Signal conversion system and method
A signal conversion system and method for converting an input signal to a pulse width modulated signal is disclosed. The signal conversion system includes a sample rate converter coupled with an associated pulse width modulation (PWM) module. A hardware and power efficient signal conversion system for resampling an audio input signal with an arbitrary sample rate to a pulse width modulated output audio signal for use in an audio processor and/or reproduction is disclosed. The signal conversion system may be particularly suitable for use in a battery operated consumer electronics device.
1. A method for generating a PWM signal from an input signal, the method comprising:
generating a carrier signal at a carrier signal frequency;
comparing the carrier signal with the input signal;
forming a triggered signal when the carrier signal and the input signal are equal to each other within a predetermined precision based on comparison of the carrier signal with the input signal;
truncating the triggered signal with a noise shaper to form a truncated signal;
comparing the truncated signal to the carrier signal to form the PWM signal; and
updating the triggered signal in sync with the carrier signal.
2. The method in accordance with claim 1 , further comprising generating a clock signal.
3. The method in accordance with claim 2 , further comprising resampling the input signal at a sample rate greater than the carrier signal frequency to form a resampled signal.
4. The method in accordance with claim 3 , wherein resampling the input signal includes:
generating a count-disparity signal from the clock signal and the input signal;
calculating a temporal correction value from the count disparity signal;
generating resampled clock signals from the temporal correction value; and
generating the resampled signal from one or more of the resampled clock signals and the input signal.
5. The method in accordance with claim 4 , wherein generating the resampled clock signals includes resampling the input signal to form a de-jittered signal having a substantially stabilized sample rate.
6. The method in accordance with claim 5 , wherein generating the resampled clock signals further includes generating a filtered intermediate signal from the de-jittered signal, the clock signal, and one or more of the resampled clock signals.
7. The method in accordance with claim 1 , wherein updating the triggered signal is performed when the carrier signal is at a maximal and/or minimal amplitude.
8. The method in accordance with claim 3 , further comprising shifting the noise of the resampled signal or a signal derived therefrom into a substantially inaudible frequency band.
9. The method in accordance with claim 3 , further comprising shaping the carrier signal and/or the resampled signal.
10. The method in accordance with claim 9 , further comprising analyzing a property of the resampled signal to generate a PWM control signal, where the comparison, shaping, or noise shifting is dependent upon the PWM control signal.
11. The method in accordance with claim 1 , further comprising:
generating a matching carrier signal with a frequency equal to the carrier signal frequency; and
comparing the truncated signal with the carrier signal to form the PWM signal.
12. A method for generating a PWM signal from an input signal, the method comprising:
generating a carrier signal at a carrier signal frequency;
comparing the carrier signal with the input signal;
forming a triggered signal when the carrier signal and the input signal are equal to each other within a predetermined precision based on comparison of the carrier signal with the input signal;
truncating the triggered signal with a noise shaper to form a truncated signal;
comparing the truncated signal to the carrier signal to form the PWM signal;
generating a clock signal; and
resampling the input signal at a sample rate greater than the carrier signal frequency to form a resampled signal.
13. The method in accordance with claim 12 , wherein resampling the input signal includes:
generating a count-disparity signal from the clock signal and the input signal;
calculating a temporal correction value from the count disparity signal;
generating resampled clock signals from the temporal correction value; and
generating the resampled signal from one or more of the resampled clock signals and the input signal.
14. The method in accordance with claim 13 , wherein generating the resampled clock signals includes resampling the input signal to form a de-jittered signal having a substantially stabilized sample rate.
15. The method in accordance with claim 14 , wherein generating the resampled clock signals further includes generating a filtered intermediate signal from the de-jittered signal, the clock signal, and one or more of the resampled clock signals.
16. The method in accordance with claim 12 , further comprising shifting the noise of the resampled signal or a signal derived therefrom into a substantially inaudible frequency band.
17. The method in accordance with claim 12 , further comprising shaping the carrier signal and/or the resampled signal.
18. The method in accordance with claim 17 , further comprising analyzing a property of the resampled signal to generate a PWM control signal, where the comparison, shaping, or noise shifting is dependent upon the PWM control signal.
19. A method for generating a PWM signal from an input signal, the method comprising:
generating a carrier signal at a carrier signal frequency;
comparing the carrier signal with the input signal;
forming a triggered signal when the carrier signal and the input signal are equal to each other within a predetermined precision based on comparison of the carrier signal with the input signal;
truncating the triggered signal with a noise shaper to form a truncated signal;
comparing the truncated signal to the carrier signal to form the PWM signal;
generating a matching carrier signal with a frequency equal to the carrier signal frequency; and
comparing the truncated signal with the carrier signal to form the PWM signal.