Motional feedback system

• US 8,401,207 B2
• Filed: 03/26/2010
• Issued: 03/19/2013
• Est. Priority Date: 03/31/2009
• Status: Active Grant

• Current Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Harman International Industries Incorporated (Samsung Electronics Co. Ltd.)
• Inventors: Stanley, Gerald R.
• Primary Examiner(s): Mei, Xu
• Assistant Examiner(s): TON, DAVID L
• Application Number:
  US12/748,097
• Publication Number:
  US 20100246848A1
• Time in Patent Office: 1,089 Days
• Field of Search: 381/96, 381/121, 381/120, 330/102
• US Class Current: 381/96
• CPC Class Codes: H03F 1/32 Modifications of amplifiers to reduce non-linear distortion by negative feedback H03F1/34
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2203/45136 One differential amplifier in IC-block form being shown
• CPC Class Codes: H03F 2203/45138 Two or more differential amplifiers in IC-block form are combined, e.g. measuring amplifiers
• CPC Class Codes: H03F 2203/45526 the FBC comprising a resistor-capacitor combination and being coupled between the LC and the IC
• CPC Class Codes: H03F 3/187 in integrated circuits
• CPC Class Codes: H03F 3/45475 using IC blocks as the active amplifying circuit
• CPC Class Codes: H04R 29/001 for loudspeakers H04R29/007 takes precedence
• CPC Class Codes: H04R 3/002 Damping circuit arrangements for transducers, e.g. motional feedback circuits
• CPC Class Codes: H04R 3/04 for correcting frequency response

Abstract

An audio amplifier is operated in an audio system with optimized source impedance to minimize distortion in a loudspeaker that is paired with the audio amplifier. The audio amplifier provides an amplified audio signal to drive the loudspeaker. A variable output impedance of the audio amplifier is controlled using a feedback control loop to allow negative output impedance at low frequencies that changes to positive output impedance at higher frequencies. The change from negative output impedance to positive output impedance occurs at a determined threshold frequency or determined transitional frequency band.

Claims

1. A motional feedback system for minimizing non-linear distortion of loudspeakers comprising:

an audio amplifier having an output with a variable output impedance, the output configured to supply an amplified audio signal to drive a loudspeaker paired with the audio amplifier;

a current sensor configured to sense a current of the amplified audio signal supplied at the output, and supply the current as a feedback current to the audio amplifier to minimize distortion of the loudspeaker;

an impedance control module included in the audio amplifier, the impedance control module comprising an active filter having a transfer function H(s) that substantially matches a load impedance of the loudspeaker paired with the amplifier, and the transfer function H(s) providing a frequency dependent phase inversion and a frequency dependent gain in order to control the variable output impedance as a function of the frequency of the audio signal to selectively transition the feedback current between a positive feedback current in a first range of frequencies, and a negative feedback current in a second range of frequencies that are higher than the first range of frequencies;

the impedance control module configured to synthesize the output impedance using the positive feedback current of the transfer function H(s) of the active filter to represent a negative impedance below a determined threshold frequency; and

the impedance control module further configured to synthesize the output impedance using the negative feedback current of the transfer function H(s) of the active filter to represent a positive impedance above the determined threshold frequency.

2. The motional feedback system of claim 1, where the active filter is included in a feedback loop responsive to the current of the amplified audio signal supplied to the loudspeaker.

3. The motional feedback system of claim 1, where the transfer function H(s) is representative of an optimum source impedance to minimize non-linear distortion of the loudspeaker.

4. The motional feedback system of claim 1, where the frequency dependent phase inversion is configured to occur within a transition band around the determined threshold frequency.

5. The motional feedback system of claim 1, where the impedance control module is configured to control the variable output impedance of the audio amplifier based on the transfer function H(s) and a current of the amplified audio signal supplied to the loudspeaker.

6. The motional feedback system of claim 1, where the active filter comprises a single operational amplifier.

7. The motional feedback system of claim 1, where the determined threshold frequency is a user specified transition band of frequencies.

8. The motional feedback system of claim 1, where the current sensor is coupled with the filter and the output, and the impedance control module further comprises a summer coupled between the filter and an output amplifier configured to supply the output.

9. The motional feedback system of claim 1, where the active filter comprises a filter input configured to receive a voltage indicative of an output current supplied on the output, the active filter further comprising a filter output configured to provide an error signal generated by application of the transfer function H(s) to the received voltage indicative of the output current.

10. The motional feedback system of claim 9, where application of the transfer function H(s) to the received voltage indicative of the output current results in frequency based phase and gain adjustments to the received voltage indicative of the output current.

11. A method of minimizing non-linear distortion of a loudspeaker comprising:

receiving an audio signal from an audio source;

amplifying the audio signal with an audio amplifier;

driving a loudspeaker with the amplified audio signal using an output of the audio amplifier, the loudspeaker being paired with the audio amplifier, and the output having a controlled output impedance;

synthesizing the controlled output impedance using an active filter having a transfer function H(s) that substantially matches a load impedance of the loudspeaker paired with the amplifier and the transfer function H(s) providing a frequency dependent phase inversion and a frequency dependent gain in order to present a negative impedance below a determined threshold frequency; and

synthesizing the controlled output impedance with the active filter in order to present a positive impedance above the determined threshold frequency;

where synthesizing the output impedance to present the negative impedance and synthesizing the output impedance to present the positive impedance comprises transitioning a feedback current between a positive current feedback below the determined threshold frequency, and a negative current feedback above the determined threshold frequency using the transfer function H(s).

12. The method of claim 11, where synthesizing the controlled output impedance to present the negative impedance and synthesizing the controlled output impedance to present the positive impedance comprises monitoring a current supplied in the amplified audio signal with the audio amplifier, and optimizing the controlled output impedance for the loudspeaker using a current feedback loop to minimize loudspeaker distortion.

