Band rejection filter comprising a serial connection of at least two pi-elements
The invention relates to a band rejection filter comprising a piezoelectric substrate and a serial connection of at least two pi-elements which are arranged on the substrate. The pi-elements respectively comprise at least two electro-acoustic parallel resonators and at least one electro-acoustic serial resonator, and are connected by a first series inductance. Said serial connection comprises, on a first inlet, a second series inductance and on an outlet, a third series inductance. Said resonators have a pole-zero plot of approximately 9% or more.
1. A band rejection filter comprising: a piezoelectric substrate; and a serial connection of at least two pi-elements which are arranged on the substrate and which each comprise at least two electro-acoustic parallel resonators and at least one electro-acoustic series resonator, wherein the pi-elements are connected by a first series inductance, the serial connection has a second series inductance at an input and a third series inductance at an output, and each of the resonators have a pole-zero spacing of 9%, or more.
2. The band rejection filter according to claim 1 , which has a bandwidth of more than 40% in the passband.
3. The band rejection filter according to claim 1 , wherein the resonators are SAW resonators.
4. The band rejection filter according to claim 1 , wherein the substrate comprises LiNbO3 YX with a cut angle of between 45° and 0°.
5. The band rejection filter according to claim 1 , wherein the substrate comprises LiNbO3 with 41XY cut.
6. The band rejection filter according to claim 3 , wherein a dielectric layer for passivation is applied to the SAW structures.
7. The band rejection filter according to claim 1 , further comprising a housing, in which the substrate with pi-elements arranged thereon is integrated.
8. The band rejection filter according to claim 7 , wherein the housing is a 10-pin housing.
9. The band rejection filter according to claim 7 , wherein the housing is a 5-pin housing.
10. The band rejection filter according to claim 1 , wherein the stop band of the band rejection filter has in total a relative bandwidth of more than 10%.
11. The band rejection filter according to claim 1 , wherein the parallel resonators are embodied as SAW resonators without reflectors.
12. The band rejection filter according to claim 1 , wherein the series resonators are embodied as SAW resonators without reflectors.
13. The band rejection filter according to claim 1 , wherein the resonators are at least partly cascaded.
14. The band rejection filter according to claim 1 , wherein the distances between adjacent electrode fingers of at least one parallel resonator embodied as a SAW resonator vary over the length of the resonator.
15. The band rejection filter according to claim 1 , wherein the series resonator of the first pi-element is offset in a transverse direction relative to the series resonator of the second pi-element.
16. The band rejection filter according to claim 1 , wherein the parallel resonators of the first pi-element are offset in a transverse direction relative to the parallel resonators of the second pi-element.
17. The band rejection filter according to claim 1 , wherein the resonant frequencies of the parallel resonators are higher than the resonant frequencies of the series resonators.
18. The use of a band rejection filter according to claim 1 in a communication terminal for mobile radio, which is further designed for reception in a frequency band that transmits video and/or audio data.