Effective suppression method for 2nd nonlinear signals of SAW devices

Linearity performances are getting one of the most important characteristics of surface acoustic wave (SAW) duplexers because nonlinear signals generated in RF front-end of cellar phone handsets deteriorate the receiver sensitivities significantly. In this paper, the generation mechanisms of the 2^nd order nonlinear signals of SAW resonators/duplexers on a 42°Y-X LiTaO₃ substrate and an effective suppression method for them are discussed. The crystalline asymmetry properties of substrates are focused on as the one possibility of the occurrence factor of the 2^nd order nonlinear signals. Additionally, based on this hypothesis, an interdigital transducer (IDT) design which realizes the cancellation of the crystalline asymmetry effect is proposed to improve the linearity. As the result, the 2^nd order harmonics level of the one-port SAWresonators and the 2^nd order intermodulation distortion (IMD2) levels of the SAW duplexers have been improved up to about 25dBm and 20dBm, respectively.