Surface acoustic wave filter

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.

1. A band-pass filter having a pair of band-pass filter input  common signal terminals and plural pairs of band-pass filter output  signal terminals, comprising:
 a pair of SAW  band- pass  filters having respective pass bands and comprising a plurality of one-port SAW  acoustic wave resonators connected in a multiple ladder structure, each having at least a first stage located at a side of the pair of band-pass filter input  common signal terminals and a series-arm resonator located at the first stage,  a pair of input terminals and a pair of output terminals;  
 the pair of band-pass filter input  common signal terminals being commonly connected to the respective pairs of input terminals of the pair  pair of SAW  band- pass  filters;  
 the plurality of pairs of band-pass filter output  signal terminals being respectively connected to the respective pairs of output terminals of the pair  pair of SAW  band- pass  filters; and  
 an inductance element located between at least  one side of only one of the SAW  band- pass  filters located at the first stage and the pair of band-pass filter input terminals and directly connected between the respective pair of input terminals of the at least one of the SAW filters and thereby in parallel to said at least one of the SAW filters  one of the common signal terminals, and no inductance element being located between the other of the band- pass filters and one of the common signal terminals.    
 
     
     
       2. 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 an antiresonance frequency (f ap ) of each of the first SAW resonators, said second SAW resonators being provided in series arms of the SAW filter; and    inductance elements respectively connected in series with the first SAW resonators in the parallel arms and formed of wires.    
     
     
       3. The SAW filter as claimed in  claim 2 , further comprising:
 a package accommodating the first and second resonators and the inductance elements; and    lead terminals extending from interiorly of the package to exteriorly thereof, said wires of the inductance elements being bonded to said lead terminals.    
     
     
       4. A band-pass filter having a predetermined pass-band characteristic and comprising:
 a plurality of SAW resonators connected in a ladder formation, said plurality of resonators being connected in respective serial arms and parallel arms; and    bonding inductance elements, said parallel arms of said ladder formation being connected to ground via respective said bonding inductance elements.    
     
     
       5. The band-pass filter as claimed in  claim 4 , wherein said bonding inductance elements comprise wires. 
     
     
       6. A band-pass filter having a pair of band-pass filter input terminals and plural pairs of band-pass filter output terminals, comprising:
 a pair of SAW filters having respective, different pass bands and each SAW filter having a pair of SAW filter input terminals and a pair of SAW filter output terminals and comprising a plurality of one-port SAW resonators connected in a ladder structure between the input and output terminals and including at least a first stage having a series-arm SAW resonator connected to one of the pair of input terminals;    a pair 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 located at a side of the pair of band-pass filter input terminals and a series-arm resonator located at the first stage, a pair of input terminals and a pair of output terminals;    the pair of band-pass filter input terminals being commonly connected to the respective pairs of input terminals of the pair of SAW filters;    the plurality of pairs of band-pass filter output terminals being connected to the respective pairs of output terminals of the pair of SAW filters.    
     
     
       7. A band-pass filter having a predetermined pass-band characteristic and comprising:
 a plurality of SAW resonators connected in a ladder configuration of respective serial arms and parallel arms, said plurality of SAW resonators being connected in respective said serial arms and parallel arms; and    bonding inductance elements respectively connecting said parallel arms of said ladder configuration to ground.    
     
     
       8. An acoustic wave filter comprising:
   a first acoustic wave resonator having a pair of terminals and a predetermined resonance frequency  ( frp ) , said first acoustic wave resonator being provided in a parallel arm of the acoustic wave filter on a LiTaO   3    substrate; and        a second acoustic wave resonator having a pair of terminals and a predetermined resonance frequency  ( frs )  approximately equal to a predetermined antiresonance frequency of the first acoustic wave resonator  ( fap ) , said second acoustic wave resonator being provided in a series arm of the acoustic wave filter on the LiTaO   3    substrate; and        an inductance element connected in series with the first acoustic wave resonator in the parallel arm, the inductance element functioning to increase the admittance of the parallel arm and decrease the resonance frequency, wherein        the first acoustic wave 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.     
     
     
       9. An acoustic wave filter comprising:
   a first acoustic wave resonator having a pair of terminals and a predetermined resonance frequency  ( frp ) , said first acoustic wave resonator being provided in a parallel arm of the acoustic wave filter on a LiTaO   3    substrate; and        a second acoustic wave resonator having a pair of terminals and a predetermined resonance frequency  ( frs )  approximately equal to a predetermined antiresonance frequency of the first acoustic wave resonator  ( fap ) , said second acoustic wave resonator being provided in a series arm of the acoustic wave filter on the LiTaO   3    substrate; and        an inductance element connected in series with the first acoustic wave resonator in the parallel arm, the inductance element functioning to increase the admittance of the parallel arm and decrease the resonance frequency, wherein        the first acoustic wave 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.     
     
