Method and apparatus for transmitter noise cancellation in an RF communications system

• US 20020072344A1
• Filed: 08/22/2001
• Published: 06/13/2002
• Est. Priority Date: 08/22/2000
• Status: Active Grant

• Current Assignee: Novatel Wireless, Inc. (Inseego Corp.)
• Original Assignee: Novatel Wireless, Inc. (Inseego Corp.)
• Inventors: Souissi, Slim Salah
• Granted Patent: US 6,567,649 B2
• Time in Patent Office: Days
• US Class Current: 455/296
• CPC Class Codes: H04B 1/123 using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

A method and apparatus is provided for reducing or eliminating the transmitter signal leakage, i.e., transmitter noise, in the receiver path of an RF communications system operating in full duplex mode. In an embodiment of the present invention, a noise cancellation loop produces an estimated transmitter signal leakage and cancels it from the receiver path to produce a received signal with little or no transmitter noise. Some of the advantages are that there is significant improvement in the isolation between the transmitter/receiver circuits, the size of the RF communications circuitry may be reduced, and the RF transmit module along with the RF receive module may be incorporated into a single RF IC chip.

Claims

1. A method in a RF communications system for improving a received communications signal during full duplex operation, wherein said RF communications system comprises a transmitter circuit and a receiver circuit, said method comprising:

determining a first estimation of a signal leakage from said transmitter circuit, when said received communications signal is not being received by said receiver circuit;

when said RF communications system is in full duplex operation and said transmitter circuit is generating a transmit communication signal, determining a second estimation of said signal leakage based on said first estimation and said transmit communication signal; and

combining said second estimation with said received communications signal, such that said signal leakage is substantially cancelled in said received communications signal.

2. The method of claim 1 wherein said transmitter circuit and said receiver circuit are on a single RF IC chip.

3. The method of claim 1 wherein said determining a first estimation of said signal leakage comprises disconnecting an antenna of said RF communications system.

4. The method of claim 3 wherein said determining said first estimation of said signal leakage further comprises connecting a dummy load emulating said antenna.

5. The method of claim 1 wherein said determining said first estimation of said signal leakage includes tuning said receiver circuit to a clean frequency band.

6. The method of claim 1 wherein said determining said first estimation of said signal leakage comprises:

generating a calibration signal based on a pseudo-random noise sequence;

splitting said calibration signal into a first signal and a second signal, wherein said first signal is sent to an estimation circuit and said second signal is further divided into a third signal sent to a dummy antenna load and a fourth signal sent to said estimation circuit; and

cross correlating said first signal and said fourth signal in said estimation circuit to produce said first estimation.

7. The method of claim 6 wherein said determining said second estimation based on said first estimation comprises:

splitting said transmit communication signal into a fifth signal and a sixth signal, wherein said fifth signal is sent to said estimation circuit and said sixth signal is sent to an antenna; and

using parameters from said first estimation, determining in said estimation circuit said second estimation from said fifth signal.

8. A method in an RF IC communications system for substantially canceling transmitter noise during full duplex operation, wherein said RF IC communications system comprises a transmitter and a receiver, said method comprising:

calibrating said RF IC communications system by sending a calibration signal to a transmit noise cancellation loop circuit;

determining loop parameters for said transmit noise cancellation loop circuit;

when in full duplex operation, estimating a transmit noise signal based on said loop parameters; and

substantially canceling said transmit noise signal from a received signal during full duplex operation.

9. The method of claim 8 wherein said loop parameters include gain and phase.

10. The method of claim 8 wherein said transmitter and said receiver are on different IC chips.

11. The method of claim 8 wherein said transmitter and said receiver are on a single RF IC chip.

12. The method of claim 8 wherein said step of calibrating said RF IC communications system includes disconnecting an antenna of said RF IC communications system.

13. The method of claim 8 wherein said step of calibrating said RF IC communications system includes increasing the power of said calibration signal relative to any received signal so that calibration is done without disconnecting an antenna of said RF IC communications system.

14. The method of claim 8 wherein said step of calibrating said RF IC communications system occurs on power-up of said RF IC communications system.

15. The method of claim 8 wherein said step of calibrating said RF IC communications system occurs during an event selected from a group consisting of power-up, idle mode, roaming mode, power-off, standby mode, connecting mode, dialing a number, or hand-off.

