Adjustable time duration for driving pulse-width modulation (PWM) output to reduce thermal noise

Patent metadata

Field	Value
Publication number	US-9847773-B2
Application number	US-201715491476-A
Country	US
Kind code	B2
Filing date	Apr 19, 2017
Priority date	Dec 16, 2015
Publication date	Dec 19, 2017
Grant date	Dec 19, 2017

Abstract

Noise introduced in an output signal of a pulse-width modulator (PWM) may be reduced by changing the time duration that a switch is driving the output node. Because the power supplies coupled to the switches are the source of noise in the output signal of the PWM, the time duration that the power supplies are driving the output may be reduced to obtain a subsequent reduction in noise in the output signal. For example, when a small signal is desired to be output by the PWM, the switches may be operated for shorter time durations. Thus, the switches couple the noise sources to ground for a duration of a cycle to reduce contribution of noise to the output. But, when a larger signal is desired to be output by the PWM, the switches may be operated for longer time durations or the conventional time durations described above.

First claim

What is claimed is:

1. An apparatus, comprising:
a controller coupled to a plurality of switches for generating a pulse-width modulation signal at an output node, and wherein the controller is configured to:
receive an input signal for conversion to a pulse width modulation representation;
determine whether the input signal is a small signal of determining whether a signal-to-noise ratio (SNR) of the input signal is below a threshold level;
when the input signal is a small signal, operate the plurality of switches at short time durations having a first time duration; and
when the input signal is not a small signal, operate the plurality of switches at long time durations having a second time duration that is longer than the first time duration.

2. The apparatus of claim 1 , wherein the controller is configured to operate the plurality of switches at short time durations by operating at least one of the plurality of switches with a duty cycle of less than fifty percent.

3. The apparatus of claim 1 , wherein the controller is configured to generate the pulse-width modulation signal at the output node by operating a first switch and a second switch of the plurality of switches to generate a pulse width modulation (PWM) representation of the input signal at the output node.

4. The apparatus of claim 3 , wherein the controller is further configured to:
adjust a time duration that the first switch and the second switch are coupled to the output node based, at least in part, on an envelope level of a desired output signal at the output node by:
in a first mode, coupling the first switch and the second switch to the output node for the first time duration;
in a second mode, coupling the first switch and the second switch to the output node for the second time duration; and
switching between the first mode and the second mode based, at least in part, on the envelope level.

5. The apparatus of claim 4 , wherein the controller is configured to adjust the time duration that the first switch is in the first phase and that the second switch is in the third phase such that the time duration is shorter at lower desired output signal levels.

6. The apparatus of claim 3 , wherein the first switch is configured such that when connected in a first phase drives the output node in a positive direction and contributes noise and when connected in a second phase does not contribute to output noise or drive the output node in any direction, and wherein the second switch is configured such that when connected in a third phase drives the output node in a negative direction and contributes noise and when connected in a fourth phase does not contribute to output noise or drive the output node in any direction.

7. The apparatus of claim 3 , wherein the controller is configured to adjust the time duration based, at least in part, on a desired volume level.

8. The apparatus of claim 1 , wherein the controller is configured to determine whether the input signal is a small signal by determining whether the input signal is below 10 decibels (dB).

9. The apparatus of claim 1 , wherein the controller is configured to determine whether the input signal is a small signal by determining whether the input signal is below 20 decibels (dB).

10. The apparatus of claim 1 , wherein the controller is configured to determine whether the input signal is a small signal by determining whether the input signal is below 60 decibels (dB).

11. A method, comprising:
receiving an input signal for conversion to a pulse width modulation representation at an output node;
determining whether the input signal is a small signal by determining whether a signal-to-noise ratio (SNR) of the input signal is below a threshold level;
when the input signal is a small signal, operating the plurality of switches at short time durations having a first time duration; and
when the input signal is not a small signal, operating the plurality of switches at long time durations having a second time duration that is longer than the first time duration.

12. The method of claim 11 , wherein the step of operating the plurality of switches at short time durations comprises operating at least one of the plurality of switches with a duty cycle of less than fifty percent.

13. The method of claim 11 , wherein the step of generating the pulse-width modulation signal comprises operating a first switch and a second switch of the plurality of switches to generate a pulse width modulation (PWM) representation of the input signal at the output node.

14. The method of claim 13 , adjusting a time duration that the first switch and the second switch are coupled to the output node based, at least in part, on an envelope level of a desired output signal at the output node, wherein adjusting comprises:
in a first mode, coupling the first switch and the second switch to the output node for the first time duration;
in a second mode, coupling the first switch and the second switch to the output node for the second time duration; and
switching between the first mode and the second mode based, at least in part, on the envelope level.

15. The method of claim 14 , further comprising adjusting the time duration based, at least in part, on a desired volume level.

16. The method of claim 13 , wherein the first switch is configured such that when connected in a first phase drives the output node in a positive direction and contributes noise and when connected in a second phase does not contribute to output noise or drive the output node in any direction, and wherein the second switch is configured such that when connected in a third phase drives the output node in a negative direction and contributes noise and when connected in a fourth phase does not contribute to output noise or drive the output node in any direction.

17. The method of claim 16 , further comprising adjusting the time duration that the first switch is in the first phase and that the second switch is in the third phase such that the time duration is shorter at a lower desired output signal.

18. The method of claim 11 , wherein the step of determining whether the input signal is a small signal comprises determining whether the input signal is below 10 decibels (dB).

19. The method of claim 11 , wherein the step of determining whether the input signal is a small signal comprises determining whether the input signal is below 20 decibels (dB).

20. The method of claim 11 , wherein the step of determining whether the input signal is a small signal comprises determining whether the input signal is below 60 decibels (dB).

Assignees

• Cirrus Logic Inc

Inventors

• Melanson John L
• Lesso Paul

Classifications

• H03F3/2171

  with field-effect devices (H03F3/2173 - H03F3/2178 take precedence) · CPC title

• H03K7/08 Primary

  Duration or width modulation {; Duty cycle modulation} · CPC title

• H03F1/303

  using a switching device (H03F1/305, H03F3/005, H03F3/38 take precedence) · CPC title

• H03M1/822

  using pulse width modulation · CPC title

• H03K3/011 Primary

  Modifications of generator to compensate for variations in physical values, e.g. voltage, temperature {(to maintain energy constant H03K3/015)} · CPC title