ACTIVE NOISE REDUCING DEVICE
An active noise reducing device includes processing circuit includes a sine wave generator for generating a sine wave having a specific frequency, a cosine wave generator for generating a cosine wave having the same frequency as that of the sine wave, and two one-tap digital filters for processing the outputs from the generators. The processing circuit also has two coefficient updating sections, which output a sum of outputs from the digital filters. Updating sections update respective coefficients of the filters based on a sum of this output from the updating sections and respective inputs to the updating sections, and the respective outputs from the generators. The noise reducing device also has an adjusting circuit for adjusting the phase and amplitude of an output from the processing circuit, the adjusting circuit thus generates a control signal of opposite phase and equal in amplitude to original noise, so that random noise such as load noise can be reduced.
1 . An active noise reducing device comprising:
a processing circuit including:
a sine wave generator for generating a sine wave of a specific frequency;
a cosine wave generator for generating a cosine wave of an identical frequency to the sine wave; and
two one-tap digital filters for processing respective outputs from the sine wave generator and the cosine wave generator;
an adjusting circuit for adjusting a phase and an amplitude of an output from the processing circuit;
a first transducer for transducing an output from the adjusting circuit into a sound wave or a vibration; and
a second transducer for transducing a sound wave or a vibration supplied to the processing circuit into an electrical signal,
wherein the processing circuit further includes two coefficient-updating sections for updating respective coefficients of the two one-tap digital filters,
wherein the two coefficient-updating sections update the respective coefficients of the two one-tap digital filters based on an output which is added a sum of outputs added together from the two one-tap digital filters and an input, and the respective outputs from the sine wave generator and the cosine wave generator.
2 . The active noise reducing circuit of claim 1 , wherein two or more than two of the processing circuits are coupled to each other in parallel, and the processing circuits respectively generate a sine wave and a cosine wave having different frequencies from each other.