IIR digital filter design using an LP approximation

The synthesis of Infinite Impulse Response (IIR) digital filters generally involves the use of a computer algorithm to solve sets of linear and nonlinear equations. There are a number of computer-aided techniques for approximating an arbitrarily prescribed frequency characteristic. Using a minimum p-error criterion, the computer program by A. G. Deczky successfully solves the minimization problem utilizing the Fletcher-Powell algorithm. Several auxiliary programs were developed to implement the main program. Procedures were developed to facilitate the program execution by the user as well as a procedure that permits the data to be entered interactively rather than using an input file. Two additional computer programs were developed which permit the output of the main program, which is given in terms of coefficients of the Z-transform of the IIR digital filter, to be plotted on the CAL-COMP plotter as well as the printer. Different methods of optimization are discussed and a detailed explanation of the Fletcher-Powell algorithm is given. A description of the parameters used in the main program is presented along with a discussion of the functions of its subroutines. The developments of auxiliary computer algorithms are discussed. Finally, four IIR digital filter design examples are presented along with plots of magnitude, gain in dB, and phase and group delay versus frequency. All are plotted on the CAL-COMP plotter as well as the printer. A user manual is presented in appendix F to assist the user during the program execution.