USRE37375EExpiredUtilityPatentIndex 92
Surface acoustic wave filter
Est. expiryOct 28, 2011(expired)· nominal 20-yr term from priority
H03H 9/6436H03H 9/64H03H 9/1071H03H 9/72H03H 9/0576H03H 9/6433H03H 2250/00H03H 9/725H03H 9/6483
92
PatentIndex Score
15
Cited by
70
References
60
Claims
Abstract
A SAW filter includes a first SAW resonator having a pair of terminals and a predetermined resonance frequency (f rp ), the first SAW resonator being provided in a parallel arm of the SAW filter. A second SAW resonator has a pair of terminals and a predetermined resonance frequency (f rs ) approximately equal to a predetermined antiresonance frequency of the first SAW resonator (f ap ). The second SAW resonator is provided in a series arm of the SAW filter. An inductance element is connected in series to the first SAW resonator.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1. A SAW filter comprising:
a first SAW resonator having a pair of terminals and a predetermined resonance frequency (f rp ), said first SAW resonator being provided in a parallel arm of the SAW filter;
a second SAW resonator having a pair of terminals and a predetermined resonance frequency (f rs ) approximately equal to a predetermined antiresonance frequency of the first SAW resonator (f ap ), said second SAW resonator being provided in a series arm of the SAW filter; and
an inductance element connected in series with the first SAW resonator in the parallel arm, the inductance element functioning to increase the admittance of the parallel arm and decrease the resonance frequency.
2. The SAW filter as claimed in claim 1 , wherein an aperture length (Ap) of the first SAW resonator is larger than an aperture length (As) of the second SAW resonator.
3. The SAW filter as claimed in claim 1 , wherein a number (Np) of electrode finger pairs of the first SAW resonator is larger than a number (Ns) of electrode finger pairs of the second SAW resonator.
4. The SAW filter as claimed in claim 1 , wherein the first SAW resonator comprises an exciting interdigital electrode and first and second reflectors respectively located on opposite sides of the exciting electrode so that β is equal to 0.4, said β being defined in the following equation:
d=(n+β)·λ
wherein d denotes a distance between the exciting electrode and each of the first and second reflectors, n is an integer, β is a real number equal to or less than 1, and λ denotes a period of the exciting interdigital electrode corresponding to the resonance frequency.
5. The A SAW filter as claimed in claim 1 , wherein comprising:
a first SAW resonator having a pair of terminals and a predetermined resonance frequency ( f rp ) , said first SAW resonator being provided in a parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals and a predetermined resonance frequency ( f rs ) approximately equal to a predetermined antiresonance frequency of the first SAW resonator ( f ap ) , said second SAW resonator being provided in a series arm of the SAW filter, wherein
the first and second SAW resonators are formed on a piezoelectric substrate including at least one of LiTaO 3 and LiNbO 3 ;
the first SAW resonator comprises an exciting interdigital electrode and first and second reflectors, each of which comprises either aluminum or an aluminum alloy containing a few weight percentage of metal, other than aluminum; and
the respective film thicknesses of the exciting interdigital electrode and the first and second reflectors are in a range of from 0.06 to 0.09 times the period of the exciting interdigital electrode.
6. The A SAW filter as claimed in claim 1 , wherein comprising:
a first SAW resonator having a pair of terminals and a predetermined resonance frequency ( f rp ) , said first SAW resonator being provided in a parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals and a predetermined resonance frequency ( f rs ) approximately equal to a predetermined antiresonance frequency of the first SAW resonator ( f ap ) , said second SAW resonator being provided in a series arm of the SAW filter, wherein
the first and second SAW resonators are formed on a piezoelectric substrate including at least one of LiTaO 3 and LiNbO 3 ;
the first SAW resonator comprises an exciting interdigital electrode and first and second reflectors, each of which comprises either gold or a gold alloy containing a few weight percentage of metal other than gold; and
the respective film thicknesses of the exciting interdigital electrode and the first and second reflectors are in a range of from 0.0086 to 0.013 times the period of the exciting interdigital electrode.
