Designing active filters with linear transformations using off-the-shelf building blocks

In the paper, passive LC filters containing tuned circuits, or inverted-L filters are simulated using linear transformations to realise active-RC filters with biquads, such as integrated AF100 or AF150 chips, as basic building blocks. These integrated circuits (ICs) are designed to realise the general biquadratic function and are easily programmable using only four external resistors. It is shown that lowpass, highpass and bandpass filters can be realised using these chips via the linear transformation method, which, as a structural simulation method, gives more insensitive structures than the one of the cascade biquads. Some examples are given to show the effectiveness of the method and the use of these ICs for active filter design by simulation of passive LC structures. Experimental results demonstrate the above statements.