System and method of changing a PWM power spectrum

• US 7,701,307 B2
• Filed: 08/07/2008
• Issued: 04/20/2010
• Est. Priority Date: 04/01/2008
• Status: Expired due to Fees

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Khoury, John, Beale, Richard
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US12/187,873
• Publication Number:
  US 20090243744A1
• Time in Patent Office: 621 Days
• Field of Search: 332/107, 332109-111, 327172-177, 330/10, 375/238
• US Class Current: 332/107
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 3/2173 of the bridge type
• CPC Class Codes: H03K 11/00 Transforming types of modulations, e.g. position-modulated pulses into duration-modulated pulses
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation

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 invert and swap the at least one PWM signal with a logic-inverted duty-cycle complement of the at least one PWM signal at discrete time intervals 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, the pulse edge control circuit adapted to selectively swap the at least one PWM signal with a logic inverted, duty-cycle complement of the at least one PWM signal at discrete time intervals to produce at least one modulated PWM signal having a changed power spectrum, the pulse edge control circuit to 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 discrete time interval is an integer sub-multiple of the frame repetition rate.

3. 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 swap operation for each sequential frame to selectively adjust a shape of the changed power spectrum.

4. The circuit device of claim 1, wherein the at least one modulated PWM signal is produced without changing an effective duty cycle associated with the at least one PWM signal from frame to frame.

5. The circuit device of claim 1, wherein the pulse edge control circuit is adapted to generate the logic inverted, duty cycle complement signal from the at least one PWM signal.

6. The circuit device of claim 5, wherein the logic inverted, duty cycle complement signal is generated such that its duty cycle nominally equal to an entire width of a frame minus a duty cycle of the at least one PWM signal within limits of quantization effects.

7. The circuit device of claim 1, wherein the swap operation is applied at a particular temporal location within a frame over a sequence of frames.

8. The circuit device of claim 7, wherein the pulse edge control circuit is adapted to swap the received at least one PWM signal with the logic inverted, duty cycle complement related to the received at least one PWM signal at a frame boundary.

9. The circuit device of claim 7, wherein the pulse edge control circuit is adapted to swap the received at least one PWM signal with the logic inverted, duty cycle complement related to the received at least one PWM signal at a temporal location within a frame corresponding to a quarter of a frame width of the frame, half of the frame width, or three-quarters of the frame width.

10. The circuit device of claim 1, wherein the pulse edge control circuit is adapted to selectively swap the received at least one PWM signal with the logic inverted, duty cycle complement related to the received at least one PWM signal according to a constructed pattern to concentrate the carrier signal energy at frequencies other than a carrier frequency of the at least one modulated PWM signal.

11. The circuit device of claim 1, wherein the pulse edge control circuit is adapted to selectively swap the received at least one PWM signal with the logic inverted, duty cycle complement related to the received at least one PWM signal according to a random pattern to whiten the power spectrum of the at least one modulated PWM signal.

12. 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 a carrier frequency.

13. A circuit device comprising a pulse edge control circuit to receive PWM signals via at least two inputs, the pulse edge control circuit adapted to selectively apply a chopping operation to the received PWM signals at discrete time intervals to produce modulated PWM signals having suppressed carriers, the pulse edge control circuit to provide the modulated PWM signals to respective outputs of the pulse edge control circuit, wherein selectively applying the chopping operation comprises selectively inverting and swapping the received PWM signals.

14. The circuit device of claim 13, wherein the discrete time interval is an integer sub-multiple of the frame repetition rate.

15. The circuit device of claim 13, wherein the common mode carriers of the modulated PWM signals are suppressed without changing a differential baseband signal associated with the received PWM signals.

16. The circuit device of claim 13, further comprising a control input responsive to control logic to selectively control the chop operation for each sequential frame to selectively adjust a shape of a carrier power spectrum of the received PWM signals.

17. The circuit device of claim 13, wherein the received PWM signals comprise a first PWM signal and a second PWM signal that is a logic inverted, duty cycle complement of the first PWM signal, the first PWM signal having a first duty cycle and the second PWM signal having a second duty cycle comprising nominally an entire width of a frame minus the first duty cycle within limits of quantization effects.

18. The circuit device of claim 13, 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.

19. The circuit device of claim 13, wherein the chop operation is applied at a particular temporal location within a frame over a sequence of frames.

20. The circuit device of claim 19, wherein the pulse edge control circuit is adapted to invert and swap the received at least one PWM signal with the inverted complement related to the received at least one PWM signal at a frame boundary.

21. The circuit device of claim 19, wherein the pulse edge control circuit is adapted to apply the chopping operation at a temporal location within a frame corresponding to a quarter of a width of the frame, half of a width of the frame, or three quarters of a width of the frame.

22. A method comprising:

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

selectively swapping the at least one PWM signal with an logic inverted, duty cycle complement of the at least one PWM signal at discrete time intervals 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.

23. The method of claim 22, wherein the discrete time interval is an integer sub-multiple of the frame repetition rate.

24. The method of claim 22, wherein selectively swapping comprises alternately swapping and not swapping the received at least one PWM signal.

25. The method of claim 24, wherein alternately swapping and not swapping the received at least one PWM signal is performed at periodic intervals to concentrate the carrier signal energy at frequencies other than a carrier frequency within the changed power spectrum.

26. The method of claim 24, wherein alternately swapping and not swapping the received at least one PWM signal is performed at random intervals to whiten carrier signal energy within the changed power spectrum.

27. The method of claim 22, wherein the at least one modulated PWM signal has reduced electromagnetic interference (EMI) and radio frequency (RF) interference at particular frequencies relative to that of the at least one PWM signal.

28. The method of claim 22, wherein the at least one modulated PWM signal has a suppressed energy at a carrier frequency.

29. The method of claim 22, wherein the at least one modulated PWM signal is produced without changing at least one of the frame repetition rate and a carrier frequency.