Sallen-Key Filter using TCOA via Commercial Integrated Circuits

Abstract

Biquad Sallen-Key type low filter in current mode that uses the True Current Operational Amplifier as an active element generates a non-monotonic course of the attenuation at the highest frequencies. This result manifests by a decrease in attenuation instead of its monotonic increase, which occurs in an ideal filter. The article presents and compares the options for solving this problem. The proposed solution is to use a modified True Current Operational Amplifier connection, consisting of positive conveyors of the second generation, which are implemented by commercially available Operational Transimpedance Amplifier type AD 844. The theoretical analysis shows the elimination of the problem of attenuation drop with such a solution.