Design simplifications for bi notch filters

Abstract

A methodology for designing FIR bi notch filters (NF) derived from second order prototype IIR NFs is suggested. Rejection bandwidth for the designed filter can be controlled by suitable choice of 'r', the pole radius of the IIR prototype NFs. The suggested bi-NF can also be adapted to eliminate second, third and fourth order harmonics of periodic noise besides the fundamental noise frequency component. Such filters find application in switched mode power regulators meant to supply ripple free dc for sensitive electronic gadgets and also in host of communication circuits. A special case when two notch frequencies x 1 and x 2 are such that [(cos x 1 )(cos x 2 ) = -1/2] has also been discussed. The IIR bi-NF design for this special case results reduction in the number of multipliers without affecting the response of the desired NF. For the afore, referred condition, the required design weights of FIR bi-NF reduce to almost half in number resulting in reduced computations. The number of zero weights further reduces with increase in 'r' value. Also, the frequency response becomes better, with reduced ripples in the pass bands, when 'r' is increased and the length 'L' of the FIR NF is chosen appropriately.