SYSTEMS AND METHODS FOR IMPROVED OVER-CURRENT CLIPPING

• US 20090169022A1
• Filed: 12/30/2008
• Published: 07/02/2009
• Est. Priority Date: 12/31/2007
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: Kost, Michael A.
• Granted Patent: US 8,081,028 B2
• Time in Patent Office: Days
• US Class Current: 381/56
• CPC Class Codes: H03F 1/523 for amplifiers using field-effect devices H03F1/526 takes precedence
• CPC Class Codes: H03F 3/185 with field-effect devices H03F3/187 takes precedence
• CPC Class Codes: H03F 3/2173 of the bridge type
• CPC Class Codes: H04R 3/007 Protection circuits for transducers

Abstract

Systems and methods for implementing over-current protection in amplifiers are provided, including systems, methods and devices for specifying a clip level at which to clip an audio signal in response to an over-current condition being detected. In an embodiment, the clip level is reduced while the over-current condition is being detected. Once the over-current condition is no longer detected, the clip level is maintained for a specified period before allowing the clip level to be increased. In an embodiment, the specified period, for which the clip level is maintained before the clip level is allowed to be increased, starts when the over-current condition is no longer detected, and ends when each of N immediately preceding sample(s) of the audio signal are not clipped to the clip level, where N is an integer, and N≧1. After an over-current condition is no longer detected, and after the clip level has been maintained for the specified period, the clip level can be increased if an over-current condition is not detected for a sample and the clip level is below a specified maximum clip level.

Claims

1. For use with an amplifier, a method for specifying clip level at which to clip an audio signal in response to an over-current condition being detected, the method comprising:

reducing the clip level while the over-current condition is being detected; and

maintaining the clip level for a specified period, once the over-current condition is no longer detected, before allowing the clip level to be increased.

2. The method of claim 1, wherein the audio signal comprises a digital signal including a plurality of samples, there is a determination of whether an over-current condition is detected for each of the samples, and wherein:

the specified period, for which the clip level is maintained before the clip level is allowed to be increased,

starts when the over-current condition is no longer detected, and

ends when each of N immediately preceding sample(s) are not clipped to the clip level, where N is an integer, and N≧

1.

3. The method of claim 2, where N=1.

4. The method of claim 2, where N≧

2.

5. The method of claim 2, wherein:

after an over-current condition is no longer detected, and after the clip level has been maintained for the specified period, incrementing the clip level if an over-current condition is not detected for a sample and the clip level is below a specified maximum clip level.

6. The method of claim 1, wherein the audio signal comprises a digital signal including plurality of samples, there is a determination of whether an over-current condition is detected for each of the samples, and in response to an over-current condition being initially detected,

setting the clip level to a level of an immediately preceding sample, if the immediately preceding sample was not clipped.

7. The method of claim 6, wherein the reducing step includes:

decrementing the clip level, after the clip level is set to the level of the immediately preceding sample, if the immediately preceding sample was not clipped.

8. The method of claim 6, wherein the reducing step includes:

decrementing the clip level, if the immediately preceding sample was clipped.

9. The method of claim 1, further comprising monitoring for an over-current condition by:

receiving an output current resulting from the audio signal, where the audio signal may or may not be clipped, wherein a magnitude of the output current is indicative of a magnitude of an analog signal that will be used to drive a load;

sensing the magnitude of the output current; and

comparing the sensed magnitude to a threshold to determine whether an over-current condition is detected.

10. The method of claim 9, further comprising:

asserting an over-current indicator signal to indicate that an over-current condition is detected, when the sensed magnitude is greater than the threshold; and

deasserting the over-current indicator signal to indicate that an over-current condition is not detected, when the sensed magnitude is less than the threshold.

11. A device, comprising:

a hard-clipping unit configured to receive an audio signal and an over-current indicator signal, and to selectively clip the audio signal in dependence on the over-current indicator signal;

wherein while the over-current indicator signal indicates that an over-current condition is being detected, the clip level is reduced; and

wherein following an over-current condition being detected, once the over-current indicator signal indicates that the over-current condition is no longer detected, the clip level is maintained for a specified period before the clip level can be increased.

12. The device of claim 11, wherein:

the audio signal comprises a digital signal including a plurality of samples;

there is a determination of whether an over-current condition is detected for each of the samples; and

the specified period, for which the clip level is maintained before the clip level can be increased,

starts when the over-current condition is no longer detected, and

ends when each of N immediately preceding sample(s) are not clipped to the clip level, where N is an integer, and N≧

1.

13. The device of claim 12, wherein:

after an over-current condition is no longer detected, and after the clip level has been maintained for the specified period, the clip level is incremented if an over-current condition is not detected for a sample and the clip level is below a specified maximum clip level.

14. The device of claim 12, wherein when the over-current indicator signal indicates that an over-current condition is initially detected, then:

if the immediately preceding sample was not clipped, the clip level is set to a level of the immediately preceding sample; and

if the immediately preceding sample was clipped, the clip level is decremented.

15. A digital audio amplifier system comprising:

a pulse width modulation (PWM) controller configured to generate PWM output signals based on a digital audio signal including a plurality of samples;

an output stage configured to receive the PWM output signals from the PWM controller and to generate an analog output signal; and

at least one sensor configured to sense a current in the output stage and to generate an over-current indicator signal that indicates whether an over-current condition exists in the output stage for each of the samples;

wherein the PWM controller is also configured to

receive the over-current indicator signal, and based thereon, detect when an over-current condition exists in the output stage,

clip one or more samples of the audio signal to a clip level, while an over-current condition exists in the output stage;

reduce the clip level, while an over current condition exists in the output stage; and

maintain the clip level for a specified period before allowing the clip level to be increased, after an over-current condition that had existed in the output stage no longer to exists.

16. The system of claim 15, wherein the specified period, for which the clip level is maintained before the clip level is allowed to be increased,

starts when the over-current indicator signal indicates that an over-current condition no longer exists, and

ends when each of N immediately preceding sample(s) are not clipped to the clip level, where N is an integer, and N≧

1.

17. The system of claim 15, wherein while an over-current condition exists, the PWM controller is configured to

set the clip level to a level of an immediately preceding sample, if the immediately preceding sample was not clipped, and

decrement the clip level, if the immediately preceding sample was clipped.

18. The system of claim 15, wherein the PWM controller is configured to increment the clip level, after an over-current condition is no longer detected, and after the clip level has been maintained for the specified period, if an over-current condition is not detected for a sample and the clip level is below a specified maximum clip level.

19. The system of claim 15, wherein the PWM controller includes a modulator, and wherein the PWM controller clips the audio signal prior to the modulator in an audio signal path of the PWM controller.

20. The system of claim 19, wherein the PWM controller also includes an interpolator, a non-linearity correction unit, and a noise shaper, each of which precede the modulator in the audio signal path of the PWM controller, and wherein the PWM controller clips the audio signal following at least the interpolator and the non-linearity correction unit in the audio signal path of the PWM controller.