate 10 is about -40 ppm/°C.

FIG. 3 is a cross-sectional view of an LC component according to Example 1. FIG. As shown in FIG. 3, the LC component 30 has a laminate 31 in which a plurality of dielectric layers 31a to 31e are laminated. Metal layers 32a to 32d are provided on the surfaces of the dielectric layers 31a to 31d, respectively. A terminal 36 is provided on the lower surface of the laminate 31 . Vias (vias 34a and 34d are shown in FIG. 3) are provided through dielectric layers 31a to 31d. Capacitors C1 and C2 are formed by metal layers 32a and 32b sandwiching dielectric layer 31b. Inductor L1 is formed by metal layers 32c and 32d.

The dielectric layers 31a to 31e are made of an inorganic insulator such as a ceramic material. The dielectric layers 31a to 31e are mainly composed of oxides of silicon (Si), calcium (Ca) and magnesium (Mg) (for example, diobside CaMgSi ₂ O ₆ ), for example, and are made of, for example, strontium titanate (SiTiO ₃ ) is added. Metal layers 32a, 32b, vias 34a and 34d and terminals 36 are made of, for example, silver (Ag), palladium (Pd), platinum (Pt), copper (Cu), nickel (Ni), gold (Au), gold-palladium alloys. Alternatively, it is a metal layer containing a silver-platinum alloy as a main component.

When the dielectric constants of the dielectric layers 31a to 31e change with temperature, the resonance frequency of the parallel resonance circuit changes. For example, if the inductance of inductor L1 is L and the combined capacitance of capacitors C1 and C2 is C, the resonance frequency of the parallel resonance circuit is proportional to 1/√LC. Therefore, by setting the temperature coefficient of the dielectric constant of the dielectric layers 31a to 31e to a desired value, the temperature coefficient of the resonance frequency of the resonance circuit 20 can be set to a desired value.

Table 1 is a table showing the temperature coefficient τf [ppm/° C.] of dielectric constant, dielectric constant εr and τf/εr of dielectric materials.

As shown in Table 1, the temperature coefficient of dielectric constant τf of MgTiO ₃ and CaMgSi ₂ O ₆ is negative. The temperature coefficient of dielectric constant τf of TiO ₂ , CaTiO ₃ , SrTiO ₃ , CaZrO ₃ and BaZrO ₃ is positive. An arbitrary temperature coefficient τf can be realized by appropriately mixing a dielectric material having a negative temperature coefficient of relative permittivity and a dielectric material having a positive temperature coefficient of relative permittivity.

According to the empirical rule of the inventors, when a plurality of dielectric materials are mixed, the temperature coefficient τf of the relative permittivity and the relative permittivity εr are determined by the volume of each dielectric material to be mixed as Vi, the temperature coefficient as τfi, and the ratio If the dielectric constant is εri, then τf=Σ(Vi×τfi) and εr=Σ(Vi×log(εri)). For example, when adjusting τf by adding a dielectric material with a positive τf to CaMgSi ₂ O ₆ , if a dielectric material with a large τf/εr is selected, τf can be adjusted without changing the dielectric constant so much. Therefore, the case of adding SrTiO ₃ having the largest τf/εr was considered.

Table 2 is a table showing τf versus volume ratio of CaMgSi ₂ O ₆ and SrTiO ₃ .

As shown in Table 2, τf is 0 ppm/°C when the volume ratios of CaMgSi ₂ O ₆ and SrTiO ₃ are 0.960 and 0.040. Reducing SrTiO3 makes τf negative _, while increasing it makes it positive. By selecting the amount of SrTiO ₃ added to CaMgSi ₂ O ₆ in this manner, the temperature coefficient τf of the dielectric constant of the dielectric layers 31a to 31e can be set to a desired value. Thereby, the temperature coefficient of the resonance frequency of the resonance circuit 20 can be set to a desired value.

[experiment]
FIG. 4 is a circuit diagram showing a multiplexer used in experiments. As shown in FIG. 4, the multiplexer has a filter 40 connected between terminals Ta and T1, a filter 42 connected between terminals Ta and T2, and a filter 42 connected between terminals Ta and T3. A filter 44 is provided.

