Fully-Differential Tunable Fractional-Order Filter with Current Followers and Current Amplifiers

The paper presents proposal of a fully-differential fractional (1+alpha)-order low-pass filter. The filter operates in the current mode. It is based on the well-known follow-the-leader feedback (FLF) topology of the the 3rd-order filtering structure utilizing fully-differential current followers (FD-CFs) and adjustable current amplifiers (ACAs), in our case, in order to approximate fractional-order low-pass filter response in particular frequency band of interest. The design correctness and proper function of the proposed filter are supported by PSpice simulations. The filter provides ability to electronically control its order in range from 1 to 2 and also offers the electronic control of the cut-off frequency. These features were tested for three different values in case of the control of the order and three different values in case of the control of the cut-off frequency.