Multiplexer with filter having increased reflection characteristic

1. A multiplexer for filtering radio frequency signals, the multiplexer comprising:

a first filter having a first passband that is a lowest passband of all filters of the multiplexer, the first filter including a series inductor and a plurality of acoustic resonators coupled to a common node by way of the series inductor, the plurality of acoustic resonators starting with a first shunt acoustic resonator from the common node, and each ladder stage of the first filter including a shunt acoustic resonator of the plurality of acoustic resonators, the first filter coupled to the common node without an intervening switch;

a second filter coupled to the common node and having a second passband that is above the first passband, the series inductor and the first shunt acoustic resonator of the first filter together arranged to increase a reflection coefficient of the first filter in the second passband; and

a third filter coupled to the common node via a switch, the first, second, and third filters being included in the multiplexer, the third filter having a third passband that is a highest passband of all filters of the multiplexer.

2. The multiplexer of claim 1 wherein series inductor and the first shunt acoustic resonator are together arranged to increase the reflection coefficient of the first filter in the third passband.

3. The multiplexer of claim 1 wherein the plurality of acoustic resonators includes a first ladder stage from the common node, and the first ladder stage starts with the first shunt acoustic resonator.

4. The multiplexer of claim 1 wherein all filters of the multiplexer are arranged as receive filters.

5. The multiplexer of claim 1 wherein the first filter is a transmit filter.

6. The multiplexer of claim 5 wherein the second filter is a second transmit filter.

7. The multiplexer of claim 1 wherein the second filter includes a front end series resonator and all other acoustic resonators of the second filter are coupled to the common node via the front end series resonator.

8. The multiplexer of claim 1 wherein the series inductor is a surface mount inductor.

9. The multiplexer of claim 1 wherein the plurality of acoustic resonators includes a surface acoustic wave resonator.

10. The multiplexer of claim 1 wherein the plurality of acoustic resonators includes a temperature compensated surface acoustic wave resonator.

11. The multiplexer of claim 1 wherein the plurality of acoustic resonators includes a bulk acoustic wave resonator.

12. A radio frequency module comprising:

a multiplexer including a first filter having a first passband that is a lowest passband of all filters of the multiplexer, a second filter having a second passband, and a third filter having a third pass band that is a highest of all filters of the multiplexer, the first filter including a series inductor and a plurality of acoustic resonators coupled to a common node by way of the series inductor, the first filter coupled to the common node without an intervening switch and the third filter coupled to the common node via a switch, the plurality of acoustic resonators starting with a first shunt acoustic resonator from the common node, the series inductor and the first shunt acoustic resonator of the first filter together arranged to increase a reflection coefficient of the first filter in the second passband, and each ladder stage of the first filter including a shunt acoustic resonator of the plurality of acoustic resonators; and

a radio frequency circuit element coupled to the multiplexer, the multiplexer and the radio frequency circuit element being enclosed within a common package.

13. The radio frequency module of claim 12 wherein the radio frequency circuit element is a radio frequency amplifier arranged to amplify a radio frequency signal.

14. The radio frequency module of claim 12 wherein the radio frequency circuit element is a switch configured to selectively couple the multiplexer to an antenna port of the radio frequency module.

15. The radio frequency module of claim 12 further comprising a multi-throw radio frequency switch.

16. The radio frequency module of claim 12 wherein the plurality of acoustic resonators includes a first ladder stage from the common node, and the first ladder stage starts with the first shunt acoustic resonator.

17. A wireless communication device comprising:

a multiplexer including a first filter having a first passband that is a lowest passband of all filters of the multiplexer, a second filter having a second passband, and a third filter having a third pass band that is a highest of all filters of the multiplexer, the first filter including a series inductor and a plurality of acoustic resonators coupled to a common node by way of the series inductor, the first filter coupled to the common node without an intervening switch and the third filter coupled to the common node via a switch, the plurality of acoustic resonators starting with a first shunt acoustic resonator from the common node, the series inductor and the first shunt acoustic resonator of the first filter together arranged to increase a reflection coefficient of the first filter in the second passband, and each ladder stage of the first filter including a shunt acoustic resonator of the plurality of acoustic resonators;

an antenna operatively coupled to the common node;

a radio frequency amplifier operatively coupled to the multiplexer and configured to amplify a radio frequency signal; and

a transceiver in communication with the radio frequency amplifier.

18. The wireless communication device of claim 17 wherein the plurality of acoustic resonators includes a first ladder stage from the common node, and the first ladder stage starts with the first shunt acoustic resonator.