Filter 40 includes capacitors C11 through C13 and inductors L11 and L12. Inductors L11 and L12 are connected in series between terminals Ta and T1. Capacitor C11 is connected in parallel with inductor L12. Capacitors C12 and C13 are shunt-connected between terminals Ta and T1.

Filter 42 includes capacitors C21 to C23, inductors L21 and L22, and acoustic wave resonator R21. Capacitors C21 to C23 are connected in series between terminals Ta and T2. Inductor L21 is connected in parallel with capacitors C22 and C23. Inductor L22 and acoustic wave resonator R21 are shunt-connected between terminals Ta and T2.

Filter 44 includes capacitors C31 to C33, inductors L31 to L33, and acoustic wave resonator R31. Capacitors C31 to C33 are connected in series between terminals Ta and T3. Inductor L31 is connected in parallel with capacitors C31 and C32, and inductor L32 is connected in parallel with capacitor C33. Inductor L33 and elastic wave resonator R31 are shunt-connected between terminals Ta and T3.

Filters 40, 42 and 44 are commonly connected at node N1. Filters 42 and 44 have capacitor C01 and inductor L01 as a common circuit between nodes N1 and N2. Capacitor C01 and inductor L01 are connected in series between nodes N1 and N2. Filter 40 functions as a low pass filter and filters 42 and 44 function as band pass filters.

Filter 40 passes low band signals and suppresses middle and high band signals. Filter 42 passes the middle band signals and suppresses the low and high band signals. Filter 44 passes high band signals and suppresses low and middle band signals.

The low band, middle band and high band are respectively 700 MHz to 960 MHz, 1710 MHz to 2200 MHz and 2300 MHz to 2690 MHz. The low band, middle band, and high band each include a plurality of bands corresponding to frequency band standards (E-UTRA Operating Bands) corresponding to LTE (LTE standards (E-UTRA Operating Bands)).

The passbands of filters 42 and 44 are provided wider than the middle band and high band, respectively. The middle band and high band have a passband width of 300 MHz or more. Thus, broadband filters 42 and 44 are formed by LC circuits. However, the passband spacing between the middle band and the high band is 100 MHz. Therefore, the filters 42 and 44 are required to have steepness between the passband and stopband. However, forming a filter with inductors and capacitors does not provide sufficient steepness. Therefore, elastic wave resonators R21 and R31 are connected. Thereby, the steepness of the filters 42 and 44 can be enhanced.

[Comparative Example 1]
As Comparative Example 1, a multiplexer of the circuit of FIG. 4 was produced. The manufacturing conditions are as follows. SrTiO ₃ was added to CaMgSi ₂ O ₆ so that the temperature coefficient τf of the dielectric constant of the dielectric layer was approximately zero. Table 3 shows the capacitance of each capacitor and the inductance of each inductor.

Acoustic wave resonators R21 and R31 were surface acoustic wave resonators using a 42° rotated Y-cut X-propagation lithium tantalate substrate, and the resonance frequency and anti-resonance frequency were set as follows.
R21 resonance frequency: 2.251 GHz, anti-resonance frequency: 2.332 GHz
R31 resonance frequency: 2.261 GHz, anti-resonance frequency: 2.331 GHz

FIG. 5 is a circuit diagram of the filter 22 used in the experiment. As shown in FIG. 5, in the high-band filter 44, a filter 22 is provided between the node N2 and the terminal T3. Capacitors C 31 , 32 and inductor L 31 form resonant circuit 20 . Capacitor C33 and inductor L32 form resonant circuit 21 . Resonant circuits 20 and 21 are formed by component 24 in which dielectric layers are laminated as shown in FIG. Capacitors C31, C32 and inductor L31 correspond to capacitors C1, C2 and inductor L1 in FIG. 1, respectively, and elastic wave resonator R31 corresponds to elastic wave resonator R1.

