Method and apparatus for cancellation of interference from a spread spectrum phase lock loop
Systems and methods for provided for reducing interference caused by leakage of signals generated by a spread spectrum phase lock loop (SS PLL). Output of SS PLL may be processed to reduce interference. For example, a sinusoidal spreading signal may be used to spread the output of the SS PLL. A notch filter tracks the frequency of the output of the SS PLL to steer the notch in the filter to the instantaneous frequency output from the SS PLL, thus allowing the notch filter to be placed in the path of signals that have unwanted leakage from the SS PLL.
1. A system comprising:
a signal mitigation module; and
a spread spectrum phase lock loop comprising:
a voltage controlled oscillator (VCO);
an adjuster operable to apply an adjustment to an output of the VCO;
a frequency source;
a controller operable to generate control voltage for the VCO based on an output of the frequency source and an output of the adjuster; and
a sinusoidal wave generator operable to generate at least a first output and a second output, wherein the first output is applied to at least one other component of the spread spectrum phase lock loop and the second output is applied to the signal mitigation module;
wherein:
the spread spectrum phase lock loop is operable to generate an output based on at least the output of the VCO; and
the signal mitigation module is operable to process the output of the spread spectrum phase lock loop, based on the second output of the sinusoidal wave generator, to reduce interference.
2. The system of claim 1 , wherein the signal mitigation module comprises a tunable notch filter.
3. The system of claim 1 , wherein the signal mitigation module is implemented digitally within a digital signal processor (DSP).
4. The system of claim 1 , wherein the adjuster comprises a divider that is operable to divide a value of the output of the VCO by a particular value.
5. The system of claim 4 , wherein the divider is operable to divide the value of the output of the VCO by a value that varies as a sinusoid.
6. The system of claim 1 , wherein at least one output of the sinusoidal wave generator is synchronized to the frequency source.
7. The system of claim 6 , wherein the at least one output of the sinusoidal wave generator comprises the first output applied to the at least one other component of the spread spectrum phase lock loop.
8. The system of claim 1 , wherein the signal mitigation module is driven by a clock synchronized to the frequency source, the clock being used to control tracking of a tunable notch filter in the signal mitigation module and being controlled by the output of the sinusoidal wave generator.
9. The system of claim 1 , wherein at least one output from the sinusoidal wave generator is a series of digital values that each represent an amplitude of a sinusoidal waveform.
10. The system of claim 1 , wherein the second output of the sinusoidal wave generator provides information indicating a frequency of a signal corresponding to the first output of the sinusoidal wave generator.
11. The system of claim 10 , wherein the information indicating the frequency of the signal corresponding to the first output of the sinusoidal wave generator is used to tune a frequency applicable to the signal mitigation module.
12. The system of claim 1 , wherein the spread spectrum phase lock loop is operable to synchronize a phase of the output of the spread spectrum phase lock loop to at least one component of the signal mitigation module.
13. A method comprising:
generating a spread spectrum signal via a spread spectrum phase lock loop, the generating comprising controlling a voltage of a voltage controlled oscillator (VCO) that generates an output corresponding to the spread spectrum signal, wherein the controlling is based on an output of a frequency source and an output corresponding to applying an adjustment to an output of the VCO;
processing the spread spectrum signal to reduce interference caused by the spread spectrum phase lock loop; and
generating via a sinusoidal wave generator at least a first output and a second output, wherein the first output is applied to at least one component of the spread spectrum phase lock loop during generating the spread spectrum signal via the spread spectrum phase lock loop, and the second output is applied during the processing of the spread spectrum signal.
14. The method of claim 13 , wherein applying the adjustment to the output of the VCO comprises dividing a value of the output of the VCO.
15. The method of claim 14 , comprising dividing the value of the output of the VCO by a value that varies as a sinusoid.
16. The method of claim 13 , comprising synchronizing at least one output of the sinusoidal wave generator to the frequency source.
17. The method of claim 13 , comprising controlling the processing of the spread spectrum signal based on a clock synchronized to the frequency source.
18. The method of claim 13 , comprising tuning a frequency applicable to the processing of the spread spectrum signal based on information indicating a frequency of a signal corresponding to the first output of the sinusoidal wave generator.
19. The method of claim 13 , comprising synchronizing a phase of the spread spectrum signal to at least function applied during processing of the spread spectrum signal.
20. The method of claim 19 , wherein synchronizing the phase of the spread spectrum signal comprises aligning a spurious signal to be cancelled with a notch frequency of a tunable notch filter utilized in the processing of the spread spectrum signal.