Method for automatically controlling the bandwidth of a digital filter and adaptive filter utilizing same
First Claim
1. A method for automatically controlling the bandwidth of a digital filter in response to changes of condition of an input signal to the digital filter, the method comprising the steps of:
- determining changes of condition of the input signal;
defining fuzzy rules between the changes of condition of the input signal and a control signal;
modifying the control signal based on the changes of condition and the fuzzy rules; and
utilizing the modified control signal to control the bandwidth of the digital filter in real time so that the digital filter achieves good transient response and noise suppression.
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Abstract
A method and an adaptive filter are provided wherein the bandwidth of the filter is varied as a function of current and past input signal values based on the amount of noise judged to be present. A first order digital low pass filter is described by the following equation:
y(k)=α(x(k)+(k+1))+(1-2α)y(K-1)
where α is a variable control signal which controls the cutoff frequency of the filter. Fuzzy logic or rules are used to determine α. To determine whether the current input signal is most likely a true signal or noise, three differences are taken between the current and past three input sample signals. Based on a comparison of these differences, α is assigned a value from 0.0 to 0.5 in accordance with the fuzzy rules. If the rules indicate that noise is predominant, the bandwidth of the filter is minimized by setting α=0.0 to suppress the noise. If the fuzzy rules indicate that the current input signal is valid, then the bandwidth of the filter is maximized by setting α=0.5. Values of α between 0.0 and 0.5 reflect an indeterminate judgment by the fuzzy rules.
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Citations
16 Claims
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1. A method for automatically controlling the bandwidth of a digital filter in response to changes of condition of an input signal to the digital filter, the method comprising the steps of:
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determining changes of condition of the input signal; defining fuzzy rules between the changes of condition of the input signal and a control signal; modifying the control signal based on the changes of condition and the fuzzy rules; and utilizing the modified control signal to control the bandwidth of the digital filter in real time so that the digital filter achieves good transient response and noise suppression. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An adaptive filter having a bandwidth responsive to changes of condition of an input signal, the adaptive filter comprising:
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means for determining changes of condition of the input signal; a digital filter; means for defining fuzzy rules between the changes of condition of the input signal and a control signal; and means for modifying the control signal based on the changes of condition and the fuzzy rules wherein the modified control signal controls the bandwidth of the digital filter in real time so that the digital filter achieves good transient response and noise suppression. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16)
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Specification