A modified fixed-point computational gradient descent Gray-Markel notch filter method for sinusoidal detection and attenuation

A Gray-Markel notch filter is used to track and significantly attenuate a narrow-band interference whose frequency drifts slowly with time. The novel feature is the use of a bandpass filter to isolate the range of frequencies over which the adaptive hardware responds and the use of a simple FIR filter to carry out the adaptation with the more complex IIR Gray-Markel notch filter slaved to the simple FIR filter. This method results in the ability to track a slow moving narrowband interference over a band of frequencies and attenuate the signal due to the interference sufficiently to allow high precision signal processing on the remaining data with little phase distortion to the data. Furthermore, an adequate implementation of the adaptive Gray-Markel notch filter can be achieved with a modest 24-bit integer hardware implementation.