Small-bandwidth integrated tunable bandpass filters for GSM applications

This paper presents an integrated tunable lumped- element filter at 831 MHz with a 3 dB-bandwidth of 77 MHz (9% bandwidth) and an embedded insertion loss of 4.0 dB. The filter is fabricated using a combination of thick high aspect-ratio silver plating and bulk micromachining that enables the implementation of high- quality factor inductors as well as high-performance fixed and tunable two-port capacitors. The third-order filter shows good thermal stability and is continuously tuned using voltage-tunable capacitors.