Synthesis of a Passive Complex Coefficient Filter Using Piezoelectric Transformers

Abstract

In this paper, two passive complex coefficient filters using piezoelectric transformers are proposed. The proposed frequency transformation is specialized for a complex coefficient filter using piezoelectric transformers. By applying the frequency transformation to a real first-order lowpass filter, we can obtain a first-order complex bandpass filter. The resulting circuit is realized by using a piezoelectric transformer, some reactance elements and terminating resistors. It is confirmed that the proposed circuit has complex bandpass characteristics through computer simulation and experiment. On the other hand, it is difficult to design higher order filters, because the circuit does not have the imaginary output. However, by allowing to use of a tight coupling transformer, a second-order complex bandpass filter can be obtained by using the proposed frequency transformation. The resulting circuit is realized by using two piezoelectric transformers, two tight coupling transformers, some reactance elements and terminating resistors. It is also confirmed that the proposed circuit has complex bandpass characteristics through computer simulation and experiment.