Method and apparatus for spectrum spreading of a pulse-density modulated waveform
Methods and systems are provided for spreading spectral density of digital-to-analog conversion output signals. A spreading circuit may spread a digital-to-analog converter (DAC) output signal over a particular frequency spectrum, with the spreading circuit receiving the DAC output signal; generating a plurality of internal control signals; and generating based on the DAC output signal and the one or more internal control signal a corresponding spread output signal. The Internal control signals may comprise at least a first control signal, generated based on sequences meeting at least one particular criterion, a second control signal, generated based on a feedback corresponding to an intermediate output generated within the spreading circuit. The spreading circuit may generate the first control signal based on zero-sum sequences. The spreading circuit may generate a stream of pulses based on the intermediate output, and may generate the feedback signal based on the stream of pulses.
1. A system comprising:
a digital-to-analog converter (DAC) circuit that generates an output signal; and
a spreading circuit that spreads the DAC output signal over a particular frequency spectrum, wherein the spreading circuit:
receives the DAC output signal;
generates a plurality of internal control signals, wherein;
the spreading circuit generates at least a first control signal based on sequences meeting at least one particular criterion; and
the spreading circuit generates a second control signal based on a feedback corresponding to an intermediate output generated within the spreading circuit; and
generates based on the DAC output signal and the plurality of internal control signals, a corresponding spread output signal.
2. The system of claim 1 , wherein generating the second control signal comprises applying an adjustment to the intermediate output.
3. The system of claim 1 , wherein the spreading circuit sets the second control signal based on applying of inversion to the intermediate output.
4. The system of claim 1 , wherein the spreading circuit generates a stream of pulses based on the intermediate output; and generates the feedback signal based on the stream of pulses.
5. The system of claim 4 , wherein the spreading circuit sets a number of pulses in the stream of pulses to equal to a number of pulses in the DAC output signal.
6. The system of claim 4 , wherein the spreading circuit sets the second control signal based on comparing of a value corresponding to the intermediate output with a pre-defined value.
7. The system of claim 1 , wherein generating the second control signal comprises applying a delay.
8. The system of claim 7 , wherein applying the delay is synchronized to the generating of the first control signal.
9. The system of claim 8 , wherein applying the delay and generating the first control signal are synchronized to the DAC output signal.
10. The system of claim 1 , wherein the spreading circuit generates the first control signal based on zero-sum sequences.
11. The system of claim 10 , wherein the zero-sum sequences comprise sequences of 1s and −1s, each zero-sum sequence having an equal number of 1s and −1s.
12. The system of claim 10 , wherein the zero-sum sequences comprise four bit long sequences.
13. The system of claim 1 , wherein the spreading circuit generates the first control signal based on randomly generated number.
14. The system of claim 13 , wherein the spreading circuit generates the randomly generated number based on linear feedback shifting.
15. The system of claim 13 , wherein generating the first control signal is synchronized to the DAC output signal and generating the randomly number is synchronized to a clock set based on a frequency of the DAC output signal.