Phase-shifted pulse width modulation signal generation

• US 7,843,242 B1
• Filed: 08/07/2009
• Issued: 11/30/2010
• Est. Priority Date: 08/07/2009
• Status: Expired due to Fees

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Zhao, Bin
• Primary Examiner(s): Cox, Cassandra
• Application Number:
  US12/537,692
• Time in Patent Office: 480 Days
• Field of Search: None
• US Class Current: 327/175
• CPC Class Codes: G06F 1/025 for functions having two-valued amplitude, e.g. Walsh functions
• CPC Class Codes: H03K 5/15013 with more than two outputs
• CPC Class Codes: H03K 7/08 Duration or width modulation ; Duty cycle modulation

Abstract

A pulse width modulation (PWM) signal generator generates multiple output PWM signals from an input PWM signal, whereby each output PWM signal has a frequency and duty ratio substantially similar to the input PWM signal and each output PWM signal is phase-shifted in relation to the other output PWM signals. The PWM signal generator samples a PWM cycle of the input PWM signal to determine various PWM parameters representative of the duration of the active portion of the sampled PWM cycle and the total duration of the sampled PWM cycle. The PWM signal generator then uses the PWM parameters to generate corresponding PWM cycles for the output PWM signals using a set of two independent counters. This process of sampling a PWM cycle of the input PWM signal and generating the output PWM signals based on the PWM parameters resulting from the sampling process can be repeated for one or more iterations.

Claims

1. In a pulse width modulation (PWM) signal generator that receives an input PWM signal and outputs a plurality of output PWM signals in parallel, each output PWM signal phase-shifted in relation to the other output PWM signals, a method comprising:

sampling, at the PWM signal generator, a first PWM cycle of the input PWM signal based on a periodic signal to generate PWM parameters representative of a duration of an active portion of the first PWM cycle and a total duration of the first PWM cycle;

initiating a first count of a first counter of the PWM signal generator responsive to a start of a second PWM cycle of the input PWM signal, the second PWM cycle following the first PWM cycle;

timing, at the PWM signal generator, a generation of a first set of PWM cycles for the plurality of output PWM signals based on the PWM parameters and the first count;

initiating a second count of a second counter of the PWM signal generator responsive to a start of a third PWM cycle of the input PWM signal, the third cycle following the second PWM cycle; and

timing, at the PWM signal generator, a generation of a second set of PWM cycles for the plurality of output PWM signals based on the second count.

2. The method of claim 1, further comprising:

sampling, at the PWM signal generator, the second PWM cycle based on the periodic signal to generate second PWM parameters representative of a duration of an active portion of the second PWM cycle and a total duration of the second PWM cycle; and

wherein timing the generation of the second set of PWM cycles comprises timing the generation of the second set of PWM cycles further based on the second PWM parameters.

3. The method of claim 1, wherein:

the first counter is driven by a first generation clock signal provided by a first frequency divider;

the second counter is driven by a second generation clock signal provided by a second frequency divider; and

the method further comprises;

initiating the first frequency divider in response to the start of the second PWM cycle; and

initiating the second frequency divider in response to the start of the third PWM cycle.

4. The method of claim 3, wherein the first frequency divider and the second frequency divider each includes an input to receive the periodic signal and implements the same frequency division ratio.

5. The method of claim 1, wherein:

the first counter and the second counter are driven by the same clock signal.

6. The method of claim 1, wherein timing the generation of the first set of PWM cycles for the plurality of output PWM signals comprises:

determining, at the PWM signal generator, a first threshold value representative of a first phase-shift delay for a first output PWM signal;

determining, at the PWM signal generator, a second threshold value representative of a sum of the first phase-shift delay and the duration of the active portion of the first PWM cycle;

configuring, at the PWM signal generator, the first output PWM signal to an active level in response to the first count reaching the first threshold value; and

reconfiguring, at the PWM signal generator, the first output PWM signal to an inactive level in response to the first count reaching the second threshold value.

7. The method of claim 6, wherein timing the generation of the first set of PWM cycles for the plurality of output PWM signals further comprises:

determining, at the PWM signal generator, a third threshold value representative of a second phase-shift delay for a second output PWM signal;

determining, at the PWM signal generator, a fourth threshold value representative of a sum of the second phase-shift delay and the duration of the active portion of the first PWM cycle;

configuring, at the PWM signal generator, the second output PWM signal to the active level in response to the first count reaching the third threshold value; and

reconfiguring, at the PWM signal generator, the second output PWM signal to the inactive level in response to the first count reaching the fourth threshold value.

8. The method of claim 7, wherein the first phase-shift delay and the second phase-shift delay comprise the same phase-shift delay.