7. The SAW filter as claimed in claim 1 , wherein said inductance element comprises a bonding wire.
8. The SAW filter as claimed in claim 1 , wherein said inductance element comprises:
a ceramic package accommodating a filter chip, the first and second SAW resonators being formed on the filter chip; and
a microstrip line which is formed on the ceramic package and extends between, and interconnects, the first SAW resonator and a terminal.
9. The SAW filter as claimed in claim 1 , wherein said inductance element comprises:
a filter chip, the first and second SAW resonators being formed on the filter chip; and
a microstrip line which is formed on the filter chip and extends from the first SAW resonator.
10. A SAW filter comprising:
a plurality of first SAW resonators, each having a pair of terminals and a predetermined resonance frequency (f rp ), said first SAW resonators being respectively provided in parallel arms of the SAW filter;
a plurality of second SAW resonators, each having a pair of terminals and a predetermined resonance frequency (f rs ) approximately equal to a predetermined antiresonance frequency of the first SAW resonator (f ap ), said second SAW resonators being provided in a series arm of the SAW filter; and
inductance elements (Ls) respectively connected in series to the second SAW resonators.
11. The SAW filter as claimed in claim 10 , wherein:
each of the first SAW resonators comprises an exciting interdigital electrode and first and second reflectors respectively located on opposite sides of the exciting electrode so that β is equal to 0.4, said β being defined in the following equation:
d=(n+β)·λ
wherein d denotes a distance between the exciting electrode and each of the first and second reflectors, n is an integer, β is a real number equal to or smaller than 1, and λ denotes a period of the exciting interdigital electrode corresponding to the resonance frequency.
12. The SAW filter as claimed in claim 11 , wherein each of said inductance elements comprises:
a ceramic package accommodating a filter chip, the first and second SAW resonators being formed on the filter chip; and
microstrip lines which are formed on the ceramic package and respectively extend between, and interconnect, the second SAW resonators and corresponding terminals.
13. The SAW filter as claimed in claim 11 , wherein each of said inductance elements comprises:
a filter chip, the first and second SAW resonators are formed; and
microstrip lines which are formed on the filter chip and extend respectively from the second SAW resonators.
14. A SAW filter comprising:
a plurality of first SAW resonators, each having a pair of terminals and a predetermined resonance frequency (f rp ), said first SAW resonators being connected in respective, parallel arms of the SAW filter;
a plurality of second SAW resonators, each having a pair of terminals and a predetermined resonance frequency (f rs ) approximately equal to the predetermined antiresonance frequency of the first SAW resonator (f ap ), said second SAW resonators being provided in a series arm of the SAW filter; and
inductance elements respectively connected in series with the first SAW resonators in the parallel arms.
15. A SAW filter comprising:
a first SAW resonator having a pair of terminals, a first resonance frequency (f rp ) and a first antiresonance frequency (f ap ), based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonator being provided in a parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals, a second resonance frequency (f rs ) and a second antiresonance frequency (f as ), based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonator being provided in a series arm of the SAW filter, wherein:
the second resonance frequency (f rs ) is higher than the first antiresonance frequency (f ap ), and
a difference between the second resonance frequency and the first antiresonance frequency is equal to a value which provides an allowable ripple range and an allowable insertion loss.
16. The A SAW filter as claimed in claim 15 , wherein comprising:
a first SAW resonator having a pair of terminals, a first resonance frequency ( f rp ) and a first antiresonance frequency ( f ap ) , based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonator being provided in a parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals, a second resonance frequency ( f rs ) and a second antiresonance frequency ( f as ) , based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonator being provided in a series arm of the SAW filter, wherein:
the second resonance frequency ( f rs ) is higher than the first antiresonance frequency ( f ap ) , and
a difference between the second resonance frequency and the first antiresonance frequency is equal to a value which provides an allowable ripple range and an allowable insertion loss, wherein:
the first and second SAW resonators are formed on a piezoelectric substrate;
the second SAW comprises an interdigital electrode which is formed on the piezoelectric substrate and which has a predetermined period; and
a normalized value, obtained by normalizing said difference by the second resonance frequency, is larger than zero 0 . 002 and smaller than α, as defined by the following equation: α = 1 ( P ( τ 2 + τ ) / 0.06 - τ )
wherein P is a ratio of an electrostatic capacitance, based on an aperture length and a number of finger pairs of the interdigital electrode of the second SAW resonator, to an electrostatic capacitance, based on an aperture length and a number of finger pairs of an interdigital electrode of the first SAW resonator.
