Active noise cancellation apparatus and method

• US 6,654,467 B1
• Filed: 02/18/1998
• Issued: 11/25/2003
• Est. Priority Date: 02/18/1998
• Status: Expired due to Fees

• Current Assignee: Heung K.I. Cho, Stanley J. York
• Original Assignee: Heung K.I. Cho, Stanley J. York
• Inventors: Cho, Heung Ki, York, Stanley J.
• Primary Examiner(s): Isen, Forester W.
• Assistant Examiner(s): PENDLETON, BRIAN T
• Application Number:
  US09/025,692
• Time in Patent Office: 2,106 Days
• Field of Search: 381/71.14, 381/71.13, 381/71.8, 381/94.31, 381/94.7, 381/71.1, 381/71.3, 381/71.4, 381/94.1
• US Class Current: 381/71.14
• CPC Class Codes: G10K 11/17821 characterised by the analysis of the input signals only
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17853 of the filter
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward

Abstract

An active noise cancellation apparatus and method for actively reducing the level of noise generated by an ambient noise source, such as a domestic appliance. This active noise cancellation apparatus has a pickup device (1, 20) to translate the noise into an electrical signal, a buffer amplifier (2, 22) to allow the distribution of those signals to a digital filter section (3) having a series of switched capacitor filters for analyzing and dividing the signal into separate harmonic signals, a dual analog delay line (4) for producing a phase shift in the signals, a summing amplifier (2,6) to recombine the signals into one signal, a power amplifier (5, 27) to drive an output loudspeaker (6, 31) which produces a phase shifted sound wave to cancel the noise generated by the ambient noise source.

Claims

1. An apparatus for canceling ambient noise, said apparatus comprising:

sensor means for picking up the ambient noise and converting it into an electrical input signal containing amplitude and temporal information corresponding to a frequency wave of ambient noise;

an input amplifier for providing gain in the electrical signal received from the sensor means;

means for analyzing and dividing the input signal into a fundamental signal and a series of separate harmonic signals;

means for introducing a half cycle phase delay in said fundamental signal and each of said series of separate harmonic signals;

means for recombining the separate harmonic signals into an output signal and providing said signal to an amplifier;

an output amplifier for amplifying the output signal for passing on to an output means; and

an output means for converting the output signal to an output noise having a frequency wave which is shifted one half cycle from the frequency of the ambient noise such that the ambient noise is virtually canceled.

2. The apparatus of claim 1 wherein the sensor means comprises a transducer.

3. The apparatus of claim 1 wherein the means for analyzing and dividing the input signal comprises a series of switched capacitor filters, each of said series of filters designed to separate the input signal into a series of harmonic signals of different frequencies which make up the input signal promulgated by the ambient noise.

4. The apparatus of claim 2 wherein the means for analyzing and dividing the input signal comprises a series of switched capacitor filters, each of said series of filters designed to separate the input signal into a series of harmonic signals of different frequencies which make up the input signal promulgated by the ambient noise.

5. The apparatus of claim 1 wherein the means for introducing a half cycle phase time delay in each harmonic signal comprises an analog delay.

6. The apparatus of claim 2 wherein the means for introducing a half cycle phase time delay in each harmonic signal comprises an analog delay.

7. The apparatus of claim 3 wherein the means for introducing a half cycle phase time delay in each harmonic signal comprises an analog delay.

8. The apparatus of claim 4 wherein the means for introducing a half cycle phase time delay in each harmonic signal comprises an analog delay.

9. The apparatus of claim 1 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

10. The apparatus of claim 2 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

11. The apparatus of claim 3 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

12. The apparatus of claim 4 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

13. The apparatus of claim 5 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

14. The apparatus of claim 6 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

15. The apparatus of claim 7 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

16. The apparatus of claim 8 wherein the means for recombining separate harmonic signals into an output signal comprises a summing amplifier.

17. The apparatus of claim 1 wherein the means for introducing the phase delay is adjustable.

18. The apparatus of claim 17 wherein the means for introducing a phase delay is adjustable by a potentiometer which can further alter phase shift between input signal and output signal.

19. The apparatus of claim 1 wherein the output amplifier is connected to the input amplifier by a feedback loop so that the output signal is fed back to the input amplifier to prevent the apparatus from trying to cancel the output noise of the apparatus.

20. A method for canceling ambient noise, said method comprising the steps of:

a. picking up ambient noise and converting it into an electrical input signal containing amplitude and temporal information corresponding to a frequency wave of the ambient noise;

b. amplifying said input signal;

c. analyzing and dividing the input signal into a fundamental signal and a series of separate harmonic signals;

d. introducing a one half cycle phase delay in each of said series of separate harmonic signals;

e. recombining the separate harmonic signals into an output signal and providing said output signal to an amplifier;

f. amplifying the output signal for passing on to an output means; and

converting the output signal to an output noise having a frequency wave which is shifted one half cycle from the frequency of the ambient noise such that the ambient noise is canceled.

21. The method of claim 20 wherein step d further comprises the step of:

adjusting the delay to alter the phase shift between the input signal and the harmonic signal.