AUDIO DRIVER SYSTEM AND METHOD

• US 20120106750A1
• Filed: 07/15/2011
• Published: 05/03/2012
• Est. Priority Date: 07/15/2010
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Thormundsson, Trausti, Regev, Shlomi I., Kannan, Govind, Lau, Harry K., Wihardja, James W., Jonsson, Ragnar H.
• Granted Patent: US 9,060,217 B2
• Time in Patent Office: Days
• US Class Current: 381/71.12
• CPC Class Codes: H04R 2499/11 Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
• CPC Class Codes: H04R 29/003 of the moving-coil type
• CPC Class Codes: H04R 3/007 Protection circuits for transducers

Abstract

A system and apparatus for constructing a displacement model across a frequency range for a loudspeaker is disclosed. The resultant displacement model is centered around the distortion point. Once a distortion model is constructed it can be incorporated into an audio driver to prevent distortion by incorporating the model and a distortion compensation unit with a conventional audio driver. Various topologies can be used to incorporate a distortion model and distortion compensation unit into an audio driver. Furthermore, a wide variety of distortion compensation techniques can be employed to avoid distortion in such an audio driver.

Claims

1. A method for distortion correction in an audio system comprising:

selecting a frequency in a frequency range;

selecting an amplitude;

causing a signal generator to generate a signal at the frequency and the amplitude;

providing the generated signal to a loudspeaker;

generating a sound signal representing sound generated by the loudspeaker using a microphone;

determining whether distortion exists;

modifying the amplitude and repeating one or more of the preceding steps until distortion is detected;

when distortion is detected, recording the amplitude as a minimum amplitude;

applying the minimum amplitude to filter an audio signal.

2. The method of claim 1, wherein determining whether distortion occurs comprises:

predicting an expected microphone signal; and

comparing the expected microphone signal with the sound signal.

3. The method of claim 1, wherein the expected microphone signal is predicted using a linear predictive filter.

4. The method of claim 1, wherein applying the amplitudes and phases recorded to filter the audio signal comprises creating complex samples from the amplitudes and phases recorded.

5. The method of claim 4 further comprising:

fitting an inverse transfer function using the complex samples; and

inverting the transfer function.

6. An audio driver comprising:

a distortion modeling system;

a distortion compensation unit;

a digital to analog converter (DAC); and

an amplifier;

wherein the distortion modeling system predicts distortion in an audio signal; and

the distortion compensation unit provides a distortion compensated audio signal when distortion is predicted.

7. The audio driver of claim 6, wherein the distortion modeling system is coupled to an audio signal output of the distortion compensation unit.

8. The audio driver of claim 6 wherein the distortion modeling system is coupled to an audio input of the distortion compensation unit.

9. The audio driver of claim 6 wherein the distortion modeling system predicts speaker displacement.

10. The audio driver of claim 6 further comprising a distortion detection unit coupled to a microphone, wherein the distortion detection unit generates revision data for the distortion modeling system if distortion is detected.

11. The audio driver of claim 6 further comprising:

a resistor in series with a loudspeaker;

a differential amplifier operable to measure a voltage across the resistor; and

a distortion detection unit operable to receive the measured voltage, wherein the distortion detection unit causes a revision in a distortion model if distortion is detected.

12. The audio driver of claim 6 further comprising a distortion detection unit operable to receive a signal proportional to a loudspeaker current, wherein the distortion detection unit causes a revision in the distortion model if distortion is detected.

13. The audio driver of claim 11 further comprising:

an analysis module; and

a signal generator;

wherein the analysis module is operable to control the distortion module by causing the signal generator to generate test signals until distortion is detected.

14. The audio driver of claim 6 wherein the distortion compensation unit comprises a dynamic range compressor.

15. The audio driver of claim 6 wherein the distortion compensation unit comprises a gain element with an automatic gain control.

16. The audio driver of claim 6 wherein the distortion compensation unit comprises a look ahead peak reducer.

17. The audio driver of claim 6 wherein the distortion compensation unit comprises an adder operable to add a DC offset or a low frequency signal.

18. The audio driver of claim 6 wherein the distortion compensation unit comprises a PID controller.

19. The audio driver of claim 6 wherein the distortion compensation unit comprise a gain element with automatic gain control and an adder operable to add an offset or a low frequency signal.

20. The audio driver of claim 19 wherein the distortion compensation unit further comprises a PID control operable to control the adder and the gain element.