The Certain Possibility of Compensation of the Frequency Response of a LP S-K Biquad Based on the Signal Flow Graph

Abstract

The Sallen-Key low-pass filter structures of the even orders have one general problem. This problem is a decreasing of the attenuation at high frequencies. This denoted decreasing of the attenuation is typical for the filters of the even orders only. Therefore, this ineligible frequency response is typical for the filters assembled exclusively from biquads. The reasons for this effect are explained in this paper and then verified by simulations. The Sallen-Key filter with fully differential i/o amplifier is a structure that eliminates decreasing of the attenuation at high frequencies. Firstly, this circuit solution is used as a reference circuit. Secondary, a structure that does not have this property is designed based on the signal flow graph. The resulted frequency response of this proposed structure is verified by computer simulation. These simulations were performed by MicroCap version 11.