17. The A SAW filter as claimed in claim 15 , wherein comprising:
a first SAW resonator having a pair of terminals, a first resonance frequency ( f rp ) and a first antiresonance frequency ( f ap ) , based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonator being provided in a parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals, a second resonance frequency ( f rs ) and a second antiresonance frequency ( f as ) , based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonator being provided in a series arm of the SAW filter, wherein:
the second resonance frequency ( f rs ) is higher than the first antiresonance frequency ( f ap ) , and
a difference between the second resonance frequency and the first antiresonance frequency is equal to a value which provides an allowable ripple range and an allowable insertion loss, wherein:
the first and second SAW resonators are formed on a piezoelectric substrate;
the second SAW resonator comprises an interdigital electrode which is formed on the piezoelectric substrate and which has a predetermined period;
said piezoelectric substrate comprises 36° Y-cut X-propagation LiTaO 3 ; and
Cop/Cos is less than 1 . 8 , wherein Cop and Cos are the electrostatic capacitances of the first SAW resonator and the second SAW resonator, respectively; and
the predetermined period of the interdigital electrode of the second SAW resonator is selected so that said normalized ratioa normalized value, obtained by normalizing said difference by the second resonance frequency, is larger than zero 0 . 007 and is smaller than a, as defined by the following equation: α = 6.67 × 10 - 2 / ( 4.22 P - 1 )
wherein P is a ratio of an electrostatic capacitance, Cop/Cos, based on an aperture length and a number of finger pairs of the interdigital electrode of the second SAW resonator, to an electrostatic capacitance, based on an aperture length and a number of finger pairs of an interdigital electrode of the first SAW resonator.
18. The A SAW filter as claimed in claim 15 , wherein comprising:
a first SAW resonator having a pair of terminals, a first resonance frequency ( f rp ) and a first antiresonance frequency ( f ap ) , based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonator being provided in a parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals, a second resonance frequency ( f rs ) and a second antiresonance frequency ( f as ) , based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonator being provided in a series arm of the SAW filter, wherein:
the second resonance frequency ( f rs ) is higher than the first antiresonance frequency ( f ap ) , and
a difference between the second resonance frequency and the first antiresonance frequency is equal to a value which provides an allowable ripple range and an allowable insertion loss, wherein:
Cop/Cos is less than 1 . 8 , wherein Cop and Cos are the electrostatic capacitances of the first SAW resonator and the second SAW resonator, respectively; and
the first and second SAW resonators are formed on a piezoelectric substrate;
the second SAW resonator comprises an interdigital electrode which is formed on the piezoelectric substrate and which has a predetermined period;
said piezoelectric substrate comprises 64° Y-cut X-preparation LiNbO 3 ; and
the predetermined period of the interdigital electrode of the second SAW resonator is selected so that said normalized ratioa normalized value, obtained by normalizing said difference by the second resonance frequency, is larger than zero 0 . 0073 and is smaller than α, as defined by the following equation: α = 1.47 × 10 - 2 / ( 4.37 P - 1 )
wherein P is a ratio of an electrostatic capacitance, Cop/Cos, based on an aperture length and a number of finger pairs of the interdigital electrode of the second SAW resonator, to an electrostatic capacitance, based on an aperture length and a number of finger pairs of an interdigital electrode of the first SAW resonator.
