2 GHz Automatically Tuned Q-Enhanced CMOS Bandpass Filter

An automatically tuned 2 GHz 0.18 mum CMOS 3-stage RF filter is presented. The bandpass filter achieves center frequency tuning while maintaining a relatively flat passband. Q-enhanced resonators allow for more than 28 dB of insertion loss compensation in the Alter response. Measured results show that the filter is tunable in frequency by 32.5%, has a 14.7 dB noise figure, a -3.9 dBm 1dB input compression point, a +5.1 dBm IIP3 intercept, and consumes 21 mA from a 1.8 V supply. Automatic tuning of the multistage filter is performed by over-enhancing each stage of the filter until oscillation occurs to set resonant frequency and then backing off the enhancement using a passive Q tuning method, which does not effect the resonant frequency. Automatic frequency and quality factor tuning control were performed using digital logic synthesized in an FPGA. The hardware in-situ automatic tuning of the multi-pole integrated filter eliminates the need for a replica filter.