6A and 6B are diagrams showing pass characteristics of the filter 22 in Comparative Example 1. FIG. In FIG. 6A, R31 is the pass characteristic when the elastic wave resonator R31 is shunt-connected, and 24 is the component 24 (that is, the resonant circuits 20 and 21 excluding the elastic wave resonator R31 and the inductor L33). is the pass characteristic of

As shown in FIG. 6A, in the pass characteristics of the elastic wave resonator R31, an attenuation pole is formed at the resonance frequency fr, and the attenuation amount is small at the anti-resonance frequency fa. At the component 24, an attenuation pole A1' due to the resonance frequency of the resonance circuit 20 and A3' due to the resonance frequency of the resonance circuit 21 are formed. The bottom frequencies of attenuation poles A1' and A3' are approximately the resonant frequencies of resonant circuits 20 and 21, respectively. The resonance frequency fr is positioned between the attenuation poles A1' and A3' so as to overlap with the high frequency side skirt of the attenuation pole A1'.

As shown in FIG. 6B, in the pass characteristics between the node N2 and the terminal T3 of the filter 22, the attenuation pole A1 mainly derived from the resonance circuit 20 and the resonance frequency fr of the acoustic wave resonator R3 mainly An attenuation pole A2 derived from the resonance circuit 21 and an attenuation pole A3 derived mainly from the resonance circuit 21 are formed. The passband between the attenuation poles A2 and A3 includes the high band HB. Due to the attenuation pole A2, the amount of attenuation between the passband and the stopband changes sharply on the low frequency side of the passband.

FIG. 7 is a diagram showing pass characteristics of filters 42 and 44 in the multiplexer of Comparative Example 1. FIG. In the pass characteristics between the terminals Ta and T2 of the filter 42, the middle band band MB is the pass band, and the high band band HB is the stop band. In the pass characteristics between the terminals Ta and T3 of the filter 44, the high band band HB is the pass band, and the middle band band MB is the stop band. Both filters 42 and 44 have steep changes in attenuation between bands MB and HB. This is because elastic wave resonators R21 and R31 are provided.

The pass characteristics of the filter 44 between the terminals Ta and T3 were measured at ambient temperatures of 85°C, 25°C and -20°C. FIG. 8 is a diagram showing the temperature dependence of the pass characteristics of the filter 44 in the multiplexer of Comparative Example 1. FIG. As shown in FIG. 8, as the temperature increases, the frequency of the attenuation pole A1 increases as indicated by an arrow 51, and the frequency of the attenuation pole A2 decreases as indicated by an arrow 52. FIG.

The temperature coefficient of the bottom frequency of the attenuation pole A1 between 85°C and 25°C is +28.3ppm/°C, and the temperature coefficient of the bottom frequency of the attenuation pole A1 between 25°C and -20°C is +62.0ppm. /°C. On average, the temperature coefficient of frequency is +42.7 ppm/°C. The temperature coefficient of the bottom frequency of the attenuation pole A2 between 85°C and 25°C is -27.4 ppm/°C, and the temperature coefficient of the bottom frequency of the attenuation pole A2 between 25°C and -20°C is -29. .1 ppm/°C. On average, the temperature coefficient of frequency is -28.1 ppm/°C.

As the temperature rises, the attenuation poles A1 and A2 approach each other, so the magnitude of the attenuation peak 54 between the attenuation poles A1 and A2 decreases as indicated by an arrow 53 (attenuation increases). Since the attenuation peak 54 has the smallest attenuation in the stopband, it is required to suppress the temperature change of the magnitude of the peak 54 .

At 85.degree. C., 25.degree. C. and -20.degree. FIG. 9(a) is a diagram showing the temperature dependence of the pass characteristics of the component 24 in Comparative Example 1, and FIG. 9(b) is an enlarged view of the range A in FIG. 9(a). As shown in FIGS. 9A and 9B, even if the temperature changes, the frequency of the attenuation pole A1' hardly changes. The attenuation of the attenuation pole A1' increases as the temperature increases. As described above, in the component 24, the temperature change of the frequency of the attenuation pole A1' is small, but the magnitude of the attenuation changes. As the temperature increases, the electrical resistance of the metal layers 32a to 32d and metal members such as vias in FIG. 3 increases. It is thought that as the electrical resistance of the metal member increases, the loss increases and the amount of attenuation increases.

