# US 9,882,547 B2 · Tunable filter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,882,547 B2 - Document ID: US9882547B2 - Status: Granted - Kind: B2 - Application number: 15/009,998 - Filed: 2016-01-29 - Published: 2016-05-26 - Granted: 2018-01-30 - Earliest claimed: 2013-08-21 - Assignees: Murata Manufacturing Co., Ltd. - Applicants: Murata Manufacturing Co., Ltd. - Inventors: Hajime Kando - Web page: https://patentgrep.com/patent/US9882547B2 ## CPC - H03H 9/54: comprising resonators of piezoelectric or electrostrictive material (comprising resonators using surface acoustic waves H03H9/64) - H03H 9/02559: {of lithium niobate or lithium-tantalate substrates} - H03H 9/25: Constructional features of resonators using surface acoustic waves {(devices for manipulating acoustic surface waves in general G10K11/36)} - H03H 9/545: {including active elements} - H03H 9/6433: {Coupled resonator filters} - H03H 9/1452: {by finger overlap length, apodisation} - H03H 2210/025: Capacitor - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) ## Abstract A tunable filter using Love waves includes an inductance for band extension connected to each of piezoelectric resonators, variable capacitances are connected to the piezoelectric resonator, the piezoelectric resonators each include a LiNbO3 substrate and an IDT electrode, and a pass band and an attenuation region are positioned in a frequency region on a lower frequency side relative to a value obtained by a calculation in which an acoustic velocity of a low-velocity transversal wave propagating in the LiNbO3 substrate is divided by a wave length defined by a period of the IDT electrode. ## Claims ### Claim 1 A tunable filter comprising: a piezoelectric resonator; an inductance for band extension connected to the piezoelectric resonator; and a variable capacitance connected to the piezoelectric resonator; wherein the tunable filter uses Love waves; the piezoelectric resonator includes a LiNbO3 substrate and an interdigital transducer (IDT) electrode provided on the LiNbO3 substrate; a pass band and an attenuation region are present in a frequency region on a lower frequency side relative to a value obtained by a calculation in which an acoustic velocity of a low-velocity transversal wave propagating in the LiNbO3 substrate is divided by a wave length defined by a period of the IDT electrode; and the IDT electrode includes a Pt film, and in a case where a film thickness of the Pt film is taken as H(λ) and Euler angles of the LiNbO3 substrate are taken as (φ, θ, ψ), θ falls within a range of −64960×H3+19831×H2−2068.4×H+169.7−10° to −64960×H3+19831×H2−2068.4×H+169.7+6°, φ falls within a range of −27° to +27°, and ψ falls within a range of −47° to +47°. ### Claim 2 (depends on 1) The tunable filter according to claim 1, wherein the thickness H of the Pt film is equal to or greater than about 0.023λ. ### Claim 3 A tunable filter comprising: a piezoelectric resonator; an inductance for band extension connected to the piezoelectric resonator; a variable capacitance connected to the piezoelectric resonator; an input terminal; and an output terminal; wherein the tunable filter uses Love waves; the piezoelectric resonator includes a LiNbO3 substrate and an interdigital transducer (IDT) electrode provided on the LiNbO3 substrate; a pass band and an attenuation region are present in a frequency region on a lower frequency side relative to a value obtained by a calculation in which an acoustic velocity of a low-velocity transversal wave propagating in the LiNbO3 substrate is divided by a wave length defined by a period of the IDT electrode; the piezoelectric resonator includes a first piezoelectric resonator that includes an elastic wave resonator and is provided in a serial arm that connects the input terminal to the output terminal, and a second piezoelectric resonator that includes an elastic wave resonator and is provided in a parallel arm that connects the serial arm to a ground potential; the inductance for band extension includes a first inductance that is connected to the first piezoelectric resonator and extends a relative band of the first piezoelectric resonator, and a second inductance that is connected to the second piezoelectric resonator and extends a relative band of the second piezoelectric resonator; the variable capacitance includes a first variable capacitance that is connected to the first piezoelectric resonator and defines a first variable resonance circuit along with the first piezoelectric resonator and the first inductance, and a second variable capacitance that defines a second variable resonance circuit along with the second piezoelectric