Improved active quasi circulator with integrated digital leakage canceler in BiCMOS technology

An improved architecture of an active quasi-circulator (QC) is proposed for monostatic FMCW automotive radars. Special attention is paid on the receiver noise figure (NF) performance as well as high transmit (TX) to receive (RX) signal isolation. The high TX/RX isolation is achieved by using a W-band CMOS based impedance tuner acting as a leakage canceler. Also process variation as well as antenna mismatch can be compensated. As the tuner can be controlled digitally, this architecture facilitates an easy system integration in state-of-the-art monostatic radar systems. A test chip including the QC, the tuner and an on-chip serial command interface (SCI) is fabricated in a 130nm BiCOMS technology. With a power consumption of 99mW, the gain in the transmit and receive path at 73 GHz is around 1.8 dB. The simulated NF at 73 GHz is less than 8.5 dB. Over a bandwidth of 2.5 GHz an isolation of 25 dB could be achieved.