Tunability of Bulk Acoustic Wave filters using CMOS transistors: concept, design and implementation

This paper presents the feasibility of a new method to tune the Bulk Acoustic Wave - Solidly Mounted Resonator (BAW-SMR) filters by adding capacitors to the shunt resonators and by controlling these capacitors using CMOS transistors that act as switches. The tunable BAWSMR filter is realized in a ladder topology. It is used for the 802.11b/g standard (2.40-2.48 GHz). Mainly, the filter fulfills the requirements for the WLAN 802.11 b/g standard, presenting a measured -3.3 dB of insertion loss, -12.7 dB of return loss and selectivity higher than 33 dB @ ±30 MHz of the bandwidth. Moreover, a measured shift of 0.5% of the centre frequency (2.44 GHz) towards higher frequencies is obtained. This tunable BAW-SMR filter has reduced dimensions (1035*1075 μm²).