13. The method of claim 11, where synthesizing the controlled output impedance to present the negative impedance and synthesizing the controlled output impedance to present the positive impedance comprises applying a frequency based gain of a filter response to a frequency spectrum of an output current of the amplified audio signal, and approximating a control source impedance for the loudspeaker to minimize loudspeaker distortion.

14. The method of claim 11, where synthesizing the output impedance to present the negative impedance comprises applying a first gain of a filter response to a first range of frequency of a current included in the audio signal below the threshold determined frequency, and synthesizing the output impedance to present the positive impedance comprises applying a second gain to a second range of frequency of the current of audio signal above the threshold determined frequency.

15. The method of claim 11, where synthesizing the output impedance to present the negative impedance and synthesizing the output impedance to present the positive impedance comprises modifying an input audio signal provided to the audio amplifier with an error signal generated with the transfer function H(s) in a feedback loop, the modified input audio signal amplified with the audio amplifier and provided to the loudspeaker to minimize non-linear distortion.

16. The method of claim 11, where synthesizing the output impedance to present the negative impedance comprises substantially negating a part of the load impedance which is substantially representative of a voice coil of the loudspeaker, and controlling the output impedance to the positive impedance comprises substantially exceeding a part of the load impedance which is substantially representative of a leakage inductance of the loudspeaker.

17. A computer readable storage media configured to store computer readable instructions that are executable by a processor to minimizing non-linear distortion of loudspeakers, the computer readable storage media comprising:

instructions to receive an audio signal from an audio source, the audio source including a plurality of frequencies;

instructions to process the audio signal with an audio amplifier;

instructions to enable output of the processed audio signal on an audio output of the audio amplifier to drive a loudspeaker, the audio output having an output impedance, and the loudspeaker paired with the audio amplifier;

instructions to receive a feedback current;

instructions to synthesize the output impedance of the audio amplifier to present a negative impedance using an active filter having a transfer function H(s) that substantially matches a load impedance of the loudspeaker paired with the amplifier, the transfer function H(s) providing a frequency dependent phase inversion and a frequency dependent gain such that the feedback current is a positive feedback current, and the negative impedance is presented at the audio output for a first band of frequencies of the audio signal below a determined threshold frequency; and

instructions to synthesize the output impedance of the audio amplifier to present a positive impedance at the audio output for a second band of frequencies of the audio signal above the determined threshold frequency in response to the transfer function H(s) providing the feedback current as a negative feedback current in the second band of frequencies, the second band of frequencies being higher than the first band of frequencies.

18. The computer readable storage media of claim 17, further comprising instructions to operate a current feedback loop that includes the active filter, the transfer function H(s) being substantially representative of an optimum source impedance for the loudspeaker over the first band of frequencies and the second band of frequencies.

19. The computer readable storage media of claim 18, where the frequency dependent gain and the frequency dependent phase inversion of the transfer function H(s) are configured so that the phase transitions from a negative phase below the determined threshold frequency to a positive phase above the determined threshold frequency.

20. The computer readable storage media of claim 19, where the frequency dependent gain of the transfer function H(s) within the first band of frequencies is less than the frequency dependent gain of the transfer function H(s) within the second band of frequencies.

21. A motional feedback system for loudspeakers comprising:

an audio amplifier having an input and an output, the input configured to receive an audio signal, and the output configured to supply an amplified version of the audio signal, the amplified version of the audio signal used to drive a loudspeaker paired with the audio amplifier;

a current sensor configured to sense a current of the amplified audio signal supplied at the output, and supply the current as a feedback current to the audio amplifier to minimize distortion of the loudspeaker; and

an active filter included in the audio amplifier and coupled with the current sensor, the active filter having a transfer function H(s) that substantially matches a load impedance of the loudspeaker paired with the amplifier, the transfer function H(s) providing a frequency dependent phase inversion and a frequency dependent gain in order to selectively transition the feedback current between a positive feedback current in a first range of frequencies, and a negative feedback current in a second range of frequencies that are higher than the first range of frequencies.

22. The motional feedback system of claim 21, where the active filter is configured with a determined transitional bandwidth of frequency within which the selective transition between the positive feedback current and the negative feedback current occurs.

23. The motional feedback system of claim 21, where the amplifier is configured to present an output impedance to the loudspeaker in response to the positive feedback current and the negative feedback current, the output impedance being a negative impedance in the first range of frequencies and a positive impedance in the second range of frequencies.

24. The motional feedback system of claim 23, where, the negative impedance is representative of a resistance of the loudspeaker in the first range of frequencies, and the positive impedance exceeds an impedance of the loudspeaker in the second range of frequencies.

25. A method of minimizing non-linear distortion of loudspeakers comprising:

receiving an audio signal from an audio source, the audio source including a plurality of frequencies;

amplifying the audio signal with an audio amplifier having an output with a variable output impedance;

driving a loudspeaker paired with the audio amplifier with the amplified audio signal;

monitoring a current supplied in the amplified audio signal;

supplying the monitored current to an active filter having a transfer function H(s) that substantially matches a load impedance of the loudspeaker paired with the amplifier, the transfer function H(s) providing a frequency dependent phase inversion and a frequency dependent gain in order to control the variable output impedance as a function of the frequency of the audio signal;

synthesizing the output impedance of the audio amplifier using the transfer function H(s) of the active filter to be a negative impedance for those frequencies below a determined threshold frequency based on the monitored current being provided by the transfer function H(s) as a positive feedback current; and

synthesizing the output impedance of the audio amplifier using the transfer function H(s) of the active filter to be a positive impedance for those frequencies above the determined threshold frequency based on the monitored current being provided by the transfer function H(s) as a negative feedback current.