Efficient narrow-band notch filter

An efficient digital narrow-band notch filter may be realized by subtracting weighted sine and cosine vectors from the input signal. The weights of the sine and cosine vectors are determined using adaptive filtering techniques while the frequency of these vectors remains fixed. The frequency and phase response of a filter constructed in this manner is absolutely flat within the passband, while the stopband rejection is 95 dB. The computational complexity of this filter is equivalent to that of a four-tap FIR filter.