A Microwave Acoustic QPSK Modulator Leveraging Poled Ferroelectrics

This article reports on the first quadrature phase-shift key (QPSK) modulator realized in acoustic wave devices. Ferroelectricity allows control over piezoelectric coefficient enabling acoustic phase inversion (API) in stacked crystal filters (SCF). API is leveraged to modulate in-phase (I) and quadrature (Q) signal components in order to produce a QPSK signal. A proof-of-principle device is fabricated. A QPSK constellation is presented. Measured two-port S-parameters are presented for each of the four data states. The QPSK modulator provides alternative to transistor-based modulators leveraging acoustic wave devices. It demonstrates analog signal processing in the acoustic domain enabling a homogeneously integrated all acoustic RF front end.