resonator and the second inductance; and the IDT electrode includes a Pt film, and in a case where a film thickness of the Pt film is taken as H(λ) and Euler angles of the LiNbO3 substrate are taken as (φ, θ, ψ), θ falls within a range of −64960×H3+19831×H2−2068.4×H+169.7−10° to −64960×H3+19831×H2−2068.4×H+169.7+6°, φ falls within a range of −27° to +27°, and ψfalls within a range of −47° to +47°. ### Claim 4 (depends on 3) The tunable filter according to claim 3, wherein the thickness H of the Pt film is equal to or greater than about 0.023λ. ### Claim 5 (depends on 4) The tunable filter according to claim 4, wherein the first inductance includes a first serial inductance connected in series to the first piezoelectric resonator. ### Claim 6 (depends on 3) The tunable filter according to claim 3, wherein the first inductance includes a first parallel inductance connected in parallel to the first piezoelectric resonator. ### Claim 7 (depends on 6) The tunable filter according to claim 6, wherein the second inductance includes a second serial inductance connected in series to the second piezoelectric resonator. ### Claim 8 (depends on 6) The tunable filter according to claim 6, wherein the first variable capacitance includes at least one of a first serial variable capacitance connected in series to the first piezoelectric resonator and a first parallel variable capacitance connected in parallel to the first piezoelectric resonator. ### Claim 9 (depends on 6) The tunable filter according to claim 6, wherein the second variable capacitance includes at least one of a second serial variable capacitance connected in series to the second piezoelectric resonator and a second parallel variable capacitance connected in parallel to the second piezoelectric resonator. ### Claim 10 (depends on 6) The tunable filter according to claim 6, wherein the first and second piezoelectric resonators are provided on the same LiNbO3 substrate. ### Claim 11 (depends on 3) The tunable filter according to claim 3, wherein the first inductance includes a first serial inductance connected in series to the first piezoelectric resonator. ### Claim 12 (depends on 3) The tunable filter according to claim 3, wherein the second inductance includes a second serial inductance connected in series to the second piezoelectric resonator. ### Claim 13 (depends on 12) The tunable filter according to claim 12, wherein the second inductance includes a second parallel inductance connected in parallel to the second piezoelectric resonator. ### Claim 14 (depends on 3) The tunable filter according to claim 3, wherein the second inductance includes a second parallel inductance connected in parallel to the second piezoelectric resonator. ### Claim 15 (depends on 3) The tunable filter according to claim 3, wherein the first variable capacitance includes at least one of a first serial variable capacitance connected in series to the first piezoelectric resonator and a first parallel variable capacitance connected in parallel to the first piezoelectric resonator. ### Claim 16 (depends on 3) The tunable filter according to claim 3, wherein the first and second piezoelectric resonators are provided on the same LiNbO3 substrate. ### Claim 17 (depends on 3) The tunable filter according to claim 3, wherein the second variable capacitance includes at least one of a second serial variable capacitance connected in series to the second piezoelectric resonator and a second parallel variable capacitance connected in parallel to the second piezoelectric resonator. ### Claim 18 A tunable filter comprising: a piezoelectric resonator; an inductance for band extension connected to the piezoelectric resonator; and a variable capacitance connected to the piezoelectric resonator; wherein the tunable filter uses Love waves; the piezoelectric resonator includes a LiNbO3 substrate and an interdigital transducer (IDT) electrode provided on the LiNbO3 substrate; a pass band and an attenuation region are present in a frequency region on a lower frequency side relative to a value obtained by a calculation in which an acoustic velocity of a low-velocity transversal wave propagating in the LiNbO3 substrate is divided by a wave length defined by a period of the IDT electrode; and in a case where a thickness of the IDT electrode is taken as H(λ) and a ratio P/PPt of a density P of the IDT electrode to a density PPt of Pt is taken as A, among the Euler angles (φ, θ, ψ), θ falls within a range of −64960×(H/A)3+19831×(H/A)2−2068.4×H/A+169.7−10° to −64960×(H/A)3+19831×(H/A)2−2068.4×(H/A)+169.7+6°, φ falls within a range of −27° to +27°, and ψ falls within a range of −47° to +47°.