Saw resonator and filter comprising same
A SAW resonator comprises two reflectors and a transducer arranged between the reflectors. A resonant space between the transducer and a respective reflector is set large enough to enable occurrence of main resonance and at least one further resonance of comparable admittance. Thus, a multiple resonant resonator is achieved that can be used as a parallel resonator in a filter circuit with a DMS track for example to improve attenuation in a stop band.
1. A band pass filter, comprising:
a first series resonator, connected to an input of the band pass filter at an antenna side thereof;
a DMS track; and
a SAW resonator comprising two reflectors and a transducer arranged between the reflectors, wherein a resonant space between the transducer and one of the two reflectors enables an occurrence of a first resonance and at least a second resonance of a comparable admittance to the first resonance, wherein the SAW resonator is circuited as a parallel resonator in a parallel branch at an output of the DMS track, a mean finger period of the parallel resonator being chosen smaller than a mean finger period of the first series resonator and assigned to a frequency above a pass band of the DMS track.
2. The band pass filter of claim 1 , wherein:
a local finger period is chirped on at least one of the two reflectors, the transducer, or both such that a local minimum of the local finger period forms in each of two transition regions that are between the transducer and one of the two reflectors; and
the local finger period is defined at least in part by a number of outermost fingers on one or both of the transducer and at least one of the two reflectors.
3. The band pass filter of claim 2 , wherein the local finger period continuously decreases towards one of the two reflectors across one of the two transition regions till reaching a minimum value and then continuously increases.
4. The band pass filter of claim 2 , wherein the SAW resonator has a symmetric structure with a symmetry plane in a middle of the transducer, wherein two minima of the local finger period are situated at interfaces between each of the reflectors and the transducer.
5. The band pass filter of claim 2 , wherein the local finger period across each of the two reflectors has a maximum at a beginning of at least one of the two transition regions, has a slope towards an outer end that faces away from the transducer where the local finger period has a value below the maximum.
6. The band pass filter of claim 1 , wherein the band pass filter comprises a duplexer comprising a transmission filter and a reception filter.
7. The band pass filter of claim 6 , wherein the duplexer duplexes reception and transmission signals of a frequency band in a 1 GHz domain.
8. A SAW resonator, comprising two reflectors and a transducer arranged between the reflectors, wherein:
a resonant space between the transducer and one of the two reflectors enables an occurrence of a first resonance and at least a second resonance of a comparable admittance to the first resonance,
a local finger period is chirped on at least one of the two reflectors such that a local minimum of the local finger period forms in each of two transition regions that are between the transducer and the at least one of the two reflectors, and is defined at least in part by a number of outermost fingers on one or both of the transducer and the at least one of the two reflectors; and
the local finger period across each of the two reflectors has a maximum at a beginning of at least one of the two transition regions and has a slope towards an outer end that faces away from the transducer where the local finger period has a value below the maximum.
9. The SAW resonator of claim 8 , wherein:
the local finger period is defined by a distance between centers of two adjacent fingers and is chirped on the transducer and at least one of the two reflectors.
10. The SAW resonator of claim 8 , wherein the local finger period continuously decreases towards the at least one of the two reflectors across the transition region till reaching a minimum value and then continuously increases.
11. The SAW resonator of claim 8 , wherein the transition region comprises 10 to 40 fingers, the 10 to 40 fingers being chosen from reflector fingers and transducer fingers.
12. The SAW resonator of claim 8 , wherein a mean finger period (PRM) of at least one of the two reflectors is greater than a mean finger period (PTM) of the transducer and 1.05 PTM>PRM>1.00 PTM.
13. The SAW resonator of claim 8 , wherein the SAW resonator has a symmetric structure with a symmetry plane in a middle of the transducer, wherein two minima of the local finger period are situated at interfaces between each of the reflectors and the transducer.
14. The SAW resonator of claim 8 , wherein the transition region is one of two transition regions that are between the transducer and a respective reflector of the two reflectors, wherein at least one of the two transition regions comprises a first number of reflector fingers (NF1Ref) and a second number of transducer fingers (NF2IDT), wherein NF1Ref<NF2IDT and the local finger period of the transducer has a maximum in a middle of the transducer wherein a respective slope of the local finger period between at least one of the two transition regions and the middle of the transducer is lower than a slope in at least one of the two transition regions.
15. The SAW resonator of claim 8 , wherein the local finger period varies between a maximum (pmax) and a minimum (pmin) wherein 0.85 pmax≤pmin<pmax within the transition region.