Self-adjusting digital notch filter
AssigneeThe United States of America as represented by the Secretary of the Air Force
InventorRainer F. McCown
Life of this patent
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Abstract
Digital filter auto-adjustment to variations in input signals is achieved by normalizing the output of the second of two substantially identical series-connected digital filter stages and subtracting the normalized output of the second filter stage from its input to provide a measure of filter signal residue power. Deviations of the signal residue power from the preset limits of a signal residue power standard are detected and signals responsive thereto are used to appropriately adjust variable bandwidth constants in both filter stages.
Claims2
The method of filtering a signal comprising the steps of
- filtering said signal with a first digital filter having given bandwidth characteristics,
- filtering the output of said first digital filter with a second digital filter having substantially the same bandwidth characteristics as said first digital filter,
- normalizing the output of said second digital filter,
- subtracting the normalized output of said second digital filter from its input to obtain the filter signal residue power, and
- varying the bandwidth control constants of said first and second digital filters in response to deviations between said signal residue power and limits defined by a signal residue power standard.
A self-adjusting digital notch filter comprising
- a first digital filter stage having variable notch constants,
- a second digital filter stage having variable notch constants, the output of said first filter stage being connected to the input of said second filter stage,
- means for normalizing the output of said second filter stage,
- differencing means for subtracting the normalized output of said second filter stage from its input to provide a measure of the filter signal residue power,
- a signal residue power standard having selected signal residue power limits,
- comparator means adapted to measure deviations between the output of said differencing means and the limits of said signal residue power standard, and
- a notch constant generator adapted to control the values of first and second filter stage notch constants in response to the output of said comparator means.
Dependencies are inferred from the claim text.