Feedback isolation by piezoelectric transformers: comparison of amplitude to frequency modulation

Signal isolation is needed in power electronics systems that include separate primary and secondary ´grounds´. The feasibility of using a piezoelectric transformer (PT) as a galvanic barrier was investigated in this study theoretically and experimentally. The research included the issues of drive, demodulation, bandwidth, and common mode rejection. In particular, two types of excitation signals were compared: amplitude modulated and frequency modulated. The frequency response of the piezoelectric isolator was studied by small signal envelope simulation using ORCAD/PSPICE as well as experimentally. It is concluded that the FM approach offers a larger BW but the AM scheme seems to be easier to implement.