19. The A SAW filter as claimed in claim 15 , wherein comprising:
a first SAW resonator having a pair of terminals, a first resonance frequency ( f rp ) and a first antiresonance frequency ( f ap ) , based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonator being provided in a parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals, a second resonance frequency ( f rs ) and a second antiresonance frequency ( f as ) , based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonator being provided in a series arm of the SAW filter, wherein:
the second resonance frequency ( f rs ) is higher than the first antiresonance frequency ( f ap ) , and a difference between the second resonance frequency and the first antiresonance frequency is equal to a value which provides an allowable ripple range and an allowable insertion loss, wherein:
Cop/Cos is less than 1 . 8 , wherein Cop and Cos are the electrostatic capacitances of the first SAW resonator and the second SAW resonator, respectively; and
the first and second SAW resonators are formed on a piezoelectric substrate;
the second SAW resonator comprises an interdigital electrode which is formed on the piezoelectric substrate and which has a predetermined period;
said piezoelectric substrate comprises 41° Y-cut X-propagation LiNbO 3 ; and
the predetermined period of the interdigital electrode of the second SAW resonator is selected so that said normalized ratioa normalized value, obtained by normalizing said difference by the second resonance frequency, is larger than zero 0 . 0074 and is smaller than α, as defined by the following equation: α = 2.273 × 10 - 1 / ( 4.52 P - 1 )
wherein P is a ratio of an electrostatic capacitance, Cop/Cos, based on an aperture length and a number of finger pairs of the interdigital electrode of the second SAW resonator, to an electrostatic capacitance, based on an aperture length and a number of finger pairs of an interdigital electrode of the first SAW resonator.
20. A SAW filter comprising:
a plurality of first SAW resonators, each having a pair of terminals, a first resonance frequency (f rp ) and a first antiresonance frequency (f ap ), based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonators being connected in respective, parallel arms of the SAW filter; and
a plurality of second SAW resonators, each having a pair of terminals, a second resonance frequency (f rs ) and a second antiresonance frequency (f as ), based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonators being connected in a series arm of the SAW filter, wherein: the first and second SAW resonators are connected so as to form a ladder-type filter structure,
the second resonance frequency is higher than or equal to the first antiresonance frequency,
a first outermost arm, closest to either an input or an output of the SAW filter, is said series arm and a second outermost arm,
closest to a remaining one of the input and the output, is one of the parallel arms, and
the respective one of the second SAW resonators connected in the first outermost arm has an impedance smaller than that of each of remaining second SAW resonators connected in the series arm and located interiorally of said SAW filter, relatively to said respective one of the second SAW resonators connected in the first outermost arm.
21. The SAW filter as claimed in claim 20 , wherein the respective one of the first SAW resonators connected in the second outermost arm has an admittance smaller than that of each of remaining first SAW resonators connected respectively in the parallel arms and located interiorally of said SAW filter, relatively to said respective one of the first SAW resonators connected in the second innermost arm.
22. The SAW filter as claimed in claim 20 , wherein the impedance of said respective one of the second SAW resonators is half that of each of the remaining second SAW resonators.
23. The SAW filter as claimed in claim 21 , wherein the impedance of said respective one of the second SAW resonators is half that of each of the remaining second SAW resonators.
24. The SAW filter as claimed in claim 20 , wherein:
a first electrostatic capacitance based on a first product is larger than a second electrostatic capacitance based on a second product;
the first product is a product of an aperture length of said one of the second SAW resonators in the first outermost arm, a number of finger pairs thereof, and a dielectric constant of a substrate of the first and second SAW resonators; and
the second product is a product of an aperture length of each of said remaining second SAW resonators, a number of finger pairs thereof, and said dielectric constant.
25. The SAW filter as claimed in claim 20 , wherein each of said remaining second SAW resonators in the series arm comprises a plurality of component SAW resonators connected in series and each of the plurality of component SAW resonators has the same capacitance as said respective one of the second SAW resonators connected in the first outermost arm.
26. The SAW filter as claimed in claim 21 , wherein:
a first electrostatic capacitance based on a first product is larger smaller than a second electrostatic capacitance based on a second product;
the first product is a product of an aperture length of said one of the first SAW resonators in the second outermost arm, a number of finger pairs thereof, and a dielectric constant of a substrate of the first and second SAW resonators; and
the second product is a product of an aperture length of each of said remaining first SAW resonators, a number of finger pairs thereof, and said dielectric constant.
27. The SAW filter as claimed in claim 21 , wherein each of said remaining second SAW resonators in the series arm comprises a plurality of component SAW resonators connected in series and each of the plurality of component SAW resonators has the same impedance as said respective one of the second SAW resonators connected in the first outermost arm.
