Circuit and method for interference reduction

• US 8,626,090 B2
• Filed: 03/23/2010
• Issued: 01/07/2014
• Est. Priority Date: 03/23/2010
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Dalipi, Spendim
• Primary Examiner(s): Hannon, Christian
• Application Number:
  US13/634,253
• Publication Number:
  US 20130005284A1
• Time in Patent Office: 1,386 Days
• Field of Search: 4551142-1143, 455/91, 375/296, 375/297
• US Class Current: 455/114.3
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/045 with means for improving efficiency
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing

Abstract

A radio frequency transmitter comprises an amplifier, an antenna port, an isolator adapted to isolate an output of the amplifier from an interfering signal of the antenna port, a linearization loop and a transmission line comprising a first part (coupling a signal source to an input of the amplifier), a second part (coupling the output of the amplifier to an input of the isolator) and a third part (coupling an output of the isolator to the antenna port). The linearization loop is adapted to reduce non-linearity of the isolator and comprises a first directional coupler coupled to the third part of the transmission line, a loop impedance, and at least one further linearization loop element adapted to adjust a linearization signal and to feed the adjusted linearization signal to the transmission line. The radio frequency transmitter also comprises an interference reducing circuit adapted to reduce an influence of the interfering signal on the linearization loop. The circuit comprises a variable gain and phase shifter, and second and third directional couplers. The variable gain and phase shifter is coupled to the third part of the transmission line via the second directional coupler, which extracts a compensation signal from the transmission line, and is adapted to adjust amplitude and phase of the compensation signal based on the amplitude and phase of the interfering signal passing through the loop impedance. The third directional coupler couples the variable gain and phase shifter to the loop feed line and feeds the adjusted compensation signal thereto.

Claims

1. An interference reducing circuit for a radio frequency transmitter, wherein the radio frequency transmitter comprises:

an amplifier;

an antenna port;

an isolator configured to isolate an output of the amplifier from an interfering signal of the antenna port;

a transmission line comprising a first part, a second part and a third part, the first part comprising a first end connectable to a signal source and a second end coupled to an input of the amplifier, the second part comprising a third end coupled to the output of the amplifier and a fourth end coupled to an input of the isolator, the third part comprising a fifth end coupled to an output of the isolator and a sixth end coupled to the antenna port; and

a linearization loop configured to reduce a non-linearity of the isolator, the linearization loop comprising;

a first directional coupler coupled to the third part of the transmission line;

a loop impedance coupled at a first port to the first directional coupler; and

at least one further linearization loop element coupled to a second port of the loop impedance via a loop feed line and configured to adjust a linearization signal and to feed the adjusted linearization signal to the transmission line; and

wherein the interference reducing circuit is configured to reduce an influence of the interfering signal of the antenna port on the linearization loop and comprises;

a second directional coupler configured to extract a compensation signal from the third part of the transmission line;

a variable gain and phase shifter coupled at a first port to the third part of the transmission line via the second directional coupler and configured to;

adjust an amplitude of the compensation signal to match an amplitude of the interfering signal of the antenna port passing through the loop impedance; and

adjust a phase of the compensation signal to be of opposite phase as the interfering signal of the antenna port passing through the loop impedance; and

a third directional coupler coupling a second port of the variable gain and phase shifter to the loop feed line and configured to feed the adjusted compensation signal to the loop feed line.

2. The interference reducing circuit of claim 1, wherein the first and second directional couplers comprise a single directional coupler, and wherein the variable gain and phase shifter is coupled to the third part of the transmission line via an isolation port of the single directional coupler.

3. The interference reducing circuit of claim 1, wherein the variable gain and phase shifter comprises a variable gain shifter and a variable phase shifter coupled in series.

4. The interference reducing circuit of claim 1, wherein the interference reducing circuit is configured for a multi-carrier radio frequency transmitter.

5. The interference reducing circuit of claim 1, wherein the interference reducing circuit is configured in combination with the linearization loop as a compensation circuit.

6. The interference reducing circuit of claim 5, wherein the linearization loop is a feed forward loop.

7. The interference reducing circuit of claim 5, wherein the linearization loop is a feedback loop.

8. The interference reducing circuit of claim 5, wherein the linearization loop is further configured to reduce a non-linearity of the amplifier.

