A synchronous adaptive noise canceller for periodic interference

A new type adaptive noise canceller for periodic interference is proposed. The operation of this adaptive filter is controlled by the phase-locked loop which captures the fundamental frequency component of the noise and generates clock pulse whose frequency is N times that of it, where N is the length of the impulse response function of the adaptive filter. This clock is used to keep the operation of the adaptive filter synchronous with the noise and also to keep the length of the impulse response function of the adaptive filter equal to the noise period. By the usual least-mean-squares (LMS) algorithm there needs 2N multiplications and 2N additions far the correction of the filter coefficients at each sampling time. However, the synchronous method needs only one multiplication and one addition. It means that the total computational cost decreases to about 1/(2N) times as compared with the usual LMS algorithm and it will be a great help in simplifying the hardware construction and also in widening the operational frequency range of the adaptive filter. A pilot study has showed the proposed adaptive filter has excellent performance.