28. The SAW filter as claimed in claim 21 , wherein the admittance of said respective one of the first SAW resonators is half that of each of the remaining first SAW resonators.
29. The SAW resonator as claimed in claim 21 , wherein:
a first electrostatic capacitance based on a first product is smaller than a second electrostatic capacitance based on a second product;
the first product is a product of an aperture length of said one of the first SAW resonators in the second outermost arm, a number of finger pairs thereof, and a dielectric constant of a substrate of the first and second SAW resonators; and
the second product is a product of an aperture length of each of said remaining first SAW resonators, a number of finger paris pairs thereof, and said dielectric constant.
30. The SAW resonator as claimed in claim 21 , wherein each of said remaining first SAW resonators in the respective parallel arms comprises a plurality of component SAW resonators connected in parallel and each of the plurality of component SAW resonators has the same capacitance as said respective one of the first SAW resonators connected in the second outermost arm.
31. The SAW filter as claimed in claim 23 , wherein:
a first electrostatic capacitance based on a first product is larger than a second electrostatic capacitance based on a second product;
the first product is a product of an aperture length of said respective one of the second SAW resonators connected in the first outermost arm, a number of finger pairs thereof, and a dielectric constant of a substrate of the first and second SAW resonators; and
the second product is a product of an aperture length of each of said remaining second SAW resonators, a number of finger pairs thereof, and said dielectric constant.
32. The SAW filter as claimed in claim 23 , wherein each of said remaining second SAW resonators in the series arm comprises a plurality of component SAW resonators connected in series and each of the plurality of component SAW resonators has the same capacitance as said respective one of the second SAW resonators connected in the first outermost arm.
33. The SAW resonator as claimed in claim 28 , wherein:
a first electrostatic capacitance based on a first product is smaller than a second electrostatic capacitance based on a second product;
the first product is a product of an aperture length of said respective one of the first SAW resonators connected in the second outermost arm, a number of finger pairs thereof, and a dielectric constant of a substrate, and the second product is a product of an aperture length of each of said remaining first SAW resonators, a number of finger pairs thereof and said dielectric constant.
34. The SAW resonator as claimed in claim 28 , wherein each of said remaining first SAW resonators connected in the respective parallel arms comprises a plurality of component SAW resonators connected in parallel and each of the plurality of component SAW resonators has the same capacitance as said respective one of the first SAW resonators connected in the second outermost arm.
35. A saw filter having an input and an output, comprising:
a plurality of first SAW resonators, each having a pair of terminals, a first resonance frequency (f rp ) and a first antiresonance frequency (f ap ), based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonators being connected in respective, parallel arms of the SAW filter; and
a plurality of second SAW resonators, each having a pair of terminals, a second resonance frequency (f rs ) and a second antiresonance frequency (f as ), based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonators being connected in a series arm of the SAW filter, wherein:
the first and second SAW resonators are connected so as to form a ladder-type filter structure,
the second resonance frequency is higher than or equal to the first antiresonance frequency, and
a first outermost arm, closest to one of the input and the output of the SAW filter, comprises said series arm and a second outermost arm, closest to the other of the input and the output, comprises one of the parallel arms, and the respective first SAW resonator connected in the second outermost arm has an admittance smaller than that of each of the remaining first SAW resonators, connected in the remaining, respective parallel arms and located interiorly of said SAW filter relatively to the respective first SAW resonator connected in the second outermost arm.
36. The SAW filter as claimed in claim 35 , wherein the admittance of said one of the first SAW resonators is half that of each of the remaining first SAW resonators.
37. The SAW filter as claimed in claim 35 , wherein:
a first electrostatic capacitance based on a first product is smaller than a second electrostatic capacitance based on a second product;
the first product is a product of an aperture length of said one of the first SAW resonators in the second outermost arm, a number of finger pairs thereof, and a dielectric constant of a substrate of the first and second SAW resonators; and
the second product is a product of an aperture length of each of said remaining first SAW resonators, a number of finger pairs thereof, and said dielectric constant.
