Acoustic wave branching filter having transmitting filter with optimal power handling
View Patent ↗A surface acoustic wave filter includes an antenna terminal, a transmitting filter and a variable branching line both of which are coupled to the antenna terminal and a receiving filter coupled to the variable branching line. The transmitting filter has a first end series-arm SAW resonator, a second end series-arm SAW resonator, a middle series-arm SAW resonator coupled between the first and second end series-arm SAW resonators and parallel-arm SAW resonators. Each of the first and second end series-arm SAW resonator has a first resonance frequency. The middle series-arm SAW resonator has a second resonance frequency that is higher than the first resonance frequency.
1. A surface acoustic wave filter comprising:
an antenna terminal;
a transmitting filter coupled to the antenna terminal, the transmitting filter including,
a first end series-arm SAW resonator having a first resistance value,
a middle series-arm SAW resonator coupled to the first end series-arm SAW resonator, wherein the middle series-arm SAW resonator has a second resistance value that is higher than the first resistance value,
a second end series-arm SAW resonator coupled to the middle series-arm SAW resonator,
a first parallel-arm SAW resonator coupled to the first end series-arm SAW resonator and the middle series-arm SAW resonator,
a second parallel-arm SAW resonator coupled to the second end series-arm SAW resonator and the middle series-arm SAW resonator, the second parallel-arm SAW resonator being coupled to the first parallel-arm SAW resonator through a common node, wherein the common node is coupled to a ground potential; and
a receiving filter coupled to the ground potential.
2. A surface acoustic wave filter as claimed in claim 1 , further comprising a power amplifier coupled to apply the electrical power to the transmitting filter.
3. A surface acoustic wave filter as claimed in claim 1 , further comprising a low noise amplifier coupled to the receiving filter.
4. A surface acoustic wave filter as claimed in claim 1 , wherein the receiving filter has a plurality of resonators.
5. A surface acoustic wave filter as claimed in claim 4 , wherein the receiving filter is a π-type filter.
6. A surface acoustic wave filter as claimed in claim 1 , wherein each of the transverse length of the electrodes of the series-arm resonators is different from that of the parallel-arm resonators.
7. A surface acoustic wave filter as claimed in claim 1 , wherein a number of pairs of the electrodes of each of the series-arm resonators is different from that of the parallel-arm resonators.
8. A surface acoustic wave filter comprising:
an antenna terminal;
a transmitting filter coupled to the antenna terminal, the transmitting filter including,
a first end series-arm SAW resonator having a first resistance value,
a middle series-arm SAW resonator coupled to the first end series-arm SAW resonator, the middle series-arm SAW resonator having a second resistance value that is higher than the first resistance value,
a second end series-arm SAW resonator coupled to the middle series-arm SAW resonator, and
a plurality of parallel-arm SAW resonators coupled to the middle series-arm SAW resonator, the parallel-arm SAW resonators being coupled in common with each other through a common node, wherein the common node is coupled to a ground potential; and
a receiving filter coupled to the ground potential.
9. A surface acoustic wave filter as claimed in claim 8 , wherein the receiving filter has a plurality of resonators.
10. A surface acoustic wave filter as claimed in claim 9 , wherein the receiving filter is a π-type filter.
11. A surface acoustic wave filter as claimed in claim 8 , wherein a distance between the electrodes of the first and second end series-arm resonators is different from that of the middle series-arm resonator.