Synthesis and active realization of a three-phase complex coefficient filter using gyrators

In this paper, a three-phase complex coefficient filter is proposed. A method is described to directly realize an imaginary resistance suitable for a complex filter with an arbitrary phase difference by using a gyrator and resistors. Moreover, in a three-phase complex filter, these resistors are rendered redundant. The proposed circuit is realized by using terminating resistors, capacitors, and gyrators. As an example, a third-order complex bandpass filter based on the frequency shifting method is designed. This is achieved by employing multi-port gyrators using negative impedance converters (NIC). It is shown that the experimental circuit exhibits bandpass characteristics (4.5-5.5 kHz) and an image rejection ratio of 51dB.