Surface acoustic wave filter and device employing it
View Patent ↗A surface acoustic wave (SAW) filter includes a first SAW resonator, a second SAW resonator connected in series to the first SAW resonator at a first node, a third SAW resonator connected in series to the second SAW resonator at a second node, a fourth SAW resonator connected in series to the third SAW resonator at a third node, a fifth SAW resonator connected between the first node and ground, a sixth SAW resonator connected between the third node and ground, and a first capacitance element connected between the second node and ground. Further, the SAW filter includes a first inductance element connected in series to the fifth SAW resonator, and a second inductance element connected in series to the sixth SAW resonator. This SAW filter has a sharp attenuation at a high frequency of a pass band, thereby widening the pass band and reducing the loss thereof.
1. A surface acoustic wave (SAW) filter comprising:
a first SAW resonator;
a second SAW resonator connected in series to said first SAW resonator at a first node;
a third SAW resonator connected in series to said second SAW resonator at a second node;
a fourth SAW resonator connected in series to said third SAW resonator at a third node;
a fifth SAW resonator connected between the first node and a ground;
a sixth SAW resonator connected between the third node and a ground;
a first capacitance element having a capacitance and being connected between the second node and a ground;
a first inductance element connect between said fifth SAW resonator and the ground such that said fifth SAW resonator and said first inductance element are connected in series;
a second inductance element connected between said sixth SAW resonator and the ground such that said sixth SAW resonator and said second inductance element are connected in series;
a piezoelectric board having a surface including said first to sixth SAW resonators and said first capacitance element disposed thereon;
a first electrode, arranged on said surface of said piezoelectric board, and extending from one of the second node and the ground, said first electrode having a first edge; and
a second electrode, arranged on said surface of said piezoelectric board, and extending from another of the second node and the ground, said second electrode having a second edge parallel to and facing said first edge of said first electrode, wherein
said first capacitance element includes:
a third electrode, arranged on said surface of said piezoelectric board, and extending from said first edge of said first electrode; and
a fourth electrode, arranged on said surface of said piezoelectric board, extending from said second edge of said second electrode, and facing said third electrode in a direction perpendicular to said first and second edges with a gap formed therebetween.
2. The SAW filter of claim 1 , further comprising a second capacitance element having a capacitance and being connected between the first node and the ground.
3. The SAW filter of claim 2 , further comprising a third capacitance element having a capacitance and being connected between the third node and the ground.
4. A device comprising:
said SAW filter of claim 3 ; and
an element connected to said SAW filter.
5. A device comprising:
said SAW filter of claim 2 ; and
an element connected to said SAW filter.
6. The SAW filter of claim 2 , wherein said second capacitance elements further includes:
a fifth electrode, arranged on said surface of said piezoelectric board, and extending from the second node; and
a sixth electrode, arranged on said surface of said piezoelectric board, and extending from the ground and facing said fifth electrode.
7. The SAW filter of claim 6 , wherein said fifth electrode and said sixth electrode have toothed portions facing each other, respectively.
8. The SAW filter of claim 1 , wherein:
said third electrode includes a first portion extending from said first edge and a second portion extending from said first portion parallel to said first edge and said second edge, so that a gap is located between said first edge and said second portion of said third electrode; and
said fourth electrode includes a first portion extending from said second edge and a second portion extending from said first portion parallel to said first edge, said second edge, and said second portion of said third electrode, so that a gap is formed between said second edge and said second portion of said fourth electrode.
9. The SAW filter of claim 8 , wherein:
said first portion and said second portion of said third electrode form an L-shape; and
said first portion and said second portion of said fourth electrode form an L-shape.
10. The SAW filter of claim 1 , wherein said third electrode and said fourth electrode have toothed portions facing each other, respectively.
11. A device comprising:
said SAW filter of claim 10 ; and
an element connected to said SAW filter.
12. A device comprising:
said SAW filter of claim 1 ; and
an element connected to said SAW filter.
13. The SAW filter of claim 1 , wherein said first inductance element comprises a wire connected to said piezoelectric board.
14. The SAW filter of claim 1 , wherein said second inductance element comprises a wire connected to said piezoelectric board.
15. The SAW filter of claim 1 , wherein said fourth electrode is parallel to said second edge of said second electrode.