Method and apparatus for reducing interfering signals in a transmitter
View Patent ↗An interference canceller 200 and corresponding method thereof operates to reduce the level of an interfering signal and includes a circulator 202 comprising a transmitter port, a receiver port and an antenna port, a transmission line 210 comprising a first end coupled to the transmitter port and a second end for coupling to a signal source; and a circuit 216 , having an input coupled to the receiver port 206 and an output coupled 220 to the transmission line, for providing a phase shifted version of a signal coupled to the input at the output, wherein an interfering signal at the antenna port is reverse coupled to the transmission line by the circulator and coupled to the input of the circuit so as to reduce an amplitude of the interfering signal at the second end 212 of the transmission line. The interference canceller concepts may advantageously be used in a single transmitter version or in a multiple transmitter version (FIG. 4 ).
1. An interference canceller for reducing the level of an interfering signal comprising:
a circulator comprising a transmitter port, a receiver port and an antenna port;
a transmission line comprising a first end coupled to the transmitter port and a second end for coupling to a signal source; and
a circuit, having an input and an output, the input coupled to the receiver port and the output coupled to the transmission line, for providing a phase shifted version of a signal coupled to the input at the output:
wherein an interfering signal at the antenna port is coupled to the transmission line by the circulator and the circuit so as to reduce an amplitude of the interfering signal at the second end of the transmission line that results from the interfering signal being coupled from the antenna port to the transmitter port of the circulator; and
wherein the circuit comprising
a directional coupler for coupling to the transmission line;
a variable attenuator for level shifting a signal at the antenna port coupled to the transmission line by the circulator and the circuit;
a variable phase shifter for phase shifting the signal at the antenna port coupled to the transmission line by the circulator and the circuit, all series coupled between the input and the output; and
a calibration apparatus comprising:
a sensor coupled to the transmission line, for providing a sensing signal, the sensing signal corresponding to a combination of the interfering signal at the antenna port coupled to the transmission line by the circulator and circuit and the interfering signal at the second end of the transmission line that results from the interfering signal being coupled from the antenna port to the transmitter port of the circulator; and
a control circuit coupled to the sensor operable to adjust one of the variable attenuator and the variable phase shifter according to the sensing signal.
2. The interference canceller of claim 1 wherein the circuit comprises a level shifter to adjust an amplitude of the interfering signal coupled to the transmission line by the circulator and circuit.
3. The interference canceller of claim 2 wherein the level shifter is a variable attenuator.
4. The interference canceller of claim 1 wherein the circuit further comprises a phase shifter to adjust a phase of the interfering signal coupled to the transmission line by the circulator and circuit.
5. The interference canceller of claim 4 wherein the phase shifter is a variable phase shifter.
6. A transmitter using an interference canceller for reducing the level of an interfering signal comprising:
a transmitter amplifier having a transmit output; and
the interference canceller comprising:
a circulator comprising a transmitter port, a receiver port and an antenna port;
a transmission line comprising a first end coupled to the transmitter port and a second end coupled to the transmit output; and
a circuit, having an input and an output, the input coupled to the receiver port, for providing a phase shifted version of a signal coupled to the input at the output, the output coupled to the transmission line;
wherein an interfering signal at the antenna port is coupled to the transmission line by the circulator and circuit so as to reduce the amplitude of the interfering signal at the second end of the transmission line that results from the interfering signal being coupled from the antenna port to the transmitter port of the circulator, and
wherein the circuit comprising
a directional coupler for coupling to the transmission line;
a variable attenuator for level shifting a signal at the antenna port coupled to the transmission line by the circulator and the circuit;
a variable phase shifter for phase shifting the signal at the antenna port coupled to the transmission line by the circulator and the circuit, all series coupled between the input and the output; and
a calibration apparatus comprising:
a sensor coupled to the transmission line, for providing a sensing signal, the sensing signal corresponding to a combination of the interfering signal at the antenna port coupled to the transmission line by the circulator and circuit and the interfering signal at the second end of the transmission line that results from the interfering signal being coupled from the antenna port to the transmitter port of the circulator; and
a control circuit coupled to the sensor operable to adjust one of the variable attenuator and the variable phase shifter according to the sensing signal.
7. The transmitter of claim 6 wherein the circuit comprises an attenuator to adjust an amplitude of the interfering signal coupled to the transmission line by the circulator and circuit.
8. The transmitter of claim 7 wherein the circuit further comprises a phase shifter to adjust a phase of the interfering signal coupled to the transmission line by the circulator and circuit.
9. The transmitter of claim 8 wherein the circuit further comprises a directional coupler for coupling to the transmission line, wherein the attenuator, the phase shifter and the directional coupler are series coupled.