A notch-feedback based 4th-order 2–4 GHz bandpass filter system for S-band radar receiver protection under the LTE and radar coexistence

This paper present for the first time all RF domain notch-feedback based 4
^th
-order LC band-pass filter (BPF) system in 0.13 μm SiGe BiCMOS. The feedback BPF system achieves less than 1% fractional BW with 160-165 dB·Hz normalized dynamic range (DR) at 2-4 GHz, breaking the inherent tradeoff between selectivity and DR in the Q-enhanced LC filters. With open-loop staggered tuning by disabling the feedback loop, BW is increased to 600 MHz with less than 200 ps group delay variation. The ultimate out-of-band rejection of the filter is > 65 dB and > 52 dB on the lower and upper side of the center frequency, respectively. The filter consumes 50-60 mW of DC power from 2.5 V supply voltage. The core chip size is 0.9×0.7 mm
²
.