System and method for providing digital pulse width modulation

• US 7,202,651 B2
• Filed: 01/06/2006
• Issued: 04/10/2007
• Est. Priority Date: 11/19/2002
• Status: Expired due to Term

• Current Assignee: Bel Power Solutions Inc.
• Original Assignee: Power-One Incorporated (ABB Limited)
• Inventors: Chapuis, Alain
• Primary Examiner(s): Han; Jessica
• Application Number:
  US11/326,813
• Publication Number:
  US 20060113981A1
• Time in Patent Office: 459 Days
• Field of Search: 323/222, 323/225, 323/263, 323/282, 323/283, 323/284, 323/290, 323/211, 327/149, 327/153, 327/159, 327/172, 327/175
• US Class Current: 323/283
• CPC Class Codes: G06F 1/025 for functions having two-valued amplitude, e.g. Walsh functions
• CPC Class Codes: H02M 3/157 with digital control
• CPC Class Codes: H02M 7/53873 with digital control
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation
• CPC Class Codes: H03M 1/661 Improving the reconstruction of the analogue output signal beyond the resolution of the digital input signal, e.g. by interpolation, by curve-fitting, by smoothing
• CPC Class Codes: H03M 1/822 using pulse width modulation

Abstract

A pulse width modulation system for use in a switching power supply circuit provides high-resolution pulse width modulated signals. The pulse width modulation system is configured to receive a control signal comprising a (m+n)-bit binary word and to provide a pulse width modulated signal with a predetermined average duty cycle having a resolution of substantially 2^−(m+n). The pulse width modulation system includes a timing circuit for providing 2^m timing signals, a dithering circuit, and a signal generator. Upon receiving the control signal, the dithering circuit is configured to provide a modified control signal, which comprises a series of up to 2ⁿm-bit binary words. The signal generator is configured to receive the timing signals and the modified control signal and to provide the pulse width modulated signal having a duty cycle, which, when averaged over 2ⁿ timing cycles, is approximately equal to the predetermined average duty cycle. The pulse width modulated signal is used by a switching power supply circuit to control at least one power switching device.

Claims

1. A pulse width modulation circuit comprising:

a dithering circuit configured to receive a digital control word corresponding to a desired duty cycle and provide a modified control signal comprising plural digital control words;

a timing circuit configured to provide plural timing signals, each said timing signal comprising a voltage pulse corresponding to a respective one of the plural digital control words; and

a signal generator configured to receive said modified control signal and said timing signals, and providing a pulse width modulated signal having an average duty cycle that is substantially equal to the desired duty cycle.

2. The circuit of claim 1, wherein said digital control word comprises an (m+n)-bit binary words, wherein m and n are integers.

3. The circuit of claim 2, wherein said modified control signal comprises a series of 2ⁿ m-bit binary words.

4. The circuit of claim 3, wherein said dithering circuit includes an n-bit binary adder circuit, an n-bit delay circuit, and an m-bit binary adder circuit, said n-bit binary adder having first input operand terminals for receiving n least significant bits of said control signal, second input operand terminals, output sum terminals being coupled with said second input operand terminals via said n-bit delay circuit, and a carry terminal, said n-bit delay circuit being activated by said at least one of said timing signals, said m-bit binary adder circuit having first input operand terminals for receiving m most significant bits of said control signal, second input operand terminals being coupled with said carry terminal, and output terminals for providing said modified control signal.

5. The circuit of claim 1, wherein each said voltage pulse has a predetermined period during a timing cycle of the timing circuit, said timing cycle being substantially equal to 2^m of said predetermined periods, wherein m is an integer.

6. The circuit of claim 1, wherein said timing signals provide said voltage pulses in accordance with a predetermined sequence.

7. The circuit of claim 1, wherein said timing circuit comprises a ring oscillator.

8. The circuit of claim 1, wherein said timing circuit includes a delay line and an inverter circuit, said delay line having an input terminal and an output terminal respectively coupled with an output terminal and an input terminal of said inverter circuit.

9. The circuit of claim 8, wherein said delay line comprises 2^m delay elements, wherein m is an integer.

10. The circuit of claim 9, wherein said delay elements comprise plural buffer circuits.

11. The control circuit of claim 9, wherein said delay elements comprise plural inverter circuits.

12. The circuit of claim 9, wherein each of said delay elements is configured to provide a delay period that is less than or substantially equal to ten nanoseconds.

13. The circuit of claim 1, wherein said signal generator is configured to provide said pulse width modulated signal with a phase shift.

14. The circuit of claim 13, wherein said phase shift is preprogrammed.

15. The circuit of claim 13, wherein said phase shift is programmable.

16. The circuit of claim 1, wherein said signal generator includes a latch circuit for providing said pulse width modulated signal.

17. The circuit of claim 16, wherein said latch circuit is configured to provide said pulse width modulated signal with a first signal state upon receiving a first timing signal and with a second signal state upon receiving a second timing signal.

18. The circuit of claim 17, wherein said first signal state is associated with a high logic level, and said second signal state is associated with a low logic level.

19. The circuit of claim 17, wherein said signal generator further includes a multiplexer circuit configured to receive said modified control signal and to select said second timing signal.

20. The circuit of claim 17, wherein said signal generator further includes a first multiplexer circuit configured to receive a phase signal and to select said first timing signal and a second multiplexer circuit configured to receive a sum of said phase signal and said modified control signal and to select said second timing signal.

21. The circuit of claim 20, wherein said phase signal comprises an m-bit binary word.

22. The circuit of claim 20, wherein said signal generator further includes a memory containing said phase signal.