At 85° C., 25° C. and −20° C., the transmission characteristics of the shunt-connected elastic wave resonator R31 were measured. FIG. 10(a) is a diagram showing the temperature dependence of the pass characteristic of the acoustic wave resonator R31 in Comparative Example 1, and FIG. 10(b) is an enlarged view of range A in FIG. 10(a). As shown in FIGS. 10(a) and 10(b), the resonance frequency fr decreases as the temperature increases. The temperature coefficient of the resonant frequency is approximately -40 ppm/°C.

The temperature change of the attenuation pole A2 in FIG. 8 is considered to be caused by the temperature change of the resonance frequency fr of the elastic wave resonator R31. The temperature change of the bottom frequency of the attenuation pole A1 is considered to be caused by combining the temperature change of the magnitude of the attenuation pole A1' in FIG. 9B and the temperature change of the pass characteristic of the elastic wave resonator R31.

[Simulation of Example 1]
Based on the measurement results of FIGS. 9(a) and 9(b), it was considered to compensate the temperature change of the frequency of the attenuation pole A1 by the temperature change of the relative permittivity of the dielectric material of the component 24. FIG. For example, the addition amount of SrTiO ₃ in the dielectric material of the component 24 is increased to make the temperature coefficient τf of the dielectric constant positive. Thereby, the temperature coefficient of the resonance frequency of the resonance circuit 20 becomes negative.

Component 24 compensates for the +42.7 ppm/°C temperature coefficient of the bottom frequency of the attenuation pole A1 in FIG. 8 and also has the same temperature coefficient as the -28.1 ppm/°C The temperature coefficients of the bottom frequency of the attenuation pole A1' of are -42.7 ppm/°C, -28.1 ppm/°C and -70.8 ppm/°C. That is, the absolute value of the temperature coefficient of the resonant frequency of the resonant circuit 20 is approximately 1.7 to 1.8 times the temperature coefficient of the resonant frequency of the elastic wave resonator R31.

FIG. 11(a) is a diagram showing the temperature dependence of the pass characteristic of the component 24 in the simulation of Example 1, and FIG. 11(b) is an enlarged view of range A in FIG. 11(a). In the simulation, the higher the temperature, the lower the frequency of the attenuation pole A1'.

FIG. 12(a) is a diagram showing the temperature dependence of the pass characteristic of the component 24 in the experiment of Comparative Example 1, and FIG. 12(b) is an enlarged view of the range A of FIG. 12(a). As shown in FIGS. 12A and 12B, in Comparative Example 1, the magnitude of the attenuation peak 54 between the attenuation poles A1 and A2 varies greatly with temperature.

FIG. 13(a) is a diagram showing the temperature dependence of the pass characteristics of the component 24 in the simulation of Example 1, and FIG. 13(b) is an enlarged view of range A in FIG. 13(a). As shown in FIGS. 13(a) and 13(b), in Example 1, the magnitude of the attenuation peak 54 changes little with temperature. Thus, in Example 1, the temperature change of attenuation in the stopband can be made smaller than in Comparative Example 1. FIG.

It is difficult to make the temperature coefficients of the resonance frequency and the antiresonance frequency of the elastic wave resonator R1 such as a surface acoustic wave resonator or a piezoelectric thin film resonator to be 0, and they are generally negative. On the other hand, the temperature coefficients of the resonant frequency and the anti-resonant frequency of the resonant circuit 20 having capacitors and inductors can be adjusted as shown in Tables 1 and 2. Therefore, generally, the resonance circuit 20 is formed so that the temperature coefficient of the resonance frequency of the resonance circuit 20 is approximately zero.

