Transducer structure that operates with acoustic waves
View Patent ↗For improved conformance of a filter operating with acoustic waves, a transducer structure is provided in which the separations between respectively two adjacent electrode fingers of an inter-digital transducer (IDT v ) vary over the length of the transducer. The variation thereby preferably follows a continuous distribution function. Reactance filters that are provided with such filters in the serial branch show an improved electrical conformance in the transmission range.
1. A reflector-based resonator structure operating with acoustic waves with one or more inter-digital transducers (IDT) arranged between reflectors (Ref), at least one IDT comprising:
two interlocking electrode combs having electrode fingers, the finger separations of the IDT, measured between finger centers of each two adjacent electrode fingers, varies over a length of the inter-digital transducer according to a continuous function and wherein a difference between the separations of adjacent electrode fingers amounts to a maximum of 5% viewed over the total length of the IDT.
2. The resonator structure according to claim 1 , wherein the variation of the finger separations corresponds to a function that, in proximity to a center, is symmetric around an axis perpendicular to a direction of wave propagation.
3. The resonator structure according to claim 1 , wherein a spreading of the finger separations over the length of the IDT is conformed to a linear function.
4. The resonator structure according to claim 1 , wherein a spreading of the finger separations over the length of the IDT is conformed to a parabolic function.
5. The resonator transducer structure according to claim 1 , wherein the difference amounts to a maximum of 2–3%.
6. The resonator structure according to claim 1 , wherein additionally widths of the electrode fingers vary over the length of the IDT, and their separation is conformed to a continuous function.
7. The resonator structure according to claim 1 , wherein the finger separations are spread over the length of the IDT such that the finger separations in the center of the transducer are the largest.
8. The resonator structure according to claim 1 , wherein the IDT is arranged in a reactance filter which comprises a serial and at least one parallel branch, in which respectively at least one resonator is arranged.
9. The resonator structure according to claim 8 , wherein the IDT is arranged in the serial branch of the reactance filter.
10. The resonator structure according to claim 9 , wherein electrode fingers of all resonators arranged in the serial branch exhibit at least one of varying finger separations and varying finger widths.
11. The resonator structure according to claim 1 , wherein the variation widths of the finger separations, with regards to an average finger separation, amount to +/−0.1% to 2.5%.
12. A reactance filter comprising a resonator structure according to claim 1 , the reactance filter having a large relative bandwidth delta f rel , in that 2%<delta f rel <5% is valid.
13. A filter on a lithium tantalate (LT) substrate or on a substrate having a poorer electro-acoustic coupling than LT comprising a resonator structure according to claim 1 .
14. The resonator structure according to claim 1 , wherein the variance according to a continuous function ensues over an entire length of the IDT.
15. The resonator structure according to claim 14 , wherein the distance between any two adjacent pairs of fingers of the IDT is not equal.