Integrated receive filter including matched balun

Patent metadata

Field	Value
Publication number	US-9306535-B2
Application number	US-201313780812-A
Country	US
Kind code	B2
Filing date	Feb 28, 2013
Priority date	Feb 28, 2013
Publication date	Apr 5, 2016
Grant date	Apr 5, 2016

Abstract

A duplexer includes a transmit filter and an integrated receive filter configured to filter a receive signal from an antenna. The integrated receive filter includes a receive filter portion having multiple acoustic resonator filter elements and a matched balun configured to convert a single-ended input signal, received at a single-ended input of the matched balun from a single-ended output of the receive filter portion, to a differential output signal. The matched balun being is located in place of a phase matching inductor of the receive filter portion, eliminating need for the phase matching inductor of the receive filter portion and a phase matching inductor of the matched balun. Impedance at the single-ended input of the matched balun includes a complex conjugate of impedance at the single-ended output of the receive filter portion.

First claim

The invention claimed is:

1. A duplexer comprising:
a transmit filter configured to filter a transmit signal from a transceiver; and
an integrated receive filter configured to filter a receive signal from an antenna, the integrated receive filter comprising:
a receive filter portion comprising a plurality of acoustic resonator filter elements to provide a filtered signal at a single-ended output; and
a matched balun coupled to the single-ended output of the receive filter portion and configured to convert the filtered signal at the single-ended output of the receive filter portion to a differential output signal,
wherein the matched balun is further configured to match the single-ended output using an input impedance comprising a complex conjugate of an output impedance of the single-ended output of the receive filter portion, and
wherein the input impedance of the matched balun matches the output impedance of the single-ended output of the receive filter portion without a phase matching inductor in either the matched balun or the receive filter portion.

2. The duplexer of claim 1 , wherein the matched balun consists of three LC elements.

3. The duplexer of claim 1 , wherein the matched balun comprises:
a first capacitor connected in series between a single-ended input and a first differential output of the matched balun for outputting a first portion of the differential output signal;
an inductor connected in series between the single-ended input and a second differential output of the matched balun for outputting a second portion of the differential output signal; and
a second capacitor connected between the second differential output and ground.

4. The duplexer of claim 1 , wherein the matched balun comprises:
a first capacitor connected in series between a single-ended input and a first differential output of the matched balun for outputting a first portion of the differential output signal;
a first inductor connected in series with the single-ended input;
a second inductor connected in series between the first inductor and a second differential output of the matched balun for outputting a second portion of the differential output signal; and
a second capacitor connected between the first and second inductors and ground.

5. The duplexer of claim 3 , wherein a first capacitance value of the first capacitor is approximately half a second capacitance value of the second capacitor.

6. The duplexer of claim 1 , wherein the receive filter portion comprises a ladder type filter and the plurality of acoustic resonator filter elements comprises series and shunt connected acoustic resonators.

7. The duplexer of claim 6 , wherein the acoustic resonator elements comprise film bulk acoustic resonators (FBARs).

8. The duplexer of claim 1 , wherein the receive signal comprises a radio frequency (RF) signal.

9. The duplexer of claim 1 , wherein an inductance of the matched balun is about 3 nH of a total inductance of the integrated receive filter when the receive signal is has a frequency of approximately 2 GHz for a 50 ohm system.

10. The duplexer of claim 9 , wherein the inductance of the matched balun varies inversely with frequency of the received signal.

11. A balun coupled to a single-ended output of a receive filter, the balun being configured to convert a filtered signal from the receive filter to a differential output signal, the balun comprising:
a single-ended input configured to receive the filtered signal provided at the single-ended output of the receive filter;
a first path comprising one first capacitor connected in series between the single-ended input and a first differential output terminal for outputting a first portion of the differential output signal; and
a second path comprising an inductor, connected in series between the single-ended input and a second differential output terminal for outputting a second portion of the differential output signal, and one second capacitor, which is connected between the second differential output terminal and ground,
wherein input impedance of the balun matches output impedance of the single-ended output of the receive filter without a phase matching inductor in either the balun or the receive filter.

12. The balun of claim 11 , wherein the first path is configured to provide amplitude balance between the first and second portions of the differential output signal at the first and second differential output terminals.

13. The balun of claim 12 , wherein the second path is configured to provide a phase delay so that the first and second portions of the differential output signal are about 180 degrees out of phase.

14. The balun of claim 11 , wherein the input impedance of the balun comprises a complex conjugate of the output impedance of the receive filter.

15. The balun of claim 14 , wherein differential impedance at the first and second differential output terminals is about 100 ohms.

16. A balun coupled to a single-ended output of a receive filter, the balun being configured to convert a filtered signal from the receive filter to a differential output signal, the balun comprising:
a single-ended input configured to receive the filtered signal provided at the single-ended output of the receive filter;
a first path comprising a first capacitor connected in series between the single-ended input and a first differential output terminal for outputting a first portion of the differential output signal; and
a second path comprising a first inductor and a second inductor, connected in series between the single-ended input and a second differential output terminal for outputting a second portion of the differential output signal, and a second capacitor, connected between the first and second inductors and ground,
wherein input impedance of the balun matches output impedance of the signal-ended output of the receive filter without a phase matching inductor in either the balun or the receive filter.

17. The balun of claim 16 , wherein the first path is configured to provide amplitude balance between the first and second portions of the differential output signal at the first and second differential output terminals.

18. The balun of claim 17 , wherein the second path is configured to provide a phase delay so that the first and second portions of the differential output signal are about 180 degrees out of phase.

19. The balun of claim 16 , wherein the impedance at the single-ended input of the balun comprises a complex conjugate of the impedance at the single-ended output of the receive filter.

20. The balun of claim 19 , wherein a differential impedance at the first and second differential output terminals is about 100 ohms.

Assignees

• Avago Technologies General Ip

Inventors

• Bradley Paul
• Ye Shen
• Kim Jeesu

Classifications

• H03H7/42 Primary

  Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns · CPC title

• H03H9/706

  Duplexers · CPC title

• H03H7/38

  Impedance-matching networks · CPC title

• H03H7/463

  Duplexers · CPC title

• H03H9/725

  Duplexers · CPC title