Design of Low-Pass IIR Digital Differentiator with Approximately Equal Ripple Group-Delay based on Iterative Reweighting Method

In minimax phase error infinite impulse response filters, the group-delay error is typically much larger at the passband edges than elsewhere. In this article, we propose an iterative reweighted minimax phase error algorithm for designing low-pass infinite impulse response digital filters with approximately constant group-delay. A revised Gauss-Newton strategy with variable step size is used to solve the minimax phase error problem with a weight function, and the revised envelope of the group-delay error is used to update the weight function of the phase error. Under the premise of meeting the requirements for passband and stopband magnitude error, an approximately equal ripple passband group-delay is obtained. Three design examples demonstrate the validity of the proposed iterative reweighting method.