Audio power amplification with reduced input power supply crest factor

• US 9,231,543 B2
• Filed: 01/13/2014
• Issued: 01/05/2016
• Est. Priority Date: 01/13/2014
• Status: Active Grant

• Current Assignee: Apple Inc., Blakely, Sokoloff, Taylor & Zafman, LLP
• Original Assignee: Apple Inc.
• Inventors: Johanningsmeier, Nathan A., Hardy, Casey L., Hogan, Roderick, Curcio, Joseph J.
• Primary Examiner(s): Kim, Paul S
• Assistant Examiner(s): FALEY, KATHERINE A
• Application Number:
  US14/153,984
• Publication Number:
  US 20150200640A1
• Time in Patent Office: 722 Days
• Field of Search: 381/28, 381/104, 381/107, 381/108, 381/120, 330/127, 330/251, 330/297, 330/199
• US Class Current: 1/1
• CPC Class Codes: H03G 3/004 Control by varying the supply voltage
• CPC Class Codes: H03G 3/20 Automatic control H03G3/005 takes precedence; combined with volume compression or expansion H03G7/00
• CPC Class Codes: H03G 3/3005 in amplifiers suitable for low-frequencies, e.g. audio amplifiers H03G3/32, H03G3/34 take precedence

Abstract

A power converter has an output that is coupled in parallel with an energy reservoir circuit and a power supply node of an audio power amplifier. The converter can set an upper limit on its input supply current that is variable in accordance with a control input. A controller is to produce a signal, coupled to the control input of the power converter, that is responsive to a measure of input supply voltage of the power converter and either output voltage of the power converter or output power of the amplifier. Other embodiments are also described and claimed.

Claims

1. A method for audio amplification, comprising:

amplifying an audio signal using a power amplifier whose power supply node is coupled to receive power from a power converter in parallel with an energy reservoir circuit; and

the power converter automatically adjusting its input supply power based on a measure of output power of the power amplifier while amplifying the audio signal, so that when instantaneous output power of the amplifier is higher than the input supply power to the power converter the energy reservoir circuit is being emptied, and when instantaneous output power of the amplifier is lower than the input supply power to the power converter the energy reservoir is being replenished by power from the power converter.

2. The method of claim 1 wherein voltage of the power converter output varies between a) maximum output voltage of the amplifier at a low end;

and b) a high end that is at least 20% greater.

3. The method of claim 1 wherein adjusting the input supply power to the power converter causes voltage of the power converter output to vary by more than 20% while supplying power to the amplifier.

4. The method of claim 3 wherein the voltage of the power converter output varies by more than 30% while supplying power to the amplifier.

5. The method of claim 4 wherein a sound volume setting for the audio signal is between 50% and 75%, and the audio signal has spectral components below 150 Hz.

6. The method of claim 3 wherein a sound volume setting for the audio signal is between 50% and 75%, and the audio signal has spectral components below 150 Hz.

7. The method of claim 1 wherein voltage of the power converter output varies between a minimum and a maximum, and wherein output voltage of the amplifier remains smaller than the minimum power converter output voltage at sound volume settings between 50% and 75 while the audio signal is a 100 Hz tone.

8. The method of claim 1 wherein voltage of the power converter output starts to fall as soon as sound volume setting for the audio signal has been increased from 0% to 25%.

9. The method of claim 1 further comprising determining the measure of output power of the power amplifier.

10. The method of claim 9 wherein the determining the measure of output power comprises a look-ahead process in which a portion of the audio signal is analyzed prior to said portion being amplified by the power amplifier, wherein automatically adjusting the input supply power to the power converter is responsive to the look-ahead process.

11. The method of claim 10 wherein the look-ahead process comprises computing a moving measure of central tendency of strength of the audio signal, and wherein automatically adjusting the input supply power to the power converter comprises raising a limit on input supply current whenever the computed moving measure of central tendency of strength is rising.

12. The method of claim 11 wherein automatically adjusting the input supply power to the power converter comprises lowering the limit on the input supply current whenever the computed moving measure of central tendency of the strength is falling.

13. The method of claim 10 wherein the look-ahead process comprises determining whether said portion of the audio signal contains a spectral or frequency component that is lower in frequency than a pre-determined threshold, and wherein automatically adjusting the input supply power to the power converter comprises raising a limit on input supply current when the portion of the audio signal contains a spectral component that is lower in frequency than the pre-determined threshold.

14. The method of claim 13 wherein the limit on the input supply current is raised only if input supply voltage to the power converter is sufficiently high.

15. A method for audio amplification, comprising:

amplifying an audio signal using a power amplifier, while an output of a power converter is supplying power to an energy reservoir in parallel with a power supply node of the power amplifier; and

while amplifying the audio signal, the power converter automatically adjusting its input supply power based on voltage of the output of the power converter so that

when instantaneous output power of the amplifier rises above the input supply power to the power converter, the voltage of the output of the power converter decreases, and

when instantaneous output power of the amplifier falls below the input supply power to the power converter, the voltage of the output of the power converter increases.

16. The method of claim 15 wherein automatically adjusting the input supply power to the power converter comprises:

allowing input supply current of the power converter to increase, as needed by the power converter when supplying power to the power amplifier, up to a pre-determined high level, in response to the voltage of the power converter output being below a limit; and

preventing the input supply current from increasing above a pre-determined low level, in response to the voltage of the power converter output being above the limit.

17. The method of claim 16 further comprising adjusting the pre-determined high level for the input supply current as a function of volume setting.

18. The method of claim 17 wherein the pre-determined low level for the input supply current is essentially zero, and the pre-determined high level for the input supply current is a maximum.

19. The method of claim 16 wherein automatically adjusting the input supply power to the power converter comprises comparing the voltage of the power converter output to a predetermined threshold, and wherein a) allowing the input supply current to increase and b) preventing the input supply current from increasing, are responsive to the comparing.

20. The method of claim 16 further comprising adjusting the pre-determined high level, for the input supply current, upward in response to input supply voltage of the power converter going upward.

21. An audio device comprising:

an audio power amplifier;

a power converter whose output is coupled in parallel with an energy reservoir circuit and a power supply node of the amplifier, wherein the power converter can set an upper limit on its input supply current that is variable in accordance with a control input; and

a controller to produce a signal, coupled to the control input of the power converter, that is responsive to measures of a) output power of the amplifier and b) input supply voltage of the power converter.

22. The audio device of claim 21 wherein the controller is to produce the signal to control the power converter such that when instantaneous output power of the amplifier is higher than its average output power, the energy reservoir circuit is being emptied, and when instantaneous output power of the amplifier is lower than its average output power, the energy reservoir is being replenished.

23. The audio device of claim 21 further comprising a battery that is coupled to provide the input supply power of the power converter.

24. An audio device comprising:

an audio power amplifier;

a power converter whose output is coupled in parallel with an energy reservoir circuit and a power supply node of the amplifier, wherein the power converter can set an upper limit on its input supply current that is variable in accordance with a control input; and

a controller to produce a signal, coupled to the control input of the power converter, that is responsive to measures of a) output voltage of the power converter and b) input supply voltage of the power converter.

25. The audio device of claim 24 wherein the controller is to produce the signal to control the power converter such that when instantaneous output power of the amplifier is higher than its average output power, the energy reservoir circuit is being emptied, and when instantaneous output power of the amplifier is lower than its average output power, the energy reservoir is being replenished.

26. The audio device of claim 24 further comprising a battery that is coupled to provide the input supply power of the power converter.