9. The method of claim 6, wherein the first phase-shift delay is zero and the second phase-shift delay is non-zero.

10. The method of claim 6, wherein timing the generation of the second set of PWM cycles for the plurality of output PWM signals comprises:

determining, at the PWM signal generator, a third threshold value representative of a second phase-shift delay for the first output PWM signal;

determining, at the PWM signal generator, a fourth threshold value representative of a sum of the second phase-shift delay and a duration of an active portion of a second PWM cycle of the input PWM signal;

configuring, at the PWM signal generator, the first output PWM signal to an active level in response to the second count reaching the third threshold value; and

reconfiguring, at the PWM signal generator, the first output PWM signal to an inactive level in response to the second count reaching the fourth threshold value.

11. The method of claim 6, wherein the second phase-shift delay is an integer multiple of the first phase-shift delay, the method further comprising:

determining, at the PWM signal generator, the first phase-shift delay and the second phase-shift delay based on a ratio of a value representative of the total duration of the first PWM cycle and a number of output PWM channels of the plurality of PWM channels.

12. A system comprising:

a pulse width modulation (PWM) signal generator having an input to receive an input PWM signal and a plurality of outputs to provide a plurality of output PWM signals in parallel, each output PWM signal phase-shifted in relation to the other output PWM signals, the PWM signal generator comprising;

a sampling module to sample a first PWM cycle of the input PWM signal based on a periodic signal to generate PWM parameters representative of a duration of an active portion of the first PWM cycle and a total duration of the first PWM cycle;

a first signal generation unit comprising a first counter, wherein the first signal generation unit initiates a first count of the first counter responsive to a start of a second PWM cycle of the input PWM signal, the second PWM cycle following the first PWM cycle, and times a generation of a first set of PWM cycles for the plurality of output PWM signals based on the PWM parameters and the first count; and

a second signal generation unit comprising a second counter, wherein the second signal generation unit initiates a second count of the second counter responsive to a start of a third PWM cycle of the input PWM signal, the third PWM cycle following the second PWM cycle, and times a generation of a second set of PWM cycles for the plurality of output PWM signals based on the second count.

13. The system of claim 12, wherein:

the sampling module further is to sample the second PWM cycle based on the periodic signal to generate second PWM parameters representative of a duration of an active portion of the second PWM cycle and a total duration of the second PWM cycle; and

the second signal generation unit is to time the generation of the second set of PWM cycles further based on the second PWM parameters.

14. The system of claim 12, further comprising:

a first frequency divider to generate a first generation clock signal to drive the first counter;

a second frequency divider to generate a second generation clock signal to drive the second counter;

wherein the first signal generation unit initiates the first frequency divider in response to the start of the second PWM cycle; and

wherein the second signal generation unit initiates the second frequency divider in response to the start of the third PWM cycle.

15. The system of claim 12, wherein the first signal generation unit times the generation of the first set of PWM cycles by determining a first threshold value representative of a first phase-shift delay for a first output PWM signal, determining a second threshold value representative of a sum of the first phase-shift delay and the duration of the active portion of the first PWM cycle, configuring the first output PWM signal to an active level in response to the first count reaching the first threshold value, and reconfiguring the first output PWM signal to an inactive level in response to the first count reaching the second threshold value.

16. The system of claim 15, wherein the first signal generation unit times the generation of the first set of PWM cycles further by determining a third threshold value representative of a second phase-shift delay for a second output PWM signal, determining, a fourth threshold value representative of a sum of the second phase-shift delay and the duration of the active portion of the first PWM cycle, configuring the second output PWM signal to the active level in response to the first count reaching the third threshold value, and reconfiguring the second output PWM signal to the inactive level in response to the first count reaching the fourth threshold value.

17. The system of claim 15, wherein the second signal generation unit times the generation of the second set of PWM cycles by determining a third threshold value representative of a second phase-shift delay for the first output PWM signal, determining a fourth threshold value representative of a sum of the second phase-shift delay and a duty period of a second PWM cycle of the input PWM signal, configuring the first output PWM signal to an active level in response to the second count reaching the third threshold value, and reconfiguring the first output PWM signal to an inactive level in response to the second count reaching the fourth threshold value.

18. The system of claim 17, wherein the PWM signal generator further comprises a signal combination module having a first input to receive a first representation of the first output PWM signal from the first signal generation unit, a second input to receive a second representation of the first output PWM signal from the second signal generation unit, and an output to provide a combination of the first representation and the second representation as the first output PWM signal.

19. The system of claim 15, wherein the second phase-shift delay is an integer multiple of the first phase-shift delay, and wherein the first signal generation unit is to determine the first phase-shift delay and the second phase-shift delay based on a ratio of a value representative of the total duration of the first PWM cycle and a number of output PWM channels of the plurality of PWM channels.

20. The system of claim 12, further comprising:

a plurality of light emitting diode (LED) strings, each LED string comprising an input to receive a corresponding output PWM signal of the plurality of output PWM signals.