The paper discusses the matters of required gain approximation in the frequency range of operation using the Chebyshev criterion and Remez exchange algorithm. The equiripple problems have been solved, which yields polynomials in the form of the fourth order multipliers that approximate the different gains with different frequency ratios. The obtained polynomials make it possible to implement bandpass amplifiers with the required selectivity and gain. The dependencies of figures of merit (for dynamic and frequency ranges, frequency response stability) on the relationship of transfer function sensitivity to element parameters deviations have been analyzed. The criterion of optimality for bandpass amplifiers circuits in the form of the product of gain by transfer function sensitivity to active element parameters deviations has been defined. A circuit design for the fourth order bandpass amplifiers employing a single active element has been suggested. Design ratios for elements’ parameters that provide the minimum value of the optimality criterion over the frequency range of operation have been calculated. Comparison of the suggested and known fourth order function implementation has been made. It has been proved that the figures of merit of selective amplifiers constructed according to the suggested circuit design can be significantly improved.

Keywords: approximation, frequency response, selective amplifier, active two-port network, integrated amplifier, sensitivity characteristics, dynamic range, intermediate frequency amplifier, a noise level, a function of sensitivity