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US 4,243,959 AGranted
Adaptive filter with tap coefficient leakage
AssigneeBell Telephone Laboratories, Incorporated
InventorDonald L. Duttweiler
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AssigneeBell Telephone Laboratories, Incorporated
InventorDonald L. Duttweiler
Estimating the term…
Adaptive filters are commonly used in echo cancelers and automatic equalizers. Usually adaptive filters include a tapped delay line and apparatus coupled to the delay line for producing a tap coefficient signal, whose sign and magnitude indicate the appropriate correction in adjusting the filter. However, in the presence of input signals having a partial frequency band spectrum, known filters tend to become unstable, e.g., tap coefficient signals blow up. The instant arrangement includes apparatus for weakly driving the tap coefficient signals to optimal values. As illustrated in a deceptively simple embodiment, a tap coefficient updating component is extended through a one's complement converter to a first input of a binary adder. A two's complement output of the adder is fed back to a second input of the adder. The sign of the adder output is also provided to a CARRY-IN input terminal of the adder. Functionally, a unit leak is introduced in the least significant bit of the adder output tap coefficient signal whenever the updating component and the tap coefficient signal are of opposite algebraic signs. Otherwise, no leak is introduced. Thereby the tap coefficient signal is weakly driven toward zero.
A digital adaptive filter including a tapped delay line and apparatus coupled to said delay line for providing a tap coefficient signal, said tap coefficient providing apparatus (100, 200, 300, 400) including leak apparatus (40, 240) for introducing leakage in said tap coefficient signal and CHARACTERIZED IN THAT said digital filter further comprises means (50, 60) for controlling the strength of said tap coefficient leakage, said controlling means including means for weakly driving said tap coefficient signal toward zero said driving means including means (410, 420) responsive to an updating component (450) of said tap coefficient and responsive to said tap coefficient (470, 480) for intermittently introducing leakage.
A digital adaptive filter including apparatus (100, 200, 300, 400) for providing a tap coefficient signal, said providing apparatus including leakage apparatus (40, 240) for introducing leakage in said tap coefficient signal and CHARACTERIZED IN THAT said digital filter further comprises:
A digital adaptive filter including a tapped delay line and apparatus coupled to said delay line for introducing leakage in a tap coefficient signal and CHARACTERIZED IN THAT said digital filter further comprises
Dependencies are inferred from the claim text.