Hearing aid output clipping apparatus

• US 6,256,395 B1
• Filed: 01/30/1998
• Issued: 07/03/2001
• Est. Priority Date: 01/30/1998
• Status: Expired due to Term

• Current Assignee: GN RESOUND AS MAARKAERVEJ 2A
• Original Assignee: GN Resound A/S (GN Store Nord A/S)
• Inventors: Melanson, John Laurence
• Primary Examiner(s): Le, Huyen
• Assistant Examiner(s): PENDLETON, DIONNE
• Application Number:
  US09/016,507
• Time in Patent Office: 1,250 Days
• Field of Search: 381/312, 381/320, 381/321, 381/120, 381/121, 381/104-109, 381/102, 381/56-58, 364/400, 364/119
• US Class Current: 381/312
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

A digital hearing aid applies clipping to the processed digital signal after at least part of the interpolation of the signal has occurred. The clipping may be incorporated into the output demodulation stage of the hearing aid. The final stages of interpolation may also be incorporated into the demodulation stage.

Claims

1. A digital hearing aid comprising:

a microphone for receiving an input audio signal and providing an analog signal;

an A/D converter connected to the microphone for receiving the analog signal, converting the analog signal to a digital signal, and providing the digital signal as an output;

a digital signal processing stage connected to the A/D converter for receiving the digital signal, processing the digital signal, and providing the processed digital signal as an output;

an interpolation stage for receiving the processed digital signal, increasing the sample rate of the processed digital signal, and providing the increased sample rate processed digital signal as an output;

a clipper connected to the output of the interpolation stage for receiving the increased sample rate processed digital signal, clipping the increased sample rate processed digital signal, and providing the clipped increased sample rate processed digital signal as an output;

a demodulation stage connected to the clipper for receiving the clipped increased sample rate processed digital signal, converting the clipped increased sample rate processed digital signal into an output analog signal, and providing the output analog signal as an output; and

a speaker connected to the demodulation stage for receiving the output analog signal and providing an audio output signal based upon the output analog signal.

2. A digital hearing aid comprising:

a microphone for receiving an input audio signal and providing an analog signal;

an A/D converter connected to the microphone for receiving the analog signal, converting the analog signal to a digital signal, and providing the digital signal as an output;

a digital signal processing stage connected to the A/D converter for receiving the digital signal, processing the digital signal, and providing the processed digital signal as an output;

an interpolation stage for receiving the processed digital signal, increasing the sample rate of the processed digital signal, and providing the increased sample rate processed digital signal as an output;

a demodulation stage connected to the interpolation stage for receiving the increased sample rate processed digital signal, converting the increased sample rate processed digital signal into an output analog signal, and providing the output analog signal as an output; and

a speaker connected to the demodulation stage for receiving the output analog signal and providing an audio output signal based upon the output analog signal;

wherein the demodulation stage includes means for clipping the increased sample rate processed digital signal prior to converting the increased sample rate processed digital signal into an analog signal.

3. The hearing aid of claim 2 wherein the demodulation stage comprises:

a clipping delta sigma quantizer including a quantizer and at least one accumulator having an accumulator arithmetic element for adding a delayed output signal from the accumulator arithmetic element to an input signal provided to the accumulator arithmetic element, wherein the accumulator arithmetic element includes clipping means, said accumulator providing a signal to the quantizer which provides an output signal and a feedback signal to the accumulator, said delta sigma modulator further including a feedback arithmetic element for adding said feedback signal to the accumulator input signal; and

a digital to analog converter for converting the output signal from the quantizer to an analog signal and providing the analog signal to the speaker.

4. The hearing aid of claim 3, wherein the clipping means comprises a saturating clipper built into the accumulator arithmetic element.

5. The hearing aid of claim 3, wherein the clipping means comprises a saturating clipper attached to the output of the accumulator arithmetic element.

6. The hearing aid of claim 2, wherein the demodulation stage comprises:

a clipping delta sigma quantizer of at least second order including a quantizer and at least two accumulators having accumulator arithmetic elements for adding delayed output signals from the accumulator arithmetic elements to input signals provided to the accumulator arithmetic elements, wherein each said accumulator arithmetic element includes clipping means, said accumulators providing signals to the quantizer which provides an output signal and feedback signals to the accumulators, said delta sigma modulator further including feedback arithmetic elements for adding said feedback signals to the accumulator input signals; and

a digital to analog converter for converting the output signal from the quantizer to an analog signal and providing the analog signal to the speaker.

7. The hearing aid of claim 6, wherein each clipping means comprises a saturating clipper built into the associated accumulator arithmetic element.

8. The hearing aid of claim 6, wherein each clipping means comprises a saturating clipper attached to the output of the associated accumulator arithmetic element.

9. The hearing aid of claim 6, wherein a single multiport adder operating in multiple phases comprises the accumulator arithmetic elements and the feedback arithmetic elements.

10. The delta sigma modulator of claim 9 wherein the single multiport adder comprises a three input adder operating in three phases.

11. The delta sigma modulator of claim 10 wherein the three phases comprise:

the first phase adds the input to the delta sigma modulator plus the previous output of the first stage plus the negative of the feedback;

the second phase adds the current output of the first stage plus the previous output of the second stage; and

the third phase adds the current output of the first stage plus the current output of the second stage, and feeds the quantizer.

12. The delta sigma modulator of claim 9, further including means for interpolating the input signal to the demodulator comprising:

means for dividing the input signal into a first signal and a second signal each having half the magnitude of the input signal;

means for delaying the first signal; and

means for combining the delayed first signal with the second signal.