System and method of changing a PWM power spectrum

• US 7,965,214 B2
• Filed: 07/30/2010
• Issued: 06/21/2011
• Est. Priority Date: 04/01/2008
• Status: Expired due to Fees

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Khoury, John M., Beale, Richard Gale
• Primary Examiner(s): JEANGLAUDE, JEAN BRUNER
• Application Number:
  US12/848,020
• Publication Number:
  US 20100296671A1
• Time in Patent Office: 326 Days
• Field of Search: 341/152, 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 comprising:

at least one input adapted to receive at least one pulse-width modulated (PWM) signal;

at least one output for providing at least one modulated PWM signal; and

a pulse edge control circuit coupled to the at least one input and to the at least one output, the pulse edge control circuit adapted to selectively phase shift the at least one PWM signal to produce the at least one modulated PWM signal having a changed power spectrum.

2. The circuit of claim 1, wherein the pulse edge control circuit comprises:

a control input coupled to the pulse edge control circuit and adapted to receive a control signal; and

wherein the pulse edge control circuit selectively phase shifts the at least one PWM signal within each sequential frame to selectively adjust a shape of the changed power spectrum in response to receiving the control signal.

3. The circuit of claim 1, wherein the pulse edge control circuit produces the at least one modulated PWM signal without changing an effective duty cycle associated with the at least one PWM signal from frame to frame.

4. The circuit of claim 1, wherein the pulse edge control circuit selectively phase shifts the at least one PWM signal within a PWM frame by a fraction of a width of the PWM frame over a sequence of PWM frames.

5. The circuit of claim 1, wherein the pulse edge control circuit is adapted to selectively phase shift the at least one PWM signal to align an edge transition of the at least one PWM signal to a boundary of a PWM frame.

6. The circuit of claim 1, wherein the pulse edge control circuit is adapted to selectively phase shift the at least one PWM signal within a PWM frame by a phase interval corresponding to one of one quarter of a frame width of the PWM frame, one half of the frame width, and three-quarters of the frame width.

7. The circuit of claim 1, wherein the pulse edge control circuit is adapted to selectively phase shift the at least one PWM signal according to a constructed pattern to concentrate a carrier signal energy at frequencies other than a carrier frequency of the at least one modulated PWM signal.

8. The circuit of claim 1, wherein the at least one PWM signal includes a first PWM signal and a second PWM signal;

wherein the first and second PWM signals form a differentially encoded signal pair; and

wherein the pulse edge control circuit is configured to selectively phase shift the first and second PWM signal by a predetermined phase to produce the at least one modulated PWM signal including a first modulated PWM signal and a second modulated PWM signal.

9. The circuit of claim 1, wherein the pulse edge control circuit is adapted to selectively phase shift the at least one PWM signal according to a random pattern to whiten a power spectrum of the at least one modulated PWM signal to produce the changed power spectrum.

10. A system comprising:

a first input terminal adapted to receive a first pulse width modulated (PWM) signal;

a second input terminal adapted to receive a second PWM signal;

a first output terminal for providing a first modulated PWM signal;

a second output terminal for providing a second modulated PWM signal; and

a pulse edge control circuit coupled to the first and second input terminals and to the first and second output terminals, the pulse edge control circuit adapted to selectively apply a phase shift operation to the first and second PWM signals to produce the first and second modulated PWM signals.

11. The system of claim 10, further comprising:

a first timing control circuit including an input coupled to the first output terminal and including an output;

a second timing control circuit including an input coupled to the second output terminal and including an output;

a first gate driver including an input coupled to the output of the first timing control circuit and a driver output coupled to a first input of an H-bridge circuit; and

a second gate driver including an input coupled to the output of the second timing control circuit and a driver output coupled to a second input of the H-bridge circuit.

12. The system of claim 11, further comprising the H-bridge circuit including:

the first input;

the second input;

a first H-bridge output for providing the first modulated PWM signal; and

a second H-bridge output for providing the second modulated PWM signal.

13. The system of claim 12, wherein the first and second H-bridge outputs are configurable to be coupled to a speaker to provide the first and second modulated PWM signals for an audio application.

14. The system of claim 12, wherein the first and second H-bridge outputs are configurable to be coupled to a switched power circuit to provide the first and second modulated PWM signals for a power control application.

15. The system of claim 12, wherein the first and second H-bridge outputs are configurable to be coupled to a motor control circuit to provide the first and second modulated PWM signals for a motor control application.

16. The system of claim 12, wherein the first and second modulated PWM signals have reduced electromagnetic interference (EMI) and reduced radio frequency (RF) interference at particular frequencies relative to the first and second PWM signals.

17. The system of claim 10, wherein the pulse edge control circuit produces the first and second modulated PWM signals without changing at least one of a frame repetition rate and a carrier frequency of the first and second PWM signals.

18. The system of claim 10, wherein the pulse edge control circuit selectively applies the phase shift operation to each pulse edge of the first and second PWM signals to produce the first and second modulated PWM signals.

19. The system of claim 10, wherein the pulse edge control circuit selectively applies the phase shift operation to at least two pulse edges of the first and second PWM signals to produce the first and second modulated PWM signals.

20. The system of claim 10, wherein a common mode carrier energy of the first and second modulated PWM signals is suppressed without changing a differential baseband signal associated with the first and second PWM signals.

21. A method comprising:

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

selectively phase shifting the at least one PWM signal 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.

22. The method of claim 21, wherein selectively phase shifting the at least one PWM signal comprises selectively applying a phase shift operation to the at least one PWM signal at discrete time intervals;

and

wherein each of the discrete time intervals is an integer sub-multiple of a frame repetition rate of the at least one PWM signal.

23. The method of claim 21, wherein selectively phase shifting comprises alternately phase shifting and not phase shifting the at least one PWM signal.

24. The method of claim 23, wherein alternately phase shifting and not phase shifting the at least one PWM signal is performed at periodic intervals to concentrate a carrier signal energy at frequencies other than a carrier frequency within the changed power spectrum.

25. The method of claim 23, wherein alternately phase shifting and not phase shifting the at least one PWM signal is performed at random intervals to whiten carrier signal energy within the changed power spectrum.

26. The method of claim 21, 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.