Digital rejection filter based on staggered couple of second order sections

This work is concerned on properties of digital rejection filter based on staggered couple of second order sections. We derived approximate expressions for amplitude-frequency response of rejection filters based on single second order section and staggered couple of second order section and relations for these filters synthesis under taking into account required rejection frequency, rejection band and squareness ratio. We found that during increasing of squareness ratio the selectivity of staggered couples grows according to square law, while selectivity of simple filter is linear (under squareness ratio is more four). Here a well-known comparative evaluation for parameters of staggered couple biquadratic sections and parameters of rejection filter by the one second order section was estimated. Therefore, we found the gain of using of staggered couples in comparison to single-section filter unit improves under squareness ratio growing. We represent results of researches of rejection filter influence on the noise immunity of DBPSK demodulator under frequency concentrated in-band interference with spectral width less then signal spectral width more then one order.