Adaptive Removal Of Resonance-Induced Noise
Tech ID: 10093 / UC Case 1997-122-0
There are many instances when it is desirable to remove an underlying operating frequency from an output signal. When the frequency range is somewhat known, this removal is relatively straightforward using a stagger-tuned notch filter. Stagger-tuned notch filters, however, introduce considerable phase lag and when the frequencies are grossly unknown, unstable, or both, so much phase lag is introduced as to make these filters unsuitable for a very important application: closed-loop control. A very narrow adaptive notch filter can be used to greatly reduce the phase lag, however, this introduces a new difficulty. A very narrow notch filter must be an infinite impulse response (IIR) filter, hence it must be recursive. This in turn makes the adaptive tracking of the notch frequency of the filter unstable, again making the situation unsuitable for closed-loop control.
DESCRIPTIONScientists at the University of California have developed a system for the adaptive removal of resonance-induced noise that overcomes this seemingly inherent instability. This problem has been solved by noting that although the narrow notch filter which removes the resonance-induced noise must have a low phase delay and therefore must be recursive, the apparatus which determines the center frequency of the notch filter may be non-recursive, and therefore stable.
APPLICATIONSThis system is capable of removing noise from the digitized output of a sensor that is subject to some undesired internal or external resonance, even when that resonance undergoes a relatively slow drift. This novel system can be incorporated into MEMS devices and has applications in a variety of areas, including:
- On-board positioning units;
- Antilock braking systems (ABS);
- Flight-control, i.e. inertial sensors;
- Rate sensors.
ADVANTAGESThis invention offers several significant advantages, including:
- System cascading. If multiple resonance lie in known bands then one can cascade this system on each individual band to remove the signal. Each filter operates independently on each band thus performing significantly better with less delay and phase distortion than conventional systems;
- Guaranteed output. The locations of the filters can be finely controlled to insure that they remain within a specified band. Unconfined adaptive filters do not have this property and changes in the band can result in changes outside the band.
This invention is available for licensing on a non-exclusive basis.
|United States Of America||Issued Patent||6,611,602||08/26/2003||1997-122|
|United States Of America||Issued Patent||5,960,091||09/28/1999||1997-122|
- Dao, Phong-Vu
- Nelson, Karl Einar E.
- Soderstrand, Michael A.
- White, Stanley A.
- Woodard, Jeffrey P.