System and method of changing a PWM power spectrum

• US 7,791,521 B2
• Filed: 08/26/2008
• Issued: 09/07/2010
• Est. Priority Date: 04/01/2008
• Status: Expired due to Fees

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Beale, Richard, Khoury, John
• Primary Examiner(s): Mai; Lam T
• Application Number:
  US12/198,457
• Publication Number:
  US 20090243688A1
• Time in Patent Office: 742 Days
• Field of Search: 341140-155, 327/231, 332/109, 375/238, 381/104, 455/127.3
• US Class Current: 341/152
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation
• CPC Class Codes: H04B 15/02 Reducing interference from electric apparatus by means located at or near the interfering apparatus
• CPC Class Codes: H04B 2215/067 by modulation dispersion

Abstract

In a particular embodiment, a circuit device includes a pulse edge control circuit to receive at least one pulse-width modulated (PWM) signal from a PWM source. The pulse edge control circuit is adapted to selectively apply a phase shift operation to the at least one PWM signal at integer submultiples of a frame repetition rate to produce at least one modulated PWM signal having a changed power spectrum. The pulse edge control circuit provides the at least one modulated PWM signal to at least one output of the pulse edge control circuit.

Claims

1. A circuit device comprising a pulse edge control circuit to:

receive at least one pulse-width modulated (PWM) signal from a PWM source;

selectively apply a phase shift operation to the at least one PWM signal at integer submultiples of a frame repetition rate to produce at least one modulated PWM signal having a changed power spectrum; and

provide the at least one modulated PWM signal to at least one output of the pulse edge control circuit.

2. The circuit device of claim 1, wherein the at least one PWM signal comprises a first PWM signal and a second PWM signal, and wherein the phase shift operation is selectively applied to the first and second PWM signals to produce modulated PWM signals that are carrier suppressed.

3. The circuit device of claim 1, wherein the phase shift operation is selectively applied to selectively shift selected pulses of the at least one PWM signal by a phase shift of plus or minus a quarter of a PWM frame width (±

T/4).

4. The circuit device of claim 1, wherein the pulse edge control circuit further comprises a control input adapted to receive a control signal to selectively control the phase shift operation for each sequential frame to selectively adjust a shape of a carrier power spectrum of the at least one modulated PWM signal.

5. The circuit device of claim 1, wherein the phase shift operation is selectively applied to a double-sided modulated PWM input signal centered about a temporal location within a PWM frame corresponding to one of a quarter of the a frame width or three-quarters of the frame width.

6. The circuit device of claim 5, wherein the phase shift operation further comprises a wrapping operation to wrap to a second frame boundary of the frame that portion of the at least one PWM signal that extends beyond a first frame boundary of a frame, when the at least one PWM signal has a pulse with a pulse width that is greater than half of a frame width.

7. The circuit device of claim 1, wherein the phase shift operation is selectively applied to the at least one PWM signal that selectively applies early and late phase shifts within the frame to the at least one PWM signal such that when shifting early, a leading PWM pulse edge of the at least one PWM signal is shifted no further than to abut a first frame boundary without crossing the first frame boundary, and when shifting late, a trailing PWM pulse edge of the at least one PWM signal is shifted no further than to abut a second frame boundary without crossing the second frame boundary.

8. The circuit device of claim 1, wherein the phase shift operation rotates a phase of the at least one PWM signal by pi divided by two (π

) radians or less within alternate frames, wherein a frame width is equal to two times pi (2*π

) radians and wherein the phase rotation is applied at integer submultiples of the frame repetition rate.

9. The circuit device of claim 1, wherein the at least one modulated PWM signal is produced without changing at least one of the frame repetition rate and the carrier frequency of the received PWM signals.

10. A circuit device comprising a pulse edge control circuit to:

receive PWM signals via at least two inputs;

selectively apply a phase shift operation to the received PWM signals at integer submultiples of a frame repetition rate to produce modulated PWM signals having suppressed carriers; and

provide the modulated PWM signals to respective outputs of the pulse edge control circuit.

11. The circuit device of claim 10, wherein the phase shift operation is applied to a double-sided modulated PWM input signal centered about a temporal location within a PWM frame corresponding to at least one of a quarter of a frame width or three-quarters of the frame width.

12. The circuit device of claim 11, wherein the phase shift operation further comprises a wrapping operation to wrap to a second frame boundary of the PWM frame those portions of the received PWM signals of the received PWM signals that extend beyond a first boundary of the PWM frame, when the at least one PWM signal has a pulse with a pulse width that is greater than half of the frame width.

13. The circuit device of claim 10, wherein the phase shift operation comprises limiting a first pulse width of a first PWM signal of the received PWM signals to half of a frame width or less, modulating a second pulse width of a second PWM signal of the received PWM signals and selectively applying a phase shift operation to the first and second PWM signals.

14. The circuit device of claim 10, wherein the phase shift operation is selectively applied to the received PWM signals to selectively phase shift the received PWM signals either early or late within a frame such that when shifting early, a leading PWM pulse edge is shifted no further than to abut a first frame boundary without crossing the first frame boundary, and when shifting late, the trailing PWM pulse edges shift no further than to abut a second frame boundary without crossing the second frame boundary.

15. The circuit device of claim 10, further comprising a control input responsive to control logic to adjust the integer submultiples of the frame repetition rate to alter a shape of a carrier power spectrum of the received PWM signals.

16. The circuit device of claim 10, wherein the modulated PWM signals are produced without changing at least one of the frame repetition rate and the carrier frequency of the received PWM signals.

17. The circuit device of claim 10, wherein independent phase shift operations are applied to the PWM input signals to produce modulated PWM signals having a suppressed common mode carrier.

18. A method comprising:

receiving at least one pulse-width modulated (PWM) signal at a pulse edge control circuit;

selectively applying a phase shift operation to the at least one PWM signal at integer submultiples of a frame repetition rate to produce at least one modulated PWM signal having a changed power spectrum; and

providing the at least one modulated PWM signal to a corresponding at least one output.

19. The method of claim 18, wherein the at least one PWM signal comprises a first PWM signal and a second PWM signal.

20. The method of claim 19, wherein selectively applying the phase shift operation comprises selectively applying the phase shift operation to the first and second PWM signals to produce first and second modulated PWM signals having a suppressed carrier in a common mode power spectrum.

21. The method of claim 18, wherein selectively applying the phase shift operation comprises selectively applying one of a plus or a minus quarter-frame phase shift to the at least one PWM signal.

22. The method of claim 21, further comprising wrapping to a second boundary of a frame that portion of a PWM pulse of the at least one PWM signal that extends beyond a first boundary of the frame when a width of the PWM pulse is greater than half of a frame width of the frame.

23. The method of claim 18, wherein selectively applying the phase shift operation comprises selectively shifting the at least one PWM signal such that pulses of the at least one PWM signal are shifted no further than to abut early or late frame boundaries.

24. The method of claim 18, further comprising:

receiving a control signal at the pulse edge control circuit; and

adjusting the integer submultiple of the frame repetition rate in response to receiving the control signal to shape a power spectrum of the at least one modulated PWM signal.

25. The method of claim 18, wherein the at least one modulated PWM signal has reduced electromagnetic interference (EMI) and radio frequency (RF) interference at particular frequencies relative to the at least one PWM signal.