Control of a loudspeaker output

• US 9,917,554 B2
• Filed: 06/06/2012
• Issued: 03/13/2018
• Est. Priority Date: 06/22/2011
• Status: Active Grant

• Current Assignee: Goodix Technology Co., Ltd. (Shenzhen Goodix Technology Co., Ltd.)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Gautama, Temujin
• Primary Examiner(s): Chin, Vivian
• Assistant Examiner(s): Hamid, Ammar
• Application Number:
  US13/489,754
• Publication Number:
  US 20120328117A1
• Time in Patent Office: 2,106 Days
• Field of Search: 381 59, 381104, 381107, 381 55, 381 58
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• CPC Class Codes: H03F 2200/03 the amplifier being designed for audio applications
• CPC Class Codes: H03F 2200/447 the amplifier being protected to temperature influence
• CPC Class Codes: H03F 3/181 Low-frequency amplifiers, e.g. audio preamplifiers
• CPC Class Codes: H03G 7/002 in untuned or low-frequency amplifiers, e.g. audio amplifiers H03G7/007, H03G7/001, H03G7/008, H03G7/02, H03G7/06 take precedence
• CPC Class Codes: H03G 9/025 frequency-dependent volume compression or expansion, e.g. multiple-band systems H03G9/10, H03G9/18 take precedence
• CPC Class Codes: H04R 29/003 of the moving-coil type
• CPC Class Codes: H04R 3/007 Protection circuits for transducers

Abstract

A loudspeaker drive circuit uses a dynamic range compressor to implement a non-linear gain function between the input signal to the dynamic range compressor and an output signal from the dynamic range compressor. The output is used to drive a loudspeaker, and the operating parameters of the dynamic range compressor are varied in dependence on a criterion, such as the estimated voice coil temperature, the power consumption or the acoustical distortion.

Claims

1. A loudspeaker drive circuit comprising:

a dynamic range compressor for implementing a non-linear gain function between an input signal to the dynamic range compressor and an output signal from the dynamic range compressor, the dynamic range compressor function having variable operating parameters to determine the non-linear gain function with a first gain portion below an input threshold level and a second gain portion above the input threshold level such that a slope of the second gain portion is smaller than a slope of the first gain portion;

a loudspeaker driver for driving a loudspeaker based on the output of the dynamic range compressor; and

a control unit for controlling the variable operating parameters of the dynamic range compressor in dependence on a control signal which represents the estimated voice coil temperature and the input signal, and in a way which influences voice coil temperature, wherein a change in the estimated voice coil temperature changes the non-linear gain function;

wherein the input threshold level is a variable that is lowered over time.

2. A circuit as claimed in claim 1, further comprising a temperature estimation unit for estimating a voice coil temperature of the loudspeaker as the control signal.

3. A circuit as claimed in claim 1, wherein the operating parameter of the dynamic range compressor which is controlled is the input threshold level.

4. A circuit as claimed in claim 2, wherein the threshold level is decreased in response to an increase in estimated temperature.

5. A circuit as claimed in claim 1, wherein the dynamic range compressor functions as a limiter, with the output substantially constant when the input is above the threshold.

6. A circuit as claimed in claim 3, wherein the operating parameter of the dynamic range compressor which is controlled is a slope of the first or second gain portion.

7. A circuit as claimed in claim 2, wherein a slope of the first or second gain portion is decreased in response to an increase in estimated temperature.

8. A loudspeaker system comprising a circuit as claimed in claim 1, and a loudspeaker.

9. A portable device comprising a loudspeaker system as claimed in claim 8.

13. The loudspeaker drive circuit of claim 1, wherein the high amplitude or high-power input signals comprise input signals that are higher than 40% of an input signal limit either measured in amplitude or in power.

14. The loudspeaker drive circuit of claim 1, wherein the control unit is configured to gradually change a slope of the first and second gain portion.

10. A method of processing an audio input signal to generate a loudspeaker drive signal, comprising:

using a dynamic range compressor to implement a non-linear gain function between an input signal to the dynamic range compressor and an output signal from the dynamic range compressor, the dynamic range compressor function having variable operating parameters to determine the non-linear gain function with a first gain portion below an input threshold level and a second gain portion above the input threshold level such that a slope of the second gain portion is smaller than a slope of the first gain portion;

driving a loudspeaker based on the output of the dynamic range compressor;

controlling the variable operating parameters of the dynamic range compressor in dependence on a control signal that represents an estimated voice coil temperature and the input signal and in a way which influences voice coil temperature, and wherein the controlling comprises;

decreasing the threshold level in response to an increase in the estimated voice coil temperature, or

decreasing a slope of the first or second gain portion in response to an increase in the estimated voice coil temperature.

11. A method as claimed in claim 10, further comprising estimating a voice coil temperature of the loudspeaker and deriving the control signal from the estimate.

12. A computer program on a non-transitory computer-readable storage medium for implementing a method as claimed in claim 10 when said program is run on a computer.