38. The SAW filter as claimed in claim 35 , wherein each of said remaining first SAW resonators connected respectively in the parallel arms comprises a plurality of component SAW resonators connected in parallel and each of the plurality of component SAW resonators has the same capacitance as said respective one of the first SAW resonators connected in the second outermost arm.
39. A SAW filter comprising:
a plurality of first SAW resonators, each having a pair of terminals, a first resonance frequency (f rp ) and a first antiresonance frequency (f ap ), based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonators being connected in respective, parallel arms of the SAW filter; and
a plurality of second SAW resonators, each having a pair of terminals, a second resonance frequency (f rs ) and a second antiresonance frequency (f as ), based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonators being connected in a series arm of the SAW filter, wherein:
the first and second SAW resonators are connected so as to form a ladder-type filter structure;
the second resonance frequency is higher than or equal to the first antiresonance frequency;
a first outermost arm, closest to an input of the SAW filter, comprises one of the parallel arms, and a second outermost arm, closest to an output of the SAW filter, comprises another one of the parallel arms; and
the respective one of the first SAW resonators connected in one of the first and second outermost arms has an admittance smaller than that of each of the remaining first SAW resonators respectively connected in the parallel arms and located interiorly of the SAW filter relatively to said respective one of the first SAW resonators connected in said one of the first and second outermost arms.
40. The SAW filter as claimed in claim 39 , wherein the admittance of said respective one of the first SAW resonators in at least one of the first and second outermost arms is half that of each of said remaining first SAW resonators.
41. The SAW filter as claimed in claim 40 , wherein:
a first electrostatic capacitance based on a first product is smaller than a second electrostatic capacitance based on a second product;
the first product is a product of an aperture length of said respective one of the first SAW resonators in at least one of the first and second outermost arms, a number of finger pairs thereof, and a dielectric constant of a substrate of the first and second SAW resonators; and
the second product is a product of an aperture length of each of said remaining first SAW resonators, a number of finger pairs thereof, and said dielectric constant.
42. The SAW filter as claimed in claim 40 , wherein each of said remaining first SAW resonators connected respectively in the parallel arms comprises a plurality of component SAW resonators connected in parallel and each of the plurality of component SAW resonators has the same capacitance as said respective one of the first SAW resonators connected in one of the first and second outermost arms.
43. A SAW filter comprising:
a plurality of first SAW resonators, each having a pair of terminals, a first resonance frequency (f rp ) and a first antiresonance frequency (f ap ), based on the first resonance frequency and a first capacitance ratio (τ) and higher than the first resonance frequency, said first SAW resonators being connected in respective, parallel arms of the SAW filter; and
a plurality of second SAW resonators, each having a pair of terminals, a second resonance frequency (f rs ) and a second antiresonance frequency (f as ), based on the second resonance frequency and a second capacitance ratio (τ) and higher than the second resonance frequency, said second SAW resonators being provided in a series arm of the SAW filter, wherein:
the first and second SAW resonators are connected so as to form a ladder-type filter structure;
the second resonance frequency is higher than or equal to the first antiresonance frequency;
a first outermost arm, closest to an input of the SAW filter, is said series arm and a second outermost arm, closest to an output of the SAW filter, is also said series arm; and
one of the second SAW resonators connected in a respective one of the first and second outermost arms has an impedance smaller than that of each of remaining second SAW resonators provided in the series arm and located interiorally of said SAW filter, relatively to said one of the second SAW resonators.
44. The SAW filter as claimed in claim 43 , wherein the impedance of said one of the second SAW resonators is half that of each of the remaining second SAW resonators.
45. The SAW filter as claimed in claim 43 , wherein each of said remaining second SAW resonators in the respective series arms comprises a plurality of SAW resonators connected in series and each of the plurality of component SAW resonators has the same capacitance as said one of the second SAW resonators provided in the at least one of the first and second outermost arms.
