Saw architecture with series connected interdigitated transducers
The present invention provides a surface acoustic wave (SAW) architecture wherein two acoustic reflectors are formed on a piezoelectric substrate to define an acoustic cavity between the acoustic reflectors. At least one alpha interdigitated transducer (IDT) may be provided, and at least three beta IDTs are provided. These IDTs are placed in acoustic series within the acoustic cavity. The alpha IDT is electrically coupled to a first interface. The beta IDTs are coupled in electrical and acoustic series and are associated with a second interface. In certain embodiments, the at least three beta IDTs are adjacent one another, while in other embodiments an additional reflector or an alpha IDT may be placed between two beta IDTs.
1. A surface acoustic wave device comprising:
a piezoelectric substrate;
two acoustic reflectors formed on the piezoelectric substrate and defining an acoustic cavity between the acoustic reflectors;
at least one alpha interdigitated transducer (IDT) formed on the piezoelectric substrate between the acoustic reflectors and electrically coupled to a first interface;
at least three beta IDTs formed on the piezoelectric substrate between the acoustic reflectors and electrically coupled to a second interface; and
each of the at least three beta IDTs coupled in electrical series with each other and aligned in acoustic series with each other and with the at least one alpha IDT within the acoustic cavity.
2. The surface acoustic wave device of claim 1 wherein the at least one alpha IDT comprises at least two alpha IDTs coupled in electrical parallel with each other and aligned in acoustic series with each other.
3. The surface acoustic wave device of claim 1 wherein adjacent edge portions of at least two of the at least three beta IDTs are chirped.
4. The surface acoustic wave device of claim 3 wherein center portions of the at least two of the at least three beta IDTs are not chirped.
5. The surface acoustic wave device of claim 4 wherein adjacent edges of the at least one alpha IDT and at least one of the at least three beta IDTs are chirped.
6. The surface acoustic wave device of claim 1 wherein the at least three beta IDTs are adjacent each other and comprise at least one inner beta IDT between two outer beta IDTs, a center portion of the at least one inner beta IDT being chirped.
7. The surface acoustic wave device of claim 6 wherein edge portions of the at least one inner beta IDT are not chirped.
8. The surface acoustic wave device of claim 6 wherein center portions of the at least two outer beta IDTs are not chirped.
9. The surface acoustic wave device of claim 8 wherein adjacent edges of the at least one alpha IDT and at least one of the at least three beta IDTs are chirped.
10. The surface acoustic wave device of claim 1 further comprising an additional acoustic reflector located in acoustic series with and between two of the at least three beta IDTs.
11. The surface acoustic wave device of claim 1 wherein the at least one alpha IDT is located in acoustic series with and between two of the at least three beta IDTs.
12. The surface acoustic wave device of claim 1 wherein the first interface is associated with a first electrical impedance and the second interface is associated with a second electrical impedance, such that an electrical impedance transformation is provided between the first interface and the second interface.
13. The surface acoustic wave device of claim 1 wherein the at least one alpha IDT and the at least three beta IDTs cooperate to provide a filter response between the first interface and the second interface.
14. The surface acoustic wave device of claim 1 wherein the first interface is an input and the second interface is an output.
15. The surface acoustic wave device of claim 1 wherein the first interface is an output and the second interface is an input.