Complex approximation of FIR digital filters by updating desired responses

In this correspondence, we present a new numerical method for the complex approximation of FIR digital filters. Our objective is to design FIR filters whose absolute error between the designed and desired response is equiripple. The proposed method solves the least-squares problem iteratively. At each iteration, the desired response is updated so as to have an equiripple error. The proposed methods do not require any time-consuming optimization procedure such as the quasi-Newton methods and converge to equiripple solutions quickly. Moreover, by multiplying the arbitrary weighting function on the desired response of the passband and stopband, the errors in the passband and the stopband can be controlled. We show some examples to illustrate the advantages of our proposed methods.