46. The SAW filter comprising:
a first SAW resonator having a pair of terminals and a predetermined resonance frequency (f rp ), said first SAW resonator being provided in a respective parallel arm of the SAW filter; and
a second SAW resonator having a pair of terminals and a predetermined resonance frequency (f rs ) approximately equal to or higher than a predetermined antiresonance frequency of the first SAW resonator (f ap ), said second SAW resonator being provided in a series arm of the SAW filter, a first electric resistance (rs) of an interdigital electrode of said second SAW resonator being smaller than a second electric resistance (rp) of an interdigital electrode of said first SAW resonator.
47. The SAW filter as claimed in claim 46 , wherein:
an aperture length (ls) of the interdigital electrode of said second SAW resonator is smaller than that (lp) of the interdigital electrode of said first SAW resonator; and
a number (Ns) of finger pairs of the interdigital electrode of said second SAW resonator is larger than a number (Np) of finger pairs of the interdigital electrode of said first SAW resonator.
48. The SAW filter as claimed in claim 46 , wherein a film thickness of the interdigital electrode of said first SAW resonator is smaller than a film thickness of the interdigital electrode of said second SAW resonator.
49. A band-pass filter comprising:
a plurality of SAW filters having respective pass bands and comprising a plurality of one-port SAW resonators connected in a ladder structure, each having at least a first stage and a series-arm resonator located at the first stage;
a pair of input terminals commonly connected to the plurality of SAW filters;
a plurality of pairs of output terminals respectively connected to the plurality of SAW filters;
an inductance element, located between at least one of the SAW filters and the pair of input terminals and connected in parallel to said at least one of the SAW filters; and
a capacitance element connected in series between said inductance element and said series-arm resonator.
50. A band-pass filter comprising:
a plurality of SAW filters having respective pass bands and SAW resonators and each having at least a first stage;
a pair of input terminals commonly connected to the plurality of SAW filters;
a plurality of pairs of output terminals respectively connected to the plurality of SAW filters;
a first one of the SAW filters comprises a series-arm SAW resonator, located at the first stage of said first one of the SAW filters, and a parallel-arm SAW resonator, connected to said series-arm SAW resonator;
a second one of the SAW filters comprises a parallel-arm SAW resonator, located at the first stage of said second one of the SAW filters, and a series-arm SAW filter connected to said parallel-arm SAW resonator located at the first stage of the second one of the SAW filters; and
a line used for phase rotation and connected in series between one of the pair of input terminals and the second one of the SAW filters.
51. The band-pass filter as claimed in claim 50 , further comprising an inductance element located between the first one of the SAW filters and the pair of input terminals, and connected in parallel to the first one of the SAW filters.
52. The band-pass filter as claimed in claim 51 , further comprising a capacitance element connected in series between said inductance element and the series-arm resonator of said first one of the SAW filters.
53. The SAW filter as claimed in claim 1 , wherein:
a product of an aperture length ( Ap ) and a number of ( Np ) of electrode finger pairs of the first SAW resonator is larger than a product of an aperture length ( As ) and a number ( Ns ) of electrode finger pairs of the second SAW resonator.
54. The SAW filter as claimed in claim 7 , further comprising input and output terminals and wires connected to said input and output terminals, wherein said bonding wire is longer than at least one of the wires which is connected to said input and output terminals.
55. The SAW filter as claimed in claim 7 , further comprising:
a ceramic package to support said first and second SAW resonators; and
a metal terminal formed on said ceramic package and coupled to an external terminal.
56. The SAW filter as claimed in claim 14 , wherein at least two of said inductance elements have different values of inductances.
57. The SAW filter as claimed in claim 14 , wherein at least two of the first SAW resonators in the parallel arms of said SAW filter have different values of capacitances.
58. The SAW filter as claimed in claim 14 , further comprising input and output terminals and wires connected to said input and output terminals, wherein at least one of said inductance elements comprises a bonding wire which is longer than at least one of the wires connected to said input and output terminals.
59. The SAW filter as claimed in claim 14 , further comprising:
a ceramic package to support said first and second SAW resonators; and
a metal terminal formed on said ceramic package and coupled to an external terminal.
60. The SAW filter as claimed in claim 16 , wherein the normalized value is larger than 1 /[ 1 . 3416 ( τ+ 100 )−τ].Cited by (0)
No later patents cite this yet.
References (0)
No backward citations on record.