SYSTEM AND METHOD OF ALTERING A PWM CARRIER POWER SPECTRUM

• US 20090243903A1
• Filed: 05/23/2008
• Published: 10/01/2009
• Est. Priority Date: 04/01/2008
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Khoury, John M.
• Granted Patent: US 7,598,895 B1
• Time in Patent Office: Days
• US Class Current: 341/143
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation

Abstract

In a particular embodiment, a circuit device includes an input to receive a pulse-width modulated (PWM) signal and an output to send a modulated PWM signal. The circuit device further includes a pulse edge control circuit coupled between the input and the output. The pulse edge control circuit receives the PWM signal via the input and includes a control input to receive a modulation control signal. The pulse edge control circuit is adapted to modify the PWM signal to provide the modulated PWM signal with suppressed carrier power and associated harmonics to the output based on the modulation control signal. The circuit device further includes a modulation sequence controller adapted to provide the modulation control signal via the control input. The modulation control signal selectively controls a sequence of the modification of the PWM signal to selectively alter an output power spectrum of the modulated PWM signal.

Claims

1. A circuit device comprising:

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

at least one output to send a modulated PWM signal;

a pulse edge control circuit coupled between the at least one input and the at least one output, the pulse edge control circuit to receive the PWM signal via the at least one input and including a control input to receive a modulation control signal, the pulse edge control circuit adapted to modify the PWM signal to provide a modulated PWM signal with suppressed carrier power and associated harmonics to the at least one output based on the modulation control signal; and

a modulation sequence controller adapted to provide the modulation control signal via the control input, the modulation control signal to selectively control a sequence of the modification of the PWM signal to selectively alter an output power spectrum of the modulated PWM signal.

2. The circuit device of claim 1, wherein the peak carrier power is suppressed relative to a nominal peak carrier power of the received PWM signal.

3. The circuit device of claim 1, wherein the modulation sequence controller selectively controls the sequence to whiten the output carrier power spectrum and to reduce peak carrier power of the modulated PWM signal.

4. The circuit device of claim 1, wherein the modulation sequence controller selectively controls the sequence to shape a power spectrum of the modulated PWM signal.

5. The circuit device of claim 1, wherein the modulation sequence controller selectively controls the sequence to shape a power spectrum of the modulated PWM signal with notches at particular frequencies.

6. The circuit device of claim 1, wherein the modulation sequence controller selectively controls the sequence to shape a power spectrum of the modulated PWM signal to reduce interference at a tuned frequency of a radio frequency (RF) receiver circuit.

7. The circuit device of claim 1, wherein the modulation sequence controller selectively controls the sequence based on the output of a delta sigma modulator.

8. The circuit device of claim 1, wherein the modulation sequence controller selectively controls the sequence by selectively switching between multiple patterns to suppress a power level of the modulated PMW signal at particular frequencies.

9. The circuit device of claim 8, wherein the modulation sequence controller is adapted to switch between patterns periodically.

10. The circuit device of claim 9, wherein a superframe sample and hold logic can cause a pattern to repeat at a selectable rate and create an extended superframe pattern.

11. The circuit device of claim 8, wherein the modulation sequence controller is adapted to randomly switch between patterns.

12. The circuit device of claim 8, wherein the multiple patterns include patterns having different pattern lengths.

13. The circuit device of claim 12, wherein the modulation sequence controller controls the sequence by selectively applying patterns of different pattern lengths to introduce notches at particular frequencies.

14. The circuit device of claim 8, wherein the modulation sequence controller controls the sequence by selectively applying patterns to reduce interference at a tuned frequency of a radio frequency (RF) receiver circuit.

15. The circuit device of claim 1, wherein the modulation sequence controller selectively controls the sequence such that a net average of the carrier suppression modifications is approximately zero over a power measurement time period.

16. A method comprising:

receiving a pulse-width modulated (PWM) signal;

modifying the PWM signal to produce a modulated PWM signal with suppressed carrier power and associated harmonics; and

selectively controlling a modification sequence associated with producing the modulated PWM signal to selectively alter a PWM carrier power spectrum to produce a modulated PWM output signal having at least one of a reduced peak carrier power and a reduced interference at particular frequencies.

17. The method of claim 16, further comprising selectively controlling the modification sequence to suppress a PWM carrier and to spread energy associated with the PWM carrier to other frequency bands in the modulated PWM output signal.

