System and method for a radio frequency filter

Patent metadata

Field	Value
Publication number	US-9941908-B2
Application number	US-201514874256-A
Country	US
Kind code	B2
Filing date	Oct 2, 2015
Priority date	Oct 20, 2014
Publication date	Apr 10, 2018
Grant date	Apr 10, 2018

Abstract

In accordance with an embodiment, a circuit includes a plurality of filter circuits having a first port, a second port and a third port, where a second port of a first of the plurality of filter circuits is coupled to a first port of a second of the plurality of filter circuits, and each of the plurality of filter circuits includes a first passive filter, a second passive filter, a first coupler and a combining network. The first coupler includes an input port coupled to the first port, an isolated port coupled to the second port, a first phase shifted port coupled to the first passive filter and a second phase shifted port coupled to the second passive filter, and the combining network includes a first input coupled to the first passive filter, a second input coupled to the second passive filter, and an output coupled to the third port.

First claim

What is claimed is:

1. A circuit comprising:
a plurality of filter circuits, each comprising a first port, a second port and a third port, wherein a second port of a first of the plurality of filter circuits is coupled to a first port of a second of the plurality of filter circuits, wherein each of the plurality of filter circuits comprises:
a first passive filter;
a second passive filter;
a first coupler having an input port coupled to the first port, an isolated port coupled to the second port, a first phase shifted port coupled to the first passive filter and a second phase shifted port coupled to the second passive filter; and
a combining network having a first input coupled to the first passive filter, a second input coupled to the second passive filter, and an output coupled to the third port, wherein at least one of the plurality of filter circuits is configured to
pass a first frequency band from the third port to the first port using a bandpass transfer function; and
pass a second frequency band and a third frequency band from the first port to the second port, and filter the first frequency band from the first port to the second port, wherein the second frequency band is lower than the first frequency band and the third frequency band is higher than the first frequency band.

2. The circuit of claim 1 , wherein the first coupler comprises a first −3 dB hybrid with quadrature output.

3. The circuit of claim 2 , wherein the combining network comprises a second −3 dB hybrid with quadrature output and an isolation port.

4. The circuit of claim 2 , wherein the combining network comprises:
a power splitter;
a first phase shifter coupled between the first passive filter and the power splitter; and
a second phase shifter coupled between the second passive filter and the power splitter.

5. The circuit of claim 1 , wherein the first passive filter and the second passive filter are tunable filters.

6. The circuit of claim 1 , wherein a second port of the second of the plurality of filter circuits is coupled to a first port of a third of the plurality of filter circuits.

7. A circuit comprising:
a first filter circuit having a first port, a second port and a third port, the first filter circuit comprising
a first passive filter,
a second passive filter,
a first coupler having an input port coupled to the first port, an isolated port coupled to the second port, a first phase shifted port coupled to the first passive filter and a second phase shifted port coupled to the second passive filter, wherein the first coupler comprises a −3 dB hybrid with quadrature output, and
a first combining network having a first input coupled to the first passive filter, a second input coupled to the second passive filter, and an output coupled to the third port, wherein the first combining network comprises a power splitter, a first phase shifter coupled between the first passive filter and the power splitter, and a second phase shifter coupled between the second passive filter and the power splitter, wherein the first filter circuit is configured to
pass a first frequency band from the third port to the first port using a bandpass transfer function, and
pass a second frequency band and a third frequency band from the first Port to the second port, and filter the first frequency band from the first port to the second port, wherein the second frequency band is lower than the first frequency band and the third frequency band is higher than the first frequency band; and

an amplifier coupled to the third port.

8. The circuit of claim 7 , wherein the first frequency band comprises a frequency range between about 2110 MHz and about 2170 MHz.

9. The circuit of claim 8 , further comprising a diplexer coupled to the second port, wherein the diplexer is configured to divide the second frequency band from the third frequency band.

10. The circuit of claim 9 , wherein the diplexer comprises a transfer function that has a shallower crossover response than the first filter circuit.

11. The circuit of claim 7 , wherein the amplifier comprises a power amplifier having an output coupled to the third port.

12. The circuit of claim 11 , wherein the first port is coupled to an antenna.

13. The circuit of claim 7 , wherein the first passive filter and the second passive filter are tunable filters.

14. The circuit of claim 7 , wherein the amplifier comprises a low noise amplifier (LNA) having an input coupled to the third port.

15. The circuit of claim 7 , wherein:
the first filter circuit is configured to filter the first frequency band from the first port to the second port by rejecting the first frequency band from the first port to the second port; and
the amplifier comprises a first LNA comprising an input coupled to the third port.

16. The circuit of claim 15 , further comprising:
a first frequency splitting circuit coupled to the first port of the first filter circuit, the first frequency splitting circuit configured to split the third frequency band from the second frequency band;
a second LNA having an input coupled to a second frequency band output of the first frequency splitting circuit; and
a third LNA having an input coupled to a third frequency band output of the first frequency splitting circuit.

17. The circuit of claim 16 , further comprising a frequency combining circuit having a first input coupled to an output of the second LNA, and a second input coupled to an output of the third LNA.

18. The circuit of claim 17 , further comprising a second filter circuit having a first port configured to provide a combine frequency output, a second port coupled to an output of the frequency combining circuit, and a third port coupled to an output of the first LNA, the second filter circuit comprising
a third passive filter,
a fourth passive filter,
a second coupler having an input port coupled to the first port, an isolated port coupled to the second port, a first phase shifted port coupled to the third passive filter and a second phase shifted port coupled to the fourth passive filter, wherein the first coupler comprises a −3 dB hybrid with quadrature output, and
a second combining network having a first input coupled to the third passive filter, a second input coupled to the fourth passive filter, and an output coupled to the third port, wherein the second filter circuit is configured to pass a first frequency band from the first port to the third port using the bandpass transfer function, and is configured to pass the second frequency band and the third frequency band from the first port to the second port, and reject the first frequency band from the first port to the second port.

19. The circuit of claim 18 , wherein the first passive filter, the second passive filter, the third passive filter and the fourth passive filter comprise tunable filters.

20. The circuit of claim 19 , wherein the first frequency splitting circuit and the frequency combining circuit are tunable.

21. The circuit of claim 18 , wherein:
the first combining network comprises a first power splitter, a first phase shifter coupled between the first passive filter and the first power splitter, and a second phase shifter coupled between the second passive filter and the first power splitter; and
the second combining network comprises a second power splitter, a third phase shifter coupled between the third passive filter and the second power splitter, and a fourth phase shifter coupled between the fourth passive filter and t

Assignees

• Infineon Technologies Ag

Inventors

• Bauder Ruediger

Classifications

• H04B1/0057 Primary

  using diplexing or multiplexing filters for selecting the desired band · CPC title

• H04B1/38

  Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving · CPC title

• H03H7/463 Primary

  Duplexers · CPC title

• H04B1/0017 Primary

  Digital filtering (H04B1/001 takes precedence; digital filters per se H03H17/00) · CPC title

• H04B1/525

  with means for reducing leakage of transmitter signal into the receiver · CPC title