Multiplexer, radio frequency front-end circuit, communication device, and multiplexer design method

Patent metadata

Field	Value
Publication number	US-9979379-B2
Application number	US-201715647514-A
Country	US
Kind code	B2
Filing date	Jul 12, 2017
Priority date	Jul 13, 2016
Publication date	May 22, 2018
Grant date	May 22, 2018

Abstract

A multiplexer includes a n number (n is an integer equal to three or more) of filters that are individually provided in the n number of paths commonly connected at a common junction point, and that have different pass bands from one another. In the multiplexer, (n−1) filters among the n number of filters except for the first filter have impedances of which imaginary components cancel each other at a pass band frequency of the first filter when viewed from the common junction point in a state of the n number of paths being not commonly connected.

First claim

What is claimed is:

1. A multiplexer comprising:
n number of filters that are individually provided in n number of paths commonly connected at a common junction point, and that have different pass bands from one another;

wherein
n is an integer equal to three or more;
(n−1) filters among the n number of filters except for a first filter have impedances of which imaginary components cancel each other at a pass band frequency of the first filter when viewed from the common junction point in a state of the n number of paths being not commonly connected;
each of the n number of filters is an acoustic wave filter includes an acoustic wave resonator; and
the pass band frequency of the first filter is different from a frequency range sandwiched between a resonant frequency and an antiresonant frequency of the acoustic wave resonator of each of the (n−1) number of filters.

2. The multiplexer according to claim 1 , wherein the impedances of the (n−1) number of filters are in a complex conjugate relationship at the pass band frequency of the first filter when viewed from the common junction point in the state of the n number of paths being not commonly connected.

3. The multiplexer according to claim 1 , wherein at least two among the n number of filters except for the first filter have impedances of which imaginary components cancel each other at the pass band frequency of the first filter when viewed from the common junction point in the state of the n number of paths being not commonly connected.

4. The multiplexer according to claim 3 , wherein the impedances of the at least two filters are in a complex conjugate relationship at the pass band frequency of the first filter when viewed from the common junction point in the state of the n number of paths being not commonly connected.

5. The multiplexer according to claim 1 , wherein the (n−1) filters have impedances of which imaginary components cancel each other at the pass band frequency of the first filter on an open side, which is a region on a right side of a center of a Smith chart, when viewed from the common junction point in the state of the n number of paths being not commonly connected.

6. The multiplexer according to claim 3 , wherein the at least two filters have impedances of which imaginary components cancel each other at the pass band frequency of the first filter on an open side, which is a region on a right side of a center of a Smith chart, when viewed from the common junction point in the state of the n number of paths being not commonly connected.

7. The multiplexer according to claim 1 , wherein regarding (n−1) filters among the n number of filters except for a second filter, absolute values of the impedances at a pass band frequency of the second filter are not less than about 500Ω when viewed from the common junction point in the state of the n number of paths being not commonly connected.

8. The multiplexer according to claim 1 , wherein (n−1) filters among the n number of filters except for a third filter have impedances of which imaginary components cancel each other at a pass band frequency of the third filter when viewed from the common junction point in the state of the n number of paths being not commonly connected.

9. The multiplexer according to claim 8 , wherein the impedances of (n−1) filters among the n number of filters except for the third filter are in a complex conjugate relationship at the pass band frequency of the third filter when viewed from the common junction point in the state of the n number of paths being not commonly connected.

10. The multiplexer according to claim 1 , wherein
n=3 is satisfied;
the n number of filters include a first filter having a first frequency band as a pass band, a second filter having a second frequency band as a pass band, and a third filter having a third frequency band as a pass band; and
the second filter and the third filter have impedances of which imaginary components cancel each other in the first frequency band when viewed from the common junction point in the state of the n number of paths being not commonly connected.

11. The multiplexer according to claim 10 , wherein an impedance of the first filter in the second frequency band and an impedance of the third filter in the second frequency band have absolute values of not less than about 500Ω when viewing a side including the n number of filters from the common junction point in the state of the n number of paths being not commonly connected.

12. The multiplexer according to claim 10 , wherein the impedance of the second filter in the first frequency band and the impedance of the third filter in the first frequency band are in a complex conjugate relationship when viewing a side including the n number of filters from the common junction point in the state of the n number of paths being not commonly connected.

13. The multiplexer according to claim 10 , wherein the first filter and the second filter have impedances of which imaginary components cancel each other in the third frequency band when viewed from the common junction point in the state of the n number of paths being not commonly connected.

14. The multiplexer according to claim 13 , wherein the impedance of the first filter in the third frequency band and the impedance of the second filter in the third frequency band are in a complex conjugate relationship when viewing the side including the n number of filters from the common junction point in the state of the n number of paths being not commonly connected.

15. The multiplexer according to claim 1 , wherein when the pass bands of the n number of filters are arrayed in order of pass band frequency, the pass band frequency of the first filter corresponds to a band other than the pass bands that are positioned at a lowest frequency level and a highest frequency level.

16. The multiplexer according to claim 1 , further comprising a phase adjustment circuit that is disposed between the common junction point and at least one among then number of filters.

17. The multiplexer according to claim 16 , wherein the phase adjustment circuit includes a microstripline connected in series in at least one of the paths in which the at least one filter is disposed.

18. The multiplexer according to claim 16 , wherein
the at least one filter is a band rejection filter; and
the phase adjustment circuit includes an inductor connected between the common junction point and the band rejection filter in series in the path in which the band rejection filter is disposed.

19. The multiplexer according to claim 18 , wherein the n number of filters include at least two bandpass filters having pass band frequencies that fall within an attenuation band frequency range of the band rejection filter.

20. The multiplexer according to claim 18 , wherein
the acoustic wave resonator of the band rejection filter includes one or more acoustic wave resonators; and
one of the one or more acoustic wave resonators of the band rejection filter closest to the common junction point is a parallel resonator that is connected in series in a path interconnecting the path in which the band rejection filter is disposed and a ground.

21. The multiplexer according to claim 16 , wherein the phase adjustment circuit is an LC matching circuit including one or more inductors and one or more capacitors.

22. The multiplexer according to claim 16 , wherein the phase adjustment circuit includes a capacitor connected in series in at least one of

Assignees

• Murata Manufacturing Co

Inventors

• Yasuda Junpei
• Takeuchi Morio

Classifications

• H01P1/213

  combining or separating two or more different frequencies (H01P1/215 takes precedence) · CPC title

• H03H9/72 Primary

  Networks using surface acoustic waves · CPC title

• H01P5/12 Primary

  Coupling devices having more than two ports (H01P5/04 takes precedence) · CPC title

• H03H9/725

  Duplexers · CPC title