However, the loss of the resonance circuit 20 changes with temperature, and the attenuation of the attenuation pole formed by the resonance circuit 20 changes. Therefore, when the pass characteristics of the elastic wave resonator R1 and the resonance circuit 20 are combined, the bottom frequency of the attenuation pole A1 changes depending on the temperature as shown in FIG. When the temperature coefficients of the frequencies of the attenuation poles A1 and A2 have opposite signs, the magnitude of the peak 54 between the attenuation poles A1 and A2 changes with temperature as shown in FIG. 12(b).

According to the first embodiment, the sign of the temperature coefficient of the frequency of the attenuation pole A1 (first attenuation pole) formed mainly by the LC resonance circuit 20 and the attenuation pole A2 (second Attenuation poles) have the same temperature coefficient sign. That is, the moving direction of the frequency of the attenuation pole A2 due to the temperature change is the same as the moving direction of the attenuation pole A1. As a result, as shown in FIG. 13B, the temperature change in the magnitude of the peak 54 between the attenuation poles A1 and A2 can be reduced. Therefore, the temperature characteristic of the filter can be improved.

Although the elastic wave resonator R1 is shunt-connected between the input terminal Tin and the output terminal Tout in the first embodiment, the elastic wave resonator R1 is connected between the input terminal Tin and the output terminal Tout. They may be connected in series. Further, although the resonance circuit 20 has been described as a parallel resonance circuit, it may be a series resonance circuit. Furthermore, although an example in which the resonant circuit 20 is formed of components in which dielectric layers are laminated has been described, at least a part of the resonant circuit 20 is formed in a substrate on which components are mounted, such as LTCC (Low Temperature Co-fired Ceramic). may be formed. At least part of resonant circuit 20 may be a chip capacitor or a chip inductor. Also in these cases, the temperature change of the magnitude of the peak 54 can be reduced.

The absolute value of the temperature coefficient of the frequency of the attenuation pole A1 and the absolute value of the temperature coefficient of the frequency of the attenuation pole A2 with respect to the average of the absolute value of the temperature coefficient of the frequency of the attenuation pole A1 and the absolute value of the temperature coefficient of the frequency of the attenuation pole A2 The ratio of the difference to the value is preferably 0.9 or less, more preferably 0.5 or less, and even more preferably 0.2 or less. This allows the magnitude of the peak 54 to vary less with temperature.

When the resonant circuit 20 is a parallel resonant circuit including a capacitor and an inductor connected in parallel between the input terminal Tin and the output terminal Tout, an attenuation pole A1 mainly derived from the resonant frequency of the resonant circuit 20 is formed. When one end of the acoustic wave resonator R1 is connected to one end of a capacitor or inductor and the other end of the acoustic wave resonator R1 is grounded, an attenuation pole A2 is formed that mainly originates from the resonance frequency of the acoustic wave resonator R1. be. At this time, the sign of the temperature coefficient of the resonance frequency of the resonance circuit 20 and the sign of the temperature coefficient of the resonance frequency of the acoustic wave resonator R1 are set to be the same. Thereby, the sign of the temperature coefficient of the frequency of the attenuation pole A1 and the sign of the temperature coefficient of the frequency of the attenuation pole A2 can be made the same.

The ratio of the absolute value of the temperature coefficient of the resonance frequency of the resonance circuit 20 to the absolute value of the temperature coefficient of the resonance frequency of the elastic wave resonator R1 is preferably 0.2 or more and 3.2 or less, and is preferably 0.5 or more and 2 0.9 or less is more preferable, and 1.0 or more and 2.2 or less is even more preferable. This allows the magnitude of the peak 54 to vary less with temperature.

The temperature coefficient of the resonance frequency fr of the elastic wave resonator R1 is generally negative. At this time, the attenuation pole A1 is set lower than the passband. Consider the case where the temperature coefficient of the dielectric constant of the capacitor of the resonant circuit 20 is approximately zero. The attenuation pole A1' caused by the resonance circuit 20 increases in attenuation as the temperature increases. On the other hand, the resonance frequency fr of the acoustic wave resonator R1 is formed on the high frequency side of the attenuation pole A1 and moves to the low frequency side as the temperature rises. Therefore, when the attenuation pole A1' and the resonance frequency fr are synthesized, the attenuation amount on the high frequency side of the attenuation pole A1 increases, and the bottom frequency of the attenuation pole A1 increases as indicated by arrow 51 in FIG. Therefore, the temperature change in the magnitude of the peak 54 between the attenuation poles A1 and A2 increases. Thus, if the temperature coefficient of the resonant frequency of resonant circuit 20 is set to approximately 0, the magnitude of peak 54 varies greatly with temperature. Therefore, the signs of the temperature coefficients of the frequencies of the attenuation poles A1 and A2 are assumed to be the same. Thereby, the temperature change of the magnitude of the peak 54 can be reduced.

