Hearing aid with digital compression recapture

• US 8,009,842 B2
• Filed: 07/11/2006
• Issued: 08/30/2011
• Est. Priority Date: 12/05/2000
• Status: Active Grant

• Current Assignee: K/S HIMPP
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Wahl, Jerry, Richardson, Garry
• Primary Examiner(s): Mei; Xu
• Application Number:
  US11/456,777
• Publication Number:
  US 20070147639A1
• Time in Patent Office: 1,876 Days
• Field of Search: 700/94, 381320-321, 381104-109, 333/14
• US Class Current: 381/107
• CPC Class Codes: H03G 1/04 Modifications of control circuit to reduce distortion caused by control modifications to reduce influence of variations of internal impedance of amplifying elements caused by control H03F1/08
• CPC Class Codes: H03G 3/3005 in amplifiers suitable for low-frequencies, e.g. audio amplifiers H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 3/301 the gain being continuously variable
• CPC Class Codes: H03G 7/08 incorporating negative feedback
• CPC Class Codes: H04R 25/356 Amplitude, e.g. amplitude shift or compression
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

Systems, devices, and methods are provided to inhibit apparent amplitude modulation in non-linear processing that causes distortion in a processed signal. One aspect of the invention includes a hearing aid. The hearing aid includes a microphone to receive an input signal, a speaker to reproduce the input signal, and a processor. The processor processes the input signal using a gain. The processor includes an inhibitor, which inhibits distortions, and an adjuster, which adjusts the gain. The inhibitor acts to smooth an envelope of the input signal to inhibit undesired modulation. The adjuster adjusts the gain if the envelope is either above or below a threshold. The hearing aid further includes a compression recapture system to supply the compressed portion of the input signal to more closely reproduce the actual input signal.

Claims

1. A method of restoring a compressed signal in an input stage of a device, comprising:

detecting when a first digital signal representative of an input signal is above a threshold value to produce a gain control signal;

reducing gain of an amplifier to a value below the threshold value based on the gain control signal; and

restoring an output signal of the input stage to include a compressed portion of the input signal, the compressed portion of the input signal represented by a second digital signal.

2. The method of claim 1, wherein restoring the output signal includes mapping the second digital signal to a compression recapture signal.

3. The method of claim 2, wherein restoring the output signal includes digitally combining the compression recapture signal and the first digital signal using a multiplier to essentially digitally reproduce the input signal.

4. An apparatus, comprising:

means for detecting when a first digital signal representative of an input signal is above a threshold value to produce a gain control signal, wherein the input signal is received at the input stage of a device;

means for reducing gain of an amplifier to a value below the threshold value based on the gain control signal; and

means for restoring an output signal of the input stage to include a compressed portion of the input signal, the compressed portion of the input signal represented by a second digital signal.

5. The apparatus of claim 4, wherein the restoring means includes a compression recapture system.

6. The apparatus of claim 4, wherein the detecting means includes means for producing a digital gain control signal using a feed back approach.

7. The apparatus of claim 4, wherein the restoring means includes means for applying an inverse of the gain control signal to restore the compressed portion of the input signal.

8. The apparatus of claim 4, wherein the restoring means includes means for restoring compression using a feed forward approach.

9. An method, comprising:

providing an input to receive an input signal and output an analog signal;

connecting a variable gain amplifier to the input to selectively compress the analog signal, the variable gain amplifier including a digital gain control;

connecting an analog to digital converter to the input to receive the analog signal and output a first digital signal;

forming a compression recapture system for outputting a second digital signal that essentially represents a compressed portion of the analog signal; and

providing an output to reproduce the input signal based on the first and second digital signals.

10. The method of claim 9, wherein forming the compression recapture system includes forming a feed forward circuit.

11. The method of claim 10, wherein forming the compression recapture system includes forming a transfer function element.

12. The method of claim 11, wherein forming the transfer function element includes forming an element to map the second digital signal from the digital gain control to a compression recapture signal.

13. The method of claim 12, wherein providing the output includes providing a multiplier that digitally combines the compression recapture signal and the first digital signal to essentially digitally reproduce the input signal.

14. The method of claim 13, wherein providing the output includes providing a digital signal processor that receives a combined digital signal from the multiplier.

15. The method of claim 9, wherein connecting the analog to digital converter includes connecting a converter having a threshold, and the variable gain amplifier compresses a portion of the analog signal that is above the threshold.

16. The method of claim 9, wherein connecting the variable gain amplifier includes connecting the variable gain amplifier wherein the digital gain control includes an inhibitor to inhibit distortions and an adjuster to adjust the gain of the variable gain amplifier, wherein the inhibitor digitally smoothes an envelope of the first digital signal so as to inhibit distortions arising from apparent modulation of the first digital signal.

17. The method of claim 9, wherein providing the input includes providing a filter to block low frequencies in the input signal from the analog signal.

18. The method of claim 9, wherein the digital gain control receives the first digital signal to control gain of the variable gain amplifier.

19. The method of claim 10, wherein the digital gain control outputs a control signal, and the second digital signal is a mathematical inverse of the control signal.

20. The method of claim 19, wherein the digital gain control includes a digital adjuster to adjust the gain and a digital to analog converter connected between digital adjuster and the variable gain amplifier.