     
       10. An acoustic wave filter comprising:
   a plurality of first acoustic wave resonators on a single piezoelectric substrate, each having a pair of terminals and a predetermined resonance frequency  ( frp ) , said first acoustic wave resonators being connected in respective, parallel arms of the acoustic wave filter;        a plurality of second acoustic wave resonators on the piezoelectric substrate, each having a pair of terminals and a predetermined resonance frequency  ( frs )  approximately equal to the predetermined antiresonance frequency of the first acoustic wave resonator  ( fap ) , said second acoustic wave resonators being provided in a series arm of the acoustic wave filter; and        inductance elements respectively connected to ground in series with the first acoustic wave resonators in the parallel arms.     
     
     
       11. A band- pass filter having a pair of band - pass filter common signal terminals and plural pairs of band - pass filter signal terminals, comprising:      a first band - pass filter having a pass band, having a band center frequency and comprising a plurality of acoustic wave resonators connected in a multiple ladder structure, having at least a first stage located at a side of the pair of band - pass filter common signal terminals, a pair of input terminals and a pair of output terminals;        a second band - pass filter having a different pass band from the pass band of the first band - pass filter, having a band center frequency which is larger than the band center frequency of the first band - pass filter and comprising a plurality of acoustic wave resonators connected in a multiple ladder structure, having at least a first stage located at a side of the pair of band - pass filter common signal terminals, a pair of input terminals and a pair of output terminals;        the pair of band - pass filter common signal terminals being commonly connected to the first and second band - pass filters;        the plurality of pairs of band - pass filter signal terminals being respectively connected to the first and second band - pass filters; and        only one impedance matching circuit located only between the first stage of the second band - pass filter and the common signal terminals.     
     
     
       12. The band- pass filter as claimed in    claim 11   , wherein the impedance matching circuit includes an inductor.   
     
     
       13. The band- pass filter as claimed in    claim 12   , wherein the inductor is formed with a metallic strip line.   
     
     
       14. The band- pass filter as claimed in    claim 13   , wherein the metallic strip line is formed on a ceramic package.   
     
     
       15. The band- pass filter as claimed in    claim 11   , wherein said impedance matching circuit includes an inductor and a capacitor.   
     
     
       16. A band- pass filter comprising:      a first band - pass filter having a pass band, having a band center frequency and comprising a plurality of acoustic wave resonators connected in a multiple ladder structure, having at least a first stage and a series - arm resonator located at the first stage, a pair of input terminals and a pair of output terminals;        a second band - pass filter having a different pass band from the pass band of the first band - pass filter, having a band center frequency which is larger than the band center frequency of the first band - pass filter and comprising a plurality of acoustic wave resonators connected in a multiple ladder structure, having at least a first stage and a parallel - arm resonator located at the first stage, a pair of input terminals and a pair of output terminals;        a pair of band - pass filter common signal terminals commonly connected to the first and second band - pass filters;        a plurality of pairs of band - pass filter signal terminals respectively connected to the first and second band - pass filters;        a circuit element used for phase rotation and connected between at least one of the pair of common signal terminals and the second band - pass filter.     
     
     
       17. The band- pass filter as claimed in    claim 16   , wherein the circuit element comprises a line formed on a glass - epoxy substrate or a ceramic substrate.   
     
     
       18. The band- pass filter as claimed in    claim 16   , wherein the circuit element comprises an inductance element.   
     
     
       19. The band- pass filter as claimed in    claim 18   , wherein the circuit element further comprises a capacitance element coupled to the inductance element.   
     
     
       20. A band- pass filter having a predetermined pass - band characteristic and comprising:      a plurality of acoustic wave resonators connected in a ladder formation, said plurality of resonators being connected in respective serial arms and parallel arms; and        bonding inductance elements, said parallel arms of said ladder formation being connected to ground via respective said bonding inductance elements, wherein:        a package in which the band - pass filter is mounted, contains a piezoelectric substrate and the ground; and        the plurality of acoustic wave resonators are on the piezoelectric substrate.     
     
     
       21. A band- pass filter having a predetermined pass - band characteristic and comprising:      a plurality of acoustic wave resonators connected in a ladder formation, said plurality of resonators being connected in respective serial arms and parallel arms; and        bonding inductance elements, said parallel arms of said ladder formation being connected to ground via respective said bonding inductance elements, wherein:        a package in which the band - pass filter is mounted contains a piezoelectric substrate;        the plurality of acoustic wave resonators are on the piezoelectric substrate; and        a first electric resistance  ( Rs )  of an interdigital electrode of a acoustic wave resonator provided in a series arm, is smaller than a second electric resistance  ( Rp )  of an interdigital electrode of a acoustic wave resonator provided in a parallel arm which is next to the series arm.     
     
     
       22. A band- pass filter having a predetermined pass - band characteristic and comprising:      a plurality of acoustic wave resonators connected in a ladder formation, said plurality of resonators being connected in respective serial arms and parallel arms; and        bonding inductance elements, said parallel arms of said ladder formation being connected to ground via respective said bonding inductance elements, wherein:        the plurality of acoustic wave resonators are on a piezoelectric substrate; and        the bonding inductance elements are respectively connected to the ground outside the piezoelectric substrate.