Small sized low loss IF SAW filters for W-CDMA based on RSPUDT utilizing high SAW reflectivity on lithium tetraborate

Small sized and low loss IF SAW transversal filters for W-CDMA have been developed using lithium tetraborate (Li₂B₄ O₇, LBO). Compared to ST-quartz, LBO is desirable for wide band and low loss filter applications such as W-CDMA, because of its larger k². Moreover, it is known that the SAW reflectivity on LBO is at least several times higher than that on ST-quartz. Therefore, it is possible to reduce the chip size by applying the high reflectivity on LBO to the RSPUDT techniques. To obtain an ideal SPUDT with the high reflectivity, EWC/SPUDT structures on LBO are investigated theoretically and modified. By using the modified SPUDT structure on LBO, IF SAW filters for W-CDMA are demonstrated in practical. Consequently, a remarkably small sized 190MHz IF filter in 3.8×3.8mm² package is achieved with a low insertion loss of 7 dB, a wide band width of 4.6 MHz, a small phase linearity of less than 2° RMS and an excellent ACS of more than 25 dB