18. The method of claim 16, wherein selectively controlling the modification sequence comprises randomly adjusting the modification sequence to suppress a peak power at a PWM carrier frequency within the modulated PWM output signal.

19. The method of claim 16, wherein selectively controlling the modification sequence includes controlling a sequencing of a phase-shifting or chopping operation to selectively place notches at particular frequencies in a PWM carrier power spectrum of the modulated PWM output signal.

20. The method of claim 16, wherein selectively controlling the modification sequence includes controlling a sequencing of a phase-shifting or chopping operation to selectively place notches at particular frequencies in the modulated PWM output signal.

21. The method of claim 16, wherein selectively controlling the modification sequence includes controlling the sequencing of the phase-shifting or chopping operation to reduce electromagnetic interference (EMI) and radio frequency (RF) interference at particular frequencies.

22. A circuit device comprising:

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

a pulse edge control circuit coupled to the at least one input and adapted to phase-shift or chop the PWM signal to produce a modulated PWM signal with suppressed carrier power and associated harmonics; and

a modulation sequence controller to selectively apply one or more modulation control sequences to a phase-shifting or chopping operation to selectively alter an output PWM power spectrum of the PWM signal and to provide a modulated PWM output signal to at least one output, the modulated PWM output signal having at least one of a reduced peak common mode power and a reduced interference at selected frequencies.

23. The circuit device of claim 22, wherein the one or more modulation control sequences comprise one or more patterns, wherein the one or more patterns have different pattern lengths.

24. The circuit device of claim 22, wherein the modulation sequence controller is adapted to place notches at particular frequencies of a carrier power spectrum of the PWM output signal.

25. The circuit device of claim 22, wherein the modulation sequence controller is adapted to randomly apply the one or more patterns having different pattern lengths and one or more associated complement patterns to shape a carrier power spectrum of the PWM output signal.

26. The circuit device of claim 22, wherein the one or more modulation control sequences comprise one or more superframe patterns having different pattern characteristics including different pattern lengths and different pattern sequences, and wherein modulation sequence controller is adapted to select at least one of the one or more superframe patterns based on at least one of the different pattern characteristics to suppress electromagnetic interference (EMI) and AM radio interference at a particular frequency.

27. The circuit device of claim 22, wherein the one or more modulation control sequences comprise one or more superframe patterns, and wherein the modulation sequence controller is responsive to a control signal to select a pattern from the one or more superframe patterns in coordination with a nearby receiver to reduce interference at a tuned frequency band.

28. A circuit device comprising:

a differential switching amplifier including at least one positive input and at least one negative input and a differential output coupled to a load;

a pulse edge control circuit coupled to the at least one positive input and the at least one negative input of the switching amplifier, the pulse edge control circuit including a differential signal input to receive differential PWM signals and including a modulation control input to receive a modulation control signal, the pulse edge control circuit adapted to phase-shift or chop the differential PWM signals to produce a modulated PWM output signal with suppressed common mode carrier power and associated harmonics without altering a differential mode characteristic of the modulated PWM output signal; and

a modulation sequence controller coupled to the modulation control input to selectively control a sequencing of the phase-shifting or chopping operation to selectively alter a common mode power spectrum of the modulated PWM output signal.

29. The circuit device of claim 28, wherein the modulation sequence controller is adapted to selectively apply one or more patterns to control a sequencing of a phase-shifting or chopping operation to whiten a common mode PWM power spectrum and reduce peak common mode power of a modulated PWM output signal.

30. The circuit device of claim 28, wherein the modulation sequence controller is adapted to selectively apply one or more patterns to control a sequencing of a phase-shifting or chopping operation to shape a common mode power spectrum of the modulated PWM output signal.

31. The circuit device of claim 28, wherein the modulation sequence controller selectively controls the sequencing of a phase-shifting or chopping operation based on an output of a delta sigma modulator to shape a common mode power spectrum of a modulated PWM output signal.

32. The circuit device of claim 28, wherein the modulation sequence controller is adapted to selectively apply one or more patterns to control a sequencing of a phase-shifting or chopping operation to shape a common mode power spectrum with notches at particular frequencies of a modulated PWM output signal.

33. The circuit device of claim 28, wherein the modulation sequence controller is adapted to selectively apply one or more patterns to control a sequencing of a phase-shifting or chopping operation to shape a common mode power spectrum of a modulated PWM output signal to reduce interference at a tuned frequency of a radio frequency (RF) receiver circuit.