Distortion compensation

• US 20070140513A1
• Filed: 12/15/2005
• Published: 06/21/2007
• Est. Priority Date: 12/15/2005
• Status: Active Grant

• Current Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Inventors: Furge, Kenneth
• Granted Patent: US 8,036,402 B2
• Time in Patent Office: Days
• US Class Current: 381/120
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2200/321 Use of a microprocessor in an amplifier circuit or its control circuit
• CPC Class Codes: H03F 2200/471 the voltage being sensed
• CPC Class Codes: H03F 2200/66 Clipping circuitry being present in an amplifier, i.e. the shape of the signal being modified
• CPC Class Codes: H03F 2200/78 A comparator being used in a controlling circuit of an amplifier
• CPC Class Codes: H03G 11/008 of digital or coded signals
• CPC Class Codes: H03G 3/007 Control dependent on the supply voltage
• CPC Class Codes: H03G 7/004 using continuously variable impedance devices

Abstract

A distortion compensation system minimizes distortion in an audio system by monitoring a supply voltage and adjusting a clipping threshold and/or compression knee. An adjustable gain circuit controls the gain of the audio signal according whether the audio signal exceeds a variable threshold. The variable threshold is adjusted within a threshold range based on the supply voltage. Distortion due to clipping of the audio signal is minimized while available power at any given time is maximized.

Claims

1. An automotive audio amplifier comprising:

an acoustic signal processor configured to control gain for at least one channel of a multi-channel audio signal, the gain being controlled according to a gain adjust signal;

a voltage sensor configured to generate a voltage sense signal associated with a battery supply voltage for the amplifier; and

a threshold detector configured to generate a gain adjust signal according to detecting whether an output of the gain circuit exceeds a threshold, the threshold being adjustable according to the voltage sense signal.

2. The amplifier of claim 1 where the threshold is reduced when the threshold detector detects that the at least one channel of the multi-channel audio signal exceeds the threshold.

3. The amplifier of claim 2 where the threshold is reduced at an attack rate in the range of about 100 dB per second to about 1000 dB per second.

4. The amplifier of claim 1 where the threshold is increased to unity gain when the threshold detector detects that the at least one channel of the multi-channel audio signal does not exceed the threshold.

5. The amplifier of claim 2 where the threshold is increased at a release rate in the rate in the range of about 10 dB per second to about 100 dB per second.

6. The amplifier of claim 1 where the acoustic signal processor is configured to control gain for a plurality of channels for the multi-channel audio signal, the gain for each channel being controlled according to the gain adjust signal.

7. The amplifier of claim 1 where the voltage sensor further comprises a low pass filter to provide a filtered signal associated with a rail voltage for the amplifier.

8. The amplifier of claim 1 further comprising a digital signal processor configured to monitor a level of each channel of the multi-channel audio signal.

9. An automotive audio system comprising:

a controller configured to control gain adjustment for each channel of a multi-channel audio signal according to whether the audio signal exceeds a threshold, and to adjust the threshold according to a supply voltage for the audio system relative to a tuning voltage; and

an amplifier configured to buffer a gain-adjusted multi-channel audio signal.

10. The automotive audio system of claim 9 where the controller lowers the threshold when the supply voltage is less than the tuning voltage.

11. The automotive audio system of claim 9 where the controller increases the threshold when the supply voltage is above the tuning supply voltage.

12. A method for compensating for acoustic distortion comprising:

controlling the gain of at least one channel of an audio signal according to whether the audio signal exceeds a threshold; and

adjusting the threshold according to a rail voltage.

13. The method of claim 12 where the rail voltage comprises a battery voltage.

14. The method of claim 13 further comprising:

sensing the rail voltage;

comparing the sensed rail voltage to a predetermined tuning voltage; and

adjusting the threshold according to the comparison of the sensed rail voltage to a predetermined tuning voltage.

15. The method of claim 14 further comprising reducing the threshold when the rail voltage is below the tuning voltage.

16. The method of claim 14 further comprising increasing the threshold when the rail voltage is above a tuning voltage.

17. The method of claim 14 where controlling comprises reducing the gain of the at least one channel of an audio signal during portions of the audio signal that exceed the threshold.

18. The method of claim 14 where controlling comprises increasing the gain of the at least one channel of the audio signal to unity gain when portions of the audio signal for at least one-channel that does not exceed the threshold limit.

19. The method of claim 12 further where adjusting comprises comprising:

detecting whether the audio signal of each channel of a multi-channel amplified audio signal exceeds a threshold limit; and

reducing a gain of a channel of the multi-channel audio signal when it is detected that the audio signal of the channel exceeds the threshold limit, the gain being reduced by an attack rate in the range of about 100 dB per second to about 1000 dB per second.

20. The method of claim 18 further comprising increasing the gain of the multi-channel audio signal when the audio signal of the channel does not exceed the threshold limit.

21. The method of claim 19 where the maximum gain comprises unity gain.

22. The method of claim 12 further comprising:

controlling the gain of a first channel of an audio signal according to whether an audio signal of a second channel exceeds a threshold; and

adjusting the threshold according to a rail voltage.

23. The method of claim 22 where the first and second channel comprise paired channels of a multi-channel audio system.

24. An audio system comprising:

a voltage supply;

a controller configured to control an output signal for channels of a multi-channel audio signal, the controller configured to detect whether a signal of a detected channel of the multi-channel audio signal exceeds a control level and to adjust an output corresponding to the detected channel when the detected signal exceeds the control level; and

a distortion compensator configured to detect a level of the voltage supply and to adjust the control level according to an instantaneous level of the voltage supply.

25. The audio system of claim 24 where the controller is configured to adjust the gain of the detected channel, where a threshold is adjusted according to detecting an instantaneous level of a voltage supply.

26. The audio system of claim 24 where the controller is configured to compress the signal of the detected channel, where a compressor knee is adjusted according to detecting an instantaneous level of the voltage supply.