Boots – shoes – and leggings
Patent
1995-01-13
1996-10-08
Mai, Tan V.
Boots, shoes, and leggings
G06F 1531
Patent
active
055638171
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with an LMS filter chip that can be used as a building block in low cost noise cancellation applications.
SUMMARY OF THE INVENTION
Prior art adaptive canceller filters have consisted of software code in digital computers, often in digital signal processor (DSP) microprocessors such as the TMS320C25 by Texas Instrument or as discrete hardware components in analog systems. The software--DSP methods lack speed while the analog methods contain an excess of parts and lack adaptability.
INMOS has produced a multiply-accumulate chip, the IMS A100, that can be used to implement digital filters but no method is provided for adaptation of the filter coefficients.
The current invention overcomes the prior an limitations while providing a standard adaptive filter module that can operate at high speed, reduces hardware parts count and will lead to reduced cost from volume production.
It works with the Digital Virtual Earth (DVE) algorithm and the AFF algorithm which achieves noise cancellation without requiring either a noise reference or a sync signal as described in U.S. Pat. No. 5,105,377 which is hereby incorporated by reference herein. It also works with the Filtered-x class of algorithms which utilize a reference signal and adapt an FIR filter to minimize the power of an error signal.
Accordingly, it is an object of this invention to provide a standard adaptive filter module for FIR or IIR filters that can operate at high speed.
Another object is to provide the architecture for a filtered-x adaptive filter module.
A still further object of this invention is to provide an adaptive filter module that will reduce the amount of hardware in active noise cancellation apparatus.
Furthermore, it is an object of this invention to provide a novel filtered -x adaptive filter for enhancing the operation of the digital virtual earth (DVE) algorithm.
These and other objects of this invention will become apparent when reference is had to the accompanying description and drawings.
FIG. 1 is a simplified block diagram of the DVE algorithm,
FIG. 2 is a simplified block diagram of a filtered-x adaptive canceller.
FIG. 3 is a block diagram of the method for measuring the external impulse response.
FIG. 4 shows a block diagram of the module configured so as to have the filter and adapter as a single module.
FIG. 5 is a chart of the system identification and calibration.
FIG. 6 is a diagram of the adaptive canceller filter module, and
FIG. 7 is a diagram of the architecture of the filter chip.
THE DVE ALGORITHM/FILTERED-X ALGORITHM
Description
The Digital Virtual Earth (DVE) algorithm holds the promise of a generic solution to active cancellation without requiring either noise reference or a sync signal. To date it has shown promise in applications which have either a relatively stationary noise signature or a simple noise spectrum.
DVE works by first estimating the original noise from the measurement of the residual and knowledge of its anti-noise output as modified by the system transfer function "C". This estimated noise is passed through an adaptive filter to then produce the anti-noise. The Filtered-X LMS adaptation of the filter then minimizes the residual signal power. FIG. 1 shows a simplified block diagram of the DVE algorithm where anti-noise as it flows through the D/A (and its reconstruction filter), through the anti-noise driver to the residual microphone, through the A/D (and its anti-aliasing filter). physical filters consistent measures. The reference signal (X--the estimated noise signal) is passed through a copy of "C" since the anti-noise signal has gone through the real "C" delivered. The anti-noise estimate is then subtracted from the residual to estimate the original noise. signal power.
This system achieves cancellation when the adaptive equalizer, "A", has a transfer function which is the inverse of C.sub.1 (the first half of "C", including the D/A, the reconstruction filter, the anti-noise driver and the transit delay to the mike). Since "A" must be causal, this inverse fun
Denenberg Jeffrey N.
Friedlander Paul
Ziegler, Jr. Eldon W.
Mai Tan V.
Noise Cancellation Technologies, Inc.
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