An Interference Tolerant RF Frontend With Capacitive Feedback for Channel Filtering

In this letter, a reconfigurable RF frontend with 4-path passive mixer is presented. Compared with the conventional method of using passive mixer at LNA output only, this design has further transferred the tunable impedance characteristic of passive mixer to the LNA input with capacitive feedback to achieve reconfigurable impedance matching at target frequency. Furthermore, the negative feedback is also able to free the conventional common base amplifier from 50 Ω impedance matching requirement to achieve better noise figure. The design was implemented with 0.18 μm SiGe BiCMOS technology. Measurement results showed a lowest noise figure of 4.6 dB from 0.6 to 1.1 GHz and an in-band IIP3 of -11 dBm, an out-band IIP3 of +3 dBm respectively.