16. The method of claim 8 wherein said step of calibrating said RF IC communications system occurs periodically.

17. The method of claim 8 wherein said step of calibrating said RF IC communications system occurs dynamically during full duplex operation.

19. The RF communications system according to claim 18 wherein said noise cancellation loop uses a calibration signal.

20. The RF communications system according to claim 18 wherein said noise cancellation loop sets parameters based on a calibration signal, said parameters used by said noise cancellation loop for generating said transmit noise signal approximation.

21. The RF communications system according to claim 20 wherein said parameters include a phase and a gain.

22. The RF communications system according to claim 18 wherein said transmit path includes a circuit for converting a transmit signal at an intermediate frequency (IF) to a radio frequency (RF).

23. The RF communications system according to claim 18 wherein said receive path includes a circuit for converting said receive signal at a radio frequency (RF) to an intermediate frequency (IF).

24. The RF communications system according to claim 18 wherein said transmit path is coupled to said antenna via a duplexer circuit.

25. The RF communications system according to claim 24 wherein said receive path is coupled to said antenna via said duplexer circuit.

27. The method of claim 26 wherein said step of determining a first estimation of transmit noise comprises:

generating a calibration signal;

splitting said calibration signal into a first signal and a second signal, wherein said first signal is sent to an estimation circuit and said second signal is further divided into a third signal sent to a dummy antenna load via said duplexer and a fourth signal sent to said estimation circuit; and

cross correlating said first signal and said fourth signal in said estimation circuit to produce said first estimation.

28. The method of claim 26 wherein said step of determining said second estimation based on said first estimation comprises:

splitting said transmit communication signal into a fifth signal and a sixth signal, wherein said fifth signal is sent to an estimation circuit and said sixth signal is sent to an antenna via said duplexer; and

using parameters from said first estimation, determining in said estimation circuit said second estimation from said fifth signal.

29. The method according to claim 28 wherein said parameters include a phase and a gain.

30. The method of claim 26 wherein said step of combining said second estimation with said received communications signal, such that said transmit noise is substantially cancelled in said received communications signal, comprises:

obtaining a seventh signal from said duplexer comprising said received communications signal and transmit noise from said duplexer; and

combining said second estimation with said seventh signal, such that said transmit noise is substantially cancelled in said received communications signal.

18. A RF communications system that substantially cancels transmitter noise during full duplex operation, comprising:

a transmit path coupled to a noise cancellation loop, and further coupled to an antenna when said RF communications system is in full duplex mode;

a received path coupled to said noise cancellation loop and further coupled to said antenna and said transmit path when said RF communications system is in full duplex mode;

said noise cancellation loop for approximating a transmit noise signal from said transmit path and for canceling said transmit noise signal from a received signal coupled to said received path.

26. A method in a RF communications system for reducing transmit noise in a received communications signal during full duplex operation, wherein said RF communications system comprises a transmitter circuit, a duplexer, and a receiver circuit, said method comprising:

determining a first estimation of transmit noise from said transmitter circuit, when said received communications signal is not being received by said receiver circuit;

when said RF communications system is in full duplex operation and said transmitter circuit is generating a transmit communication signal, determining a second estimation of transmit noise based on said first estimation and said transmit communication signal; and

combining said second estimation with said received communications signal, such that said transmit noise is substantially cancelled in said received communications signal.

31. A RF IC chip that substantially cancels transmitter noise during full duplex communications, comprising:

a calibration path, comprising a transmit path coupled to a noise cancellation loop and via a duplexer to an antenna dummy load, said calibration path for determining parameters associated with an estimate of a first transmitter noise signal from said duplexer, when a calibration signal is sent to said antenna dummy load; and

a full duplex operation path, comprising;

a first path comprising a transmit path coupled to said duplexer and an antenna for transmitting a first communications signal;

a second path comprising a transmit path coupled to said noise cancellation loop for determining an estimate of a second transmitter noise signal, using said parameters and a portion of said first communications signal; and

a third path coupled to said antenna and said duplexer for receiving a second communications signal; and

a fourth path coupled to said duplexer and a receive path for canceling transmitter noise added by said duplexer to said second communications signal by using said estimate of said second transmitter noise signal.

32. A RF IC chip of claim 31 wherein said parameters include a gain and a phase of said first transmitter noise signal.