High-Isolation Low-Power Active Quasi-Circulator for 44GHz Transceiver with Power and Noise Optimization in 0.18 Micrometer BICMOS

Circulator is an important directional component in RF, microwave and millimeter wave communication front ends for certain communications, which requires transmitting and receiving signal simultaneously in the same band without switching of antenna from transmitter to receiver. As modern trend of wireless communication, conventional ferrite circulator is huge, bulky and heavy to be integrated with analog and digital baseband processing circuits. Active circulators provide a compact high isolation solution for low power application with smaller size and less cost with compatibility with modern IC. Previous works are majorly working at low frequency and paid little attention to power and noise requirement of active quasi-circulator working at the front end of a transceiver. A BiCMOS active quasi-circulator at 44GHz is designed in 0.18 ?m process to provide high isolation low cost solution, which is comprised of in-phase divider and out-of-phase active combiner, with noise and power optimization. Moreover, techniques employed to improve isolation such as high Common mode rejection ratio(CMRR) balun design, common mode feedback, and novel method of power splitting and noise optimization, impedance matching scheme are discussed.

High isolation of cascode structure is analyzed and major tradeoffs among characteristics are investigated, such as: gain and transmission-reception isolation; output impedance, matching and noise; linearity, power and efficiency. The circulator operates around 44 GHz with 3dB bandwidth of 4.53GHz, achieves maximum 2.897dBm input and 2.32dBm output power. Noise Figure (NF) is 10.62dB for reception path, only 0.03dB higher than NFmin.

Linearity is reasonable for both in-phase divider and out-of-phase active combiner. OIP3 of in-phase divider is 8.15dBm, IIP3 is 4.48dBm, P1dB,in is -5.97dBm. OIP3 of out-of-phase active combiner is 5.18 dBm, IIP3 is 3.85dBm, P1dB, in is -2.79dBm.

All the isolations better than -37 dB are achieved and forward gains better than 4 dB are achieved with power consumption 56.83mW. Large signal TX-RX isolation is 51.837dB. The circuit takes merely 1.415mm*1.014mm area. This active quasi-circulator offers a low cost substitute solution for circulator in low power applications.