Duplexer and method for increasing the isolation between two filters

Patent metadata

Field	Value
Publication number	US-9577606-B2
Application number	US-201414466885-A
Country	US
Kind code	B2
Filing date	Aug 22, 2014
Priority date	Sep 1, 2008
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

A duplexer includes an antenna terminal, a transmission amplifier terminal and a reception amplifier terminal. The transmission amplifier terminal is coupled to the antenna terminal via a transmission filter. The reception amplifier terminal is coupled to a reception filter and the reception filter is coupled to the antenna terminal via a band-stop filter.

First claim

What is claimed is:

1. A duplexer, comprising:
an antenna terminal;
a transmission amplifier terminal;
a reception amplifier terminal;
a transmission filter, wherein the transmission amplifier terminal is coupled to the antenna terminal via the transmission filter, wherein the transmission filter has a passband, and wherein the transmission filter comprises at least one resonator;
a reception filter coupled to the reception amplifier terminal;
a band-stop filter, wherein the reception filter is coupled to the antenna terminal via the band-stop filter, wherein the band-stop filter has a stop band in the passband of the transmission filter, and wherein the band-stop filter comprises at least one same resonator as the transmission filter;
at least one matching circuit, wherein upon reception of a reception signal
the transmission filter constitutes an open circuit from the point of view of the reception filter, and
reflections between the reception filter and the antenna terminal are minimized;

wherein upon transmission of a transmission signal
the reception filter constitutes an open circuit from the point of view of the transmission filter, and
reflections between the transmission filter and the antenna terminal are minimized; and

wherein an isolation between the transmission amplifier terminal and the reception amplifier terminal in a transmission frequency band is 50 dB or better.

2. The duplexer according to claim 1 , wherein the transmission filter and the band-stop filter comprise ladder structures having series resonators or parallel resonators.

3. The duplexer according to claim 2 , wherein the transmission filter has at least one parallel resonator and a plurality of series resonators and wherein at least one parallel resonator of the transmission filter has a resonant frequency that is lower than resonant frequencies of the series resonators of the transmission filter.

4. The duplexer according to claim 2 , wherein at least one series resonator of the band-stop filter is the same resonator as a parallel resonator of the transmission filter.

5. The duplexer according to claim 2 , wherein at least one parallel resonator of the band-stop filter is the same resonator as a series resonator of the transmission filter.

6. The duplexer according to claim 4 , wherein a resonant frequency of at least one parallel resonator of the band-stop filter differs from resonant frequencies of the remaining parallel resonators of the band-stop filter.

7. The duplexer according to claim 1 , wherein the resonators of the transmission filter and the resonators of the band-stop filter are BAW resonators and are arranged on the same substrate.

8. The duplexer according to claim 1 , wherein the resonators of the reception filter and the resonators of the band-stop filter are BAW resonators and are arranged on the same substrate.

9. The duplexer according to claim 1 , wherein the resonators of the transmission filter, the resonators of the reception filter and the resonators of the band-stop filter are BAW resonators and are arranged on the same substrate.

10. The duplexer according to claim 9 , wherein the reception filter comprises at least one SAW resonator.

11. The duplexer according to claim 1 , wherein
the resonators of the transmission filter and the resonators of the band-stop filter are SAW resonators and are arranged on the same substrate, and
wherein the SAW resonators of the reception filter, of the transmission filter and of the band-stop filter are constructed on a common substrate.

12. The duplexer according to claim 1 , wherein the at least one resonator of the transmission filter comprises a GBAW resonator.

13. The duplexer according to claim 1 , wherein at least one of the resonators of the band-stop filter has a first resonant frequency and a first static capacitance, and comprises at least a number N of resonators, wherein
the number N is greater than or equal to two,
the N resonators each have a static capacitance that is N times greater than the first static capacitance,
the N resonators are connected in series with one another, and
the resonant frequency deviates from the first resonant frequency by up to 3% at least in one of the N resonators.

14. The duplexer according to claim 1 , wherein at least one of the resonators of the band-stop filter has a first resonant frequency and a first static capacitance, and comprises at least a number N of resonators, wherein
the number N is greater than or equal to two,
the N resonators each have a static capacitance that is N times less than the first static capacitance,
the N resonators are connected in parallel with one another, and
the resonant frequency deviates from the first resonant frequency by up to 3% at least in one of the N resonators.

15. The duplexer according to claim 1 , wherein
the band-stop filter has a first terminal and a second terminal, wherein the first terminal is connected to the antenna terminal and the transmission filter and the second terminal is connected to the reception filter,
the matching circuit comprises a first inductance and a second inductance, wherein the first inductance connects the first terminal to ground and the second inductance connects the second terminal to ground.

16. The duplexer according to claim 15 , wherein the band-stop filter comprises a first series resonator that is connected to the first terminal.

17. The duplexer according to claim 16 , wherein the first series resonator has an antiresonance lying in the passband of the transmission filter or up to three percent below that in terms of frequency.

18. The duplexer according to claim 16 , wherein the band-stop filter further comprises at least one parallel resonator, wherein a first terminal of the at least one parallel resonator is connected to ground, and the other terminal of the at least one parallel resonator is connected to the second terminal and the first series resonator.

19. The duplexer according to claim 18 , wherein at least one of the first terminals of the at least one parallel resonator is connected to ground not directly but rather via an inductance, or a capacitance, or a combination of an inductance and a capacitance.

20. The duplexer according to claim 19 , wherein the first series resonator has an antiresonance in the region of the lower passband edge of the transmission filter and the parallel resonator has a resonant frequency lying in the region of the center of the passband of the transmission filter.

21. The duplexer according to claim 16 , wherein
the first series resonator is the same as a parallel resonator of the transmission filter, but has an additional mass coating that reduces the resonant frequency of the first series resonator relative to the resonant frequency of the parallel resonator, and
the parallel resonator connected to the second terminal is the same as a series resonator of the transmission filter.

22. The duplexer according to claim 16 , wherein the first series resonator has an antiresonance but has no resonance.

23. The duplexer according to claim 16 , wherein at least one parallel resonator has a resonance but has no antiresonance.

24. The duplexer according to claim 1 , wherein
the band-stop filter comprises a first terminal and a second terminal, and two series resonators connected in series via a connecting node, of which one series resonators is connected to the first terminal and the other series

Assignees

• Epcos Ag

Inventors

• Link Andreas
• Bader Bernhard

Classifications

• H03H7/38

  Impedance-matching networks · CPC title

• H01Q1/50

  Structural association of antennas with earthing switches, lead-in devices or lightning protectors · CPC title

• H03H9/6483

  Ladder SAW filters · CPC title

• H03H9/6409

  SAW notch filters · CPC title

• H03H9/547

  Notch filters, e.g. notch BAW or thin film resonator filters · CPC title