As shown in FIG. 3, capacitors C1 and C2 have a pair of metal layers 32a and 32b (electrodes) sandwiching dielectric layer 31b. At this time, the temperature coefficient of the dielectric constant of the dielectric layer 31b is assumed to be positive. If the inductance of the inductor of the parallel resonant circuit is L and the capacitance of the capacitor is C, the resonant frequency of the parallel resonant circuit is 1/√LC. Therefore, the temperature coefficient of the frequency of the attenuation pole A1 becomes negative. As a result, the signs of the temperature coefficients of the attenuation poles A1 and A2 are both negative, and the temperature change of the peak 54 can be reduced.

Resonant circuit 20 comprises two capacitors C1 and C2 connected in parallel with inductor L1. One end of acoustic wave resonator R1 is connected to node N3 between two capacitors C1 and C2. This makes it possible to sharply change the amount of attenuation between the passband and the stopband.

As shown in FIG. 3, the resonant circuit 20 includes a plurality of dielectric layers 31a to 31e stacked like the LC component 30 and a metal layer provided on at least one of the dielectric layers 31a to 31e. 32a to 32d (wiring patterns). Metal layers 32a through 32d include the electrodes of capacitors C1 and C2 and inductor L1. In this way, in the case of a laminated component, the temperature coefficient of the dielectric constant of the dielectric layers can be arbitrarily set by changing the composition of the dielectric layers 31a to 31e.

Although a triplexer having three filters 40, 42 and 44 has been described as an example of a multiplexer to which the filters of the first embodiment are applied, the multiplexer may be a diplexer, duplexer or quadplexer.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention described in the scope of claims. Change is possible.

20, 21 resonant circuit 22, 40, 42, 44 filter 24, 30 component 31a-31e dielectric layer 32a-32d metal layer

Claims (7)

an input terminal;
an output terminal;
an LC resonant circuit connected between the input terminal and the output terminal and forming a first attenuation pole;
It is connected between the input terminal and the output terminal, and between the passband and the first attenuation pole, the moving direction of the frequency of the attenuation pole due to temperature change is the same as the moving direction of the first attenuation pole. an acoustic wave resonator forming a second attenuation pole;
A filter with the LC resonant circuit includes a capacitor and an inductor connected in parallel between the input terminal and the output terminal;
one end of the acoustic wave resonator is connected to one end of the capacitor or the inductor, and the other end of the acoustic wave resonator is grounded;
2. The filter according to claim 1, wherein the sign of the temperature coefficient of the resonant frequency of said LC resonant circuit and the sign of the temperature coefficient of said acoustic wave resonator are the same. The elastic wave resonator has a negative temperature coefficient of resonance frequency,
3. The filter of claim 2, wherein the frequency of said first attenuation pole is lower than said passband. The capacitor has a dielectric layer and a pair of electrodes sandwiching the dielectric layer,
4. The filter of claim 3, wherein the dielectric layer has a positive temperature coefficient of dielectric constant. the capacitors are two capacitors connected in parallel with the inductor;
5. The filter according to any one of claims 2 to 4, wherein one end of said acoustic wave resonator is connected to a node between said two capacitors. The LC resonant circuit includes a plurality of laminated dielectric layers including the dielectric layer and a plurality of wiring patterns provided on at least one dielectric layer of the plurality of dielectric layers,
5. The filter according to claim 4, wherein said plurality of wiring patterns includes said pair of electrodes and said inductor. A multiplexer comprising a filter according to any one of claims 1-6.

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