9. A radio frequency transmitter comprising:

an amplifier;

an antenna port;

an isolator configured to isolate an output of the amplifier from an interfering signal of the antenna port;

a transmission line comprising a first part, a second part and a third part, the first part comprising a first end connectable to a signal source and a second end coupled to an input of the amplifier, the second part comprising a third end coupled to the output of the amplifier and a fourth end coupled to an input of the isolator, the third part comprising a fifth end coupled to an output of the isolator and a sixth end coupled to the antenna port; and

a linearization loop configured to reduce a non-linearity of the isolator, the linearization loop comprising;

a first directional coupler coupled to the third part of the transmission line;

a loop impedance coupled at a first port to the first directional coupler; and

at least one further linearization loop element coupled to a second port of the loop impedance via a loop feed line and configured to adjust a linearization signal and to feed the adjusted linearization signal to the transmission line; and

an interference reducing circuit configured to reduce an influence of the interfering signal of the antenna port on the linearization loop and comprising;

a second directional coupler configured to extract a compensation signal from the third part of the transmission line;

a variable gain and phase shifter coupled at a first port to the third part of the transmission line via the second directional coupler and configured to;

adjust an amplitude of the compensation signal to match an amplitude of the interfering signal of the antenna port passing through the loop impedance; and

adjust a phase of the compensation signal to be of opposite phase as the interfering signal of the antenna port passing through the loop impedance; and

a third directional coupler coupling a second port of the variable gain and phase shifter to the loop feed line and configured to feed the adjusted compensation signal to the loop feed line.

10. The radio frequency transmitter of claim 9, wherein the isolator comprises a circulator.

11. The radio frequency transmitter according to claim 9, wherein the radio frequency transmitter comprises part of a communication device.

12. The radio frequency transmitter according to claim 11, wherein the communication device is a radio base station or a mobile terminal.

13. An interference reduction method for a radio frequency transmitter, wherein the radio frequency transmitter comprises:

an amplifier;

an antenna port;

an isolator configured to isolate an output of the amplifier from an interfering signal of the antenna port;

a transmission line comprising a first part, a second part and a third part, the first part comprising a first end connectable to a signal source and a second end coupled to an input of the amplifier, the second part comprising a third end coupled to the output of the amplifier and a fourth end coupled to an input of the isolator, the third part comprising a fifth end coupled to an output of the isolator and a sixth end coupled to the antenna port; and

a linearization loop configured to reduce a non-linearity of the isolator, the linearization loop comprising;

a first directional coupler coupled to the third part of the transmission line;

a loop impedance coupled at a first port to the first directional coupler; and

at least one further linearization loop element coupled to a second port of the loop impedance via a loop feed line and configured to adjust a linearization signal and to feed the adjusted linearization signal to the transmission line; and

wherein the interference reduction method reduces an influence of the interfering signal of the antenna port on the linearization loop and comprises;

extracting a compensation signal from the third transmission line via a second directional coupler;

adjusting an amplitude of the compensation signal to match an amplitude of the interfering signal of the antenna port passing through the loop impedance;

adjusting a phase of the compensation signal to be of opposite phase as the interfering signal of the antenna port passing through the loop impedance; and

feeding the adjusted compensation signal to the loop feed line via a third directional coupler.

14. The interference reduction method of claim 13, wherein the first and second directional couplers comprise a single directional coupler, and wherein the step of extracting the compensation signal from the third transmission line vi the second directional coupler comprises extracting the compensation signal from an isolation port of the single directional coupler.

15. A method of manufacturing a radio frequency transmitter comprising:

coupling a signal source to an input of an amplifier via a first part of a transmission line;

arranging an isolator to isolate an output of the amplifier from an interfering signal of an antenna port by;

coupling the output of the amplifier to an input of the isolator via a second part of the transmission line; and

coupling an output of the isolator to the antenna port via a third part of the transmission line;

arranging a linearization loop to reduce a non-linearity of the isolator by;

coupling a first directional coupler to the third part of the transmission line;

coupling a loop impedance at a first port to the first directional coupler;

coupling at least one further linearization loop element to a second port of the loop impedance via a loop feed line; and

arranging the at least one further linearization loop element to adjust a linearization signal and to feed the adjusted linearization signal to the transmission line;

arranging an interference reducing circuit to reduce an influence of the interfering signal of the antenna port on the linearization loop by;

configuring a second directional coupler to extract a compensation signal from the third part of the transmission line;

coupling a variable gain and phase shifter at a first port to the third part of the transmission line via the second directional coupler;

configuring the variable gain and phase shifter to adjust an amplitude of the compensation signal to match an amplitude of the interfering signal of the antenna port passing through the loop impedance, and to adjust a phase of the compensation signal to be of opposite phase as the interfering signal of the antenna port passing through the loop impedance; and

coupling a second port of the variable gain and phase shifter to the loop feed line via a third directional coupler to feed the adjusted compensation signal to the loop feed line.