Spur cancellation in a digital baseband transmit signal using cancelling tones

1. A method for reducing spurs within a transmit signal comprising:

determining a cancelling tone;

adding the cancelling tone to a baseband transmit signal in the digital domain to obtain a baseband transmit signal with cancelling tone;

reducing a spur in the transmit signal using the cancelling tone by:

modulating the baseband transmit signal with canceling tone to form a modulated baseband transmit signal with canceling tone;

converting the modulated baseband transmit signal with cancelling tone from a digital signal to an analog transmit signal using a digital to analog converter (DAC); and

mixing the analog transmit signal with a local oscillator signal generated by a voltage controlled oscillator (VCO) and a phase locked loop (PLL) to form a mixed transmit signal, the local oscillator signal comprising a local oscillator frequency and at least one spur at multiples of the local oscillator frequency;

amplifying the mixed transmit signal to form the transmit signal with the reduced spur; and

transmitting the transmit signal with the reduced spur using an antenna.

2. The method of claim 1 , wherein determining a cancelling tone comprises selecting a frequency of the cancelling tone.

3. The method of claim 1 , wherein determining a cancelling tone comprises determining an amplitude of the cancelling tone.

4. The method of claim 1 , wherein determining a cancelling tone comprises selecting a phase of the cancelling tone.

5. The method of claim 1 , wherein a spur in the mixed transmit signal is reduced by the cancelling tone.

6. The method of claim 1 , further comprising:

determining an amplitude of a spur in a received signal;

adjusting an amplitude of the cancelling tone to match the amplitude of the spur; and

iteratively repeating to optimize spur reduction in the transmit signal.

7. The method of claim 6 , wherein the received signal is received from a duplexer.

8. The method of claim 6 , wherein determining the amplitude of the spur in the received signal comprises:

mixing the received signal with a receiver local oscillator signal at a spur frequency to obtain a mixed received signal;

filtering the mixed received signal;

converting the mixed received signal from an analog signal to a digital signal using an analog to digital converter (ADC); and

determining the amplitude of the spur using digital signal processing.

9. The method of claim 8 , wherein a mobile station modem (MSM) sets the magnitude of a gain applied to the cancelling tone.

10. The method of claim 6 , further comprising:

shifting the frequency of the baseband transmit signal to obtain the cancelling tone; and

amplifying the cancelling tone using a variable gain amplifier.

11. The method of claim 1 , wherein the cancelling tone has a non-flat top to compensate for baseband filter attenuation over frequency.

12. The method of claim 1 , wherein the spur is a single tone spur and the cancelling tone is a single tone cancelling tone.

13. The method of claim 1 , wherein the spur is a wideband spur and the cancelling tone is a wideband canceling sideband.

14. The method of claim 1 , wherein the method is performed on a wireless communication device.

15. The method of claim 1 , wherein the method is performed by a transmit signal chain without a surface acoustic wave (SAW) filter.

16. A wireless device configured for reducing spurs within a transmit signal comprising:

circuitry configured to:

determine a cancelling tone;

add the cancelling tone to a baseband transmit signal in the digital domain to obtain a baseband transmit signal with cancelling tone; and

reduce a spur in the transmit signal using the cancelling tone by:

modulating the baseband transmit signal with canceling tone to form a modulated baseband transmit signal with canceling tone;

converting the modulated baseband transmit signal with cancelling tone from a digital signal to an analog transmit signal using a digital to analog converter (DAC); and

mixing the analog transmit signal with a local oscillator signal generated by a voltage controlled oscillator (VCO) and a phase locked loop (PLL) to form a mixed transmit signal, the local oscillator signal comprising a local oscillator frequency and at least one spur at multiples of the local oscillator frequency; and

amplify the mixed transmit signal to form the transmit signal with the reduced spur; and

a transmitter configured to transmit the transmit signal with the reduced spur.

17. The wireless device of claim 16 , wherein determining a cancelling tone comprises selecting a frequency of the cancelling tone.

18. The wireless device of claim 16 , wherein determining a cancelling tone comprises determining an amplitude of the cancelling tone.

19. The wireless device of claim 16 , wherein determining a cancelling tone comprises selecting a phase of the cancelling tone.

20. The wireless device of claim 16 , wherein a spur in the mixed transmit signal is reduced by the cancelling tone.

21. The wireless device of claim 16 , further comprising:

an adjustable amplifier configured to adjust an amplitude of the cancelling tone to match an amplitude of the spur.

22. The wireless device of claim 21 , further comprising a duplexer used to receive a received signal.

23. The wireless device of claim 21 , wherein the circuitry is further configured to determine the amplitude of the spur in a received signal, and wherein determining the amplitude of the spur comprises:

mixing the received signal with a spur frequency to obtain a mixed received signal;

filtering the mixed received signal;

converting the mixed received signal from an analog signal to a digital signal using an analog to digital converter (ADC); and

determining the amplitude of the spur using digital signal processing.

24. The wireless device of claim 23 , wherein a mobile station modem (MSM) sets the magnitude of a gain applied to the cancelling tone.

25. The wireless device of claim 21 , wherein the circuitry is further configured to:

shift the frequency of the baseband transmit signal to obtain the cancelling tone; and

amplify the cancelling tone using a variable gain amplifier.

26. The wireless device of claim 16 , wherein the cancelling tone has a non-flat top to compensate for baseband filter attenuation over frequency.

27. The wireless device of claim 16 , wherein the spur is a single tone spur and the cancelling tone is a single tone cancelling tone.

28. The wireless device of claim 16 , wherein the spur is a wideband spur and the cancelling tone is a wideband canceling sideband.

29. A wireless device configured for reducing spurs within a transmit signal, comprising:

means for determining a cancelling tone;

means for adding the cancelling tone to a baseband transmit signal in the digital domain to obtain a baseband transmit signal with cancelling tone;

means for reducing a spur in the transmit signal using the cancelling tone, comprising:

means for modulating the baseband transmit signal with canceling tone to form a modulated baseband transmit signal with canceling tone;

means for converting the modulated baseband transmit signal with cancelling tone from a digital signal to an analog transmit signal using a digital to analog converter (DAC); and

means for mixing the analog transmit signal with a local oscillator signal generated by a voltage controlled oscillator (VCO) and a phase locked loop (PLL) to form a mixed transmit signal, the local oscillator signal comprising a local oscillator frequency and at least one spur at multiples of the local oscillator frequency;

means for amplifying the mixed transmit signal to form the transmit signal with the reduced spur; and

means for transmitting the transmit signal with the reduced spur using an antenna.

30. A non-transitory computer-readable medium encoded with computer-executable instructions for:

determining a cancelling tone;

adding the cancelling tone to a baseband transmit signal in the digital domain to obtain a baseband transmit signal with cancelling tone;

reducing a spur in the transmit signal using the cancelling tone by:

modulating the baseband transmit signal with canceling tone to form a modulated baseband transmit signal with canceling tone;

converting the modulated baseband transmit signal with cancelling tone from a digital signal to an analog transmit signal using a digital to analog converter (DAC); and

mixing the analog transmit signal with a local oscillator signal generated by a voltage controlled oscillator (VCO) and a phase locked loop (PLL) to form a mixed transmit signal, the local oscillator signal comprising a local oscillator frequency and at least one spur at multiples of the local oscillator frequency;

amplifying the mixed transmit signal to form the transmit signal with the reduced spur; and

transmitting the transmit signal with the reduced spur using an antenna.